Compression ratio

S

six shooter maverick

Active member
Ok I'm trying to work out rod and piston combos that will live with a 60cc log head or the aluminum head.
My question is what would be the best static range that would work on a 250 and pump gas. I'm trying to get close on paper before I get the wrong parts.
 
Dont use the conventional replacement cast iron conrods with cast in part numbers like D6 or D8.

At a personal advice level only...Dont use 2300 HSC or 2500 HSO 4 cylinder cast alloy pistons with the 90 thou gudgeon/wrist pin offset. Plenty of people have used them and Does10s and TurboChicken (Will & Kelly) did a lot of 10 second dashes between the 1320 foot lines with 450 hp and 16 pounds of boost. Ecconoline uses the 2.5 liter Taurus HSO version remachined. Four members here have had major skirt failures with the 2.3 liter Silvolites. Since Silvolite make pistons for the Australian six cylinder Ford 250's, then you should by reliable crack free, American made Aussie 250 pistons and not have any issues.

Conrods to use are any forged steel 5.78" center to center C9 1969 to 1976 4.1 liter or perhaps 6.00" center to center E6 2.5 liter Taurus HSO.

For custom pistons, look at sleeving down the block to 3.63w or 3.700", and use 4032 alloy RaceTech or Australian spec but US made CP pistons with custom dishes to control compression dish to about 8.5 to 12 cc's. Don't use the 2618 alloy unless you are able to cope with the piston slap.

Compression calculations, talk to pmuller9.

Basically, for iron heads, the six week old gas ratings differ from the rated pump dispensor octane RON/MON average , but the pump call numbet should be your maximum static compression ratio. 87 can hack 8.7:1 static. 89 octane, 8.9:1. 93 octane, 9.3:1.

Aluminum's thermal conductivity allows a 0.5:1 safe increase in static compression. 87 octane, 9.2:1. 89 octane, 9.4:1. 93 octane, 9.8:1.

Mike1157 runs five pounds boost on 89 octane with a 10.7:1 compression ratio aluminum head 250 without methyl alcohol. It has a high duration roller cam, and runs 25 total advance with a degree retart for every pound of boost. It uses no knock sensor.

Others will weigh in this discussion. One thing is Ford, starting in the 5.8 V8 for 1980, used piezo electric knock sensors on various LTD's and then the F150 4.9s, 5.0s, 5.8s. They took out total timing in the Duraspark II or TFi module, and compression ratios skyrocketed in EFi Australian Ford from 8.8:1 with 91 octane in 1986 to 9.7:1 in 1993 with the same gas. So did the alloy head Sohc per bank Explorer in 1997. The knock sensor is simple to tune as it dials in to a frequency of 4800 to 5400 cycles per second, a triggers a drop in total timing.

The port EFi 5.0 for 1986 in the Mustang used 9.2:1 and 89 octane with TFi ignition and a knock sensor.

Your actual Dynamic compression and cam and timinig gear retard or advance then has to be matched to your ignition timing curve and type. If you go MegaJolt, reprogramed Thin Film Ignition or EDIS 6, you can go right to 9.7:1 on 87 octane if the peak advsnce curve is trimmed by a 30 dollar knock sendor.
 
"...is trimmed by a 30 dollar knock sendor...."
where placed? Meamega muncher but pre-1980s engines - little to noinfoe...
I leave em to da boss & no not 2 ask Qs...
 
I think you'd put it in the block drain on the passengers side.

Xtasy has given you some good advise. You said 60cc log or the aluminum head, the aluminum head has 55cc chambers if your lucky. If you want to be able to use pump gas and have a head with 55cc or less chamber volume you're going to need pistons with large dishes. Supposedly the aluminum can take more compression, better conductivity and better chamber shape, but I wouldn't count on it for a daily driver. The 2.5 rods help make up for the deck issue w/o to much decking.

This thread has everything you need to know:

viewtopic.php?f=1&t=77057
 
As for rods I'm looking at the 2.5 USC. I been running the calculator on dish cc's. I also calculate both heads stock at 60- 62 cc and alu at 54cc.... th aussie pistons with a 28cc dish is way to much and 6.5 cc not enough my head is spinning so fast
 
"...not enough my head is spinning so fast..."
yeah, me too, but not on my block...on my shoulders...8^0
har dee har har !
 
