More power out of a 928 motor?

[Danglerb]

Does anyone think someone is going to seriously crack the rpm barrier with a reliable (turns left with sticky tires) 8000+ rpm 928 motor?

Lots of threads are active right now with ideas on how to increase the power of the 928 motor, lots of fancy intakes, porting heads, etc., but I am wondering if there is much point to it all unless the useful redline can be substantially increased. There seems to be some low hanging fruit between 5000 and 6500 rpm that is worth going after, but that shouldn't take rocket science, just some old school hot roddery.

*** sorry boosted guys, I know this doesn't apply to you, but I still have no interest in boost.

[Eep]

I feel like it would be a shame to sacrifice the nice broad shoulders of the 928 engine for a screaming top-end, unless you're doing so for a pure racing vehicle.

[EIPtuningR32]

Originally Posted by Eep

I feel like it would be a shame to sacrifice the nice broad shoulders of the 928 engine for a screaming top-end, unless you're doing so for a pure racing vehicle.

i agree. also a v8 that rev. to 8000+ rpm isnt really old tech. i mean take the new M3.

[Griffinroydonal]

I never turn over 4,000 RPM in any of the Porsches I own - Why would you ?
2,000 rpm = 60mph in the 87s4 and thats fast enough for me.

[fb111]

What's the point in owning the car if you are not going to hear it sing?

[DMRK]

Originally Posted by Danglerb

Does anyone think someone is going to seriously crack the rpm barrier with a reliable (turns left with sticky tires) 8000+ rpm 928 motor?

Lots of threads are active right now with ideas on how to increase the power of the 928 motor, lots of fancy intakes, porting heads, etc., but I am wondering if there is much point to it all unless the useful redline can be substantially increased. There seems to be some low hanging fruit between 5000 and 6500 rpm that is worth going after, but that shouldn't take rocket science, just some old school hot roddery.

*** sorry boosted guys, I know this doesn't apply to you, but I still have no interest in boost.

Why no interest in boost?
I think these cars are perfect for a low boost application.

[Roy928tt]

I've only been messing with motors for 30 yrs, and if there is one thing I've learned, it's that revs are expensive.

As you increase the peak revs, the forces acting on the various internal components of your engine rise exponentially, suddenly you find, you need stronger valve springs, stronger valves, lighter lifters, solid lifters, stronger conrods, lighter pistons, better bearings, a better oiling system etc. etc. etc

You will learn what you need next as your latest rebuild goes bang! again, so you might expect to build half a dozen "experimental" motors till you come up with somthing close to what you were hoping for.

And when you get there you find that it is a peaky, tempermental, pig of a thing to drive and it still makes less power than "brand X" blower system.

To make horsepower you only have to increase the amount of air the engine consumes!

If you really desire a high revving 400hp V8 find yourself a new BMW M3 engine and fit it to a 928.

If you could make a 5 litre 928 engine rev to 8250 rpm it would probably make 500hp, a bit like a M5 V10 really!

Much wiser to simply boost your 928 engine.

Cheers Roy

[rhjames]

Roy is absolutely correct---

our Quick 16/32 motor is capable of turning 8500 with ease. the power band is there (dyno-ed 1000hp and 750 ft lbs torque from 6500 up) but when you use the upper limits weekend after weekend--the rpms take a serious toll. Chuck and I came to a quick conclusion that if he were to run it at the limit for a full season, tear down and rebuild would be more expensive than backing off of the revs by 500 or so. Same goes for track length---Chuck prefers to run 1/8 mile instead of 1/4, again, because of rpms at the top end of the track. the engine is now two seasons old, without a tear down or any issues. Change oil and plugs every weekend, and you're good to go. it's consistent to the point of show up and win (he won last weekend) and that's what it's all about.


With the 928, it's really pointless to test the upper limits of rpm's due to the high speed gearing of the car (even when you're using the 2.75 gear set) unless you are trying for the Silver State or Pecos run......on the street it's useless.

I have a contact that can build a set of buckets to live at 9000 rpms, another contact that can build a set of billet 16V cams that will make power beyond that, and then it's nothing but building a sheetmetal intake to accommodate either a large 4 barrel Holley (1150 CFM) or aftermarket EFI throttle body. My heads will make power to 7000, but above that they will need thin stem/bigger diameter valves and more porting.


that said, for the money involved in either way you go---John Kuhn's twin turbo is by far the easiest way to put power on the ground.

rpm's are not the best solution.



--Russ

[Danglerb]

Boost is not an option in Calif, pulling it off every two years gets old fast, and they are even thinking of making targeted annual inspections.

Valve train 7k, sure, 8k, why not, oil system, still waiting on that.

[123quattro]

I don't think it makes much sense to spin a non-variable cam timing engine to 8k rpm. What you can gain on the top end, you give up down low. For a street engine that's a bad compromise.

