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.

If closed decks blocks are the end all answer I’m sure we would see a lot more Z’s beating the dog shot out them. 800+whp. I had a buddy who had a closed deck block, and blew a HG a week after the build, his car came from a very well known Gtr shop in Ga.

The bottom line...it is more about the block itself. I may not be able to take a beating at the 800whp+ regardless on how much the cylinder walls are reinforced.

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What about knock sensitivity on octane 93 (not talking E85 here), high compression ratio and super fast spooling twin turbos?

I cant run 12 degrees of timing on even 8psi and go WOT with 3000 rpm or I'll run into timing retard issues with my stock compression ratio. Whilst modern cars can? A built engine wont change that right? But lowering compression will?

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I pretty confident a properly sleeved block will be able to handle that abused far better then a closed deck block. Just ask your engine builder.

[QUOTE=Martijn_b;3899647]What about knock sensitivity on octane 93 (not talking E85 here), high compression ratio and super fast spooling twin turbos?

I cant run 12 degrees of timing on even 8psi and go WOT with 3000 rpm or I'll run into timing retard issues with my stock compression ratio. Whilst modern cars can? A built engine wont change that right? But lowering compression will?

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Who’s your tuner?

LMAO, I am counting on it! There is a lot of speculation and I am hopeful that better minds will prevail but so far there is little evidence. The one motor that I am familiar with that has sort of held up has constant over heating issues. I am not looking for four digit whp numbers or close to it. 700 to 750 and I am goo to go!

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You should be fine. Only way to tell is try it and see. A redo is dang expensive.

I hear ya! Just had to stir the pot a little. You have done your homework and so all you, I and Elmo can do is pay our money and take our chances! I am up for it regardless of outcome!!!

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I hate redo's with a passion. The definition of insanity is doing the same thing over and over again expecting a different result each time.

I thought about wet sleeving as well. But I read, in multiple places, that there are temp issues after. I will be driving this on the road as well and do not want temp issues.

Our Idea for closing the block is different than any I have seen. I am off to the machine shop tomorrow to discuss my ideas and see if they can do it.

I have read the same. Most I read about were pushing water. Only one way to do that and that is if the sleeve machine work was not done properly. I would suspect headgasket issues from a sleeve dropping. I am still researching this. Just any old machine shop won't do. Darton East had major issues years ago from what I was reading. The machine shop must have a 3 or 4 axis CNC and the tolerances are a thousandth to 1/2 a thousandth. It has to be perfect.

Right, I haven't read any info saying that using a wet sleeve has worked in any form.

Between the info out there on sleeves and the info out there on current shops closing decks has made me want to go my own route and try something different. I think our ideas on closing these decks will work, but I will just have to prove that after the build. -- Or I might never get our ideas off the ground. Depends on if I can get a machine shop with the proper equipment to work with me. Unfortunately I do not have a CNC :shakes head:

Not everybody get's on the forums. High end builds definitely do not. The sleeves are working all the way up to 1200hp with proper tuning on a VQ35DE block and our blocks are stronger due to the way the mains cradle is integrated into the upper oil pan. I am still researching on the best route to take.

For what it's worth, I went with 9:1 compression on my rebuild and did 685hp 615 tq on 91 octane at 20 lbs of boost. I don't have the low end problem spooler was talking about, I think that's mostly credit to Seb's tuning abilities with the throttle response. From what Seb explained to me the main limiting factor to running higher boost is the intake manifold.

Looks like Adam LZ has already lost his head gaskets. Not sure about it but it sure does look like it.

Given what the motor is pushing out HP wise, I believe you are right. It seems like he and his folks are playing catch up a little with this platform. I mean he clearly has connections/money to dump into it, but why not take a more measured approach and "measure twice and cut once"?

HE is a clout chaser. Plus sure his builders want to do their own thing and not listen to anyone

Mazworx maybe?

The manifold becomes a problem on low compression high boost builds. Once you go above 24 psi the manifold becomes a factor as well.

That sounds familiar. LOL