Lowering Compression Ratio

[jimmycuda71]

I was looking at possibly buying an engine with an 11.5:1 CR. Since this will be a street motor 95% of the time. What would have to be done to lower the compression to a more streetable CR. Between 10.2:1 and 10.5:1. The motor is a 440 Stroker with Indy Aluminum EZ Heads
Thanks
jimmycuda71

[72cudamaan]

I was looking at possibly buying an engine with an 11.5:1 CR. Since this will be a street motor 95% of the time. What would have to be done to lower the compression to a more streetable CR. Between 10.2:1 and 10.5:1. The motor is a 440 Stroker with Indy Aluminum EZ Heads
Thanks
jimmycuda71

That depends on what was done to raise the CR. Larger chamber heads, dished pistons, thicker head gasket are just a few choices
but again it depends.  Keep in mind that you can safely run about 1 point higher in compression when using
aluminum heads as well.

[HP2]

I'd ask what is the cranking cylinder pressure is rather than what is the static compression ratio. The reason being is that as a stroker with a big bore, with aluminum heads, and a big camshaft, it may have cylinder pressure that is low enough to utilize pump gas, despite its claimed 11.5:1 ratio. Oh, operating altitude matters too as higher altitude can also tolerate more compression.

[jimmycuda71]

I am less than a thousand feet in altitude. Somewhere around 850 I think.
The heads are the EZ-1 295cc 355 Cfm and flat top pistons. Not sure what the Combstion chanber size is.
Are the EZ-1 good heads for the street?
I would not be against replacing the pistions with a dish pistons to get the compression down if that was what it took.

[Changin Gears]

You could always just bolt it in and try it.  If it has a healthy enough cam you might be able to get away with it.  If it ain't broke, don't fix it...

[berna4406]

I dont know if they are still offered,but they used to sell cylinder head spacers to bring down the compression.I may even have a set in the basement.I will check.Never used them so I will try to find some info. Sam

[cudabob496]

Ya, first try backing off on total timing. I'd lose the vacuum advance, if you have it.
Run a cooler thermostat will also decrease cylinder pressure slightly.
Goal is to prevent knocking.
A little octane boost can help, instead of messing with timing, perhaps.
And, as mentioned, a cam with more duration can help as well.
NGC makes plugs for diff compression ratios too!
Less aggressive timing curve can also help!!

Basically, don't spent a lot of money for a situation that may have easy solutions. And if not a daily driver,
maybe live with it, and enjoy the more power! Octane boost at Walmart ain't very expensive!

[HP2]

Since you're looking at buying it, I assumed it was together. If it is not, then you have options, but it lead me to believe it was together.

If it is together, again, I'd ask for cranking pressure readings. This tells you exactly how much cylinder pressure it is producing and what octane levels you may need to make it live on the street. If it is marginal on pressure/octane requirements, you can add a h20/alcohol injection system for considerably less than replacing hard parts inside the engine. If this is a pretty hopped up engine, it may be safe to assume it has been balanced or blue printed and if so, simply swapping pistons (like that it is even a simple exercise) could impact the balance which would lead to additional machine costs to restore balance or a less than optimal combo after the swap. Additionally, a quench combo at a higher compresion point may actually be less detaonation prone than a lower static compression reading with no quench. It all becomes a very component dependant answer.

Here is a calculator you may be able to play with if you know a few important variables: http://www.rbracing-rsr.com/comprAdvHD.htm

[moper]

The best way would probably be by repalcing the head gaskets with something thicker. That being said, if the block and head were not surfaced properly you may have issues with the MLS type gaskets leaking. But - that's the easiest way.
What camshft is in it? 11.5 with aluminum heads may not need any changes for pump premium. You need to know more details on the build.

[jimmycuda71]

The engine has a complete Indy Top End. The Cam is the R2 Solid Roller for the 440 mopar. Not a very streetable cam at least it looks to me. But I am not much of an engine guy.

[moper]

The engine has a complete Indy Top End. The Cam is the R2 Solid Roller for the 440 mopar. Not a very streetable cam at least it looks to me. But I am not much of an engine guy.

What's an "R2"? Who makes it? Bullet? Comp? Hughes? Do you have a part or grind number and manufacturer? I need a lot more info on that cam.

[ted]

dont buy it

[Chryco Psycho]

dont buy it

I love the logic , maybe Ted wants to buy it out from under you , the reasoning is awesome !!
 I have run 10.6 with pump gas & Iron heads so 11.5 may work well , Cometic makes gaskets in a number of thicknesses , if he has the recieps & the price is good & allows some room to modify cam & or compression why not buy it ?

[ted]

because i wont buy someone  work,

[jimmycuda71]

You are probably right. I can always make changes late. I think it is a little more motor than I need, but it is better to have to rather much than not enough.
Thanks Guys