All this cool talk about heads gots me thinkin....

[rich]

I was drewling over the work work Russ is having done in the Euro Heads vs US heads post. I almost hi-jacked it with the following but decided to start a new discussion. Here goes...

I was talking to my machinist friend about valves when he repaired my damaged "S" head. He was surprised by how fat the stems for the 928 heads are. He thought he could easily source much more modern light weight valves with smaller diameter stems.

Questions:

Does anyone know if the "S" throttle body, plenium, and spyder can handle increased flow from larger valves and higher lifts and longer duration cam profiles?

Are the current "S" heads choked by the "S" intake now? I mean, if you were to use like 8 throttle bodies in place of the spyder and have this as your only change would it allow more air/fuel flow?

Or will the stock "S" spyder handle and deliver more air/fuel to the pump than the current heads allow?

The reason I'm asking is: In theory, why work the head numbers if the intake is the limiting factor.

I know in Russ' case it sounds like they de-designed the intakes, but what if you want a stock look?

Anyone ever write about this?

I thought about experimenting with a set of US heads.

[Danglerb]

My two cents ...

You run out of practical upper RPM before you hit the wall with even minor improvements over the stock Euro S. IIRC MarkA used to run his Euro based motor up to 7500 in race trim, but I don't think those were motors that lasted a long time. With something like a 7000 rpm redline my guess is "around" 350 rwhp is possible with a Euro based 5.0L

Further guessing that "about" another 50 to 75 rwhp is on the table for a full race design like Louis Ott's ITC or a massive runner sized dual plenum like MarkA runs now on his stroker.

****************

If you search a bit on rennlist you will find some threads on using different valves, such as nascar cast offs that are cut to fit. Springs and valves have improved since the 80's, unfortunately heads have improved even more and we can't easily change the basic design of our old heads.

The question I ask myself is how far up the 16v tree do I want to climb, when 32v heads easily exceed there performance?

Answer is unknown until I "need" to take off a set of heads, but something like the .500 lift cam in the other thread, bump the intake valve size to whatever the practical limit of the bore is, port Euro heads to match the larger valves, and fabricate a "looks like stock" ID to match the heads intake.

More likely is that I flip flop and work from a 85/86 US 32v base and just bump valve size and leave the cams alone. A 5.4L motor using 968 pistons is also a thought.

************

Thinking about the 914, seems like its not that hard to get 550 hp out of the Subaru motor and pick up a load of reliability at the same time.

[rhjames]

A few comments---

the 32 valve heads do not necessarily exceed the 16 valve heads. it depends upon the CFM numbers on the flow bench. (remember, bigger is not necessarily better when dealing with porting) sure, they will get the intake/exhaust charge past the valve quicker than the 16V heads, but the ports (intake entrance, exhaust exit) are nearly the same size, thereby limiting their potential. again, look at the individual CFM numbers for each.

when choosing (16 V) Euro versus US heads, you are starting with bigger ports in the Euro's---less work for the machinist.

valves can be changed out----a good way to go is a titanium valve, with smaller diameter stems. lighter valve and less restriction in the port.

the stock intake (again, Euro) is good for at least 6500 rpms, maybe more, while retaining lower rpm power. Individual throttle bodies will remove the lower rpm throttle response, but will open the engine up on the upper rpm range to more power. I, too, have had thoughts of building a sheetmetal intake, but have since decided it is not the way to go...

cams are another question---here again, bigger is not better, but you should choose a profile that matches what you intend to do with the car. you would not want to use a top fuel profile in a street car......

and lastly, no one has talked much about cam lifters (buckets).....we are dealing with hydraulic lifters here, which are limited in rpm range to about 6500. now if we had a hydraulic roller, or solid, or a full roller tappet, then we could extend the rpm range with less worry of lifter failure or float. I do know of one guy who can build a set of buckets that will take upwards of 10K rpm's, but his work is very, very expensive......and then we're back to cam shaft grinders, which is a very sore subject for him.


my 15 cents worth-

[rich]

Interesting contribution. Thanks! I have done a little searching on the list but never seem to have time these days to read through a couple dozen posts.

Keep it coming and don't worry about hi-jacks or changing the discussion to cams, lifters or anything else that helps make HP. It's all good.

BTW: I know we could use a higher lift cam or longer duration cams in our engines, but does anyone know how much air will flow through a stock "S" as it was manufactured? That would be interesting to get a real base line on the engine as a unit, then work your way up from there.

