Compression Test - more than just checking for wear.

[XPC66]

Only because Stubby suggested it I'll post a method of how to determine your CR from the compression test gauge reading. I thought I might just waffle a bit and write on the run. So forgive me if it isn't eloquent.

Most will be aware that CR is a handy way of guessing the performance of an engine. For instance with high CR we run higher octane fuels, have a cam that probably opens and blows down a little earlier, thus a few degrees extra LSA, etc. But best of all it's still good for bragging rites and big noting......"my engine is running CR 12.5, what size is your dick?"

CR in isolation doesn't help when trying to figure if we are going to get det or not. That's when the effective or dynamic compression ratio comes in handy. It's simply the ratio of volume available after the intake cycle divided by the clearance volume (clearance volume is all that space above the compression ring). The theory is that while the intake valve is open there isn't much compression happening.

Suprisingly we can use this to fairly accurately determine our expected compression pressure and by extrapolation the BMEP too, which is a bonus.

So lets take a Ford 3984cc O/head cam six from the EA -EF series Falcons as our example.

What we know ( I hope I'm right here, because I'm not really a Ford type):
CR = 8.8:1
Bore diameter = 92.25
Stroke = 99.31mm
Compression 1010 kPa minimum
Camshaft advertised events 65/11 17/63
Conrod length (centreline) 153.92mm

Note: I'm using metric here, but you can use inches if you want.

1. The core calculation is to find the displacement of the piston left to travel to top dead centre (TDC) once the intake valve has closed. This is fairly easy if you know trigonometry. and can be found by using::

Effective stroke = RL- SQRT(RL^2 - (0.5 x S x Sin°)^2) + (0.5 x S x Cos°) +(0.5 x S)

where RL = Rod length = 153.92, S = stroke = 99.31mm, ° = inlet closing angle =63, ^2 = squared (raised to the power of 2)

So in a very convoluted way;
effective stroke = 153.92 - SQRT(153.92^2 - (0.5 x 99.31 x 0.891)^2) -(0.5 x 99.31 x 0.454) + (0.5 x 99.31)
=153.92 - SQRT(23691.4 - 1957.4) + 22.54 + 49.655
=153.92 - 147.42 + 22.54 + 49.655
= 78.695mm

2. From this we can work out our effective compression ratio if we know the static compression ratio, which we do in this instance = 8.8:1

DCR = (Effective stroke ratio x (CR-1)) + 1
effective stroke ratio = 78.69/99.31 = 0.792
= (0.792 x 7.8 ) +1
= 7.1776

3. then we can apply our ideal gas law and find the our expected reading on the compression gauge to see things are going well with our rings and valves:

(DCR^0.283 x atmos pressure x DCR)- atmos pressure
(7.1776^0.283 x 101.32 x 7.1776 ) - 101.32
=1169 kPa

4. But what if you want to work out what the clearance volume is (for some obscure reason) and you don't want to take the head off and start the onerous task of finding the combustion volume, ringland volumes, gasket volumes, etc

Well we take the gauge reading and work out the DCR by rearranging variables with simple algebra and get:

DCR = (1169kPa +101.32/101.32)^(1/1.283)
= 12.5377^0.77942
= 7.1775

we know from the previous calculation the effective stroke is 78.695mm

we also know that CR = (Full stroke swept volume/clearance volume) +1

so it follows that DCR =(effective swept volume/clearance volume) +1

therefore clearance volume = effective swept volume/(DCR-1)

effective swept volume = (92.25^2 x Pi x 78.65)/(4 x 1000) = 525.68 cc

so clearance volume = 525.68/6.1775 = 85cc

5. Knowing the clearance volume you can easily work out the CR value, if it's important to you.

.........................

What is the use of DCR you ask? Well it is particularly useful in predicting detonation. And none of us want det, because it has a nasty habit of causing erratic power and damage. It is also is a good predictor of BMEP, which is a good predictor of something novices like to brag about ..... engine torque.......which is really just cross product vector of power and annular velocity .

You can use DCR to select the correct fuel octane rating. And very importantly you can maximise the compression ratio for use in turbo or huffer applications, without sticking to that old chestnut that CR must be around CR 8 to prevent catastrophic failure.

How did I do? Clear as mud?

 

[CZLN6]

Howdy Back:

WOW!!!! Thanks. You have shown how to objectively quantify dynamic compression. I'm sure that I didn't get the math the 1st time through (Or even the 2nd or 3rd time) but the concept is a great big "A-haa!!!!".

Thanks for sharing.

