Cheburator

Agree with all of the above,

yet, it still does not answer my question - the hydraulics were good enough for Porsche and VW to use in Motorsport applications in very high revving engines, with very aggressive cam profiles... Why are we re-inventing the hot water? To prove a point?

Strosek Ultra

Cheburator, as Tuomo said the hydraulic VW lifters will not be the limiting factor. In my case I have to use oversize lifters in order to be able to change the valve inclination angle to make room for large valves. Having lightweight solid motorcycle lifters in different sizes readily available that is the way to go. I probably could have used the 38mm 16V hydraulic lifters but they are very heavy (94 grams less oil vs. 42 grams) and expensive.

Ake

Cheburator

Ok... fair point... My heads are fitted with 39mm 968 valves and I did not have to change the inclination of the valves... I guess you went with even bigger... then it makes sense...

Strosek Ultra

Well Cheburator, 39mm intakes valves is way too small for a high power 7 liter engine. I am going for 42/36mm valves. 44mm intake valves would be the optimum but creates another problem of the intake valves sitting too close to each other. Increasing the spacing between the valves would do the trick but I am not sure there is enough meet in the heads for a good porting job when the valves are moved away from each other. Furthermore a high power NA engine need a fair amount of overlap to make good power and with the adjustable intake cams I have the overlap can easily be changed. That is another reason why I need more space between the intake and exhaust valves in the combustion chamber. More overlap means more lift at TDC during overlap and at a certain amount of lift the valves will interfere with each other. If you are running stock rod bearings you should change to Clevite CB-1628HX racing rod bearings.

Ake

BC

Keep us posted Strosek.

Simard got almost 100hp per L. Not bad.

Cheburator

My engine is tiny - only 5.5 litres oversize as my class rules limit me to 6.2litres and because the block has already been sleeved once, installing bigger dry liners is a problem. Anyway, I saw 438rwhp on a Mustang Dyno out of the lump, so you should see better with an extra 1.5 litres and a bit more hi tech stuff than my agri lump...

GregBBRD

The 39mm valves will flow enough air to make over 600hp and the hydraulic lifters work fine (with the proper valve springs) to 7500+rpms.

Adequate for what most people are doing.

To turn a 928 engine over 7500 rpms is going to require quite a few different pieces in more places than just the lifters.....virtually a complete redesign of the entire engine is required.

And before you go down this path, you have to ask yourself if the loss of torque is worth the gain of the higher rpm horsepower.....very difficult to do both

Cheburator

I think you have it nailed on the head...

One other thing - most of you guys in the US drive the high powered race cars in dry weather... Over here, we have to live with rain too. You should try driving a 500+ crank 928 on 1200/800 springs and 305/285 tyres. Unfortunately we have to run semi-slicks and not full wets...

Strosek Ultra

Cheburator, radiused lifters, tappets, followers is nothing new. Triumph motorcycles, which are manufactured in your native country, got radiused cam followers more than sixty years ago, maybe they even had it before WWII which I am not fully aware of.
http://www.ebay.com/sch/i.html?_kw=Cam+Follower+Tappet

Mr. Brown is correct 39mm intake valves will flow enough air for more than 600 HP but if your goal is set higher than that, especially if you like to see a big engine spin high, 39mm valves are not enough.
These Chevy Big Block 4-valve heads do have up to 51,3mm dual intake valves. For 108mm bore (same as a 928 7L stroker) they use dual 46,7mm or dual 49,3mm intake valves. The flow they are showing for the smallest valves at .600" of lift will theoretically support 900+ HP.
http://www.araoengineering.com/Chevy/chevybb.htm

Ake

Cheburator

Ake,

I am not disagreeing with you... With the risk of straying away from the original topic, I just wanted to point out that perhaps too much power is not a good thing either... First, driveability suffers, and then my car is designed to run for up to 4hrs at full race pace at a time... I would imagine that the chances of granading a transaxle at 900hp are probably 4 x higher than with a 500hp car...

ptuomov

My opinion: If one can get a big displacement engine to turn 8500 rpm safely and wants to maximize the engine, then almost everything on the intake tract is really small. Valves, cams, intake runners, everything need to be really big. The trick is to get the engine to turn 8500 rpm safely.

Strosek Ultra

Cheburator, I do not think we will ever see a NA 928 engine putting out 900HP at the crank. That is simply not possible. I just wanted to show you what they do and what valve sizes they use for the really big engines. On the other hand Tuomo continuously developing the twin turbo setup will probably in time be way north of the 900HP.
My seven litre stroker is only an experimental engine. Having been in this business for almost fifty years I think it is time to make something fun for myself. I just want to see how far the 928 engine can be pushed in terms of power and rpm.
Being on Rennlist for a few years I am really grateful to all you guys sharing information making it possible for me to get a good picture of the weaknesses of the 928 engine and what to do to overcome these weaknesses. Something I otherwise probably have had to learn the hard way. Tuomo is a smart very theoretical guy with some good ideas that can or cannot be put into practise.

Ake

Strosek Ultra

Tuomo, as you are familiar with Mike´s engine being red lined at 7700 rpm, I think if you study the dyno chart you can see the engine would spin well over 8000 rpm without losing hardly any power. I am convinced another 500 rpm would not make any difference of the reliability of the engine whatsoever thinking of how well built it is. Probably Mike was a bit cautious when setting the red line.
Ake

GregBBRD

Piston speed....piston speed.....piston speed.

Do some calculations of the piston speeds when using a long stroke crankshaft....however, one doesn't need to strain their brain cells too far, when there are so many readily available examples.

The "uber trick" Kaltech all aluminum small block Chevy engines (for the GTP program) made 740hp and were limited to 7,600 rpms.....and they were actually frightened that this was too high, but had to allow the engines to rev that high, because peak power was at 7,200. They ran 3.7" stroke crankshafts and were working "hand in hand" with the very best engineers that Chevy had and with the very best pieces that money could buy.

And they had "short gears" that allowed them to stay in the correct rpm range.

High RPM horsepower sounds good....and is fun to brag about....but with the inherent "long gears" that a 928 has, an engine with torque is going to be very difficult to "catch", in rear life.

I'm not sure how many times I need to tell this story, before people begin to grasp reality.

I ran 1/2 of a team that IMSA raced air cooled RSRs. We had two cars....a one year old 964 RSR and a brand new 993 RSR.

The brand new 993 had the factory engine removed (345hp) and got a brand new uber trick Porsche Motorsports "Sprint" engine, which made over 410hp. Bigger cams, bigger valves, aftermarket fuel injection, more rpms. The 993 also had its 6 speed gearbox converted to an "active" 6 speed, with very close ratio gears.

The 964 got the brand new stock RSR engine out of the 993 and still had the old 964 5 speed.

The 964 consistently turned faster laps, at Sebring, even with the "lessor" drivers (The 993 was the "primary effort" and had professional drivers. The 964 was the "rent-a-ride" car.)

Long story short, two of the professional drivers decide to find out what was going on and slowed down the two cars on the back stretch at Sebring, got side by side at 50-60 mph, and raced to the start finish line. The 964 won by 10 car lengths.

The ultimate test of horsepower versus torque.

I build my engines to make torque, with horsepower and rpm a secondary goal.....always have, always will.

ptuomov

Greg -- Can you tell me numerically what you think is the minimum torque at each rpm that you think 928 needs to be "fun" to drive? Assume say '87 5-speed transmission. Trying to get a sense of what you think is required in terms of the low-end torque.