Forced Induction Compression Ratios
 

What are you guys thoughts on compression ratios when going Forced Induction.

I know most people just keep the stock compression ratio even when rebuilding.

I'm thinking of going 9:1 or 10:1 since I don't have E85 local and I will be running 93 for 95% of my driving. I cannot see it making more than a 10-20 HP difference when using E85 and perhaps no HP loss when using 93 octane, since the timing can be pushed.

I do plan on pushing high boost at some point! I am building this motor to handle big boost and big HP! So the common thought as with most platforms would be to drop the compression ratio.

Thoughts? There is a wealth of knowledge out here and guys who have tried it all.


Thanks

The problem is off boost throttle response. It will be a dog in the lower RPM ranges. You will loose the VE of the motor. Also, it will take more boost to make the same HP on a car with a lower compression ratio. It is the old school way of thinking. With today's electronics and fuel that is available it just doesn't make any sense to drop the compression ratio. There is a point where the HP and boost get's high enough that the compression ratio will need to be dropped. I am not sure where that level is.

You can order in Ignite E90 or E85 in 55 gallon drums. You won't be running around on high boost all the time. I am not sure of what you consider high hp.

I would take Spoolers advice on this, as he and a few others, are in the "black hole" of boost and power with the VQ. You also may wanna look into head lift and cylinder walk as well, since you are looking to push a lot of boost. If you haven't read Spoolers thread cover to cover, you should (http://www.the370z.com/forced-induct...torsports.html)! A TON of useful info there from not only him, but other vets in the VQ community!

There are a ton of TT build threads with various compression ratios. As Spooler has pointed out the reason you don't hear anything is that it really doesn't matter as the head gasket cylinder walk issue ends them all. As for fuel, 93 octane will not give you the same result as e85 or race fuel. You will be down about 30 to 50whp. There is little difference between e85 and race fuel in the whp game. Race fuel cost more but you get less mpg with e85. E85 because of is high alchohol content run extremely cool so it doesn't add heat to system.

Early on most were doing 9:1. At low compression you need more boost to get XXX whp. So the failures were happening at 23+psi. So now we are seeing failure at 18+ psi with folks doing 11:1.

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Well, I am trapped in an area with all "old school" builders lol. No one in the import scene and no one with first hand knowledge of the VQ close to me.

That is why I wanted to ask about our platform here. As I said the wealth of knowledge is plentiful.

Just to clarify, I was comparing 93 octane to 93 octane with difference compression ratios. Was just stating that you can add more timing as you would have less knock with lower compression.

There is no comparison from 93 octane to E85 :rofl2:

Yikes!!!!!, I would suggest you look for a qualified builder and tuner. Don't make a blunder. It get's expensive quick.

I know about the walk issue and head lift issue as that is what killed my engine a couple months ago. :ugh2:

I know spooler doesn't like the closed deck system (or that is what it sounds like :hello:) but I have some machinist working with me to close my deck via insert.

So, I'm in rebuild mode right now! I am building the block to handle big HP but more likely to stay conservative for a while. (say 700 on E85).

Here is a good resource for E85. Not sure where you live.

https://afdc.energy.gov/fuels/ethano...arest?fuel=E85

It is not that I don't like the closed deck design, it is just because it doesn't work. How many people do you need examples of?

LOL, my bad but that being said I think answered your own question. With e85 knock become less of a concern and so running a higher compression ratio works.

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Saying it doesn't work any better than an open deck can only be stated that nothing has held together very long at +18 psi. The real question is when does it quit working compared to an open deck and no one has done a comparison test. I doubt anyone will as the search is to find a solution beyond just a closed deck block.

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I think he is just staying closed deck blocks don’t help with cylinder distortion. At what whp level that happens compared to open deck is up for debate. Not to throw any shops business out on social media, but spooler is right closed deck block especially the you have don’t hold up well to big power over a prolonged periods of time, they have split, cracked, even a team had welded the block and it still failed.

Well hopefully your machinist can insert them far enough into the block and tight enough so they hold. No other shop has been able to do so.