Adios, David

 

[lyonsy]

thanks for that xpc so what do you mainly muckaround on?
this should be a sticky

 

[rbohm]

How did I do? Clear as mud?

8) very clear, as quick sand. it is an excellent piece on dynamic compression. i am going to have to work on wrapping my head around the mathmatics though as it has been some time since i have dealt with this level of math.

 

[Stubby]

8) I knew the math would be huge on this one. I have never delved that deep into compression. It will also take some time for me to digest and play with those computations. However, if a guy could insert those formulas into a spreadsheat, he might could just fill in the proper blanks on the variables and have an easier way to compare.

I started putting some of down on paper without the metric system, and it doesn't look quiet as intimidating.

Thanks XPC66

 

[XPC66]

It's really not that hard. It just looks like it because there's a few steps.

Yes Stubby I wrote it so a spreadsheet can be used. I have written little Javascript routines for another site that work quite well too.


Ok this might also help, especially for all those budding turbocharger guys who think they have to decompress their babies, when all they have to do is change their camshaft.

This info is based on guys spending their own money to prove my assertions over the years. So far so good, but I don't take any responsibility for failures, only the platitudes of success.

You've worked out your DCR, pat yourself on the back for finally figuring out what the cos and sin buttons are for on the calculator, then sit around twiddling your thumbs wanting to know what to do with the figure. Well you could use it for a BMEP calc (e.g exhaust temp, power, torque, etc) or better still you could whack in a turbocharger and have some beasty fun.

So the limiting factor for most street car DCRs is fuel, more succinctly the ability of the pump fuel to resist det.


a DCR of 7.0 -7.5 is for MR McGoo motoring, it's safe as houses, you can run on just about any old pump fuel. Typically your car has a small bore exhaust to keep the torque up in the low and middle range revs, plus the intake side is strangled to stop reversion and it's a real aesthmatic when it comes to top end performance. Great family car for economy.

a DCR of 7.5 is really the bottom limit for those that want to beat that Datsun 120Y or Proton Satria that seems to always want a drag at the traffic lights. This is generally where you can feel the seat back when you punch the accerator. Will run quite well on regular unleaded.

inching up into the DCR 8 range you are starting to look at PULP as a necessity. By 8.5 you will definitely need to be running PULP otherwise it's likely you will have the occassional carillon of bells that ring out from the engine as pinking starts (det has probably already been pocking the pistons). At 8.5 you need strong internals.

by the time you have a DCR 9 you should be looking at race cocktails.

If you are contemplating a turbocharger you need to knock a full point of the above DCRs. So in our example of the Falcon with a DCR of 7.2, with a turbo it would be equivalent of a DCR 8.2 unforced engine for fueling requirements. This tells you that some serious thought to semi forged pistons and forged rods is in order. A safe as houses turbo engine usually has strengthened rods and pistons anyway, but will run quite happily until the clutch gives out when the DCR is around 6.8 on regular fuel. Don't go too overboard on getting kryptonite rods and pistons, the forces on the piston are far less jarring than on an unforced engine.

For those that insist that a turbo should have a CR of 8 , think again, because while that figure was derived from aviation tests circa WWII, they didn't have the metalurgy nor microprocessors we enjoy. One project I'm currently giving advice on is street VH45 running CR9+ with 20 -25 pound boost... you can do the maths on what sort of power that is.

Most times the LSA dictates the best driveabilty for purpose ( vacuum brakes, lope, economy, etc). So with that limitation, the static compression ratio (CR) gets driven down.

 

[xctasy]

Cool, you show the proper use of they key absolutes in science, which is what I like.



Depending on who you listen too, the key idea is to maintain the stock Cold Cranking Compression figure as the stock engine when you do any performance upgrade. So if its 1130 kPa, then the kPa after turbo or cam changed shoudl be the same. Other engineers who screw together big buck engines with forged pistons say just keep it below 1300 kPa.

XPC 66, your excellent work is a fine amalgam of two pivitol works, Dynamic Compression one dating back to the 70's, the other, a comparitively new thing from Car Craft and Hot Rod, called Cold Cranking Compression


Firstly, the calculation for DCR listed above was discussed and used in British book called 'Practical Gas Flow' back in the early 80's, but was in existance before then in books like the late Aussie Repco and Vincent engineering technician Phil Irving wrote. He posted it in 'Tuning For Speed' in 1960 something.

DCR calculation you listed is correct, and has a past precedent. It already exists on the internet, and was shown in a post back in 2003 by Jeremy Diamond/Panic/Kitabel.


