Need Compression, lots of it

[yeyo_racing]

Yeah, but the rings got shot using the stock setup, which had vacuum. It was after the compression test that I changed the setup due to the huge blowby and awfull oiliness in my intake. Besides, I don't think there's a restriction on which side you choose as the breather and where you install the PCV as long as its hooked up correctly, or is it?

I'm running a RMT setup, should I install the slashcut after or before the turbo, or it doesn't matter? Both valve covers or just the PCV one?

[yeyo_racing]

Huh, wait. My wideband is after the turbo so I will need to install this after the WB.

Damn, one more thing to solder. Need to find a me a nice place to install this, cause that tubo exit is shooort.

[TGP37]

Yeah, but the rings got shot using the stock setup, which had vacuum. It was after the compression test that I changed the setup due to the huge blowby and awfull oiliness in my intake. Besides, I don't think there's a restriction on which side you choose as the breather and where you install the PCV as long as its hooked up correctly, or is it?

I'm running a RMT setup, should I install the slashcut after or before the turbo, or it doesn't matter? Both valve covers or just the PCV one?

Depends, on my valve covers one side had a shield to prevent drawing oil into the PCV. The other side does not. With out the shield, the exhaust would draw oil blasted out of the pushrods and smoke (assuming).

After the turbo for sure, slash cut. Otherwise the exhaust pressure before the turbo would pressurize the crankcase.

Must be after the O2 sensor or else the fresh air will alter the readings.


The fresh air feed should be vented to atmosphere with filter or gets fresh air after the filter but before the turbo. Avoid creating a draw in the fresh air supply. That would reduce the over all pressure difference and reduce effectiveness.

ambient air >>> crankcase >>> catch can >>> check valve (optional) >>> slash cut



EDIT: Hey man, you do some real nice work there. Just looked at your pics from the link. Looks clean and professional.

Are you sure where the compression loss is from? Maybe burnt exhaust valves or weakened springs from the high cam lift?

[yeyo_racing]

ambient air >>> crankcase >>> catch can >>> check valve (optional) >>> slash cut

Ok, so it should be the PCV valve cover. Perfect, cause that is the closest to the turbo. Lot less plumbing. Is the Catch can required?

I'm thinking of using this kit.

http://www.summitracing.com/parts/SUM-120108/

Hey man, you do some real nice work there. Just looked at your pics from the link. Looks clean and professional.

Are you sure where the compression loss is from? Maybe burnt exhaust valves or weakened springs from the high cam lift?

Thanks for the compliments.

I'm not 100% sure it's from the rings, but they were 90-ish across all cylinders and went up to 100-ish when added oil, so that gives me a 50% it's the rings. Burnt exhaust valves, maybe. Need to open it up to be sure. Weakened springs, not so sure. Springs were installed new for the rebuild. I'm using Comp Cams 26981 Beehive Springs @ 1.700; they couldn't have weakened that fast do they?

[pocket-rocket]

gets fresh air after the filter but before the turbo.

Right here I would like to add to the sentence "and before the MAF" if you are using one, otherwise air that is accounted for by it won't be getting used for combustion and you will be running richer than you planned on.

Sent from my HTC One X using Tapatalk 2

[yeyo_racing]

No worries, it's a speed density setup, no MAF here. Nevertheless the breather side is hooked at the air filter box so if there were a MAF it would be covered.

[ericjon262]

Ok, so it should be the PCV valve cover. Perfect, cause that is the closest to the turbo. Lot less plumbing. Is the Catch can required?

I would run a catch can of some kind to keep oil out of the exhaust.

[TGP37]

I would run a catch can of some kind to keep oil out of the exhaust.

Absolutely, because it may be fine w/o a catch can in the driveway or around the block. But one hot day, beating the throttle, the oil may find it's way into the exhaust. It only takes a tiny bit of oil to smoke a long way. One good draw of oil into the exhaust will get you smoking for a little bit for sure.

I remember when my old turbo lost it's ring seal and dumped oil into the downpipe. Even after hosing the DP clean (off block) it still smoked for a few days.

[yeyo_racing]

Back to the compression topic.

Does everyone agree that using milled 2.8 forged slugs on a 3.1 crank would not survive 6psi of boost?

[ericjon262]

wouldn't touch the 2.8 pistons, but I also wouldn't be playing with an iron head motor either...

[yeyo_racing]

I also wouldn't be playing with an iron head motor either...

LOL...yeah at this point in time, me either. Unfortunatelly, modern engines are not cheap down here in the tropic. It is cheaper to purchase a whole car, than just an engine. Not to mention all the money I have invested in this Gen 1 setup.

I don't know man, I'm really inclined on doing this. Bear in mind these are forged, so technically they should hold better after milled.

Does anyone know the thickness of a 3.1 piston from the top ring land to the top of the piston? Iron headed, of course.

[TGP37]

Back to the compression topic.

Does everyone agree that using milled 2.8 forged slugs on a 3.1 crank would not survive 6psi of boost?

My opinion is the PCM tune will determine if the pistons survive or not. Noting I can run 12 psi on hyper pistons and all is well so far.

Just keep the fuel rich and the spark retarded during boost. Avoid detonation like the plague.........cooler plugs, good intercooling. Maybe even get h2o/meth injection while in boost.


After they are milled, the pistons, cryogenic treatment would help relieve stress points and increase strength. Not too expensive considering the investment in the vehicle. I heard NASCAR loves to cryo everything under the hood.

[yeyo_racing]

My opinion is the PCM tune will determine if the pistons survive or not.

True. No worries, I got that covered. My tune right now is smooth, retarded timing and about 10.5 AFR under boost across the whole rev range. I can always run a mix of 93 and 100 octane fuel, or some race gas to ease things up. The way I see it, I just need to richen the whole map more with the new setup.

Also, I'm thinking of using .060 head gasket. That should lower the compression to an "acceptable" level of 9.85, according to the compression calc.

I'm going to talk to my machinist next week to get his feedback about this setup. He's a very known race car builder here in PR. We'll see.

[yeyo_racing]

Here's the math based on the Engine Rebuild thread. Quoting info from betterthanyou and project89

Piston protrudes 4mm which is .157 inches.

From the top of the ring land to the top of the piston measures .330 (on stock cast, need to measure forged)

If we take off .157 that leaves us with .173 left (not .176 as stated) for the top ring land.

- End of quote -

So theoretically, if I shave .150 I'll end up with .180 and 10.0 compression. Assuming TRW forged have equal measurements as cast.

I'll need to do two things.

1- measure the forged pistons and compare with cast.
2- if measurements differ, then I'll need to open up both engines and install the 2.8/3.1 setup and measure how much they protrude.

[TGP37]

Won't the CR drop if you shave the pistons? Since the compressed volume increases but the stroke remains the same.

The protruding is ideal for quench. Don't want to reduce quench too much at all.

And if you change the head gasket thickness, you may need to gasket match the LIM to the heads and get pushrods to match the changes....if the change is great enough.


I bet if you tossed in a standard set of forged pistons with new rings capable of handling the heat from the turbo, along with a good cross hatching.....you will be happy. Then if you want more power, just up the boost more.