ribs

Alright guys, I talked to my mechanic, who is a very good mechanic and has been working on porsches for many many years. He has had 3 951's and currently has a 91' 944S2 coupe and an 81' 928 and another 928 parts car. He told me that I am going to blow my head gasket in a short amount of time if I put a MAF kit on there (running 14 psi too). He said forget about a bigger turbo, it will be even worse. He told me to expect to replace my head gasket often if I drive spiritedly with a MAF on there.

Well, I asked him about a wide fire headgasket and an O-ringed head, and he said they will help, but not much.

Am I missing something here? I have been lurking on the rennlist web board for a year and a half and have heard maybe two or three 951 owners complain about a blown head gasket. Of those, maybe one was upgraded.

Attention all you people with MAF's, bigger turbos, and other high power upgrades, have you had many problems with head gasket failure? Other reliability problems? Drivability issues?

I want to do a MAF by the end of the summer, as I think I am going back to college in the fall and quitting my job, therefore no $$$ for fun stuff, and I want to make my car fast while I have a chance. I just want to know what I am getting myself into. While I value and trust the opinion of my mechanic (he is the only mechanic I have ever met who I feel I can trust!), he is only one person and doesn't have the experiences of all of you people, too. Let me know. Thank(god its friday!!!!!!)s.

Tabor

Is it just me or, can't you run more boost with a more efficient turbo that doesn't heat the air as much? Not that I own a turbo charged car.

Maybe he was confunsed and thought that 10psi = 1bar or something weird. Everyone makes a mistake sometimes.

David J. Harrington

I have never had a blown gasket, but here is some advice:

In theory, a bigger turbo WILL help. There will be less backpressure from the exhaust side. Also, you don't need as much boost pressure to flow the same amount of air. Second, it would seem to me that making sure you never ran lean would help prevent blowing the headgasket(this is just a thought of mine). Also, try and make sure your car is running as cool as possible.

I would agree with you that from the posts on this board, a head gasket failure is not all that common. My car, for instance, is still on the OEM gasket(I know, I know, I'm replacing it soon with a widefire). I ran 17psi of boost for a while, and commonly run 15psi. I haven't had any problems, knock on wood.

Dave

IceShark

I would probe him as to why he feels this way. My guess is that the MAF will allow you to develop more HP and that more HP will stress the engine to a greater extent. And he is right.

The question is how much more and if it is worth it. The jury here says yes, but we are a strange lot that think nothing of taking a weekend off to fix everything we just broke on our babies. Something for you to consider as you head off to school.

I would put it this way: ask him which would be worse, running a MAF or cranking boost over stock in the first place? I know what my answer would be. Booooost.

ribs

My mechanic said that it isn't the boost pressure that will necessarily blow a head gasket, but the amount of air flowing (CFM).

Extreme example: put a restrictor between your AFM and your air filter that allows 1/2 the air as the stock set up to flow into the engine. All though your turbo may be able to provide 15 psi of boost to your intake manifold, your engine would suck this air down quicker and have less horsepower because of its anemic flow and not being able to have the turbo fill the cylinders with air.

Now take the restrictor off and put in a MAF kit that flows say 30% more air, running at the same boost pressure. Now your turbo is going to be able to push more air into your engine with each valve opening, creating more air registered to your DME, pushing more fuel into your engine, giving a larger bang and more power.

Where am I going with this? I don't know. Just note that CFM of air has more to do with blowing a head gasket than PSI from your turbo, according to my mechanic.


As far as I know, running a newer turbo will give you better efficiency, as far as flow rate (CFM) and heat are concerned. You can run a stock turbo at 22 psi, but it is out of its efficency range for the amount of air it is flowing, therefore is going to heat the air up a lot, leading to detonation, light undense hot air going into the engine, which is not going to give much of a HP increase over running 18 psi. Now with an upgraded turbo designed to flow xxx CFM of air a minute, you could run at 22 psi, and as long as it could suck it in fast enough (where the MAF comes in), you will be able to provide cooler denser air to your engine, and the 22 psi of air from the cooler, more efficent turbo is going to weigh much more than the hot air from the stock turbo, allowing more fuel to be burned, allowing for more HP. At least thats how I see it.

This is why running a MAF and a larger turbo would be bad according to my mechanic (I am extrapolating from what he told me) - the cooler denser air allowed by increasing the efficency of a MAF and/or better turbo would lead to more HP being made, causing additional stress to the engine, probably causing the head gasket to blow, etc...

what do you think?