[Danglerb]

I don't think there isn't a lot of reliable data for the two valve head on the 928, but there is a LOT for the 944. I figure if the race max for a 2.5L 944 is about 250 hp NA, a 5.0L 928 is going to be maybe 500 hp, with the caveat that it may take 8200 rpm so the 928 might be less at a lower rpm.

Every hp above what you get with a stock Euro motor gets more expensive and less reliable or predictable, and more difficult to transfer to the pavement. Why am I doing this should be the first question.

[Fabio421]

92 Developements (Phil Threshie) in CA were working on a Ti valve train to minimize the load on the timing belts and to increase the rpm range of the valve train. I'm not sure what happened with that project. They have closed up shop. There are some articles about their work in 928 Forum magazine issue 1 vol 2 .

[rhjames]

Originally Posted by Danglerb

I don't think there isn't a lot of reliable data for the two valve head on the 928, but there is a LOT for the 944. I figure if the race max for a 2.5L 944 is about 250 hp NA, a 5.0L 928 is going to be maybe 500 hp, with the caveat that it may take 8200 rpm so the 928 might be less at a lower rpm.

Every hp above what you get with a stock Euro motor gets more expensive and less reliable or predictable, and more difficult to transfer to the pavement. Why am I doing this should be the first question.

your hp figures are a little light......

John's is already over 500 rwhp, Louie Ott is over 500 NA, several of the SC cars are over 500, etc......

yes, some of the 944 work could be transferred to the 16V 928, but as to a direct correlation, this may be a stretch.

[Danglerb]

Originally Posted by rhjames

your hp figures are a little light......

John's is already over 500 rwhp, Louie Ott is over 500 NA, several of the SC cars are over 500, etc......

yes, some of the 944 work could be transferred to the 16V 928, but as to a direct correlation, this may be a stretch.

6.5L vs 5.0L, 30% more cubic inches gets 30% more HP.

SC and Turbo don't count in a "pure" discussion of heads etc. too many things change with forced induction vs NA.

I'm not seeing what the "big" difference might be between the 944 and 928 in terms of heads, and cams. Most of the parts are interchangeable and the ones that aren't its mostly stuff like the different timing of the cam etc. If you look at MarkA's fancy carbon fiber intake, dam if it doesn't look like two 944 intakes.

The 944 is widely raced and has very decent amount of support from aftermarket suppliers. Places like Lindsey and Jon Milledge have done large numbers of ported heads etc that at worst should be a great starting point for work on a 928 two valve head.

The biggest issue I see isn't 944 vs 928, its that almost everything they do reflects limitations of the 944 racing classification which we don't need to be limited by. Breaking the rules could be where some easy hp can be found.

[rich]

I'm wondering how a guy could set up a flow bench to not only test the head flow at a given lift but the effect the spyder has on the flow. Now that would be some interesting data. I suppose if this were a chevy there would be 10 guys that have set this up and tested it bu now.

[Danglerb]

Originally Posted by rich

I'm wondering how a guy could set up a flow bench to not only test the head flow at a given lift but the effect the spyder has on the flow. Now that would be some interesting data. I suppose if this were a chevy there would be 10 guys that have set this up and tested it bu now.

Why would this be a problem?

Are you talking static flow loss or the tuned length of the runner stuff?

[rhjames]

Originally Posted by Danglerb

6.5L vs 5.0L, 30% more cubic inches gets 30% more HP.

SC and Turbo don't count in a "pure" discussion of heads etc. too many things change with forced induction vs NA.

I'm not seeing what the "big" difference might be between the 944 and 928 in terms of heads, and cams. Most of the parts are interchangeable and the ones that aren't its mostly stuff like the different timing of the cam etc. If you look at MarkA's fancy carbon fiber intake, dam if it doesn't look like two 944 intakes.

The 944 is widely raced and has very decent amount of support from aftermarket suppliers. Places like Lindsey and Jon Milledge have done large numbers of ported heads etc that at worst should be a great starting point for work on a 928 two valve head.

The biggest issue I see isn't 944 vs 928, its that almost everything they do reflects limitations of the 944 racing classification which we don't need to be limited by. Breaking the rules could be where some easy hp can be found.

