cb951

Background --
After increasing boost to 15psi with TiAl 38mm WG, Profec B Spec II EBC, Fabspeed 3" cat delete and cat-back exhaust, and 951Max chips (see signature for complete mod list), I had a general lean condition. My AutoMeter vac/boost gauge showed 19 in hg at warm idle, which seems pretty good, but since Russell told me that the chips were programmed to run richer than my dyno AFRs showed , there must be some other issue.

So I started to check for vacuum/boost leaks by pressurizing the intake system (through the j-boot). When I had only about 2lbs built, and lost that VERY quickly, I decided to go ahead and do the venturi delete and silicone vacuum lines. Just to be sure, I also replaced the ISV (ICV), thermo-vacuum valve (near the cv location -- has two vac lines for the purge system), added Laust's vacuum manifold with new aluminum sealing rings for the intake banjo bolt, new dipstick tube o-ring, new speed and reference sensors (because the old connectors disintegrated), new Victor Reinz intake manifold gaskets, and also new heater control valve and hoses.

After it was all back together, a new pressure test with soapy water and listening through a hose, indicated a substantial leak between the intake manifold and head at the #4 runner.

I pulled the IM again and checked for flatness/straightness with a metal straightedge. Head seemed perfect. IM had a little wobble, showing maybe .003" - .004" of light between the IM and straightedge. So, I had the IM resurfaced at a local machine shop after which it shows perfectly true with the straightedge. I reassembled everything using new Victor Reinz IM gaskets (with some high-tack spray on the IM side to hold them in place), and again had the same leak at the #4 runner. Can't build more than about two psi. Tried torqueing down the IM bolts (new from Paragon) a little more, then can't build any pressure at all. Soapy water test and hiss from #4 IM runner to head connection shows leak.

Both times I installed the IM, I tightened the IM-to-head bolts before tightening the support bolt near the TB or the support bolts near the oil filler. With the support bolts loose, the manifold was seated in the supports fully. I also tightened the IM bolts in stages (all finger-tight, then all snugged with a ratchet, then all tightened to roughly 15 lb/ft).

This doesn't make sense to me, since flat is flat, with new gaskets. All surfaces were perfectly clean. I'm not sure what else to do, short of using some rtv sealant (probably grey) on the gaskets. Is there some trick to ensuring correct mating? Am I missing something?

KuHL 951

Any chance there's a hairline crack in the intake flange at a bolt hole? I doubt the head would have a crack, especially on the intake side. I've never heard of the head/IM leaking like that especially after the testing and machining you done.

cb951

Yeah, it's just bizarre. I didn't see any visible cracks, but I guess it's possible. But the soap bubbling seems to come from the gasket, though I imagine it's possible that it may be a crack leaking into the gasket area.

When I removed the IM the second time, I could see the water/soap soaked into the gasket on the under (head) side of the gasket on the outer (passenger) side of the gasket, indicating that the it seeped under the gasket.

Since it occured at the same spot even after resurfacing the IM, I'm afraid that it just might be a crack.

Is it worth it to have the IM x-rayed, or should I just get a used IM and have it resurfaced (about $50.)? (Btw, I just cleaned out the carbon in mine with a wire brush on a flex shaft connected to a drill, cleaned it up really well, and also re-seated and sealed the fitting for the banjo bolt.)

Could there be another issue besides a crack?

KuHL 951

Hopefully you will find the problem. I would just buy another IM. Even after getting it checked for cracks ($35)you would still need to weld repair it ($75) and that's iffy at best. There are so many used 951 manifolds floating around. I have 2 spares myself because I'm polishing one of them for that extra 15HP of bling
Hopefully it isn't a boogered up tapped hole in the head that releases tension under load. If it's damaged threads in the head a Helicoil is the best and only option.

David Floyd

Double up on intake gaskets and see if that cures it.

F18Rep

Is there a chance there is something wrong with the intake support bracket - holding the side opposite the head the a bit high - which in turns means the bottom of the intake/head flange don't mate?

