What is a safe boost?

[seb928s]

What is a safe boost to run in an 86 951 with the stock gaskets and stuff? I'm thinking about running 15psi I pretty sure that is still a safe boost pressure.

[lordgrommit]

Wolfrpi ran up to 25PSI boost with stock gaskets thought it did blow after about six months. I'm going to be running 15PSI Max boost with a widefire gasket. I wouldn't think that should be a problem

Matt

[wolfrpi]

The car was fine for about the first 5.5 months on 18 psi with the occasional ping after it was sorted. I could go over 20psi on the highway and when it got cold outside.

Within a month of getting the California mandated 91 octane rodent piss, the car blew the headgasket.

Another factor is the deck design on the block. The cylinders may in fact "wobble" at high boost pressures and ruin the head gasket. I remember running over 20 psi and smelling a strong odor after about 20 minutes worth of spirited driving (but maybe it was only the clutch...lol).

The Honda guys have "blockguards" to prevent the cylinders from rocking. No one to date offers this for the 951 as far as I know.

I'd stay with 15 psi and a 3 bar regulator and listen for knock. If no knock, you're probably safe.

In addition, when you run high boost you have to be very careful with fueling. The curve isn't necessary linear for required fuel flow as you have to add more fuel to cool the mixture as you raise the boost. You end up having way too much fuel pressure for the injectors for anything other than high boost. I ended up shooting 10-20 foot fireballs from the rear of my car on high boost/redline (7000rpm) shifting.

Good luck,

Erick

[seb928s]

I should be safe with 15psi on the engine I heard a lot of people running 15 on stock gaskets. I'm getting chips to it, I don't think I need a fuel pressure regalater.

[wolfrpi]

LOL - there is no way you won't blow a gasket with the original regulator...

Erick

[seb928s]

Ok thank you all a bunch All I needed to know was that. What happens when or if it blows? I heard no real damage is this true?

[wolfrpi]

Let me make it a little simpler....

Follow this steps...

1) You are adding another 40-50 hp to your car with chips and 15 psi (assuming your wastegate is not toast - which is a big assummption)

2) You are not changing the fuel pressure (assuming you stay with stock)

3) Use your common sense...is there any car that can reliably handle about 25% more hp without any changes whatsoever in its fuel system? Especially a turbocharged car that needs extra fuel for cooling (to prevent knock)?

4) Answer - no, none that I know of, especially none with the puny stock injectors of a 951.

If you've followed so far you will know by now that it would be insane to forgoe the $35 or so for a 3.0 bar regulator and upgrade your fuel system.

You can thank me later

Erick

[seb928s]

<font face="Verdana, Arial" size="2">Originally posted by wolfrpi:
Let me make it a little simpler....

Follow this steps...

1) You are adding another 40-50 hp to your car with chips and 15 psi (assuming your wastegate is not toast - which is a big assummption)

2) You are not changing the fuel pressure (assuming you stay with stock)

3) Use your common sense...is there any car that can reliably handle about 25% more hp without any changes whatsoever in its fuel system? Especially a turbocharged car that needs extra fuel for cooling (to prevent knock)?

4) Answer - no, none that I know of, especially none with the puny stock injectors of a 951.

If you've followed so far you will know by now that it would be insane to forgoe the $35 or so for a 3.0 bar regulator and upgrade your fuel system.

You can thank me later

Erick</font>

Where can I get that at? I saw the the fuel pressure regulator at huntley for 165$ or is that something else?

[Lawrence Coppari]

My 3 bar regulator was about $85 from PowerHaus, in late 1996. It was a "must" with the K27 they said.

Car has run well since then. Good power and mileage.

[Sergio]

Im running chips and a shimmed waste gate with an LBE...stock turbo and stock injectors Boost on the guage will go to 2bar absolute so I guess Im around 14.8 or so... Should I upgraded the fuel regulator??

[Mike B]

Somebody needs to write a book on this stuff...How about you Erick...You could have a best seller with your picture on the back cover...."Erick, also known as Wolfpri, is a noted Porsche performance enthusiast specializing in the Porsche 944 turbo..."

You would make a million...I would buy a copy..autographed of course... ...