I did realize you were comparing non blower motors......

if you are comparing just the head work, then yes, there's pretty much no difference between 944 and 928 variants.

making statements about absolute max hp levels leaves a lot open.

as far as rules, I recall you are fond of pointing out how many folks are really abiding by some racing sanctioning body rules with a particular car-----maybe 20 world wide?

in other words, how many guys are racing a 928 (either 16V or 32V), so that you can see where the numbers of potential buyers of the head work service really is...? Who is doing the R&D and who's paying for it? If it's street car (ie: hotrod), what will the owner pay for how much gain?

Heck, look what it costs just to do a standard rebuild on a 928 engine (pick any of them)......it ain't like building a SBC or SBF.

[rich]

Originally Posted by Danglerb

Why would this be a problem?

Are you talking static flow loss or the tuned length of the runner stuff?

I'm talking about what the flow would be if the throttle body, plenium, spyders and heads were set up on a flo bench. I think this would measure the restrictions created. Then when you made a change you would know what direction you were going in.

I think the limiting factor would be money and any return on time spent. If you did this on a sbc you would be able to use the data a couple hundred time over the course of a couple three years. But as stated how many 928's are going to get built and modded using the data. I'm thinking very few...

It would be cool to know though!

[Danglerb]

Regarding both the 5.0, 6.5, and 944 HP comments, I'm thinking HP/ cubic inch, 6.5L get 30% more for cubes, and 944 gets half as much for half the cubes, so 928 should be able to do about double the 944 HP.

A lot of 944's are raced, nearly as many as 911's, my guess is that they are the cheapest track car to build and race, which may be a big part of it. The other part of popularity I am again guessing is how close the cars are to each other in race trim, which makes breaking rules maybe easier to detect. OTOH if you don't win the rules aren't so sticky, but for a serious competitor there are so many classes, just pick the level you want to compete at. All that leads me to think if the rules say 45mm max intake valves, that most of the head work will use that max, and for a 928 we don't need to.

On the 928 I'd say approximately nobody is racing 16v with more than ported Euro heads. Greg Gray in Oz may be the only person in the world actively pushing the envelope for heads on the 16v.

R&D is not only expensive, but you need to be willing to put in serious money and not cry about it when it doesn't work. Greg Brown's stroker motor currently owns the 928 performance world, they work, work well, seem reliable, so people have to have a real woody for different to even try anything else.

******************************* Flow stuff

I don't think it would hard at all to measure the flow through all the intake parts, but its even easier to use a pressure probe on a running engine and measure the pressure drop vs flow. People have done it, measured pressure drop through the filter box, MAF, U, throttle, and down the intake runners. Most of it behaves in predictable pipe law ways.

Sometime I think the easiest way to think of the 928 world is to look at state of the art in hot rod Ford and Chevy motors, and subtract for what we can't practically do that they do.

[rhjames]

Originally Posted by Danglerb

Sometime I think the easiest way to think of the 928 world is to look at state of the art in hot rod Ford and Chevy motors, and subtract for what we can't practically do that they do.

I think you could do most anything, as you say, that the domestics do, it's just that the 928 stuff is decades behind the domestics.....

[Danglerb]

Nothing we can do about valve geometry, vs the new canted designs, or basic orientation of the intake and exhaust ports.

We can use new spring technology, new valve materials, porting improvements, and most of the combustion chamber tricks.

I'd say the differences are big in head to head racing terms, but not in seat of the pants enjoyment. I suspect most of the last 15% or so in HP will be at the expense of streetability, shifting the power band higher etc. Thats where the 32v shines, a solid bump in low end torque, and better breathing at higher rpms. At some point throwing money at the 16v it stops making sense compared to the cost of a 32v motor.

[rhjames]

Originally Posted by Danglerb

Nothing we can do about valve geometry, vs the new canted designs, or basic orientation of the intake and exhaust ports.

We can use new spring technology, new valve materials, porting improvements, and most of the combustion chamber tricks.

I'd say the differences are big in head to head racing terms, but not in seat of the pants enjoyment. I suspect most of the last 15% or so in HP will be at the expense of streetability, shifting the power band higher etc. Thats where the 32v shines, a solid bump in low end torque, and better breathing at higher rpms. At some point throwing money at the 16v it stops making sense compared to the cost of a 32v motor.

try looking at it this way......

the Kuhn brother's two cars. Sonnett's is only around 100hp less (but with less boost) than John's 32V monster.

crank up the boost on the 16V and the differences fade away.....except for the S4's additional purchase cost---and there's the rub.