I'm very familar with it, and have used it since 1991 when I used it for getting a special cam made up for an old car I was working on.


Secondly, the actual assigned pressure is really the Cold Cranking Compression value (CCC). I'll give you that one too.


It is absolutely known to stagger around quite a bit, by virtue of some of the things you have stated, plus some other aspects. It looks fair enough, but there is a grain of salt against other dimensional variables which can themselves vary by =+/- 5% each

They are influenced by

1)real cam timing (advanced, retarded, heads up, even a worn link belt chain can hurt the CCC figure by 50 kPa),

2)valve lash or lifter bleed down
3)the seal from oil and rings (varies for any given pressure by quite a large amount),
4) ring blowby or wear.

Although the last two are ony 5 cfm at best at 5000 rpm on a good I6, they are the values that influence the results the most. Wear, as you noted, could triple or quadruple blow by at 5000 rpm, and technically, on a cold cranking compression basis, it could go down 500 kPa on a very tired engine.

I've found that when you go back through all old Car Craft and Hot Rod articles that started linking awfull street performance of race cameed cars being healed by having cold cranking values below 1300 kPa (190 psi), they locked on to a whole range of ways to make a , say, 320 degree cammed 350 run at 190 psi when it used to run at 210 psi.
Thats where I got 1, 2,3, and 4 from.


Car Craft and Hot Rod articles also discused the actual level of difference in blow by from the few times a piston marker actually was bold enough to put a figure on ring flutter and blow by, and do a X Y plot. This was done in 1995 by Car Craft from Keith Black development work on a 305 Chev engine. Thats where the 5 cfm per 5000 rpm comes from.

Of honouable mentions is David Vizard's assessment of the Compression ratios which keep out of incipenet knock for Ford Pinto and A-series Mini and Healy Sprite engines. He graphed it against total cam duration and static compression ratio. He locked down the dimensional variables, and got the science related back to the field.


I totally accept your rationale that has been used in this case.

Despite this, I would, from hard earned partical experience never, ever use it because the numbers that CCC yield is a sort of like a health card or like a measure of potential insurance risk. Ford engines are the exception, because Ford engines detonate like no other. Proof is in the large amount of totally nerked Ford engines which have grenaded while leading races. The pre 1985 Cleveland V8's, X-flow I6's and Pinto OHC 4 are going to detonate well below the 1300 kPa CCC values Car Craft/Hot Rod suggested because the problem is either plug placement, chamber or inlet port stagnant flow (lack of axial spin), and they could well be scrap well below the values you quote when boosted or a reprofiled cam is added.

I've seen this first hand with the figures on my friends 351C 2V we made back in 1988. 185 to 200 psi was the Phase 3 GTHO recommended cold cranking pressure with the often quoted 10.7:1 figures and a 290 degree, 500 thou cam. On my mate Blair Gregories engine, detonation killed $8 000 worth of work at just 10:1 compression on 97 octane leaded with a nice high lift 296 degree Heatseeker cam. The damage was not noticed until an issue with cold piston slap forced a rebuild. This is an issue so common with Fords, that I have to say keep away form the formula, and get a reality check.

The modern engine is detonation limited: and the whole reason why Chevy run high spin 2 valve per cylinder V8's from 1996, and why Ford re-energized the old Windsor 5.0 back in 1980 was because running modern canted valve Cleveland/Pinto/X-flow engines on 87 to 93 octane unleaded creates dangerous detonationation at even 1130 kPa. I've done it on my X-flow with 9.7:1 compression, 256 degree Heatseaker cam, and 98 octane Rockgas...detonation so bad it melted the exhast port around the valve seat.

 

[XPC66]

You are giving yourself away as old school. I wondered who'd pop their head up... trust a kiwi to be first off the blocks.

I'm not going to respond to the wear, slack, etc, because, of course you are right. Should I have taken those variables into account, there'd be too many if, buts , maybes and I'd be forever including caveat emptors.

Insofar as the formula, well that's no biggy, it's just Pythagorus. Which I might add, I was discussing on those BBS forums way back in the early 90's and have used since circa 1960's when every guy with a black T shirt and a pack of Peter Stuyvesant rolled in his sleeve would use a similar, but simplified version.. probably known for over a century.

I found your info on the clevo motors suffering det very interesting. I've always had a soft spot for those from the moment I set eyes on the last GTHO. I seem to remember they relied heavily on swirl and lead to keep the exh seats cool and stop valve cordial breaks plus tuliping. Of course having big diameter exhaust valves always creates problems with adequate quenching, even with stiff springs and good seating. Fairly remarkable motor though with Valve area to Bore area such a relatively poor ratio.