'cause I'm in the same boat...'86 951 with a K27, APE stage 2 chips not yet installed and a LBE...If I read the post right without a FPR I am asking for head gasket problems???

Where is the best place to get an adjustable FPR...Huntley, Windward...

[wolfrpi]

You can get an adjustable unit - but i think its a waste of money if you are not going to go balls-out with modifying your car (turbo, etc.).

The 3 bar should be about $35 from Paragon Products and will work well on a mildly modifed stock turbo car very well. Correct me if I am wrong on the pricing.

When you go with a bigger turbo, you should proabably get an FPR to be on the safe side. Paragon has them also for about $160 I believe. This will be most beneficial above 15 or so psi. If you are disciplined and can keep it under 15 psi, the three bar will probably be fine.

In a nutshell, the higher you go with boost, the more (more than linear) fuel you will need. Things start to get very intersting in the high rpm range above 15 psi or so on street gas. At this point knock can come into the equation, the stock turbo will be huffing, and you'll need a significant increase in fuel to cool the mixture.

People do run 2.5 bar regulators on chipped 951s (non S), but these older 951s frequently have worn wastegates, thus limiting boost and negating the need for more fuel at high rpm. If your wastegate is weak, you may be fine with the 2.5, although your car will be down on power.

Best thing to do is get an air/fuel meter like the one Lindsey Racing sells for $99 to monitor the mixture at high rpm.

I've found the safest setting to be where the last green light is lit on the gauge until redline.

Although i did eventually blow the headgasket, I ran the 1/4 mile at 108.6 in 85-90 degree weather on 91 octane. This was done with the car tuned as stated above. Without an LSD and with the stiff rear torsions, I doubt the car would go much faster running it leaner.

The difference with a good aftermarket turbo (when used with a strong wastegate) is that it tends to hold your preset boost until redline. Almost like a safety valve, the K26 (with stock MAF and Cat) will not do the same. When you run 18+ psi on 91 octane at 6500-7000 rpm, some strange things happen inside that poor engine. Incidently, high rpms is where you will notice a bigger turbo the most.

They say that every psi is something like 10 hp on a 951. If you can get your K27 to 15 psi at 6000 or so rpm, you will have plenty of power and the air will not be significantly heated. I would guess that a stock K26 could be made to produce somewhere around 12-13 psi at redline. 30-40 hp over the stock K26 is probably a realistic goal for 15 psi, assuming everything else is in proper working order. Probably somewhere around 290-300 flywheel, although I don't have personal experience with the K27.

Good luck

Erick

[Mike B]

Thanks Erick...That's great info.

[monteness]

Well I guess I'm going to find out; but not to 20 psi. My brother backed out buying the car so.........she is going to stay in my hands forever now,,I might even give her to my two year old when he turns 18.

87 951, 72k, stage II, LBE, AFPR, K&N, clean cat, LR wastegate, manual controller, LR stage I intercooler.

Coming soon to my garage:
LR package,,Stage V turbo, new injectors, new chips, and the Kokeln intake system but still run the stock air meter, LR stage 2 head with WFR.

goal 13 psi 230-245 rwhp, 15 psi 270-290 rwhp, 17 psi, 311-340 rwhp.

AFter talking to Dwain Dement for about an hour, discussing the J-boot and the factory air box "vane", which everyone complains about to sell an MAF kit, if you get rid of the J and clean up the flow,,they have dyno'd the factory meter to 400 rwhp! Thats where it hits the wall. The J-boot pretty much hits it at 280 or you'll blow boots at 15 psi if you upgrade the turbo.

I probably won't do this until December(little more money to hide from my boost controller),,but the shop that will help me(I have a great mechanic who also teaches when you ask him right)also has a dyno in the floor; so hopefully I'll get to do some tuning. $250 for 1/2 a day. I'll get back here and post them.

[adrial]

14.5psi with a stock fuel pressure regulator is completely safe IMO
Autothority stage 2 = chips (dme, klr) and banjo bolt = 14.5 psi
No FPR necesary...
Check out Perry951's thread on the rennlist: Running rich with autothority chips
Basically he has a huntely stage 2 turbo with stock fuel pressure and autothority chips and is running very rich @ 14.5 psi and even 18psi under full boost.

By the way im speaking from experience of my 951S...