The battery strap hookes to the front passenger side head stud/bolt that goes right through to the water pump. The knock sensor bolts on that for 1986 to 1991 overhead valve 3.3 and 4.1's. The Electronic Spark Timing pulls out 10 degrees of advance from the TF ignition.

For Aussie OHC/DOHC's from 1993 to 2016, the knock sensors were block mounted into the water jacket just like the 1987 to 1996 EFi 4.9 Big Sixes. Water doesn't change knock frequency or sound as the sensor bolts to an iron bolt or iron block, which picks up knock like a tunning fork attracts a spider on a web.

Every Ford in line small six from the 1960 144 to the 1983 200 had the same earthing strap access bolt on the US passenger side front head bolt. It just bolts right in like everything else in the 200/250 engine series.
 
six shooter maverick":2k1r8893 said:
As for rods I'm looking at the 2.5 USC. I been running the calculator on dish cc's. I also calculate both heads stock at 60- 62 cc and alu at 54cc.... th aussie pistons with a 28cc dish is way to much and 6.5 cc not enough my head is spinning so fast
Click to expand...

Pat Kelly wrote a great little DCR calculator available at the bottom of this page. It will help you a lot figuring all this stuff out and with your cam choice.
 
The base timing is controlled by what was the white wire( but now the pink wire inder the new wiring colors) to the spark control unit. Blue strain relief takes 5 degrees off when cranking. Yellow strain relief takes off another 2 degrees. (DS ii for turbo and feedback carb 2.3/4.2/4.9/5.0 ) and Brown (Central Fuel Injection Duraspark 3) has a wire that electronically pulls spark. Red and green module strain reliefs are for Duraspark I's, the units are really strong, but can potentially kill people without the DS 2 safety wiring.

The knock sensor is a "do if true" test. If it detects knock, it cuts voltage to zero from 2.5 to 3volts, and then a signal is given to the spark unit to stall the spark timing via the pink wire. Its conveyed by a little knob used on feedback carbs on Jeeps, Ranger pickups before 1986, and all six cylinder feedback 4.9 carb trucks.

Process is this for the retard process on the carb 2.3 turbo

https://fordsix.com/viewtopic.php?f=34&t=78616&p=606558#p606558

The later stuff is like this

https://fordsix.com/viewtopic.php?f=7&t=78760
 
Ok if I calculate a static ratio of say 9.8:1 then figure in the cam and it creates a dcr of 8.13:1. I should be in the good range right or would it need to be lower?
 
A 3.71" bore six can tolerate DCRs in the 7.5 to 8.0 range with 87 to 93 octane pump gas with the iron head.
The aluminum head allows higher.

I would lower the DCR to the middle of the range to give you margin and to keep the tune-up from getting critical.

My advice is to get the connecting rods FIRST then have Autotec make the pistons for the correct compression ratio with the pistons at zero deck.

What rpm do you intend to turn the engine?
 
It would be safe to say I wont get to 5000rpm. I'm looking at the 264/274-108 or 264/274-110 cam. Those tamed the 5.99 rods and aussie 8cc dish pistons with the log head. Been calculating with a estimated 60 cc chamber and felpro gasket.
 
I'm showing w/ the 264/274 110, advanced 4 degrees, felpro gasket, 60cc chambers, 3.71" bore, 5.99" rods, 8cc dish, and a .013" deck height brings you to 9.8:1 sc/r and 8.26:1 dc/r.

Cam installed with no advance brings the DCR down to 8:1, 2 degrees advanced takes it to 8.15:1

.000 deck height, 12.9cc dishes(silvolite 3332H), cam 4 degrees advanced yields ~9.5:1 scr and ~8:1 dcr. With 54cc chambers that becomes 10.2:1 scr and ~8.6:1 dcr.

Now if you were to plan on 54cc chambers and shoot for 8:1 DCR, all other specs being the same, you'll need a 19cc dish or 12.9cc dishes and .035" of deck height. That would give you a safe zone with the aluminum head and the iron head and you could still mill the head further to take it higher. With the latter option killing any quench effect of course.
 