My turbo Audi engine (I built) with fixed cam timing spins to 8200 rpm. It starts making real power at 4k. I wouldn't consider it really streetable. It can get annoying, and draw a lot of attention, when you start shifting at 8k rpm while in traffic.

[rhjames]

the problems with high rpms are pretty basic.

above 6500 with hydraulic lifters/buckets you will get valve/lifter float.

above 6500 you will need to go to a solid lifter/bucket or a roller.

above 7000 you will need to go to a stiffer valve spring package.

above 7000, to make power you will need a cam profile with more overlap than you would want to drive on the street (rough idle, very low vacuum, peaky power band, etc). Cost? Billet cams= $3500 and up for 16V. Custom buckets for up to 9000 rpms= $300 per bucket. Ask me how I know.....

if you're running a slushbox, a cam profile that produces power above 7000 will require a high stall torque converter for the car to even be drive-able, much less work. Where are you going to get one of those for a 928? Sure, you can get anything for a GM, Ford, or Chrysler, but for a Porsche? Try having ATI or TurboAction build you a converter that will stall 3500 and up...... good luck with that. Cost? Try $1K and up.

I understand your concerns about the smog cops and their issue with adding pieces that weren't offered by the factory.....but why bother with this endeavor? How do you think you'll pass the sniffer test as well?

You are not going to drive the 928 to it's fullest potential on the street, so what's the goal by twisting it to the moon?

Build your engine to produce torque and HP down low, use it from stop light to stop light, and you'll come out better for it.


--Russ

[dprantl]

Couldn't you make a twin-turbo kit that is virtually hidden from view? With the air tubes going front to back and full belly pans, there's no way they will see the turbos. Do they really know the air tubes are not supposed to go through the inner fenders? Or is it because they can see the intercooler?

[MPDano]

Hidden from who? Smog Police? If so, they break out the mirrors, flashlights and sometimes crawl under the car to make sure all is there. Either way front or rear, you can't hide a Turbo from them.

[Danglerb]

Actually I was not proposing spinning the motor faster, just commenting that with our 5 liter air pumps that don't spin well faster doing a lot of head work may be pointless.

More cubic inches seems like the only thing that slips past the smog check.

With boost, I wouldn't try to hide it, just make it as easy to remove as possible. I'm already halfway thinking my track car might end up getting a semiannual motor refresh and smog check.

[MPDano]

Mike, you need a trailer to haul your Track Car around. Forget the smog equipment and make it a 100% non-street legal Track only car. Heck, I'll volunteer to drive it on the track for you and you can admire your awesome car from the Pits.

[Eep]

It might be easier to move somewhere more enlightened than to try to beat the smog police.

[rhjames]

Originally Posted by Danglerb

Actually I was not proposing spinning the motor faster, just commenting that with our 5 liter air pumps that don't spin well faster doing a lot of head work may be pointless.

More cubic inches seems like the only thing that slips past the smog check.

With boost, I wouldn't try to hide it, just make it as easy to remove as possible.

there is power to be gained with spinning it faster, but it's darn sure more expensive to do it.

my head work was done to be OK for a modified street motor, but not get stupid about it. I could have put a lot more into it.....

cubic inch additions are fine, but again, the gain is expensive versus other mods. one only has to look at Louie's stroker and see what's there, but getting it to pass any smog check may be a challenge.

as to blower additions that are easy to remove, I believe Dave Robert's twin screw may be the deal---compact package, no intercooler/plumbing to remove/replace, etc...

What's wrong with California's smog rules? they are un-informed and lazy.

you can build a motor that's environmentally friendly, and still produce little emissions.

What's attached to the engine externally is irrelevant----if it can pass the tailpipe test.



--Russ

[MPDano]

Originally Posted by rhjames

What's wrong with California's smog rules? they are un-informed and lazy.

you can build a motor that's environmentally friendly, and still produce little emissions.

What's attached to the engine externally is irrelevant----if it can pass the tailpipe test.



--Russ

Having gone through this recently (last week). I can tell you that they will ALWAYS do a visual, and most use a book to verify smog parts. California Smog Rules are plain stupid. If you can pass tailpipe emissions, then you would think it would be good to go. Nooooooo, not in California it isn't.

[MrGST]

I've lived here all my life and I agree, California's smog rules suck. There must a lobby to protect the car manufacturer's interest because it doesn't make any sense from an environmental standpoint to require antiquated emissions equipment. Modern electronics could make older cars more efficient, powerful, and clean burning. I can't think of any car enthusiast that would mind spending money to make their engine better in every way...

[rjm65]

I think the powers that be would just rather you take public transportation then fiddle around with high tech gadgetry in order to make antiquated technology go faster and/or cleaner.

Get with the program Glen, Arnold wants us to all take the bus! Resistance is futile!