I'm not talking about motors that everyday street cars run to meet epa standards. Go to a drag strip and look at 95% of the cars running. If you want to make a reliable motor that make good HP 16v is the way to go. Less moving parts. You not only have lift but duration as well. Good luck on your project but imho I would look for some decent euro spec heads.

 

The valve sizes and the camshaft would have to be seriously bigger for a 16 valve head to produce near 500rwhp. Since huge valves and big camshafts hurt low rpm air velocity, these items aren't always the best thing for other than race engines.

One of the things that the 928 engine does very well, is the ability to make "boat loads" of low rpm torque. Since there are many factors that limit the 928's ability to make high rpm horsepower (oiling and intake system come to mind) it is probably better to try and "amplify" the stock engine's qualities....which is our goal when we build a stroker engine.

Certainly, it should be possible to redesign the 928 engine to work really well with 16 valve heads, aggressive camshafts, and a large four barrel carburator on a custom intake system. Combine this with a 6.5 liter stroked and bored bottom end and you will have an extremely potent $30,000 2 valve engine than looks, runs, and sounds remarkably like a $5,000 "crate" Chevy engine.

 

I'm not convinced the Euro spec 16v 928 motors are anything to get excited over. All the 32v 928 motors can easily make as much or more rwhp than the advertised crank hp. The 16v Euro spec motors never get close. Not close to matching 32v power with the same bottom ends. It's no comparison. Reliability? I've not heard of a 32v engine breaking the left cam like happens with the 16v engines. I think 2v motors are used on the drag cars because they can't get a 4v motor with large displacement. 2v heads with nitrous will make power.

 

Here is a video of Ken in his 85 twinscrew at Mid Ohio; it's a DE but his lap times were faster than some of the race times.

 

The 2v-vs-4v argument really comes down to simple math. There is simply more valve area available for a given combustion chamber size with 4 valves than with only 2. You have only to look at the highest-output NA engines to see that they all are 4 or even 5 valves per cyl.. At max valve size, a 4V engine will flow more than 2V., its as simple as that....you could even look at the "import" drag engines for comparison- the NA Hondas are making more HP/cu.in than any 2V available...no disrespect intended, just a fact.

 

> Chips from your heads fly, this coming Monday. Yeah, I know it's a holiday, but the porting thing takes a whole bunch of concentration and non-interruped time. (Tough to get during the week.)


Sweet! Labor day flying aluminum chips!

 

Hi Rick,

I presume you understand there is a big difference between DE and racing with respect to the demands put on the motor. I have something like 50 days of DE and 20 days of race experience, and know my experience may be different from others. Most of my DE days are in the top run group or with the instructors, so there is the opportunity to drive a car as hard as can be done at a DE. Yet, because DEs are controlled, passing is restrained in a number of ways and certainly the cars are farther apart. The end result is that there is less overall stress on the car and motor (not to mention the driver).

I am not "dissing" SC cars, nor am I saying they can't be as fast or faster. But I have yet to see an SC 928 road raced consistently and reliably. Of course there is always a level of probability that it is happening but I don't know about it.

I am definitely anxious to see an SC 928 get out there, mix it up, and do well

 

yes, but the 16V ports are not as limited as you think.


Mmm.....a little rich on that estimate, aren't you? Try less than $15K (in parts).....For less than $25K, you can install a 1000hp/850 ft lb tq domestic engine (V-8.....pick your flavor). For the same $$$, with a 928 engine, you might get 600hp/550tq on a good day. Of course, there are some who've spent twice that, and only come up with 450HP.......but I digress.


The 32V 4 cam Arias (based on a big block Chevy--500 CI /or in Porsche speak, about 8.2 liters) was used in Top Fuel for a while, but the added expense and more parts to changeout between rounds essentially doomed it to "not a great package" in drag racing. You can, however, still find a few of these in tractor pulling competition......


True, but with 928 comparisons, rarely is it discussed port CFM flow rates and actual cam specs. Considering that the (stock) port sizes are pretty much the same size, the only advantage for 32V is that the 4 valve allows the gases to enter/exit the chamber faster-----then you're back to the port size issue. 300 CFM is still 300 CFM, no matter if you've got 2 valves or thirty. Some will argue velocity in and out, but then we'll get into a argument about theory and open another huge can of worms.


Comparing 16V engines to 32V engines is more than just saying "because it has more valves it will make more power." Cam dims, port CFM's/design, fuel systems, intakes, exhaust systems.....all of this comes into play, but is unfairly used (or not used) when discussing the apples and oranges argument.

I suspect that if all things were equal, the 32V would just be more headache due to the (number of) parts issue alone.

(no offense to anyone---just an opinion)


--Russ

 

Hi Stan,
Like you I am not aware of any SC cars racing, outside of Open Road Racing. That's why I posted Ken's DE video, it's the closest example i could think of.

 

sounds great.

what were those times that were faster than the "race times"?

SCCA T1 times are in the 1:22 to 1:25 range.
mk

 

1:45.1

I was trying to search for some typical track times but only found this:
2007 Panoz DP01 Champ Car Test 1:06.280
[2007 IRL Dallara Helio Pole] 1:06.8375
Zytek 04S 1:11.333
Lola EX257/AER 1:12.431
Audi R8 1:12.935
Chevrolet Corvette C6-R 1:18.033
Porsche 911 GT3 RSR 1:22.663
Toyota MR2 1:52
Porsche 944 spec 1:43.0 (Pro configuration)
Porsche 944 Cup 1:41.9 (Pro configuration)
Spec Miata ?:??
Dodge Viper ?:??
Spec Focus 1:47 (Club Course)
Porsche 911 1:45

 

Shawn
Any updates?

 

3 valve heads rock. ford makes a pretty cool head on a 5.4L that can put out 500ft lbs ctq and 445 chp w/only a 6psi twinscrew on top of a stockish bottom end. iirc, the best we've seen on a 928 6psi motor was about 380 rwhp/350 rwtq. oops. this is a pcar site. sorry. didn't mean to start any trouble. hahaa

 

Shawn,

Any updates?

 

Funny, i seemed to remember a stock 928 engine with stock 4 valve heads putting out 445 chp with only fuel changes and a reprofiled stock 85 cam. Oh, did i mention it was a 5 liter too! Imagine what this 928 motor could do with some added mods besides just a cam reprofile. Oh yeah, did i forget to say that it didnt have a blower either?


mk