Options for lowering boost and keeping headgasket intact.

RonA

RonA

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Feb 26, 2008
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Head's been holding for the last 4 years(PDR stage 2 w/orings and ARP studs). An occasional run up to around 68psi or so but have been checking the studs every 6 months( I drive around 8k miles per year). Installed a 13mm pump and a larger primary(GT4718) hoping that the larger primary wouldn't overspool. Unfortunately it does and I'm seeing a bit more pressure out of it than I would like even with the plate and afc back. 73-74 total with around 45 out of the primary. Lost the head gasket on the first full throttle run. Going to have the head checked out and try a set of 625 studs this time. Been thinking about adding a wastegate in the hotpipe. Seeing 85psi drive now, but sliding the plate forward is going to bring it up quickly. Running a 64/71/16SS on top and a 1.08 ex housing on the primary. Would I see a drop in boost going to a larger top charger like a Silver Bullet, and going to a 1.2 exhaust housing on the GT47? I have heard that running an aftermarket intercooler might drop my boost by as much a 5psi also? I'd appreciate any suggestions to get the numbers down a bit(besides less fuel).

RonA
 
Ron, I like the idea of duel gates but I have also ran that same O-Ring setup with zero issues to 80-85 psi, I was at 1 to 1 at 78.

Jim
 
Better seal....IMO 85 psi isn't bad, I was seeing peaks of over 100 psi (can't say just how high gage reads to 100) when I wasn't flowing enough through the gate on my secondary.
This is on a common rail though....MLS gasket - no oring. 625's

Was running about 45 psi primary as well.
 
It's been holding steady for quite a while, I guess the added boost and timing was a bit too much. I was told to start at about 24 degrees of timing. It took 30 degrees of plunger lift to get 24 degrees of timing with the timing light. That might be the problem. I've heard of there being 2-3 degrees of difference between the two methods, but 6 is quite a bit.
I think I could see closer to 1-1 if I ran a larger ex housing. The new pump spools this setup like my old pump spooled towing twins. I thought about trying the next size up Garrett, but they get pricey at this point.
 
RonA said:
Head's been holding for the last 4 years(PDR stage 2 w/orings and ARP studs). An occasional run up to around 68psi or so but have been checking the studs every 6 months( I drive around 8k miles per year). Installed a 13mm pump and a larger primary(GT4718) hoping that the larger primary wouldn't overspool. Unfortunately it does and I'm seeing a bit more pressure out of it than I would like even with the plate and afc back. 73-74 total with around 45 out of the primary. Lost the head gasket on the first full throttle run. Going to have the head checked out and try a set of 625 studs this time. Been thinking about adding a wastegate in the hotpipe. Seeing 85psi drive now, but sliding the plate forward is going to bring it up quickly. Running a 64/71/16SS on top and a 1.08 ex housing on the primary. Would I see a drop in boost going to a larger top charger like a Silver Bullet, and going to a 1.2 exhaust housing on the GT47? I have heard that running an aftermarket intercooler might drop my boost by as much a 5psi also? I'd appreciate any suggestions to get the numbers down a bit(besides less fuel).

RonA
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I WOULD GET THE HEAD OR THE BLOCK FIRERINGED AND BE DONE WITH IT
 
I'm not an expert but I agree with Smokem, 1.08 is a little tight, might try something more along the lines of 1.32 like is commonly used on S400 based primaries.
 
RonA said:
I thought about trying the next size up Garrett, but they get pricey at this point.
Click to expand...

They are pricey at your point now...

I would go with the 1.2 A/R and drop back on the timing some. I'd bet the timing had more to do with it then the DP in this case. However at 45psi in the cold pipe you are getting dang near all of that 138 lbs/min.

Of course mine is a hybrid 4518 so not apples to apples, but I am using a 1.15 A/R and it is on the tight side too.
 
soulezoo said:
They are pricey at your point now...

I would go with the 1.2 A/R and drop back on the timing some. I'd bet the timing had more to do with it then the DP in this case. However at 45psi in the cold pipe you are getting dang near all of that 138 lbs/min.

Of course mine is a hybrid 4518 so not apples to apples, but I am using a 1.15 A/R and it is on the tight side too.
Click to expand...

Yours probably chokes more than mine because of the smaller turbine. Bet it spools fast. With the fuel down, this 1.08 is almost ideal, but I am going to want to try moving things forward and putting in larger injectors. I think I will try adding a gate in the hotpipe first, and then look into a housing change later. The GT55 isn't much larger on the comp side, but is alot bigger on the turbine side.
 
Doing the hotpipe wastegate sounds like a good plan to me.

A good intercooler will drop boost a couple of psi, but it is costly.

Doing more port work on the head will also drop boost. Jerry (at Source Automotive) ported the one on my 05, and I dropped about 4psi.

UnBroken suggested that you put a popoff valve in the cold pipe. This is also a good (and cheap) suggestion, if you don't already have one. Don't try to use it to limit max boost, but it does work well to dampen boost spikes. Set it to about 5 psi above where your wastegated boost is.

Paul
 
Wouldn't the boost drops from a ported head, or a better intercooler, just 'cure' a symptom, and not the cause? With those, you are either reducing a restriction, or increasing the density of the charge. So you are getting the same mass of air into the cylinder as before, and once you start compressing it in the cylinder, you'll still be at pretty much the same point you were before?
 
OT-OF-Here said:
A port job would take care of that.
Click to expand...
Head was ported when I bought it.(PDR stage 2 head). I've thought about trying the zzfab route, but have not heard any before and afters. I'm still using a stock intake too.(everyone says not to change unless it's a 3rd gen).
 
Tate, I think you're onto something. What head gasket thickness are you running Ron? A thicker gasket would reduce the peak cylinder pressure. I believe that's what you're going towards, right? The drawback is increased smoke and trouble starting if your pistons have a little compression taken out of them.
 
joefarmer said:
Tate, I think you're onto something. What head gasket thickness are you running Ron? A thicker gasket would reduce the peak cylinder pressure. I believe that's what you're going towards, right? The drawback is increased smoke and trouble starting if your pistons have a little compression taken out of them.
Click to expand...

I'm running a .010 over gasket right now.
 
Hmm... If you don't want the cold smoke, I would go with either the wastegate around the primary which keeps the good spoolup or go with the bigger A/R exhaust housing. Or, possibly offset o-ring the block and the head?
 
I'm prob the least knowledgable person in this thread. But Tate's post was exactly what I was thinking too...

A thicker HG would prob help a lot.
 
thicker headgasket will put the spray pattern out of the bowl with less timing than a thinner one.

if you are looking to lower the boost then there are only two ways to do it. housing swap or add another wastegate.
 
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