Short Stroke 2.8

[1972_911T]

Originally posted by Henry Schmidt
High port velocity is necessary for maximum volumetric efficiency. Port shape and size not just port size is important for engine performance. Bigger is better only in a full throttle situation. must engines don't run full pedal all the time.
I would recommend a maximum 40 mm port for a 2.8 SS with an intake manifold of 38 mm. This lip at the transition will assist in the control of intake pulses caused by cam overlap and is exaggerated by large duration cams.

Big ports = poor low end possible good high end
small port = good low end possible reduced high end throttle response

Calculate CFM for your projected max RPM and run the smallest port to accomplish that volume.

With a 2.8 @ 7600 RPM 38 mm manifold is appropriate. Add 2 mm to the port for pulse control and you win.

8500 race on a race engine with proper gearing and bigger is better.

On my planned 3.0 MFI engine im using large port SC heads 39mm, as this is a mainly road car low end is important, do you think the 39mm port is sufficient? What should I open the exhaust upto? 37mm? Im using DC40 cams

[1972_911T]

Originally posted by svandamme
also understand now, how MFI Throttle bodies work on bigger engines , cause i always wondered how that worked , since you can't bore the TB's to big...


38 mm is exactly the size of the TB's, at least the top part ( T TB's) so all that is needed now, is to bore out the lower part below the valve, which shouldn't be a big problem ...

thx again Henri , you're a star !

Some good info here about stack boring

http://forums.pelicanparts.com/showthread.php?threadid=306105

Steve

[svandamme]

i'm having trouble scoring a 930/52 case
i guess this is the last of the 930 cases that takes the 66mm crank
but if i find another 930 case like an 02 , i guess those would work too, and still be a relatively strong case to work from??

what other good cases are there in the 930/1 to 930/52 range?

[YTNUKLR]

Stijn, the case obviously has to be a 3.0L (930 Turbo or Carrera 3.0) case that takes the 6-bolt crank. This is 930/52, 930/02, perhaps others? The flywheel end is recognizably for a 6-bolt crank..kinda like this


Cheers
Scott

[svandamme]

the problem is i can't see em for sale
so i'm putting up a wanted ad

came up blank for a 52
so needing alternatives

if an 02 works, that's great
does anyone know more case/type numbers that work?
might as well list em in this thread for others

i suspect that higher number is better, due to more revisions/strenght improvements... but in the end, an 02 if done well should hold just the same, they had 260 DIN hp out of hte box, and i suspect there's plenty reserve strenth in the case, right?

[YTNUKLR]

Physically the 930/52 and 930/02 are the same. The numbers refer to what engine it was--a Carrera 3.0 (930/02) or a 930 Turbo 3.0 (52).

[svandamme]

right, and there will be more 02's around , so i'll hunt for one of those



thanks Scott !


edit,

looks like the other 930 cases are of no use

930-10, 930-20, 930-25 have a housing bore of 65 mm dia and the mainbearings of the crank have 6o mm dia

so the old cranks won't fit in those...

[mcinturff]

Techincally couldn't you build a 959 out a 930? (with the proper case). Correct me if I'm wrong but you could take a 930, use a short stroke crank, calculate the compression ratio and order the right pistons to achieve 8.3:1 compression (stock 959, though personally I'd be more comfortable closer to 8:1), and twin turbo it, right? The hard part to mimic is the sequential turbos (one big, one small).
Btw, is Motronic injection good for twin turbo? I've seen it done, but is there a better injection (not EFI)?

[kenikh]

Originally Posted by mcinturff

Techincally couldn't you build a 959 out a 930?

No. The 959 had 4 valve, water cooled heads, to start. Then there are the myriad other differences. You could mimic bore and stroke, CR, etc. but it wouldn't even be close.

[mcinturff]

i was refering to bore, stroke, and cr. it would take 962 (or 956?) heads to come even close. obiously you would have a whore part motor to even be able to compare.

But imagine a 2.8 twin turbo...what injection system would any of you use?

[kenikh]

Originally Posted by mcinturff

i was refering to bore, stroke, and cr. it would take 962 (or 956?) heads to come even close. obiously you would have a whore part motor to even be able to compare.

But imagine a 2.8 twin turbo...what injection system would any of you use?

Cool; now I see. I'd use any one of number of the EFI systems on the market today.

[safe]

Originally Posted by kenikh

Cool; now I see. I'd use any one of number of the EFI systems on the market today.

Are there anyone that could manage a sequential twin turbo system?

