mark kibort

I have a pretty good launch. I did ok with the speed WC GT standing start. I liked that part the best! anyway, the trick is not to get too much wheel spin. BUT, it is REALLY hard on the CV joints. you can almost hear them screaming!

Now, why in the heck dont they make these things to use 30 to 90 or 60-100 like i do for HP assesment? its easy to do, and a much more clear picture of HP based on weight. Ive been doing this for years at 3500lbs with a full car of gear to 2950lbs race ready, as well as with all the mods and issues over the past 7 years. after 2-3 runs I can tell if im off 10-20hp or so pretty easily.

try it yourself. 60 -100mph should take a 3000lb package about 6 seconds for over 300rwhp. right now, at 370rwhp, its more like 4.7 seconds
You can even do the 60-80 mph to get just over 3 seconds. (2 for the larger motor)


mk

mark kibort

I just bought it and it doesnt seem to work very well. I wonder if my g meter in the I phone has issues. the results are very spotty. it doesnt seem to know how fast im going and the starts, sometimes dont even set off the gauges MPH meter.

maybe i need to calibrate it again.

Mk

dprantl

60-100mph was easy in 3rd with my old 928 with the 2.2. With the GT, 100mph in 3rd would be bouncing the rev-limiter. One thing I can't stand in my car is hitting the limiter, so I have never tried it.

Dan
'91 928GT S/C 475hp/460lb.ft

IcemanG17

I use the dynolicious program on my Iphone....when sharky had "issues" and was down on HP due to bad knock sensor, hall sender and flappy I was consistantly loosing about .8-1 second on my 0-60 times using my standard easy launch... wheel HP calculation was down too....here are the messed up #'s compared with messed up + power brake launch to the everything working right numbers (standard launch not power brake) so the 1st (messed up) and 3rd (fine) comparo are very close (except for the missing HP & torque):

Messed up (power brake) Good
0-10 1.18 .82 1.19
0-20 2.24 1.85 2.04
0-30 3.39 3.02 3.03
0-40 4.73 4.26 4.00
0-50 6.01 5.54 5.03
0-60 7.45 6.92 6.19
0-70 --- 8.92 7.58
0-80 --- 11.23 9.18
0-90 --- ---- 10.93
0-100 --- ---- 13.58
0-1/4 --- ---- 14.44 @103.3mph
WHP 194 205 260

My car ran as quick 0-60 5.98 on my G-tech...& ran a 14.54 @ 95.1mph at the drag strip with an easy launch...... So dynolicious thinks I was down 55+whp!!!! ALL BETTER NOW!!!

RyanPerrella

Does the butt dyno notice the 55 missing (and now returned) RWHP?

IcemanG17

HELL YEA big time.....even my somewhat larger butt dyno noticed that many ponies missing

Peter F

Hi Mark.

best results if the iphone lies down and is strapped solidly to the car so it can not move at all.(top facing forward)
I found that passenger seat between the foam shaping up and down is a good spot to pinch it in place.
Took a while to figure out a good launch method which gave consistent readings.
And yes the calibration is key together with estimated weight etc. of your car.

/Peter

IcemanG17

I hold it in place just ahead of my raised armrest over the buttons for the windows-sunroof.....I always use the same location for repeatable results

RyanPerrella

it took me about 20 minutes in search to find this. So im bumping it.

To all those that haven't seen this, give it a read. It is one of my very favorite threads and one that seems to get my mind moving thinking of fun 928 projects.

for that reason

BUMP

PS: is there any update on this engine? have there been any other modifications made to this monster, any more tuning done? any new graphs to salivate over? I cant believe the last post was 9 months ago!

slate blue

I commented on this thread I think on page 2 with a big well done but after Ryan brought it back I decided to have a closer look. I am sure this is a powerful engine don't get me wrong but if from reading this thread and looking at the graphs if the estimated or claimed power of the engine is around 450 flywheel HP at 6000 rpm. I would have to say that doesn't seem to add up. The best way to compare engines is Brake Mean Effective Pressure, or BMEP.

The formula for this is BMEP = 150.8 x TORQUE (lb-ft) / DISPLACEMENT (ci)
So if we have 450 hp the sum is 450 x 5252/6000 = 393.3 which is your torque. There for 150.8 x 393.3/302 = 196.7 psi for the 928 screamer

Lets take a current state of the art Porsche engine, the GT3, peak power of 415 hp at 7,800 rpm, the sum then goes 415 x 5252/7800 = 279.4
There for 150.8 x 279.4/220 =191.5 psi for the GT3

So I find it hard to say that a 20 odd year old mildly modified 928 engine can have more BMEP than the GT3, to further put this in context a Nascar engine has roughly 210 psi. The GT3 also has smaller ports as the 928s ports are too big to develop the higher air speeds in standard displacement sizing that are required to get very high volumetric efficiencies.

