All Small Six Bumping up those cranking numbers?

This relates to all small sixes
clochard68

clochard68

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My 200 is running happily on 90 octane (95 octane RON here in Europe) with a cranking pressure of ~175 PSI at around 8:1 DCR.

I am pulling my cylinder head and got the chance to bump up the compression, I was thinking about ~195 PSI.
Fuel would be changed to 93 octane (98 octane RON).

Anyone any experience with higher compression on iron heads? Good idea, bad idea? What does the forum think...
 
I dont think I coulld predict the future availability of higher octane fuels but maybe others here can.
higher compression means more piston ring blow by, but maybe that's not a problem.
others here know the engine better so they can probably give better answers from experiences.

My personal choice woudl be to try to increase the bore size, polish ports mate up the manifolds nicely, balance and maybe a different cam and still have the ability to run the fuel thats available.

i think I'd make decisions based upon what I knew about the condition of the bores and pistons.

a source of error may be in the battery voltage when doing compresion tests, a weak battery may crank the engine slower and that could potentially skew the readings ? if it;s an eevn 175 , so to me that means it doesnt; need new pistons so I might like to opt to not fix what's not broken some depends on the time and budget of course.

if you want more pick up and go , lower gears maybe? in my 66 volvo I put in overdrive and it was a bit too high geared so I changed by crown and pinion and while at it, every bearing too. I could not get new spider gears so I set it all up best as I could and I think I got that all nice. with the lower gears it not only increased its pick up and go but it also felt better as doing so removed a lot of the backlash from the drivetrain.

if you jack up one back wheel and put it in gear , how far can you turn the wheel? thats an easy way to get a measurement of this lash at least comparing versions of the same car. what I found is it didn't affect it under hard driving but in slow traffic the lash in an old car can become a bit annoying. When driving at 4 K per hour along with new cars that are happy to do that, id be in second and feathering my cluttch otherwise it was l too jerky, my first gear is very low. It comfortably starts off in second but I;d just be slipping the clutch a little and rolling along to go that speed. too fast clutch in to slow clutch out, like that.

you may to want a lower ratio you'd have to think about how much highway driving you do and what rev you are at at your highest speeds, In my case the overdrive covered that issue as it went from 1-1 in 4th to to 1-1.25 in OD

I think if you can do stuff to make it tight and have good compression , thats preferable. and if you can increase its' RPM range then thats a way of gaining top speed , and then maybe lower gears make more sense. If you can do stuff like matching displacement and balancing the parts then it shoudl run at higher RPMs and feel comfortable. if you are ointo changing cams and top end parts then maybe there are some gains there.
others here are more knowledgeable but what suprised me with the 300 is the freakishly low RPM range. Its a solid engine so I guess the racers are able to advise on that.. but to me it seems overbuilt and with pretty low performance and rather poor mileage as a stock engine. durability was where it shined.

shaving the head or a thin gasket wouldn't be my preference although its not very expensive. I thinnk you can get more
power without needing high octane fuel, but it probanbly also costs more to do so , so the budget has a big influence on those decisions.

most of my experience is with old volvos but what i see in common is they are both rock solid engines that never were designed as performers. That means when you go hopping them up, they can still hold together. I think balancing the parts makes a big difference and that may not be so expensive as first imagined. the other thing in common is the weight , you can't get a good power to weight ratio like a new import unless you start removig OEM stuff to reduce weight. because that starts at the design phase. of course that also ruins any collectability value at least unless you are in the vintage racer crowd.

in my case with my car being old enough to be soeme what collectable ( although a bit rusty) I did not want to change too many physical features but I did swap to a larger valve head, hotter cam, porting, balancing , stuff the casual viewer can't see and that was my personal preference. i was able to increase the bore size from 1800 to 2 litres so that of course gave me more power. I could do that because the block was so thick and overbuilt. my aim wasnt; to win races or anything but to be able to keep up to modern traffic more comfortably.

my results were that the thing is now so much fun to drive and it soumds great up at higher revs and that makes me smile so much that I need to refrain from driving it. Ill go for a mad blast and get that sh_ eating grin on my face a few times a year and say to myself . ok what a blast, now settle down, or youll wreck your fun toy or wipe it out lol.. You can go so far that it's not practical as a daily driver but that's fun too. I'd think about your preferred end goal and then ask the more knowledgeable here what to to to achieve that, and consider the cost of such a process. Maybe you can go to a larger valve head?

now some have nice cars and they are so original that they care about things like matchingnumbers. at least a head gasket is pretty easily reversible and it would be hard to see anything like if you do put i ti n shows. If you are lucky enough to have a rather stock car then there is some prestigue in keeping it like that and not modifying. in some cases it may decrease value I bet there are a lot more modified mustangs left and less originals. to collectors, originality can mean a lot.