I wondered if there would be a low buck way to oring the intake, seems do-able...Bruce

JustinL

I think you may be chasing your tail a bit here. If you can pull 19inHG (pretty good) of vacuum, but can't build any boost I would start looking on the other side of the throttle body for leaks. Also start thinking about your turbo and wastegate.

cb951

I was able to build the desired 15psi of boost (with the usual trail-off down to about 12psi in the upper rpms), along with my 19 inHG at warm idle. The problem then was that my AFRs were generally lean given the programming of the 951MAX chip programmed for my mods. A similar lean curve appeared on the "before" dyno with the original stock configuration. Russell (chip programmer) suggested that there might be some issue other than the chip programming. That's why I started to check for vac/boost leaks. (Sometimes there could be a leak under pressure (boost), and not under vacuum.)

After I did my first leaky pressure test, my gauge showed 17 inHG at warm idle. Apparently the test disturbed something.

Btw, I also resealed the TB and replaced the j-boot and EVERY other rubber hose and clamp in the intake system.

I think my very definite intake leak at #4 may have been there for a while, though I've never had any problems with idle or driveability.

JustinL

I see... Something still doesn't fit right for me. If you do in fact have a leak, the behavior of the AFR doesn't fit with what you are describing. Let's assume there is a leak. Under vac the engine will pull extra air from some point past the MAF/AFM, and you're right this will cause a lean condition. However, under boost, you will be blowing some of this metered air out of the leak and not into the engine, while still injecting the fuel that is measured by the MAF. This will cause the engine to run rich and not lean like your dyno graph.

Just doesn't add up for me...

HTH
Justin

cb951

I rechecked the surfaces for strightness and thought I found a high spot on the head, but I was mistaken. Another check revealed that my straightedge is too flexible and a slight curvature gave me a false reading. (Doh!) So, once again, flat is flat.

Since the leak is on the outer side (closer to the cam housing), it would seem that the manifold might be tilted slightly downward on the TB side. But the leak only occurs on the #4 port.

Right now, I'm considering using some rtv, but just know that it would make removing the IM again all that much more difficult. And with my luck lately, the rtv won't solve the problem and I will have to remove it again.

What to do?...What to do?...

m73m95

I don't think I can add anything to this but....

Aren't the bolts supposed to be torqued to 25ft lbs.?

Also, doesn't someone make a deadsoft copper gasket set for this? I know there are people with higher pressure than 15psi with no problems. Copper wouldn't go anywhere, and its soft enough to fill all the little imperfections in the aluminum.

cb951

Factory manual and Clark's say 14 ft/lb. Haynes says 15 ft/lb.

I have copper gaskets for exhaust. Have never seen them for intake.

m73m95

Hmm ok

Would the NA and turbo be different torque? I can't remember right off hand, but it seems like I torqued mine to 25. I could be wrong.

Yeah, copper is common on the exhaust. I've never seen them for intakes either. It just popped into my head, so I thought I would ask.

cb951

After some some fiddling and checking, it does indeed seem that the rear support bracket (next to the oil filler) may be a bit high. Since the attachment bolts down behind the turbo down-pipe look very rusted, I don't think the support bracket has ever been moved.

However, after a cooling system issue, the head warped at the rear and was milled a substantial amount (I don't know exactly how much), but not enough to warrant a thicker head gasket (all according to Powertech). Could the reduced head height be the issue? Especially in combination with the resurfaced IM...

Anyway...
Can the rear IM support bracket be ajusted? (I tried tapping it with a small hammer and block of wood. No change.) The Porsche PET illustration shows slotted holes. My biggest concern is being able to access and loosen the very rusted lower bolts. Is it possible without removing the turbo and/or downpipe?

I guess the alternative would be to shave down the pad on the IM where it sits on the support bracket.

cb951

Okay, I was able to loosen one of the two bolts and the bracket was loose enough to move. However, it seems that it was already at the lowest point. Still too high.

Looks like I'll have to either grind down the pad on the IM, or make some spacers for the IM to head mating.