I'll still stand by what I've posted, but I appreciate your caution. The idea was to throw one aspect of good engine design into the soup. There's always mitigating circumstances, just as there are always workarounds.

 

[XPC66]

:....., and why Ford re-energized the old Windsor 5.0 back in 1980 was because running modern canted valve Cleveland/Pinto/X-flow engines on 87 to 93 octane unleaded creates dangerous detonationation at even 1130 kPa. I've done it on my X-flow with 9.7:1 compression, 256 degree Heatseaker cam, and 98 octane Rockgas...detonation so bad it melted the exhast port around the valve seat.

I'd be interested in workshopping this one to see where things went pearshaped for you. Do you still have the specs, ignition timing, egt, cht, CO%, etc?

 

[lyonsy]

can some one please work out my effective compression ratio from these i dont have a scitific calc handy.
head camber 50cc
head gasket bore 3.779
head gasket thickness .46 thanks xpc
head gasket volume 8.45cc
pistons down bore .000
piston volume 4.6cc
comp 12.1
this is for a 2v standerd head which is about to have 200rod xflow pistons dished with 15thou taken off giving zero deck.
the cam will be a wade 140
ivo 40 ivc 70
evo 74 evc 41
lobe 105.8
valve overlap 81
inlet duration 290
exhaust duration 295
lift in .432
lift ex .432

carby will be a 500holley on a standerd intake with pacemaker tuned length extractors

thanks in advance
mark

 

[XPC66]

You can do it yourself with google, using this form:

RL - sqrt((RL^2) - ((0.5 * S * sin(x degree))^2)) + (0.5 * S * cos(x degree)) + (0.5 * S)


e.g. if you put the equation into google search for the example I worked out earlier it would be :

153.92 - sqrt((153.92^2) - ((0.5 * 99.31 * sin(63 degree))^2)) + (0.5 * 99.31 * cos(63 degree)) + (0.5 * 99.31)

copy and paste it and you'll see what I mean.

Good luck with that DCR and pressure.

 

[lyonsy]

thanks for that
iam a bit lost but been a few years since yr12 math
153.92 - sqrt((153.92^2)
so this is the conrod length?
- ((0.5 * 99.31 * sin(63 degree))^2))
cam timing inlet?
+ (0.5 * 99.31 * cos(63 degree))
cam timing exhaust?
+ (0.5 * 99.31)
stroke length?
so how did you get the 63deg ?
and i am very unsure what the result is being
78.6935799

159.33 - sqrt((159.33^2) - ((0.5 * 99.31 * sin(63 degree))^2)) + (0.5 * 99.31 * cos(63 degree)) + (0.5 * 99.31)
= 78.4638197

i think you used the 6in rods whre ill being the 6.27in ones 159.33mm long
so is the comp bad or good for pump fuel
thanks for that although i am a little more confussed lol

when in doubt read read read read read i think iam getting on right track

the calc before was for the effective stroke of the engine when it was compressing the air with the valve closed.

so the next part is
78.4638197/99.31
effective stroke/act stroke
= 7.90
so i then go
(0.790x12.1) + 1
= 10.559 act comp

so the specs whoul;d be 12.1 static comp
10.5 dianamic comp
swept cyl volume 696.33cc
total combustion vol 62.84
bemp of 159.8 psi

iam unsure on this part but
((10.55000^0.283) x 101.32 x 10.55000) - 101.32 = 1 980.90706
is that x correct and is that 1980 kpa
or 287psi
if so i think it may be a bit high for pump but whould love methnol lol

so did i get the calculations right?

 

[XPC66]

The example was for my original calc. I just threw together figures I gleaned from my EB manual.

for yours the calc would be:


159.258 - sqrt((159.258^2) - ((0.5 * 99.31 * sin(70 degree))^2)) + (0.5 * 99.31 * cos(70 degree)) + (0.5 * 99.31)

= 73.626 mm

effective stroke ratio = 73.626/99.31 = 0.741

your static compression is 12.1 you say so the DCR
= (0.741 x 11.1 ) +1
= 9.23

 

[lyonsy]

thanks thats a bit less comp i was just starting to work out comp for a different set of pistons lol
ok so with the sin and cos there cam timing on closing
so should they be in 70 ex 74?
thanks for all your help on this to xpc gotta get us vics beating those cheating south aussies lol

