10:1 pistons

esgtbird

Registered User
i have my motor apart ready to go to the michine shop should i put 10:1 pistons in it? would this help with hp or only when i am using hi boost
 
blower motors run lower compression. that high of a comp ratio could cause you to hurt your motor under boost. keep ot around 8:1 to 8.7:1

you can however, go to brcpistons.com, and call in and order a set of really nice really light forged aluminum ceramic coated pistons and some stronger rods
 
You CAN bump up the compression on a boosted engine... IF you are building a RACE engine and plan to have it tuned properly and run the right fuel.

Kevin Leitem is running 10:1 in his car, but that's not the only thing he did to it either. It is not quite as simple as dropping in 10:1 pistons and calling it a day.

Research the whole project and decide if that is where you wanna go. If it is, then by all means, get-r-done. Just make sure you understand EVERYTHING that needs to be done to get there before you start buying parts.

Contact Dave Dalke (XR7 Dave) by the link in his sig. He should be able to help you with what you need and help you source the parts to get it done.
 
You can run 10:1 if you want to. It only becomes a problem if you start running high boost. 12psi with 10:1 will be near the same as 17 PSI at 8:1. So all you have to do is run less boost, which is more efficient anyways.

Other than that, if you want to run high boost then you will have to get a alcohol injection kit or run race gas.
 
For members, a very interesting old post regarding Less boost being more"
http://www.sccoa.com/forums/showthread.php?t=34275&highlight=compression+ratio+boost

Here is a good thread where compression ratio and boost were discussed.
http://www.sccoa.com/forums/showthread.php?t=18930&highlight=compression+ratio+boost

Unless it's for drag racing only, I wouldn't recommend 10:1 pistons. Our intake system and combustion chamber doesn't really support that compression ratio when you start adding boost on top of it. You'd need some very high octane fuel to prevent detonation.
 
esgtbird said:
i have my motor apart ready to go to the michine shop should i put 10:1 pistons in it? would this help with hp or only when i am using hi boost
A higher compression will help n/a characteristics and require less overdrive so in theory, you should see improvements all around. There is certainly nothing wrong with upping the compression if you plan to keep the boost lower..... less parasitic loss and less heat from the blower. There is also no reason why you will not be able to use pump gas daily so long as the car is properly tuned.
The theory most people have presented about keeping compression ratio low to acheive more HP is that there is more room to squeeze more oxygen in the cylinder. Personally, I would aim for 9:1-9.5:1 for a street driven vehicle. The below chart should aid in a visual understanding of boost and compression ratio:

boost_vs_comp_ratio.jpg



Paul
 
I have been running my car for years at the 10:1 compression, I had the tops of the pistons ceramic coated to deflect the heat away from the piston. Untill last year i ran a 100% stock tune with sunoco ultra 94 pump gas. I was running 12.2 on the pump gas then and at 3,800 pound race weight. i ran NGK 4554 spark plugs which is a pretty cold race plug that is shorter plug than stock and is a non projected tip. Now all of the plug threads are encased by the head to elimate hot spots and cause detonation. I now run the Evans waterless coolant which i think helps alot with my 20+ pounds of boost, which i still run pump gas on the street. That coolant dosen't boil till 375 degrees, which helps elimate air pockets around the cylinder and once again elimates hot spots.
 
Gotta love that Evans:O)..

Kevin are you running a Tstat or a restrictor plate?..And what is your normal operating temp?
 
DamonSlowpokeBaumann said:
Gotta love that Evans:O)..

Kevin are you running a Tstat or a restrictor plate?..And what is your normal operating temp?
I run a 160 stat with a 6 pound radiator cap. on a very hot day, cruising around town it may hit 200. but typical 80 degree day usually around 180
 
I think that 9.2:1 is more reasonable for a street car/ daily driver. I am planing to get around 9.3:1 - 9.5:1 CR by the time I am done with my motor. I am useing 0.030 over 3.8 Hypereutectic 9.2:1 CR pistons with 94/95 connecting rods decking the block to .005 and installing 1.87 intake & 1.58 exhuast ss valves in the stock seats and haveing the heads resurfaced to take MLS gaskets. I will not know what my CR will be unless I cc the heads after I get done with my bowl work. Here is a link to the pistons I plan to use
http://moranav6racing.com/category.html?categoryID=21
I am not getting them from Morana though, I ordered them trough David D.
I also plan to run around 17.5-18 lbs of boost with this setup:eek: I am keeping my fingers crossed that this will all hold up:eek:
 
Kevin,

Were those flat top pistons or with a small dish? Which is better for avoiding detonation in this case?
 
they are pretty much a flat top with just a little dish to it. as for the detonation question i really don't know!
 
The dish is used to determine the quench area, and the final compression ratio. You'd want the dish matched to the dimensions of the combustion chamber in the head to improve detonation tollerance. The better the quench, the less of a tendancy to create odd points of combustion, thus detonation.
 
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