slate blue

First of congrats on your engine John, I was really impressed, I think the DTA setup is awesome too, I can't wait to see the airbox. As to being disapointed with the power of a 2 valve stroker I don't know about that, it would depend on where you draw the line in the sand.

A fellow here has recently built one, I don't know all the details but here are some, 6 liters, ported heads, I don't what size valves but they are no where near the size of my valves, this means flow will be down, my heads on the bench flowed 600 hp, if his heads flow well with the smaller valves I would guess that he would be around the 500 hp front in terms of airflow through the heads. (My euro heads with standard valves flowed 485hp) He does have a modified cam, 4, 2 barrel webers

He was looking more for torque than HP also, he wanted the car to pull out of corners hard. Remember also that this car has standard ignition and the dyno run was done on a Dyno Dynamics dyno and they will always read lower than a DynaJet for example.

This 2V stroker achieved 297 Kw at the wheels which is about 400 hp what that is at the flywheel I'm not sure, but I think you could see that if it was a bigger capacity had big flowing heads and the latest engine management it would produce some big numbers, it has to run the old tech stuff because of the rules in the class it races. Also Bob DeVore's street motor used to reportadly produce 580 hp and we all know when his race motor over revved on the dyno that it hit over 700 hp. I think if you get over 500 hp from a 2 valve engine you shouldn't be disapointed especially as you don't need to spend quite as much, it is also a bit different too.

Please post some more pics of your monster when you get them.

Cheers Greg

Jim bailey - 928 International

Greg...."Also Bob DeVore's street motor used to reportadly produce 580 hp and we all know when his race motor over revved on the dyno that it hit over 700 hp." those numbers I believe are part of an Urban Myth having never ever seen any dyno sheets although I did once see the car run at Willow before I worked for Mark and recall that Mark's 400-425 hp would out pull the 580-700 hp car down the straights. An engine at 400 RWHP is about 460 at the crank which is perhaps possible with the modified improved intake nice cross ram !

GaryJ

Thanks again guys,

just more food for thought.

Gary

Normy

Rhetorical:

[What I was trying to post last night before I fell asleep at the keyboard; sorry, long day~]

My understanding is that 2-valve heads can produce within about 3% of what 4 valve heads are ultimately capable of. This is with perfect porting, on racing engines. The reason that Porsche modified the original M28 to include 4 valve heads had nothing to do with horsepower- they could easily have made the same maximum power on their largest production M28 engine [5.4 liters] with the same basic two-valve heads [huge savings in design costs] if they had put just a small amount of effort into the design of the intake to better improve low-end torque with the hotter camshafts [only...] that a 2-valve design would require.

The 4-valve head was designed to meet emissions and driveability standards with the increased horsepower standards required to sell their 928 automobiles successfully. It wasn't just a sort of horsepower "band aid" or anything like that. If Porsche was really interested in MUCH higher output, they would have sold the car with a turbocharger.

So, it occurs to me that something is preventing the 2-valve head from flowing gas as efficiently as it could. Exhaust manifold? We've been there, the cast-iron manifold the 2-valves came with makes a great boat anchor and nothing more [so far I still own two of them, unfortunately...], but what happens if you port this thing and then match-port a good Euro intake? NOW...stroke this and see what happens.

N!

[PS: Y'all don't go anywhere with that last sentence!]

GaryJ

Thanks Normy:

Just when I thought I had put this thing to bed, you give me more to think aobut.

Gary

FBIII

Gary get Greg Gray to chime in again. He has done some extensive and wonderful work on the 2v's. He was expecting over 500 hp from an offset ground crank, some expensive rods and piston and some heavily massaged heads. Pick his brain or do a search on his earlier posts. He is doing really quality pushing the envelop stuff to the 2 V's

hacker-pschorr

Normy,
Excellent post! People are way too caught up on 4-valve heads around here. Ob's suffer from the same sickness as N/A 944's. The common mentality to making more HP with a 16V is met with "Oh just buy an S4".

S4 vs. EuroS is only a 17ish horsepower difference in stock form. So if an S4 stroker can make 500+hp. Why would 450hp with a 16V be out of the question?

I prefer the boosted method - it's so easy making power this way.

John Veninger

Do you have the flow data of a 928 2V head vs. 928 4V head that has had the same type of work done to it?
I don't doubt that the 2V head can flow, but would it really be 3% if "money is no object"was done to both heads?

hacker-pschorr

If I ever decide to cash in my 401k for my 928 hobby - Todd and I are going to find out

BC

Did I hear EFI?

hacker-pschorr

You have a PM

BC

There is no doubt that a 2V can be massaged to a large degree and flow very well. But is still a sort of twisted wedge 2V head with the inherent restrictions, and the fact that a REALLY large intake valve actually would start going into the bore. The Cam boxes are quite heavy. They leak. Cork gaskets for the front and rear were yearly items for me.

The 4V heads have a much much better combustion chamber for boost (hacker mentioned boost). In a conversation I had with Todd one time I talked about Chevy heads, and the ease of use of Chevy and it came to a point in the discussion where the actual BEEFYness, at least of the 89+ 4V heads, was mentioned. They are REALLY quite solid. There seems to be good room for porting both sides, and there is also good material for opening and unshrowing the valves when you go to the big bores.

We are limited on the valve size because of the lifter cages. Thats fine. The S2 944 springs fit just fine, and anderson has used them with a 7200rpm shift point for years.

BC

I Responde vu

FBIII

Aren't the S4 heads limited somewhat in the cam department? If my recollection is good don't the S4 heads have problems idling if the cams start to get aggressive.

hacker-pschorr

On the 2V head - I had a chat with our 944 brothers in a different forum, found this:
http://clarks-garage.com/phpBB2/view...315&highlight=
Assuming this is true - think of the potential of a 5.0 16V.