Remember this, small high flowing ports will always beat big high flowing ports, the 928 S4 and the like have an approximate cross sectional area (CSA) of 2.42 sq" I thought that the ports may have been filled to get the air speed up as such this higher efficiency would make more sense but it is stated that they are unchanged.

Running these numbers through Pipemax to achieve an average power figure of 440 hp and max figure of 450 hp requires 120% volumetric efficiency and believe me that is very very high and to make matters worse the air speed is only a little over 200 feet per second (@28") at 6000 rpm. The program says torque loss with reversion, our cams in general are small as such reversion is limited due to little overlap.

The engines that are state of the art in terms of american domestic engines operate at the 310 feet per second mark. If you look up something comparable in terms of RPMs, "Engine Masters Challenge are limited to 6,500 rpm and they always have high airflow associated with high air speed.

Our 4 valve engines have high airflow but not high air speed in standard displacement engines. The strokers address this problem by increasing the capacity. More air through the same sized port means higher air speeds and higher inertia ramming effects. In theory our 4V engines should have higher air speeds than what the domestic stuff does due to the straighter nature of the ports.

Back to some more BMEP, a standard 928 S4 or GT lets say 320 hp, the sum is 320 x 5252/6000 = 280.1 there for 150.8 x 280.1/302 = 139.9 psi

What about a stroker? O.K lets say 650 hp at the flywheel and we will use 6,500 rpm, best of everything, headers, bigger valves, heads tidied up throttle bodies etc, the sum is 650 x 5252/6500 = 525.2 there for 150.8 x 525.2/394 = 201 psi. That engine basically must be more efficient as it has higher airspeed (around 290 feet per second) It has more highly developed manifolding and we also know that the strokers with standard manifolds do not produce BMEP any where near this range. A standard stroker, say 450 hp at flywheel achieves around 150 psi.

O.K another engine would be my 5.0 2V Porsche engine, I estimate it to have at least 380 hp to a max of 400 hp. Let's take the middle number,

390 x 5252/6000 = 341.4 there for 150.8 x 341.4/302 = 170.4 psi.

To back up this power figure another type of comparison is real world on road performance, again the GT3, its weight in the Road and Track test was 3365 pounds (without driver?), my car was tested with a passenger so I will add that weight to my total but not include myself at around 3400 pounds and that was with 1/3 to 1/2 a tank of fuel.

Quarter mile trap speeds are important as this is not so traction dictated, GT3 was 115 mph and my 928 was 110 mph. Acceleration of the GT3 from 0 to 110 mph was 10.7 seconds and the 928 was 13.4 however to be fair to the 928 the car cannot get traction on a dusty surface. If we compare from 50 mph to 100 mph where the traction is no longer a problem for the 928, we have 6.6 seconds for the GT3 and 6.4 seconds for the 928 which is slightly better probably due to gear changes. The full figures below.

----GT3 928
0-30 1.4 2.3
0-40 1.9 3.0
0-50 2.6 4.5
0-60 3.9 5.4
0-70 4.8 6.9
0-80 5.8 8.1
0-90 7.7 9.4
0-100 9.2 10.9

So the GT3 is slightly lighter and slightly more powerful and it pulls ahead accordingly. I believe that this backs up my power figure and as such my BMEP figure. (There is also dyno runs that verify a power figure in the range calculated)

I wrote this as i am going down the development path and it is so important to have accurate data to come off and if you get scewwed results it doesn't help anybody. I also try to run my car with other 928s when we dyno it as that gives a good comparison too, the last time we dynoed I got a lower number but it was still more than 50 hp extra than a GTS auto. So dyno results will vary.

As I discussed with Mark Kibort in the Max top speed thread, Nascar use a 5% loss figure on Dynojet dynos, I know this was a Mustang but I believe the correction factor is off, quite a lot. I would if you could find one, run the car on a Dyno Dynamics dyno in "Shootout" mode (Only in Shootout) and that will give you a better idea of what is going on. That dyno has a controlled ramp rate as such the operator has little to do with the results. EVO magazine also uses this dyno to try a guesstimate the engine figures. They seem to get it pretty close too.

If I have anything wrong here about the assumptions I have made, happy to have a look at it and correct it.