159.33 - sqrt((159.33^2) - ((0.5 * 99.31 * sin(70 degree))^2)) + (0.5 * 99.31 * cos(74 degree)) + (0.5 * 99.31) = 70.3272538

70.32725/99.31 = .708

(0.708 x 12.1) + 1 = 9.5668

((9.5^0.283) x 101.32 x 9.5) - 101.32 = 1 718.86096
249psi

so does that all work out to be right? i think it does?

ok using using 250 rods 149.35 with an 8.6cc dish zero decked with a 60thou copper head gasket
149.35 - sqrt((149.35^2) - ((0.5 * 99.31 * sin(70 degree))^2)) + (0.5 * 99.31 * cos(74 degree)) + (0.5 * 99.31) = 70.8177
70.8177/99.31 = .713
(0.708 x 10.98 ) + 1 = 8.82874
((8.8^0.283) x 101.32 x 8.8 ) - 101.32 = 1 548.61353
1548kpa 224 psi

ok so basicly i have to run stock low comp pistons with like a 20cc dish to be able to run the engine with out any problems and may be why i had the ring lands fail on the old pistons which had a 11cc dish which with a standerd gasket gives around 11.0:1
but it did not ping once but may have had high speed det.
i still cant understand how some guys are getting away with 11/12.0:1 comp on xflows if there det prone any idea's?
thanks for the help xpc much appreicated

 

[xctasy]

:....., and why Ford re-energized the old Windsor 5.0 back in 1980 was because running modern canted valve Cleveland/Pinto/X-flow engines on 87 to 93 octane unleaded creates dangerous detonationation at even 1130 kPa. I've done it on my X-flow with 9.7:1 compression, 256 degree Heatseaker cam, and 98 octane Rockgas...detonation so bad it melted the exhast port around the valve seat.

I'd be interested in workshopping this one to see where things went pearshaped for you. Do you still have the specs, ignition timing, egt, cht, CO%, etc?

It's nothing to see 480 000 kilometer XE Falcons out there, but mine expired at 185 000 km due to messing with the basics. My old XE Falcon had stock automatic XE ignition, 9 btdc timing, and stock 2-bbl Weber ADM 34 with Landi Hartog mixer. The compressions were 165 psi before and after the head was rebuilt. The cam specs were HS10E, a brand new cam based on a reworked version of Fords standard OHV master cam used in the Cleveland and X-flow. I've got specs somewhere.

Basic issue was that the cooling system on NZ spec Falcons was very small. There was no EGR on these engines, so no means of heating was causing problems. The LPG and general CO count was very lean, below Landi Hartogs recomendations for at load CO. Idle Co was fine. The fuel consumption was poor (12 to 17 imperial Miles per gallon, 20 to 16 litres per 100 Km), despite under load CO's were a little leaner than the LPG technician would like. He said the mixer was basically Twin Cam 2000 cc Fiat 131 for ADM 32 and 34, and too small.

The fully rebuilt Alloy Head engine suffered less than ideal performance, poor fuel consumption, and the base idle on the vac gauge was only 60 kPa. It detonated under load, insignificantly, and this was not noted by sole driver (my beloved) and it expired with head gasket failure between 5 and 6, exhast seat failure on No5, and removal showed that there may have been underlying issues with head gasket replacement, but it was none the less still the stock Monotorque gasket. I don't belive it to be water jacket corrosion, although the radiator and cooling system were never serviced properly.

I installed a 3 core A/C EFI spec radiator, then added 2-bbl 500 cfm throttle body with 432 cfm A5 300A Impco carb and L-series converter. Deleted heat stove, used 74 mm tall, 254 mm diamter 318 Dodge truck AF1 spec A391 Ryco air cleaner,no cool air ducting. Added extractors.Under bonet heat was actually worse 20 degrees more with Raytek infrared detector checks. Gas flowed the intake via radius and die grinder work, anti reversion plates to creat a port miss-match, port missmatched 12 mm Redline Holley Weber 5200 to Holley 2300 adaptor. Basic idle vac dropped to 57 kPa, but fuel economy improved 22% on open road. Stock ignition settings still used, never a detonation problem again. In my opinion, if the wrong choices on carb, or maintenace can push an engine with normal factors of safety into detonation, then that's proof that the detonation treshold is too close.

The issue for me is that a bunch of people have cited the canted valve high swirl engines as having problems with detonation stock. cf. XF Falcon Alloy Head II especially. Other notible mention, the closed chamber 302 2V (like Blairs) and the closed chamber 4V 351 heads specifically. Both have black marks from me, because they've done me and others I know wrong even with a high anti knock idex fuel like old Super Leaded 97 and good NZ spec lp gas.