[mcinturff]

it might be possible to build one using solenoids to turn a diverter valve (basically have the exaust split into a fork and have a valve blocking the pipe going to the larger turbo) and sensors coming from the wastegate. anyone know of the porsche design?

[mcinturff]

someone ask wayne if he knows about the seq. turbos like in his 959. maybe some part diagrams?...

[turboteener]

Skip the sequential stuff. Leave it to the manufacture to over complicate the situation. Order the properly sized twins and tune it right. it will be better all around.

Can you offset grind a 70.4 crank to 66-67mm? Maybe offset grind it to a smaller rod journal using the Honda 1.8in rod bearing.

[mcinturff]

henry, do you think the 66mm 2.0/2.2 crank can handle upwards of 400hp? Shouldn't rebuilding a 3.0 turbo with a 66mm crank and special ordered pistons(7.5CR?) be possible (stock, as in no mods other than crank and pistons...maybe cam) without any complications?

[Walt Fricke]

Brett

My understanding is that the 70.4 crank is basically an offset grind from the 66. So you'd have just that much less to work with. Maybe if you went to a smaller journal you could do it. 57mm to 52mm to 45.7/1.8". 52-4.4=47.6=doable?

McInt - the factory reported 620 hp from the 66mm crank in the 1983 2.7L race turbo motor. And 480 from the '74 2.1. Of course, was that the then old and out of regular production forged counterweighted 66mm crank we would purchase used out of a production engine, or something special?

The 66mm crank was reputedly stronger because of more overlap of the rod/crank journal circles. Didn't stop the factory from increasing stroke and power, though.

Walt Fricke

[mcinturff]

Wow! Do you have any links to more info on the '83 2.7 turbo motor (specifications).

[Walt Fricke]

Not right at hand. That information came from my well thumbed Anderson's engine specs table. He gives bore, stroke, some cam info, port and valve size, boost, and peak torque/hp and rpms for same. There are a variety of books setting out various details on the factory racing turbos. In addition to Bruce, Frere has some information. So does Ludvigsen. Aichele only has a little. Starkey's 930 to 935 has a fair amount of information. Doubtless there are others not in my library. None of these authors set out to help gearheads make their own mega hp turbos in their backyards, though. They are more chronicalers of Porsche racing history.

When I thought I would like to make a 2.1L turbo I looked into this stuff. Fascinating, but my wife put her foot down. Too much learning by breaking and blowing up, she said. She was probably right. So I set off to build a SS 2.8. I've been moving slowly. However, for the 2.1 project I never thought the crank would be a problem. They seem pretty stout. I know of a couple of 70.4 cranks which have broken in mag case 2.7s. And the factory had issues with the long stroke 2.8 RSR and its cranks, decreasing rod bearing width and increasing the journal fillet radii among other things in order to beef them up (per the authors).

Everybody who has followed this discussion recognizes the practical advantages of being able to use an SC crank if it could be offset ground to a 66mm throw and live. But this isn't really a discussion about turbos. There is a whole other forum for that. You might want to snoop around there.

Walt Fricke

[Henry Schmidt]

Originally Posted by mcinturff

henry, do you think the 66mm 2.0/2.2 crank can handle upwards of 400hp? Shouldn't rebuilding a 3.0 turbo with a 66mm crank and special ordered pistons(7.5CR?) be possible (stock, as in no mods other than crank and pistons...maybe cam) without any complications?

The crank can easily handle a number like 400 horse power. We built a 2.5 turbo some 10 years ago that made 375 without breathing hard and never had a crank issue. The engine was disassembled after track 60 hr. and showed little or no abnormal wear. If you are looking to build something really trick, grind the rod journals on the 2.2 (66 mm) crank the except 3.0 rods. When you grind the crank properly, you can get a larger radius fillet that will greatly increase the crank rigidity. Knife edge it and it gets almost as light as a non counter weighted crank.
At this point you can install the GT3R Pankl titanium rods [130 mm center to center length] and use a standard piston as you will have restored a the standard dimension to the crank and rod combination. In a 2.5 you use a 90 mm RS piston to get 7.6:1 @ .060 deck.
With a 95mm 8.5 CIS piston (78-79 SC) you get the same CR .7.6:1 @ .060 deck.

For those of you ready to try this modification we have the crank and rods in stock ready to go. Crank is knife edged, oiling mod, GT3R journal mod and heat treated (ion-plasma nitride). Pankls are still in the box. We even have the factory GT3R rod bearings in stock.