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Boost pressure VS Compression for E85 T70 build........

16MustangVet

16MustangVet

New member
Alright so a few questions here.

8.5:1 for L67
or
9.4:1 for L36

I can find either cheap enough and easily enough. I've always thought of higher compression as kind of "free" HP, so which block to go with?

I have a set of MLS gaskets already, use all the layers or leave one or maybe 2 layers out?

What about the heads, I plan on dropping a set of L67 heads I have off at a shop to have them checked out.

simple valve job, magna fluxed, new guides and seals, machined to prepare for a ST5 cam, and how about having the heads milled to jack up the compression?

Should I leave everything alone and use low comp block, all the layers of the MLS gaskets, and NOT have the heads milled?
or is it worth it to jack the compression up a little more around the 10:1 or higher for compression?

Keep in mind this engine will NEVER see pump gas only E85 and likely nitrous too. part of the reason to use the l67 heads is with a NA lower intake I will have an extra set of injector holes ready for nitrous. Its all going in a stupid light car so at the very least id like to make 500whp/500wtq is the goal.

Hoping the turbo guys will chime in on this.
 


Using 2 layers would get me to about 10.0:1 compression on a L36. Worth it to mill the heads a little?

In theory higher compression should make a more effecient engine and require less boost to make the same hp.

So if the car will never see pump gas can i get it up to maybe 11.0:1? not using stupid mega buck pistions to get the compression up so im basically looking for max compression with a L36 block, 2 layer mls gasket, and possibly milled heads.
 
with a turbo car, boost pressure is easy, getting rid of detonation is harder.

low compression and high boost

l36 is still weaker than the L67 just from the smaller wrist pin and thinner piston crown

you dont want the injector holes for the nitrous, you want NA heads drilled and tapped for direct foggers where the injectors normally would be...and run the sc VC to clear em.

not enough iron in the heads to tap it for a plug thats drilled and tapped to the right angle to point the fogger right at the valve.

500/500 is stupid easy to make...a trans to hold up to it, not so much, save yer money so you can dump nearly 10k into your trans, yet the stock as a rock l67 is humming along with nothing other than oil changes....yay
 
even with only using e85 still go with the lower compression l67 block?

skip using the l67 heads or just run them and use a dry shot instead? shot would only be 75-100. i already have the zex dry kit. if i were to do direct id just need a few more odds and ends to convert it to wet.

as for the trans its gong in zachs old black caged gtp thats dow to about 2600#s. if i blow up the trans and destroy a 7/8s wih some good hard parts ill justsuck it up and switch to the 4t80 i refuse to cough up the cost of unobtanium gmr parts. i hope i can get a trans to survive beings the car is pretty light.
 
Yes; because like stated...you get higher in the compression points, and the knock becomes exponentially worse and more difficult to maintain.

It's not the weight of the car so much as it's the shock in power that normally shreds crap...so keep that in mind.
 
Right I understand the "shock" point but im hoping the weight will help keep a trans alive without unobtanium. If the trans doesn't survive I'll be forced to figure out a 4t80e, I cant justify spending 3kish for just a chain and diff.

The car doesn't need to make any hp records either. Im just hoping I can get it to shake down a 10.99 or faster.
 


I'd vote for the low comp l67 block as well. Turbo's seem to like lower compression in my experience as generally they are more efficient in the higher PSI, which is easier on a low comp block. So turn down the compression and turn up the boost. Even on E85. :-)
 
So all in favor of the L67 full mls gasket kit and just get the set of l67 heads refreshed?

Basically everyone says low compression, E85, and crank up the boost.
 
Thanks for the heads up. I plan on taking my sweet time and chasing all the threads for the heads too and I'd like to gasket match the lim once I make up my mind. Think it will just be a lot bottom end and a na upper.
 
use a cut off disk to put two or three grooves down the length of the threads of your old head bolts and use that to chase the block threads if you use a tap you're going to cut more iron away which will weaken the threads in the block besides which you don't need to all you have to do is clean out the threads with a slotted bolt
 


Thats what I was told to do by bill also. Thanks. Prep will be surgical clean. I sent email on some head studs but no response back yet. Besides 80# injectors and head studs pretty much all the parts are collected up, well piled up at gregs anyways..........
 
Eh, I always had great luck with stock GM gaskets.

Why not use those and get customer length pushrods and mill the heads to help bump the compression...valve clearance?
 
I wasn't considering custom pushrods? benefit vs cost? I didn't realize if I had the heads milled and used a partial MLS gasket I'd need shorter pushrods. Makes sense I guess, so then the question is throw a stock L67 together with a na upper? Or spend a little money on milled heads and 2 layer MLS to gain some compression? even more compression with a NA bottom end obviously.

Main reason for the MLS gaskets is id like to hit it with a bottle eventually. (speaking of nitrous stay stock bottom end with NA upper because it would be easy to duplicate if I chunk it on the bottle?)

Last anyone know if milled heads and 2 layers from the MLS gaskets would cause clearance issues?
 


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