The modern canted valve Ford engine is detonation limited. Compression ratios are way above the pack. We never got the low compression standard fuel Taxi Pak XC, XD 3.3 and 4.1 cars over here, all were the 8.9 to 9.15:1 or higher versions. Even an iron head X-flow is rougher and less refined than the old wedge headed non cross flows. Same deal when comparing a Windsor to a Cleveland. The former is refined and well mannered, the Cleveland is a bit of a mongrel with choppy idle even without ADR 27 gear on it.

I endorse the views of Bill Santacocione and Kevin Bartlett. These engines run close to incipient detonation. I always underline that running close to detonation is courting calmity because these Ford engines are rough and hard core even with the little cams on stock engines, so you never, ever notice when they are getting close to the Big Bang. My TD Cortina C3 Auto ran a 9.2:1 Cortina GT engine, with manual ignition, and it was an impossibly difficult engine to tune the detonation out of. Just a few degrees of added advance, and it was a victim of blown head gasket and early replacement on a 30 thou over block which had seen only 15 000 km's.

From 1969 to 1985, all canted valve Fords carried way too much geometric compression stock for anything other than 97 octane leaded. They gave great performance at the expense of engine life if any change to Fords specified fuel brew was made. 98% of Aussie Clevelands were shopping duty engines, and they had components downgraded on the up spec GTHO engines. These often suffered an adversely short service life, especially when the high Benzene low lead fuels with really awfull 6 week anti knock indexes were used by fuel companies in NZ from 1996 onwards...valve springs, collets, retainers, pushrods, sled fulcrums, and main bearings showed some stress when they had coped with leaded 97 for years. When aromatic hydrocarbons are above 41%, you get real problems with canted vlave engines running.

I've got a few engine builder mates, and they saw something strange in the mid 1990's. Come unleaded 96, a comon XF or Cleveland rebuild showed very acute detonation hall marks..rod bearings and main bearings exhibited faults like what Bill Santacocione saw in QC Phase Falcon engines. With respect to a Cleveland, how on earth a 2.75 main and 2.31 rod bearing could show signs of impact load on a nodular iron crank? It is beyond me, unless the engine was detonating for a long time. Stripped down engines after 96 frequently show this, even though most had been fed a diet of good multigrade oil, 96 octane super, and were well serviced.

From the factory data, we all know that the recomended cold cranking pressures were easily around 1130 kPa in these engines. Even an open chamber 351C carried 8.9:1 to 9.2:1 compression depending on year, according to Fords 95 th percentile engine specs.

Worst thing is, these engines ran high compression with fairly mild cam durations, poor cylinder filling, big ports, good carbuartion. Igntion ramps were mean best torque. Results were often the worst scenario for detonation you could get.


The Cortinas ran 264 degree cams with big ports, Falcons had 256 (or 264 degree on later EFI 4.1's). It is these frequently rebuild and benchmarked engines, not the wild Hoey's that suffered damage.


Ocassionally you'd get any one of the wild GTHO spec 290 or 300 degree cams, and if it was run of avgas or good 96 octane with some aditive, it'd be fine.


I know this is all anectotal, and it doesn't plot to the math inputs. There is not a list of service data a mile high with details gathered to any rational standard. So most car makers say unless there is proof to the contray, its all to do with service life of 20 to 40 year old engines, not a fuel or incipient knock issue.

I respect math and logic, but if the real "works in progress" are showing some evidence of seamingly UFO influenced damage, then there is a cautionary exclamaition mark to be applied.

Sadly, the evidence is lost in engine builders lamentalble lack of ability to document the differenece in service life of these engines, but factory pre 1986 engines in service around 1996 suffered greatly when fuel composition changed. No X-flow ohv engines are managed to use knock sensors and fuel feedback O2 sensor, so a protective mechanisim of all post 1993 Ford engines is gone.

I don't accept that safety occurs with the use of the details, because the evidence is that canted valve fords from 1969 to 1985 are a real risk, and even low compresson Falcon Utes from 1986 to 1993 are not immune from longievity problems.

