nik

Hi!

I'm going to install my AVC-R soon and change to Cup-chips. I wonder who much I can increase the boost whitout blowing the head gasket? We are talking stock gasket, no o-rings (yet :-)!
By the way, is it ok to use stock wastegate together with the AVC-R?

Of course it depands on the "status" of the gasket, when it was changed but that I don't know.
I'm planning on trying 1 bar of boost, is that too high?

My car is a -90 951 with 12000 km (75k miles) on it.

Best Regards
Niclas, "the Swede"

IanM

One bar should be fine. Keep in mind though that blowing a head gasket has more to do with heat and detonation than it does with boost pressure. A well tuned car should be able to run 16psi+ all day long, as long as the a/f ratios and timing advance curves are optimized, the ignition system is strong, etc. However, a marginally tuned car that may be okay with 14psi of boost, could blow a head gasket at 16psi due to the added boost pressure. At the end of the day, you can o-ring your head and use whatever gasket you'd like, and still blow head gaskets with a poorly tuned motor.

Danno

Yup, it's not the combustion pressure that blows a headgasket (common misconception). The intense heat generated by detonation & knock due to inappropriate air/fuel ratios will literally burn through your headgasket. Part of the issue is that steel conducts heat a lot slower than aluminium, so the headgasket may actually be the hottest part of the combustion chamber.

I know of guys who've blown numerous wide firering headgaskets just weeks apart. I also know of another guy who's running 25-psi on a stock bottom-end engine. And he's got nitrous on top of that! So it's all in the tuning and maintaining knock-free air/fuel ratios and ignition timing.

M@951

Have not installed my AVC-R because of the stock head gasket. It's ok for me to boost 15.5psi in the cold winter in OKlahoma. With Tial WG & SFR 3" Race exhaust and APE II chips the engine started to ping @16psi. How long you think I could keep the stock head gasket with my MAF3 52lb inj, and AVC-R installed. I guess about 3sec. What's your guess? The MAF3 would probably yeild an extra psi from the density alone. My AFPR is @3bar. I would be more comfortable with race heads & rebuild before I start installing a MAF and a EBC and a BB SFR turbo. Besides, how much hp would net with EBC & MAF3 set @ 16psi limit ? I rather build a strong motor w/ large turbo & set it at 17-18psi and forget about it. I am maybe 250-260rwhp on K26-6. My 951project is to make 350rwhp @18psi on built motor with huge SFR turbo w/o Total Engine Management on 2.5L. It will take many dyno runs to achieve since I don't track test it.

aka 951

Toss the APE chips. Too much timing and too much fuel in the midrange. To get rid of the knock you have to back off the timing as you are really not running that much boost. Doing a wholesale retard will ruin your overall performance (via the DME). Retarding the timing through a better chip or through a TMC1 would probably be a better alternative. One thing for sure though - headgasket failures and pinging are directly related.

M@951

Nick,
I also have a Euro 951. I got ahold of a grey market light '86 with 80k miles for $10k in '99 with 17" C2's and chips and orig paint and PCA owned.

M@951

He we go again on the chip debate. Better make some room, cause this thread will be infinate now [grin]

<a href="http://www.novustelecom.net/~fkassam/dyno/dyno.html" target="_blank"> Dyno day</a>

TurboGuy

I run 17 psi on a K27/6 with 110 octane all the time with no problem. Boost requires octane or you buy headgaskets. On pump gas you are at risk running 14 psi for long durations. So buy the octane or buy the headgasket. Simple answer.

M@951

I put 101 Sunoco on dry tank for weekend kicks. But I don't have EBC installed or mechanical gauge. Not sure what effect other than a cleaner burn @15.5psi on K26-6.

Pump gas at Phillips 66 is 93 and cleaner than Texaco and others here. Quicktrip convienent store has a cheap grade '93 that put a '91 S4 in protective mode to the shop and also a RX-7TT got bit by QT '93 gas. They are both stockers. It gummed up the wire boots and burned some plugs and had to reset brains for those cars. 928 driver was credited for $25 gas, they blew off the RX-7TT driver ha ha.

Glad I just have chips sometimes than expensive factory Eng Man.

aka 951

there's a great thread on the 911 board displaying the stock, autothority, and weltmeister fuel and ignition curves for a 911 chip. Your stomach may turn when you see how much fuel and ignition the autothority chips through into the chip. From what I hear, they take a similar approach to 951 chips.

M@951

Tony Garcia don't think much about his APE chips.
I think Autothority riches the fuel to allow for other mods, they state this in their instructions.

I hear SFR has chips. I bet those have dyno comparisons. <a href="http://WWW.SPEEDFORCERACING.COM" target="_blank">SFR</a>

nik

Interresting, so if I use fuel with higher octane I will "spare" the gasket more. At the gasstaions in Sweden we have 98 octane unleaded fuel, you don't have that in the US?

Increase the octane and I will be able to go for a higher boost!?

Regards
Niclas <img src="graemlins/roflmao.gif" border="0" alt="[hiha]" />

Russ Murphy

[quote]With Tial WG & SFR 3" Race exhaust and APE II chips the engine started to ping @16psi. How long you think I could keep the stock head gasket with my MAF3 52lb inj, and AVC-R installed. <hr></blockquote>

Expensive engine management? The list of goodies above is what, $5000.00? Thats right you've got expensive engine management.