Greg

mark kibort

Interesting information. It doesnt seem that in reality, that the engine is too far off. Especially since when I dynoed my car, on numerous dynos, mustang and different dynojet dynometers, I got over 320rwhp out of a stock 5 liter and a set of stock 85 cams (or GT cams) if you count the original dyno runs.
I got 335rwhp and 334rwt. seeing that Dennis' engine had only cam work, the real question is that can a set of cams produce 30hp alone? This is what they saw before shark tuning. after, they got the power in the 385rwhp range.

As a validation, I did have a chance to run around the track with Dennis. His car did have an unusual amout of pulling power. I was able pull on him as I let him by to test acceleration. The advantage my engine has being a stroker, allows for an average HP of 360 to the rear wheels from beginning to end of gear, vs Dennis' who starts out near 300rwhp and ends up near 385whp, averging near 340rwhp. I passed him like i had a 20hp advantage. (very slight). you have also seen how my car accelerates vs known entities like the Viper comp coupe and comp coupe WC GT version. The only thing keeping me close is a very flat HP curve, and lighter weight than these two beasts.

I dont know why it is such a stretch to see an engine with much less than 100hp per liter at 7000rpm, when a GT3 at 3.8Liters can make well over this . (i.e. 445rwhp out of a 3.8Liter NA)

I think the main queston is that can cams alone give a 35hp adder to a stock 928 5 liter engine?

As far as the dyno runs of the nascar and their 5% multiplyer to flywheel hp, you have to take that with a grain of salt too. Was it in top running gear, straight cut gears, bias ply tires, etc. If Vipers and their Hollinger gear boxes are near 8% from what Ive heard, I guess it is not too far of a stretch to see more efficiency out of a nascar gear box.

Good points. We need to dig a little deeper to see if things really do add up.

One thing i notice by your calculations, is that you mention the air velocities go up with the stroker. Is that true everywhere in the flow path, or just at the MAF? Doesnt the fact that each stroke is near 15% longer, provide the same velocity, but for a longer duration. Also, the port size vs GT3s is a little misleading isnt it, due to the fact that there are 2 more cylinders to spread the flow through. Is that taken into account?

slate blue

By Mark KibortFirst of all this is complicated subject when you get right into it but relatively simple in reality, the air speed I refer to has zero to do with the MAF and it is confined to the head's ports, however the intake tract from the bellmouth needs to be considered as that is also very important.(Part of the package) It also has nothing to do with the amount of cylinders so it is not misleading in the slightest.

As to comparative acceleration it would be interesting if you would post your figures.

By Mark kibort
In my engine development story I saw basically zero gain from changing stock cams for cams that had 239 degrees duration @0.050" on the intake side (stock is about 217 degrees) so to see 30 hp at the wheels is a lot. The GT got a 10 hp increase. Think about this, to get a gain your cams must be limiting the airflow. The airflow from these heads in terms of needed capacity is excessive. Normally you don't want excessive airflow as it normally means that you will have slower air speed, that is you are passing up extra volumetric efficiency through inertia ram effect.

If you have Phil Threshie article from the 928 Forum magazine he mentions that Mark Anderson put on much better flowing heads and saw little or no gain with the new high flow heads. Phil hypothesized that the (given he had found the manifold to be restrictive when flowed tested and bolted to the head) manifold was the cause of the lack of improvement. It may be whole or partly correct, Phil did have the right idea with tapered runners, they have proven to normally be superior to constant radius runners.

Erland *** who is a very respected engine builder has done a set of 4 valve 928 heads, he described them as huge and filled them in with epoxy, I have requested photos. As I mentioned the 4 V ports are around 2.42 sq" and from the program I have they may well be optimized around 1 sq" smaller, it is trial and error though. So port velocity may be very well just as important as the manifold restriction on the 4 V 928 engine.

Have a look at this website it will be worth your time if you want to find out more about port sizing and epoxy work. About the third of the way down when discussing the intake cycle, that is very pertinent.

http://www.mototuneusa.com/think_fast.htm

Read what he says about small fast flowing ports, that is the reason I made my 2V port for my stroker just under 2.20 sq" and it probably flows as well as a stock 4 V port on a per sq" of port area basis. In the end we will have to see how it runs on the engine to find out which is more efficient. Going back to my engine that saw no gain with the bigger cams, it may all be down to airspeed.

