Thread: raising compression ratio via pistons...Attention Tech Inspector

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Hello out there. Have another question for you all. As I have stated before, I have an 81 vette with a 190hp small block. I would like to inprove the power of the engine, but I am not looking to spend big bucks, then again I am not looking for HUGE POWER. Anyway, here it is. Stock smallblock with 76cc heads and dish pistons comes out to 8.2 CP ratio. Small cam from the factory, about 390 lift and around 190 duration. HAD an electronic q-jet and a electronic advance dist, and a very slow stupid outdated computer.
And to top it of, the rear gears are 2.87...
Anyway, as I said I am on a budget, for 2 reasons, I have other bills, and another, the car isn't worth alot. No sense in dumping alot of cash into something I will never get it out of.But, I do enjoy working on it and don't as it gives me something to do.
So far, I have found a new q-jet and a 650 holley. Have both in my possession. Both are electric choke, and NON computer, as I don't think holley makes a computer controlled carb anyway.
I have an older HEI with a vacume advance, which I can do away with the electronic advance, and computer as well.
Next, I will remove the heads,today. I was considering putting 64cc heads on it, but, once the heads are off I was considering instead just putting a set of dome pistons in it. Pistons are much cheaper, and will boost my compression ratio alot. What do you think? I am aware that head flow ect makes power, but I am not building a race engine, just want it to have about 300hp at the flywheel. The heads I could get are just a set of older iron heads from a friend. I understand the flat tops are the way to go with smaller chambers, but will I get almost the same results with the pistons?? Will I notice any power increase with the higher cp ratio and a cam, say 262dur and 460 lift??
Let me know what you think. Just remember, this is just a toy car that I drive on the street , not a 1/4 mile car..
BASICALLY: If I put a carb, dist, dome pistons and headers and a cam listed above , will I have a noticable increase in power from stock, or am I way off track..

I don't know much but it seems more logical to me to just rebuild the top end *heads, cam, intake, carb and exhaust*.... because breaking down the block and pulling crank & pistons you may need to do some machine work and it would probably get more involved than you would want to go... just my opinion.

Vortec top end ,heads and intake.......700-800 bucks.new cam also.....

To put in new pistons, you have to pull the engine, buy a set of pistons w/ pins and rings, remove the engine, pull the intake and heads, pull the rods and pistons, have the block bored, honed and fit for the new pistons, have the old pistons removed from the rods, have the new pistons installed on the rods, reinstall the pistons, reassemble the top end, reinstall the engine. May need a balance job, also.

Heads and cam sounds a lot easier.

I like the idea of the vortec heads. I have read that they flow well, and I believe they come in 64cc chambers. To be honest with you, I had the heads off the engine today in about 2 hours. ( I work as a mechanic in a dealer for the last 15 years(flat rate)) I could have the oil pan off in another 1/2 hour and pop the pisons out the top. No big deal to me. Air tools and a lift do wonders. I can press my own pistons ect..The reason I made the post is because all day long I FIX cars, but what I don't do is hot rod them. That is where I need the advice. As I said before, I am not tring to go super fast, but a mid 13 sec car would make me happy. I like the idea of the vortec top end, sounds good. Now, will it produce a much more power than just installing a set of std. dome pistons?? This is where I need the help.Pistons from speed Pro and rings run me $195 my cost.Heads and intake $700-800. See where I am getting at? I am not tring to be a pain in the ass, just don't know if I should spend $500-$600 more for the same thing.Or, will it in fact make a big difference in power.et me know.Thanks.

Hmm... depends on the age of the engine and how far you want it to travel. If it has under about 20k miles on it since the last rebuild you might be able to go with just honing it enough to brake the glaze. BUT: this is very difficult because:
1) you have to get all the grit out of the engine without any getting in any oil galleries or some sort of plave you don't want it.
2) honing makes a horrible mess, you can't actually do it with the engine in the car.
3) without honing, your rings won't seat properly. Wear will be very high at the beginning and if you have just a small ridge it might kill a compression ring, and then
In other words: if you know what you're doing and trust your abilities (I read you're a mechanic), then you can try. Make a small mistake (grit in the oil, ridge, wrong honing...) you'll lose that engine in under 10k miles...
Always remember: you can only chose two of the following:
good - cheap - fast
I would use a vortec top end, maybe a holley 4Di injection off ebay or something, they come quite cheap and can be set by computer, then you don't need to fool around with needles etc to get the best out of a carb. If you don't find a Vortec, go for closed chamber heads like the 492 or 041 or 186 or similar, they also flow very well and are easily obtainable off ebay for as low as 300 bucks a pair rebuilt... Heads can also be bought off ebay used, as a mech you can rebuild them yourself. A new cam will make a good difference, but be sure not to go too far on the duration as it will kill low end power and driveability. Maybe put higher gears in. What trans are you using? What gears you use depends a lot on the tranny and the lowest ratio you have there to get you off the line. Don't overdo the static compression ratio, otherwise you'll want a longer cam, which kills low end again. And it's almost always better to go for flat tops and small chambers, you get better burn because there's no dome to mask the spark plug at TDC
Plan first, build then
Hope I could help you out a bit,
Max

Seems like the heads might be better. To get the most out of a set of pistons you will need the block out to bore and get the squish height right on the block. If the block has many miles on it at all, chances are it is going to require boring and oversize pistons. It's nice to get out cheap, but not really worth it if the results are a car that runs in the 13's and burns oil because the cylinders to piston clearance is excessive due to cylinder wall wear.

JC- I don't think you want to go with domes on the street, it's going to push your CR up too high for your combo for pump fuel. Run a set of 10.5:1 flat tops with a second stage RV cam and the 64cc heads and it will put you where you want to be.

Okay , maybe I should just do the heads, and leave the dish pistons,bottom end alone. Let me ask you this. If I have 8.2 cr now, and I put a set of 1970 64cc chamber heads on it(I have a set of done heads), will I get much more out of it? Will I notice a difference verses using my 76cc heads?? I guess it will raise the cr about 1 point. I am not sure how much of a gain I will get doing this, and adding the cam and intake and headers.Neeed some more input. So far, I am gonna leave to he bottom end alone. Now, are my set of 64cc heads gonna do the trick? Also, the car came stock with an alum. intake q-jet. I have an adapter and a holley 650 I rebuilt, I took off the electronic q-jet. Do I need to get a new intake, or will the adapter work okay??

You should notice a definite increase in power, especially because of the better breathing heads and change of cam. Some of those smogger heads had pretty poor flow characteristics. If you use Vortec heads, you will have to use a new manifold as the bolt pattern is different. I am not a fan of adapters, so if you decide to use a different kind of head, I would get a new intake as well. The Edelbrock RPM manifold flows better than a stock GM aluminum manifold, and it would be money well spent.

Sometimes,it is cheaper to get another motor,with better compression than to pay all the machine costs! If you want serious power,and want to do it on a budget,go different motor and sell your block. Just a thought,and it all depends on budget and future intended use of the car.

Changing the pistons will not give enough additional power to justify the work and cost. You'll most likely end up with more problems with rings seating and so forth. Leave the bottom end alone and add some 64cc heads along with a Voodoo 268 cam kit and an intake without an adapter. You'll love the results.