I know if Im looking to buy a car, Im really not interested in someone elses hot rod project, Id prefer an old original car and if I wan to go all out and do some performance upgrades . then Im not fixing some mess that someone else created for me. or buying a car that was driven really hard. same with sterios, a big boom box, to me it just means some kid previously owned it and probably thrashed it. I think we often wreck our first couple of cars. I'd pay more for originality than mods.
 
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relevant earlier post:
keep it simple - run some Compression-calcs' for head chamber volumes until they seem to match your target CR, then consult ..

actual volume measurement is best but can be tedious, my machinist simply subtracts how much has been milled from the OEM specs on the head which is OK IF head is uncut already... Typically, milling the head .010" will result in an approximate reduction in volume of 2cc's.
from CI pages:
'actual chamber volumes may vary considerably, which means they must be re-measured (cc'd). The key is to measure carefully and record the results, then mill the head accordingly to obtain the desired compression ratio.'
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typically, milling the head .010" will result in an approximate reduction in volume of 2cc's. For example: if your cylinder head currently has 62cc chambers, and you want 52cc's, you would need to mill .050" off the head to reduce the chamber volume by 10cc's.

it's said small block six cylinder heads can be safely milled .090". (??)

DODE _70 Mav' 170 'closed chamber ' head OEM @ 54cc's measured and typical later 200/250 @ 62cc chamber head.

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'63 moredoor wagon has a C8DE Maverick 170 with a D7DE head cut @ .070 (@ 48CC Chambers) with an early steel shim 144/170 - 3.75 bore head gasket ( @ .025 ) ( 200/250 = 3.81" bore) yields up SCR @ 9.5 or higher... . (Unfortunately the thinner steel shim gaskets are virtually unobtainable for the 200/250 3.81 cylinder bore ) BTW - flat top 170/144 pistons skew the compression calcs' results from 200/250 recessed piston cc's measurements. The '63 170/T5 is plenty adequate for modern driving with @ 93 Octane (U.S.) .
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I am at 46.5cc chambers at the moment, if I bump up the compression I will do it by shaving the head.

@powerband do you know your cranking pressure on your 170?
 
clochard68 said:
I am at 46.5cc chambers at the moment, if I bump up the compression I will do it by shaving the head.

@powerband do you know your cranking pressure on your 170?
Click to expand...
If the required fuel is available, and you don't mind paying for it- more compression= more torque across the board.
clochard68 said:
My 200 is running happily on 90 octane (95 octane RON here in Europe) with a cranking pressure of ~175 PSI at around 8:1 DCR.

I am pulling my cylinder head and got the chance to bump up the compression, I was thinking about ~195 PSI.
Fuel would be changed to 93 octane (98 octane RON).

Anyone any experience with higher compression on iron heads? Good idea, bad idea? What does the forum think...
Click to expand...
 
? - 46.5 cc chambers sounds small resulting in high compression already , did you run 46.5 Comp Calc with 200 Deck, Gasket etc ..? .
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( PB = No don't know Cranking Pressure )
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have fun
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The chambers are measured as seen in post #138:

clochard68

All Small Six Thread '68 small log head porting [ including final DYNO RESULTS ]'

Hello,

I'm currently working on my 68 small log head.
First, I just wanted to state that I am fully aware that the small log head isn't worth porting/upgrading/throwing money at it, that the large log or aluminum or OZ 2V would be better choices. Two things make it hard for me to upgrade to one of the mentioned heads: I live in europe and they are hard to find online and I am obligated to keep my L6 as stock locking as possible to keep my vehicle registration (my 68 Mustang is registered as a classic car).

So I want to get as much out of my small log as I can, with porting, back cutting...
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My calculated compression ratio is 9.08:1 (7.95:1 DCR) at the moment.
It seems that nobody thinks more compression should be too much of a problem if paired with the right fuel, so I think I will try to get the CR to 9.6:1 (with 8.4:1 DCR) and see how the engine likes it.

Thanks everyone for the input, as always!
 
BTW - I use ARP head fasteners on the higher comp builds. The 250 with Vortech VII has a basically stock @ 62 cc chamber head with ARP fasteners to hold it down at 5-8 lbs boost (or more) at enthusiastic moments before running out of road... ...
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Thanks for the advice, didn't think about upgrading the head bolts at all...
I will order some ARP bolts, better safe than sorry ;)
 
@powerband would it make any difference if I used head studs or head bolts?

I would go for the studs because with them I don't have to worry too much about bottoming out in the block (luke with the bolts) since the head got shaved off quite a bit...
 
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