differences between turbo and na pistons?
 

iam looking into turboing my '86 944.. now, i know i'd be better off buying a factory turbo car, yadda yadda etc etc....

how ever, i would be going with a bigger turbo than the factory kkk, and bigger injectors, full map based stand alone engine management, so by the time i got done replacing every thing, none of the factory components that make the 951 car special would be there any more anyway.. well accept for the lsd.. but that's beside the point.. just for the sake of conversation..

so, all need to know, is are the na pistons cast or forged ?(iam assuming they are cast) and are the turbo pistons cast or forged? and does any one make forged pistons for them (aftermarket)

turbo pistons are forged, NA pistons are cast
JE Pistons makes custom pistons for just about any application, and they are forged

I think the rods may be different too. Sid has done a SC setup on one of his n/a's. It's an 83 though and I think in 83 they used the same pistions and rods in all models. You have an 86 and from what I know Stijn is correct. Try a PM to Sid at Blown944. He has a handful of posts on here that go into good detail too. He'll be more than happy to talk to you.

there were no turbo's in 83, so yes, all the same that year :D

lol... that would explain that then I guess! :)

I think the pistons used in the early n/a's were the same pistons they did use when they did get around to making the turbos. :) The forged pistons. Any input on the rods?

nope, the Turbo has different compression

a NA has 2 small valve pockets
while a turbo has one big oval valve pocket, it's not really a valve pocket, more a pocket to drop the compression from 10.6:1 (ROW) or 9.5:1 on the NA to 8:1 for turbo (ROW and US are the same)

the conrods on Na were forged untill 84, from then on they were cast
turbo conrods were sinter forged

bit small, but you can see the pistons in this pic

http://forums.pelicanparts.com/uploa...1183909200.jpg


also shows all the parts, unique for the 951...

nice research! :)

i'm an obsessive rightclicksaveas'er on this board

All those parts sure looked nice when they were brandy new!

i think most if not all of em can still be ordered new
time to max out the Credit cards @ Pelicanparts :D

the early cars 83 nd 84 had forged slugs with 9.7:1 compression.

The later ones have cast and are high compression.

the turbo are forged 8.5 :1

When I looked at the rods I saw no difference.

It would be best to source some turbo slugs they are quite spendy aftermarket though. maybe find a turbo shortblock. I kniow where one is for 1k.

I am eventually going to do a sleeved block using chevy pistons and rods myself all for just over the cost of aftermarket pistons for the 951. Of course I have the top of the line chevy stuff already (I guess this is a little off subject)

8.5:1??? the worksshop manual specifies 8:1 for turbo?

The answer to your question as far as the piston is concerned is that turbo pistons are 8.0 to 1 and the n/a pistons of all years 2.5L 8v except 88 are 9.5 to 1. The 88s n/a are 10.2 to 1. The 85.5 pistons look different from earlier pistons but have the same compression ratio. These are U. S. specs I am refering to. If you are thinking of using the n/a higher compression pistons, you will be limited to very little boost and little power gains or you will have things like cracked cylinder walls (as in the case of Danno's turbo). We tried the n/a short block in a turbo and have seen others do it. The result in all cases end with very short engine life and less power than a chipped stock turbo.

If you are going to replace absolutely everything in the car, then it won't matter since all the replaced parts that are better than a stock turbo will cost you in the tens of thousands of dollars. However, by starting with a turbo, you get most of the stock parts people keep when they modify their car such as turbo head(ceramic coating, sodium filled valves etc), turbo low compression pistons, turbo engine aluminum mount (drains oil lubricating turbo), headers/crossover pipes, intake manifold, larger radiator, intercooler (good for 500hp), coolant tank with provision for watercooling to turbo, turbocharger electrical auxiliary water pump, 4 piston calipers, larger rotors, stronger transmission, taller gearing (matchs powercurve) for more power, lighter forged rods than even the early n/a, turbo cam, bigger clutch, turbo flywheel, external oil cooler with different housing at the side of the motor, and bigger sways. This is assuming you don't want the better looking body of the turbo. If you want to convert the body, then add fenders, header panel, bumper cover, bumper support, bumper shocks, fog lights, batwing, headlight covers, rear lower valence, etc.

These are only thing things I can think of at the top of my head that most people leave stock on a turbo when they modify the car unless you are going for crazy power but most people going for over 500hp start with a 968 engine and turbo it which will cost you about $15k just for the engine + mods not including labor. I am sure I am forgetting some other items like shifting fork and other stuff like that. This is assuming you are buying a bigger turbo ($1k+), standalone engine management ($1.5k+), aftermarket wastegate, airbox, injectors, fuel pressure regulator, etc. You can also get a guards or quaif LSD for $1.5k.

I guess I am just lazy. It makes more sense for me to buy a running turbo for about $4 to 5k, buy a bigger turbo, injectors/fp regulator, wastegate, and map piggyback, and have about 450hp for much less labor and money.

I guess I'm off a .5 point :)

While I agree starting with a 951 is a wise choice I have to take exception to ALL cars NA being boosted ending up in failure, as I have had mine on the road for 2 years and have raced it to show the performance level it has attained.

As a direct comparison my car has run a 14.0 at 5800 ft and has some more room left in it while another car on this board 951 has ran just shy of that using MS and about 14.5 psi.at sea level.

see here

http://www.dragtimes.com/Porsche--944-Drag-Racing.html

I am not disputing that the 951 is the way to go (I am actually buying one today) but when monitored correctly and using the proper parts the NA can be moderatly boosted and achieve very similiar results to a modeately modified 951, for general driving situations anyway.

Not trying to start any arguments here, but I just can't let ALL cars be generalized in this way. Especially when I have one in my garage that I drive regularly that is not in this catagory :)

Sid, I think we agree here. My last post mention "you will be limited to very little boost and little power gains OR you will have things like cracked cylinder walls". These cars I mentioned with n/a blocks were not drag cars. They were street cars driven every day on the streets with normal boost levels or more of a stock 951 and higher, which is too high for the high compression pistons and grenaded soon after the install. 2 of the cars started as 951s. We just swapped out the blocks and installed the n/a shortblock. I think Danno (of Guru Racing) was trying to develop a bolt on n/a to turbo conversion so we installed the n/a shortblock when his 951 2.8L steel sleeved shortblock broke on the track.

The new Darton steel sleeves are extremely strong. If you don't go stupid with the compression and keep it to a sane level (maybe 8.5:1 tops, or run lower boost levels, or both) you should be fine. If you go running the 9.5:1 n/a stock compression on a stock engine and expect to throw 18 psi of boost on it right out of the gate, yea - you're going to have problems.

My turbo conversion is using steel sleeves, JE pistons and Carillo rods. I'm planning on 8.25:1 c/r and running a maximum of 18 psi boost (maybe a little more eventually with H2O injection, but that's way down the road).

You can certainly do forced induction on an n/a car, but there's a "right" way and plenty of "wrong" ways. They're both expensive.

Yea I think we're in agreement. The power levels are limited for sure. I am not going to go out and try to blow it up just to se what happens but it does handle 12 psi very well at this point.
I am fortunate to know a bit about using methanol and how it can help with some of the above issues.

Methanol would be very cool to see on a 944. I've wondered for a while how these engines would do with a healthy dose but to my knowledge, that's unchartered territory.