 

[XPC66]

thanks thats a bit less comp i was just starting to work out comp for a different set of pistons lol
ok so with the sin and cos there cam timing on closing
so should they be in 70 ex 74?
thanks for all your help on this to xpc gotta get us vics beating those cheating south aussies lol

159.33 - sqrt((159.33^2) - ((0.5 * 99.31 * sin(70 degree))^2)) + (0.5 * 99.31 * cos(70 degree)) + (0.5 * 99.31) = 73.626 mm

73.626 mm
/99.31 = .0.741

12.1 -1 =11.1

(0.741 x 11.1) + 1 = 9.23

((9.23^0.283) x 101.32 x 9.23) - 101.32 = 1652 kPa
so does that all work out to be right? i think it does?

ok using using 250 rods 149.35 with an 8.6cc dish zero decked with a 60thou copper head gasket
149.35 - sqrt((149.35^2) - ((0.5 * 99.31 * sin(70 degree))^2)) + (0.5 * 99.31 * cos(70 degree)) + (0.5 * 99.31) = 74.11
74.11/99.31 = .746
(0.746 x 9.98 ) + 1 = 8.445
((8.445^0.283) x 101.32 x 8.445) - 101.32 = 1464kpa = 212psi

ok so basicly i have to run stock low comp pistons with like a 20cc dish to be able to run the engine with out any problems and may be why i had the ring lands fail on the old pistons which had a 11cc dish which with a standerd gasket gives around 11.0:1
but it did not ping once but may have had high speed det.
i still cant understand how some guys are getting away with 11/12.0:1 comp on xflows if there det prone any idea's?
thanks for the help xpc much appreicated

I think I edited that enough to follow.

Guys get away with high comp figures, because they lie mostly, have very long duration cams, run correct fueling, have fast flame fronts, precise ignition timing, etc.

 

[XPC66]

xecute, thanks for that. In the meantime I did my own checking and indeed the cleveland was a casuality of the emmissions rules. Thanks for the run down though. Sounds more like they suffered from insidious knock, rather than incipient.

 

[xctasy]

Sounds more like they suffered from insidious knock, rather than incipient.

I really like Clevelands and X flows. I guess they don't have all the precautions of the post 93 Fords, and yet they need to be 'kid golved' only with respect to knock/detonation, and perhaps, the cylinder wall quality on the US sourced Cleveland engines. The Aussie engines were rather better than the US ones, for casting thickness at the cylinder walls.

You've summarised my 16 years of one of the joys of math and engineering into a few short lines. Keeping using you talent to inform us

I applaud you for having a good, logical script format, and a good logical means of assessing compression. You clearly disccues the varaiables first up. This is general ledger discussion, where you declare the variables, and then back it up with the facts. If discussions were all based on bringing knowledge to the table, man, what advancement there is!

That's why we have sections like this. Application of just a few grams of grey matter to green iron sands of practical experience makes the I6 sections of the internet one heck of a lot of fun.


The forth commendable thing is its not ......"my engine is running CR 12.5, what size is your dick?"

No-one has the monopoly on the truth if it comes with an acusational attitude of ' your privy members too small, mines bigger, your brains too slow, mines faster, your too dumb, I'm smarter'.

Go look anywhere else, and thats what you find on the net, and that's the reason I stay here...you guys are realistic enough to discuss it without bringing anything else but experience to the debate.

I'll find those HS 10E figures somewhere...hmm, it may have been a 252 degree cam... http://www.kastang.net/fsp/xecute.html

 

[lyonsy]

how did you get this i understand the rest just not this
12.1 -1 =11.1

 

[xctasy]

It's okay, brother. This is hardcore. That means its a little too hard to explain everything, but we won't call you names for asking.

Think laterally, and you'll get it. I'm stupid enough to respect every member, and I'm a 6750-AA (Dipstick)

12 point 1 minus 1 is 11 point 1.

Its not 12 * 1 - 1

Only Europeans and Math teachers use the decimal point as a times sign.



You'll see it soon. Mean time, read these.

Actual call centre conversations !!!!!

