If you want to save money and don't mind doing the work. Put thicker head gaskets on it to drop some compression. You can use a compression calculator and figure in what thickness of gaskets you need to get the compression your looking for...

 

How do you come up with 12.5 c.r.?

Even with zero deck, .041 gasket and 58 cc heads and -6 cc for valve reliefs I get 11.8. If your pistons are .025 in the hole it's 11.01, both a little high, but you should be able to tune it to run on 93 gas.

That being said, at zero deck, and 64 cc heads you have 10.35, 72 cc's will get you 9.54.

You're also over carbed IMO, what trans and gear, car weight? 11:1 is a little high, but isn't unheard of for good pump gas if you have the right tune and setup.

 

thanks for the replys!!! yeah the gasket would help. i thought about that too. so heres the story. i bought the car from a guy that built the engine for a dirt car. he then dropped it in the el camino then lost interest in it and it sat for 20 years. he said it had 12.5 compression and built the engine so i was just taking his word. it dont seem like that much but i know its high like probably 11.5. im not to sure on all the specs on the engine. all i know is what i typed. i did notice that it seems to run smoother on e85 and it doesnt want to choke or cough when i shut if off anymore. i just want to rum pump gas. i dont want to have to fill up jugs everytime i need gas. i dont think its every had a tune. it did run really good before i switched it though. i think the carb is a 830cfm. thats just what it came with when i bought the car. it has a muchie 4 speed with 373 gears.

 

yeah i was thinking some 64cc int202 ex 160 heads. would that be good? then get a thicker head gasket. how thick you think? also how are you coming up with the 11.8 compression? i would like to get about 10.5 and run 92 octane

 

Here's one of many free calculators online, it'll help.

 

ok so i was messing around with the calculater and i came up with 12.7 compression. did i type in something wrong? heres what i did

cylinder di. 4.030 in

stroke length 3.75 in

cylinders 8

chamber 58 cc

pistons flat top 0

gasket .041

i found if i go with 74cc heads i would drop down to 10.5 if everything is correct above. would 74cc heads with flat top pistons be best or 64cc heads with dish pistons. im lost on the difference between the two besides the size. i want to gains power and still drop compression.

 

ok so i was messing around with the calculater and i came up with 12.7 compression. did i type in something wrong? heres what i did

cylinder di. 4.030 in

stroke length 3.75 in

cylinders 8

chamber 58 cc

pistons flat top 0

gasket .041

i found if i go with 74cc heads i would drop down to 10.5 if everything is correct above. would 74cc heads with flat top pistons be best or 64cc heads with dish pistons. im lost on the difference between the two besides the size. i want to gains power and still drop compression.

You need to know piston to deck to know what the compression ratio is I don't see that you included that. Your flat tops are not likely zero CCs of relief. They are probably 6cc or close to it.

Gain power and drop compression? Probably not going to happen without a power adder or a cam swap done as well. Which brings up another thought, you may be able to just leave the compression and use a cam that has more overlap, duration thus building less cylinder pressure.

There are other things you can do to make the engine less pone to ping.

160-180* stat
Overkill cooling system
Overkill ignition system
Cold air intake
Thermal coatings on intake, pistons, exhaust ports
Lower gear ratio in diff to take the load off the engine
Use no more total timing than needed
Polish combustion chambers
Block off heat crossover (if currently used)
.
.
.
Plus more

 

If you want to save money and don't mind doing the work. Put thicker head gaskets on it to drop some compression. You can use a compression calculator and figure in what thickness of gaskets you need to get the compression your looking for...

BZZZZZTTT, wrong answer. Thicker gaskets will lower the static compression ratio, but they will also increase the squish, resulting in the motor detonating worse than it does now.

 

how much cam do i need. i have a pretty big one right now. also one person says -cc pistons the other +cc. on the calc it said 0 for flat - for dish + for dome. i think im going to just go with some 72cc heads and get a tune. that seems to be the best im going to get. just use a .041 gasket. i dont know what deck it has but assuming a 0 deck would be the worst case right

 

yeah i get what your saying. i just dont know much about the engine i bought the car that way it is. i mean how much cam do i need to drop compression and gain power? i have a 4 speed muchie. 373 gears the guy said max rpm is 6500 but i pushed it to 7000. so 72cc aluminum heads with drop the compression but will they also add hp or will the drop in compression and the aluminum heads just even out to where i am now?

