Pistons with too much dish?
Pistons with too much dish? Made the mistake of going with dished pistons instead of flat tops (dish is -15cc, flat tops were -5cc) this is an lq4 bored .030 over. I was planning on using the original 317’s but with a 70cc combustion chamber would put my motor at 8.78:1 compression ratio. I have a set of 799 heads as well with the 64cc chamber. That would put my motor about 9.5:1. Would you even be able to feel a difference between a half a compression point? This is a turbo car
Not as much as you would think. HP From CR Change Calculator
Last edited by LLLosingit; Nov 30, 2018 at 07:31 PM.
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Joined: Jun 2013
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From: Moose Jaw SK, Canada
It really depends on what your goals are etc.
6 guys do it one way, half dozen the other.
Personally prefer the idea of a low compression motor with extra boost poured into it, but everyone has an opinion.
6 guys do it one way, half dozen the other.
Personally prefer the idea of a low compression motor with extra boost poured into it, but everyone has an opinion.
You might have more comp. than you think, LQ4's had dish pistons, not sure the vol., but you
also bored it, which will raise the comp. You could take a slice off your heads, or use 243 heads,
lower comb. CC's.
also bored it, which will raise the comp. You could take a slice off your heads, or use 243 heads,
lower comb. CC's.
Last edited by forcd ind; Dec 1, 2018 at 06:37 AM.
It’s a single billet 7875, 4l80e, 9 inch, 3600 triple disk stall setup with a LJMS stage 2 turbo cam. It’s just a weekend fun car but it will be driven on the street more than the track. The car is also on e85 only, so I now realize I could probably get away with more compression. I’m just worried it’s going to feel gutless out of boost and it won’t be enjoyable to drive under normal conditions
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Not as much as you would think. HP From CR Change Calculator
It’s a single billet 7875, 4l80e, 9 inch, 3600 triple disk stall setup with a LJMS stage 2 turbo cam. It’s just a weekend fun car but it will be driven on the street more than the track. The car is also on e85 only, so I now realize I could probably get away with more compression. I’m just worried it’s going to feel gutless out of boost and it won’t be enjoyable to drive under normal conditions
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Verdad Gallardo No I think that calculator is pretty accurate it makes sense. I think I’ve decided to just run the dish pistons with the 799 heads. With Ls9 headgaskets it should get me close to stock LQ4 compression of 9.4:1. It’s still on the low side of what I could probably get away with but I think it will work just fine.
I had a 408 nitrous build with AFR heads on it at 11.1 to 1 static compression. When I eventually hurt that motor I had it rebuilt with dished pistons to lower compression to 9.5 to 1 static for boost. Same cam, same heads, same intake (fast 90), same everything just lowered compression. I drove it for a while with no boost before I ended up selling the car. It was a huge difference in response in street driving. It even sounded different. A point of compression is huge in a street car and I even had cubic inches to help with low end.
TECH Enthusiast
Joined: Mar 2013
Posts: 503
Likes: 38
Not as much as you would think. HP From CR Change Calculator
I had a 408 nitrous build with AFR heads on it at 11.1 to 1 static compression. When I eventually hurt that motor I had it rebuilt with dished pistons to lower compression to 9.5 to 1 static for boost. Same cam, same heads, same intake (fast 90), same everything just lowered compression. I drove it for a while with no boost before I ended up selling the car. It was a huge difference in response in street driving. It even sounded different. A point of compression is huge in a street car and I even had cubic inches to help with low end.
By seat of the pants I’d say lower rpm was way more effected then peak. Keep in mind my comparison was NA to Na. Depending on how your boost comes in it may not be as noticeable. Honestly for me with the only change being compression ratio NA it wasn’t even fun to drive any more on the street even with 400 plus cubic inches. All we did is go from 4.030 bore to a 4.040 bore with custom dishes pistons.