[ 08-06-2001: Message edited by: ribs ]

Tabor

Did you ask him about using an o-ringed head with a copper head gasket?

I know that Garrity has set customers up like this before.

ribs

yes I did...I think his exact words were "it will help you out for a little while, but will still blow. Its just a matter of time."

then later he told me that that would help a lot. Don't know what to think. Maybe he was having a bad day at work or something. He is changing jobs soon to a mercedes dealership...

IceShark

Ribs, you are young, money ain't growing on trees, etc. Wait a bit and do the engine management system with a MAP if you are serious about keeping the car. As you research that you will answer all your questions.

TurboTim

Actually boost pressure is what blows headgaskets if no other factors are involved(detonation,excessive combustion pressure & temperature,overheating,etc...)and not CFM.For example.You use a turbo that flows 750 cfm at 18 psi of boost.Now you put a turbo on that flows 750 cfm at 25 psi of boost.They are both flowing the same amount of CFM at their respective boost levels. However, one has to use a much higher boost level to flow the same amount of air.Essentially what happens is that the turbo that is running 25 psi will be putting more pressure and temperature inside the combustion chamber and cylinders.Excessive cylinder pressure will kill a headgasket quickly.It can cause the head to lift and then its over. The main problems with blowing headgaskets is caused by detonation, though. If you do not detonate, then the chances of blowing a headasket are minimal.Even if you use biggeer turbos,etc.....Another factor to consider is the octane rating of the gas you are using and the anticpated boost you want to run.A higher octane gas will allow a greater threshhold for deotnation and combustion chamber temperature.This is only to a point though and then you still have to deal with excessive cylinder pressure.Now Tabor mentioned using a bigger turbo that has less of a charge air temp and this is correct to a point.Now what you have to be concerned with is not excessive temperatures in the cylinders but again....excessive pressure in the cylinders(assuming you runs lots of boost).To sum it up....detonation, excessive cylinder temperatures and pressures and overheating is responsible for most of the headgasket failures associated with these cars.

Tim
86 951 http://www.speedforceracing.com

ribs

So let me get this straight...manifold air pressure (which equates to cylinder pressure once the valve is opened) aka boost is what kills turbo engines? Makes sense...Which turbo would be able to make more HP, assuming they are both flowing the same CFM...18 psi efficient or 25 psi inefficient? I would guess the 18 psi turbo would, because or reduced air temperature, better efficency, less back pressure in the intake manifold because of lower boost levels, etc.

I would also think that the mechanical stress (not accounting for heat) of the powerful explosion of more dense air from the 18 psi turbo (lower boost but cooler therefore denser, and the AFM/MAF/MAP would sense the large CFM coming in and put more fuel in, and make a bigger explosion) would be the same on the head/head gasket as the 25 psi turbo during and after ignition of air and fuel because the same amount of air is reaching the cylinders and is being compressed, and the explosion in the cylinder should put about the same strain on the head as the 25 psi explosion, because after the air/fuel mixture is exploded and before the exhaust valve is opened, the same amount of air (PV=nRT...cool stuff) is mixed with the same amount of fuel, causing the same explosion, all though it may be more efficient in the 18 psi turbo's case because of the cooler air, making more expansion of gases because of a cooler starting point and making more power causing more pressure on the head/head gasket before the exhaust valve is opened.

note: I normally would go back and edit that last sentance into usable chunks, check for gramatical errors, and make sure I didn't say the same thing 5 times (which I think I did), but since that may be the single longest sentance I have ever written, I think I will keep it.

So what is my point? I don't know, do you. I don't really feel like going back and reading through all that stuff to remember what I was trying to say.

Anyways, turbo tim, what effect would putting extremely cold air into a turbocharged engine, saying you had this hypothetical intercooler that would take your charge temp from 250 deg F to 0 deg F, if the intercooler had very good air flow?

Gosh, I don't think I have done any work what so ever today. TGIF.

aka 951

Your mechanic is full of it. Its hard to believe that he has 3 951s..lol. On the stock fuel system though you will cook a headgasket unless you have at least a FPR with high boost (and wastegate)and injectors with a bigger turbo.

Erick

ribs

He has HAD 3 951's, over the years, not all at one time . Only 1 of them did he ever get saucy with, though.

[ 08-06-2001: Message edited by: ribs ]