Hi, Im a bit into an engine build for my syclone. I am wondering what would be the optimal or minimum compression ratio to run with fully cnc ported -10 lil brodies? The builder is saying Im going to need at least 11.5:1. I wasn't expecting to hear that. Is staying around 10:1 possible?
Comp ratios
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RealFastV6
@jb_and_his_coffee
Compression ratio alone isn't everything - overall cylinder pressure is a factor of compression ratio, your cam, and finally boost. Your fueling then becomes a balance of that overall cylinder pressure and octane.
Factory compression ratio is 8.35:1.
A more peppy compression ratio is 9:1 or even 9.5:1 but again depends on your cam.
Is it possible that your engine builder doesn't know you're building a forced induction motor? 11.5:1 is N/A on Racegas territory.
Factory compression ratio is 8.35:1.
A more peppy compression ratio is 9:1 or even 9.5:1 but again depends on your cam.
Is it possible that your engine builder doesn't know you're building a forced induction motor? 11.5:1 is N/A on Racegas territory.
That makes sense. I'm not sure what he thinks to be honest when I dropped off the heads and explained everything he was pretty nonchalant about the whole deal. I've had him do vortecs for me before and he mentioned that these were going to flow great, but I think he is just about getting the flow numbers. You are probably right he may be thinking na. It just caught me off guard, but got me thinking. I am ultimately trying to get some rpm out of this build. So basically is it safer to run more boost of more motor to get into the 9s?
RealFastV6
@jb_and_his_coffee
Is this a Bowtie build or a stock block build? If he's working on the heads you might want to circle back and confirm the compression ratio before he does something like deck the heads.
Just shoot for 9:1 unless you're planning on something exotic.
Just shoot for 9:1 unless you're planning on something exotic.
Its a stock block short filled 4bolt. He is just cnc porting them, and doing the valve job right now. That's actually where this came up is he asked me what cr I was looking for and then hit me with the 11.5:1 and it threw me off. I was reading about some success with running a higher cr and still being able to keep knock in check. Ed Hess I think ran some heavy compression and a few others. Im just not sure how the longevity was on their builds. I would like to stick to e85 tho.
RealFastV6
@jb_and_his_coffee
Yeah supposedly according to the article in GMHTP, Ed was running 11.5:1 but that was on a Bowtie with a Solid Roller Cam tuned specifically for 118 octane gas. Not a real relevant data point though for real life. His solid roller was also super secret squirrel so you don't know what his effective compression really was.
If you really want to deviate from some of the "off-the-shelf" combinations you'll find info about on this forum, you need to call somebody like Alex at Steve Morris who will use the tools they have to design a custom cam for your goals and take a more holistic look at the combination to include your compression ratio, fuel, weight of the truck, converter, turbo, etc.
If you really want to deviate from some of the "off-the-shelf" combinations you'll find info about on this forum, you need to call somebody like Alex at Steve Morris who will use the tools they have to design a custom cam for your goals and take a more holistic look at the combination to include your compression ratio, fuel, weight of the truck, converter, turbo, etc.
I think Id like to bump my compression up a bit to try to keep my boost a little lower. I don't want to run meth with e85 which I've read some do it just seems to be another thing to go wrong. I've run into a couple snags using meth and high boost that could have been worse on my previous motor. I'm hoping that if I do run into knock problems with the e85 It wont be the end of the world to switch over to c16. Thanks for your help its much appreciated.