 

no its a wide ratio muchie 4speed. its not a drag car. i just want to have a low 12 high 11 sec street hot rod. i'll take it to the track a little still. im not to worried about the gears. i like the 373 thats in it now. the car is a 64 el camino. i still would like to know more about smaller and larger cc heads. is that all just based on the pistons you have and compression you want to make?

 

when i was mixing gas it ran a 13.1 and 108. i was thinking about the AFR 195 eliminators heads

 

yeah i get what your saying. i just dont know much about the engine i bought the car that way it is. i mean how much cam do i need to drop compression and gain power? i have a 4 speed muchie. 373 gears the guy said max rpm is 6500 but i pushed it to 7000. so 72cc aluminum heads with drop the compression but will they also add hp or will the drop in compression and the aluminum heads just even out to where i am now?

Not sure what the specs for your cam are, but look at it this way. The more duration and more overlap in the cam means less cylinder pressure build up during the compression stroke.

Have you done a PROPER cranking compression test?

From what I have heard, small CC heads and dished pistons is better than big CC heads and flat tops. Another thing to think about. Aluminum heads are always nice.

 

yeah i'll give afr a call and talk with them. i was just looking at the cam. it has a 72 overlap. it did seem to run a little rough at idle then smooth off when i got on it. another thing i should bring up is it has a lot of blow by. what is that about?

 

hhmmmmm interesting. well it has some weird breather system. theres a steel line coming off both valve covers that go to cylinder with two breathers on it. when i get on it hard oil wants to leak out

 

no the motors strong. dosent smoke or anything. just has a lot of blow by from having so much compression. im going to try the aluminum heads and get it dyno tuned and see what happens.

 

ok so i was playing around with wheelspin.com CR calc and this is what i came up with.

1 for inches

bore 4.030

stroke 3.75

head gasket bore 4.06

head gasket thickness 0.021

chamber cc 58

flat top pistons cc -6

deck 0

i get a 12.4 CR

so to get down to 10.5 would it be best to go 0.041 head gasket thickness and some 68cc heads OR 0.021 head gasket and some 72cc heads?

 

ok yeah so i can go .041 gasket with a 68cc head and that will get me to my number. what do you guys get when you calc it?

 

ok yeah so i can go .041 gasket with a 68cc head and that will get me to my number. what do you guys get when you calc it?

Did you actually confirm the 6cc relief in the pistons or are you just saying that because that what it probably is?

And a ZERO deck? I highly doubt that.

 

they are flat top pistons so im just trying to get close. what deck would you say? im just trying to get close so i know what heads and gasket i should go with

 

Elky, at the very least you could employ someone with a bore scope and *try* to identify the pistons by the valve reliefs in the top...i.e. stock originals vs. TRW rebuilds, etc. I mean, that's what I would do if removing the heads wasn't a feasible option, but I don't really know anything about Bowties so I don't know if the valve reliefs are distinctive.

Below is a link to a really decent dynamic/static CR and CID calculator. I like this one because it accounts for many variables including cam specs. Although the cheater links are for Pontiacs, it will work with whatever numbers you plug in.

http://www.projectpontiac.com/ppsite15/compression-ratio-calculator

"how much cam do i need. i have a pretty big one right now. "(that's what HE said..hehe ) No on a serious note though, I'm by no means an expert, but when you get down into the 10.whatever:1 range of compression, "big" cam becomes relative. To you, what is a "big" cam? Tons of lift? Duration? Some people can run a pretty surprising amount of SCR with cast heads and some ping like crazy at anything 10.0 or above. The cam is usually the smoking gun and if I were you, I'd research this subject in depth and get a really good understading of duration, overlap, lobe sep angle, etc. That way if you DO swap heads (or not) you can better fine-tune your set-up to get the most out of it. Not saying you don't know that stuff, just a suggestion FWIW.

Now I'll take my small-brain-havin-*** back to the kitchen where I belong and stop talkin out of turn.... :evil:

 

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

 

If high compression is the only issue, which it doesnt sound like, E-85 should work fine I would think.

'peace
Hog

 

e85 to hard to get. so im confused are flat top pistons a negative or a postive 6cc? im getting two answers on that.

 

e85 to hard to get. so im confused are flat top pistons a negative or a postive 6cc? im getting two answers on that.

To me negative, but using a compression calculator, it depends how the program is written. I wrote my own, where a dish uses a neutral number, no +/-, and domes a + number.