hacker-pschorr

FWIW - just throwing info into the pool - there is a 928 up here running stock 944 turbo pistons and rods up to 7,500 rpm with 24psi of boost (recently knocked down to 22psi due to a lean mixture issue). The pistons and rods, and crank (also stock) have not been the issue. I understand you are not doing a boosted motor, just sharing info. Hope this helps in some way.

Edit -
I'm brain dead - the pistons have the skirts cut off and holes added by the wrist pin to aid in oil drainage. It might have squirters - not 100% sure on that. Some 1987 928S4 motors had squirters from the factory. I can't remember if that is the motor he used to build this one.

StupEd05

I agree 100%!!! Now just think, if we could stop all the arguing and B*tching and all pitch in on stuff like this, we might be able to cover real significant ground. I sure know im learning a TON off of this thread.

hacker-pschorr

I remember a few years ago some of the top 928 tuners were staying over 500rwhp on a 928 was so close to impossible there was no way just a supercharger would work.
Same people also said no way a stock 928 could handle over 4-5psi
Vortec said there was no way their supercharger would give a 140+hp gain at 7ish psi
Right now is a almost stock (pistons dished for lower CR) with 14psi putting 550rwhp to the ground.

It's easy to point fingers and say "that's impossible, don't waste your time"
It's not easy to ignore them and continue your develpment.

Keep up the work guys - I expect to see a 400hp 8500rpm 968 motor in the future!

There is a guy in the 928 forum (sterling) that worked with Bob Norwood in fitting a pair of 968 heads onto a 928 engine - do a search for his threads. Awesome setup he has.

Geo

AMEN to that!

Duke

http://www.928sg.com/

NineMeister

Danno,
Sorry for not answering your last question, I have been very busy of late. I use a couple of different engine modeling packages, both DOS based but with a very intelligent program behind the facade. I would rather not name them here since I sometimes do consultancy work on engine design and I do not want to spend the next 4 years explaining how to use them and putting myself out of business, but you can call me if you want more details.

However I just thought that I better explain my views to everyone in more detail. Let's talk about flow requirements first before we all rush off to Del West for bigger valves eh?

If we are designing the engine for peak hp at a certain RPM, with a bit of maths (unfortunately not simple though) we can deduce the peak piston velocity which always occurs when the rod and the crank c/l to pin axis are at 90 degrees to each other, usually around 78 degrees ATDC. It is this peak piston velocity at the chosen peak power rpm that will solely define the peak intake flow requirement of the valve. Once you have calculated this you can then size the optimum valve for this peak flow requirement. Then for a given engine design you should reduce the port size as much as possible but without harming the flow of the valve/port combination. In simple terms these are the fundamental design requirements of the intake system, and without these the engine could possibly make the same power but would definitely lose out on a lot of torque that the small port will generate at lower engine speeds.

The theory is something like this:
Once the intake valve is open the moving piston excites the column of air in the intake runner by reducing the pressure on its surface, hence the column of air starts to move in order to fill the void left by the piston. At peak piston speed the column of air will also reach a peak and this ideally needs to be around 600ft/s. Note that this occurs well before the centreline of the cam and hence BEFORE peak valve lift. Now the interesting bit is further on in the cycle when the valve starts to close, because the high inertia column now has energy, once it "sees" the valve closing it will begin to "back up" behind the valve and slow down. Bernoulli's equation tells us that if you slow down a moving gas you increase its pressure, therefore the moving column of air begins to produce a high pressure pocket behind the intake valve that forces its way past the valve and into the cylinder. Since the cylinder is now past BDC and on its way up, the pressure will be above atmospheric so you have now achieved intake supercharging.

The 600ft/s port velocity is a bit of a yardstick, since if you try to achieve more than this the energy required to get the gas moving is more than that generated in filling the cylinder. The physicists out there could probably calculate the relative increase of pressure generated on a body in front of moving air (or alternatively a moving body (think car) in static air), but to help you along at 600ft/s the increase is around 25-28%. That's 28% of 14.5psi or in other words 4psi of boost. Without a supercharger in sight.

So, all you need to do once the port velocity is up is to extend the duration of the cam to allow the air enough time to get into the cylinder. That's how we got 103bhp/litre from a 103mm bore 911 engine with just 49mm valves. And that's how I plan to exceed 100bhp/litre from a 968 engine without breaking the bank. All I need now is a volunteer to pay for the head development or a clone of myself so that I can get the job done rather than just talk about it.

I best log off now otherwise I will bore everyone to sleep....

hoffman912

first you want everything balanced as close as humany possable.. everything in low and top end.
i would only trust this to a few machine shops. competition engineering comes to mind 1st.

you will also want to have everything as light as possable. rods, crank, probably racing pistons (light, higher compression, and very strong), fly wheel. i do not know if there are dual valve springs for 944s.. if there are you will want them.


on a 912 this is done the same way pretty much. the biggest things are bal;ance, dual valve springs, carello rods and especially use a scatt crank. you cannot use a stock crank on a 912 if you wanna rev beyond 6k. you will want a scatt ultra light billet crank. i dont know what the equiovalent is on the 944... but im sure you would want the same kinda deal.. ultra light, super strong..

if yoyure going this far you want to have the heads ported, have the manifolds machined to match and balance the intake ports on the head for even better flow (this will add hp believe it or not). im sure there are many other things that will apply. your best bet is to speak with some of the 944 racers on rennlist (ie.. people who really race.. like scca, and pca racing etc). maybe email one of the big performance racing places (who have real race teams) for 944s.. maybe even racers group.

BBailey

Bump to this thread. Curious what ever became of it???

Anyone, anyone?

Given the new GT rules for PCA Club Racing, a high output normally aspirated 968 can now actually compete. So I'd think the market for development would now exist.

V2Rocket

first off, that thing must be making INSANE power.


anyways...the new GT3 revs to 8400RPM.

see if any of that valvetrain can be retrofitted.

bad_monkey

I wonder how this went? There was no discussion of windage/blowby and similar... :-S I hope I can assume that anyone trying this would run a crank scraper and windage tray... at least?

whalebird

Everyone keeps saying stronger valve springs and I would agree under most circumstances. However would'nt lighter valves(Ti) with stock springs in effect do the same thing while reducing occilating mass. And another thing, has anyone ever used Extrudehone on a project. It may offer better flow. Unnamed has used this as cheater in "stock" '92 930 competing in support series now gone in IMSA. That "stock"3.3 turbo made well over 450hp.

944obscene

As with a lot of Chevy guys, the issue with stock springs may also be resonance. You need stiffer springs with a higher resonance to avoid issues with rapid compression/decompression issues. Stronger springs would be a must. Lighter valves would be nice, but I wouldn't bank on a large advantage with them. Not unless they were also cut to be the right size and shape for optimum intake velocity. There's an expensive head already, right there.

Zero10

Is this just another failed project on rennlist?... where's the picture of the tumbleweed

PorscheDude1

There goes one now......

Duke

I don't know if I would call this another failed Rennlist project.

My guess is it's just as simple as that.