When I look at the silvolite web site the 3332h it says there 28cc dish. I even calculated the dish volume and came up 28cc. I'm mainly building for the log since the alu head is pricey. just don't wanna make it where it couldn't happen
 
Trust your calculations.

Silvolite know there stuff, but fitting a non US application piston means you have to use non US application advice. Same goes for putting a 2.3 or 2.5 piston into a six cylinder engine.

Volume Area times depth. Area is Pi * diameter.

This is pi * Diameter * Depth

3.14159 * 2.843 * 0.278 is 2.48 cubic inches.

1 cubic inch is 16.3870 cc's so 27.9 cc is it if you allow for the chamfer.

I let people make there own decisions.

The pistons are often on back order, so you can ask some questions.

Core data is here

XFLOWPISTONS3332H_3328H_3327H.jpg


XFLOWPISTONS3332H_3328H_3327H_002.jpg



These are hypereutectic pistons, and Silvolite put the measurements in so its Buyer Do The Calculation. The ring packs cause drag on the 3327H and 3328H, but as long as your not doing 5500 rpm all the time, they will be fine.



Ecconoline had his 2.5 pistons with 90 thou wrist pin offset machined to 12 cc.
viewtopic.php?f=1&t=73711&p=566245&hilit=3332H+SILVOLITE#p566245
c9hl.jpg


If you look at the options, a 6" (5.990") rod closes up the at least 103 thou piston short fall all stock US 250's with a 9.469" deck have...and the bigger trough makes up for the 17.95 cc's that longer rod wipes off the dish volume.

When you are truly satisfied your questions are answered, then proceed.

If you teach people to fish, you will feed yourself and others.
 
Thanks again xctacy.... I was off 2 cc on the 3328h I think those are the pistons I'm going to run. I don't know why everyone's saying the 3332h is 12.9cc that's way off.
 
Yep, that was an error I read through, and had to recheck.

Back then, I didn't like to say anthing on a post that had a lot of contractictory info. Silvolite cast alloy 4 cylinder posts and ring selections are contentious. Thats just because I saw 15 years of evidence from four people who have had problems with blow by and piston skirt loss, and I don't like telling excellent engine builders how to do there job.

Anyone who can make a 250 engine take 16 pounds of boost, well, they prove me wrong about Tempo/Topaz/Taurus replacment pistons, and I didn't want to be "that guy" who stops a sale. Its called slander or false witness if you don't have evidence. Its called a technicality if you do have evidence. Mustangaroo, his son Jason, Will/Kelly, parkwood60 and Brian here were enough for me to rule the 1185p and its replacements out, but each of these guys told differing details, and its most likely a ring and cylinder bore machining issue...or just giving a cast piston too many revs or too much boost. Will says a frozen wrist pin took out a cylinder wall, NOT the Tempo piston, so I believe him, but have a persoanl reservation.

In the old days, they TIG welded the oil slots and drilled holes like the European Touring Challenge Cologne V6 piston by Mahale.

Anyway, its easy to deck the iron head down to 80 to 90 thou to about 42 cc's to make up for it.

For the aluminum head, you can tig weld the chamber down like the closed chamber 144/170 head if you have to. By adding alloy via TIG, then machine back.

Talk with the engine builder about the right rings and bore texture.

Ian Tate from the Bathurst XU1 Torana days and his son in Australia wrote the book on bore texture and ring clearance, sumps and windage trays, and making cast alloy pistons, back in 73, 6500 rpm, 238 hp at 6500 rpm, 240 lb-ft at 4500 rpm, but by 1990, those same engines would last at 7500 or even 8000 rpm in 202 cubic inch engines. No forged pistons were ever used or needed.

11:21-12:21, and 19:24 to 20:00.

three 58DCO's from Maserati/ Ferrari with three 45 mm chokes. 10.3:1 compression on 97 octane leaded gas.

Ian_Tate_1973_Bathurst1000km_race_1120.jpg

https://www.shannons.com.au/club/video/ ... otorsport/
http://www.gmh-torana.com.au/forums/top ... cam-specs/

Basically, what I'm saying is do your homework, and decide on performance, not cost.
 
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