Customer: "I've been ringing 0800 2100 for two days and can't get through to enquiries, can you help?".
Operator: "Where did you get that number from, sir?".
Customer: "It was on the door to the Travel Centre"
Operator: "Sir, they are our opening hours".
-----------------------------------------------------------------------------------------------------------------
Samsung Electronics
Caller: "Can you give me the telephone number for Jack?"
Operator: "I'm sorry, sir, I don't understand who you are talking about".
Caller: "On page 1, section 5, of the user guide it clearly states that I need to unplug the fax machine from the AC wall socket and telephone Jack before cleaning. Now, can you give me the number for Jack?"
Operator: "I think you mean the telephone point on the wall".
----------------------------------------------------------------------
RAC Motoring Services
Caller: "Does your European Breakdown Policy cover me when I am travelling in Australia ?"
Operator: " Doesn't the product name give you a clue?"
----------------------------------------------------------------------
Directory Enquiries
Caller: "I'd like the number of the Argoed Fish Bar in Cardiff please".
Operator: "I'm sorry, there's no listing. Is the spelling correct?"
Caller: "Well, it used to be called the Bargoed Fish Bar but the 'B' fell off".
----------------------------------------------------------------------
Then there was the caller who asked for a knitwear company in Woven.
Operator: "Woven? Are you sure?"
Caller: "Yes. That's what it says on the label; Woven in Scotland ".
----------------------------------------------------------------------
Tech Support: "I need you to right-click on the Open Desktop".
Customer: "OK".
Tech Support: "Did you get a pop-up menu?".
Customer: "No".
Tech Support: "OK. Right-Click again. Do you see a pop-up menu?"
Customer: "No".
Tech Support: "OK, sir. Can you tell me what you have done up until this point?".
Customer: "Sure. You told me to write 'click' and I wrote 'click'".
----------------------------------------------------------------------
Tech Support: "OK. In the bottom left hand side of the screen, can you see the 'OK' button displayed?"
Customer: "Wow. How can you see my screen from there?"
----------------------------------------------------------------------
Caller: "I deleted a file from my PC last week and I have just realised that I need it. If I turn my system clock back two weeks will I have my file back again?".
---------------------------------------------------------------------- -------------------------------------------
There's always one. This has got to be one of the funniest things in a long time. I think this guy should have been promoted, not fired. This is a true story from the Word Perfect Helpline, which was transcribed from a recording monitoring the customer care department. Needless to say the Help Desk employee was fired; however, he/she is currently suing the Word Perfect organization for "Termination without Cause".
Actual dialogue of a former WordPerfect Customer Support employee. (Now I know why they record these conversations!):

Operator: "Ridge Hall, computer assistance; may I help you?"
Caller: "Yes, well, I'm having trouble with WordPerfect."
Operator: "What sort of trouble??"
Caller: "Well, I was just typing along, and all of a sudden the words went away."
Operator: "Went away?"
Caller: "They disappeared."
Operator: "Hmm So what does your screen look like now?"
Caller: "Nothing."
Operator: "Nothing??"
Caller: "It's blank; it won't accept anything when I type."
Operator: "Are you still in WordPerfect, or did you get out??"
Caller: "How do I tell?"
Operator: "Can you see the C: prompt on the screen??"
Caller: "What's a sea-prompt?"
Operator: "Never mind, can you move your cursor around the screen?"
Caller: "There isn't any cursor: I told you, it won't accept anything I type."
Operator: "Does your monitor have a power indicator??"
Caller: "What's a monitor?"
Operator: "It's the thing with the screen on it that looks like a TV. Does it have a little light that tells you when it's on??"
Caller: "I don't know."
Operator: "Well, then look on the back of the monitor and find where the power cord goes into it. Can you see that??"
Caller: "Yes, I think so."
Operator: "Great. Follow the cord to the plug, and tell me if it's plugged into the wall.
Caller: "Yes, it is."
Operator: "When you were behind the monitor, did you notice that there were two cables plugged into the back of it, not just one??"
Caller: "No."
Operator: "Well, there are. I need you to look back there again and find the other cable."
Caller: "Okay, here it is."
Operator: "Follow it for me, and tell me if it's plugged securely into the back of your computer."
Caller: "I can't reach."
Operator: "Uh huh. Well, can you see if it is??"
Caller: "No."
Operator: "Even if you maybe put your knee on something and lean way over??"
Caller: "Oh, it's not because I don't have the right angle - it's because it's dark."
Operator: "Dark??"
Caller: "Yes - the office light is off, and the only light I have is coming in from the window.
" Operator: "Well, turn on the office light then."
Caller: "I can't."
Operator: "No? Why not??"
Caller: "Because there's a power failure."
Operator: "A power......... A power failure? Aha, Okay, we've got it licked now.
Do you still have the boxes and manuals and packing stuff your computer came in??"
Caller: "Well, yes, I keep them in the closet."
Operator: "Good. Go get them, and unplug your system and pack it up just like it was when you got it. Then take it back to the store you bought it from."
Caller: "Really? Is it that bad?"
Operator: "Yes, I'm afraid it is."
Caller: "Well, all right then, I suppose. What do I tell them??"
Operator: "Tell them you're too stupid to own a computer!!!!!"