The data I took was that the engine at 6000 rpm was producing around 375 to 380 rwhp not at 7,000 rpm that makes a very big difference. Now as to not being that far away, have a look at these top end vehicles, compared to 197 psi for the 928 Screamer
McLaren F1 achieves 182 psi
Ferrari F430 achieves 172 psi
BMW M5 achieves 168 psi

Here is a graph of two engine masters winners

http://www.epi-eng.com/epi_general_i...ters_rules.htm

You will notice at peak power they have around the same BMEP as the Nascar engine, these are highly modified engines. Very High air speeds, note the epoxy in the manifold

http://www.popularhotrodding.com/eng.../photo_20.html

Jon Kaase actually has these heads cast to his design, note how small the ports are compared to the gasket.

http://www.popularhotrodding.com/eng.../photo_15.html

Now as to the dyno readings which i think is reasonable for this issue, the difference in the dynos can be huge and from the numbers i have seen the differences are so big it is not surprising there is conflict on this topic.

This fellow dynoed his car on a dynojet and Dyno Dynamics same day just across town within a couple of hours.
The Results:
ATP (Dynojet) - 275.8whp and 232.2 torque
Vishnu (DynoDynamics) - 224.7whp and 192.2 torque

That is a huge difference

Here's the link
http://forums.nasioc.com/forums/showthread.php?t=286440

A bit about shootout mode
http://www.towler.com.au/shootout.html

Another disbeliever about the differences in the losses, here's a list of other cars dynoed on the DD
Ferrari Modena makes 280 whp
Ferrari F430 makes 355 whp on Dynamics
M3 E36 makes 225 whp
M3 E46 makes 245 whp
M5 E39 makes 280 whp
E46 330ci makes 150 whp.

http://www.m5board.com/vbulletin/e34...s-results.html

This thread talks about a correction factor needed to compare the DD to a Dynojet, I had to laugh at that one, sorry.

http://www.efi101.com/forum/viewtopi...43172d975a61b9

Greg

ptuomov

Kao's screamer motor also had a higher static compression to match those cams. There were many details done right, and can't underestimate the importance of those. (I know you aren't underestimating those, since you are changing everything on your engine that leads to higher efficiency, starting from the journal sizes.)

For what it's worth, just replacing S4 cams with S3 cams nets an almost 30 hp gain in a simulation by moving the peak hp rpm up by about 500 rpm. Simulation assumes that tuning was correct in both experiments. I have no illusion about the accuracy of these sims, they aren't accurate. However, I think they are not useless either, consider it as one data point:



Kao's engine of course has bigger and almost certainly better Elgin 65-6 profiles. I don't understand why everyone doesn't have these cams in their engines, by the way.

One would have to know much more about those "better flowing" heads before drawing many conclusions from that. But of course you know that, since I learned that from the cd's I bought from you! ;-)

The Porsche 928 Cup Car also had a custom made intake manifold. I think it's clear at this point that the intake manifold is one of the main restrictions in the 928 inlet tract for making high rpm power. Why isn't anyone offering an intake manifold for these cars?

Here are the port areas for my intake. These are very close to stock, no material added and only very little removed:

Location, Area sq inch, Area % of valve area
Valve face (std), 3.333, 100%
Seat @ 45, 3.101, 93%
Insert bore , 2.454, 74%
Bowl, 2.554, 77%
At guide, 2.490, 75%
Throat, 2.463, 74%
Port opening, 3.121, 94%

It's safe to say that with well matched cams my slightly ported heads that flow 320 cfm at 0.500" lift in a SF-600 at 28" depression will not be the restriction with the stock manifold or anything that is derived from the stock manifold.

Perhaps I am reading too much between the lines, but I am not as negative on the 928 4V heads as you are. Not that I am any kind of expert or anything, bu I think they are nice heads. With a better intake manifold or ITBs, better cams, and oiling system that can hold higher rpms they would probably work very well in a 5 liter or larger engine.

Is this no gains from bigger camshafts based on simulation or actual experiment? Because what we have for the 4V heads is some experimental data that cams do make a difference. From S4 to GT or S3 does seem to give 15-30 hp increase, which is 5%-10%. Again, I don't understand why everyone doesn't run S3's or Elgin 65-6's on these engines (or Colin's Colt Cams when those are available).

ptuomov

You know, I think you've just paid the highest possible compliment to Dennis Kao, Bill Ball, and Jim Morton! ;-)

Now dynos are dynos, and there are differences that make comparisons difficult across dynos and days, but one thing stands out here. They found 25 hp across the board by tuning the car. This is on the same dyno on the same day, so it's a pretty well controlled experiment.

In my opinion, the answer to the BMEP puzzle is right here. A production car has to use the same parameters for any engine within the manufacturing tolerances and for the hundreds of thousands of miles that the engine wears. Of course it has to be very conservatively tuned. Now, if you have a pro working on a recently rebuilt engine and tuning it specifically to that engine in that condition, the potential for gains is huge. Comparing a specifically tuned car with a production car is in my opinion apples and oranges comparison.

The moral of the story is that everyone should have their cars tuned by a professional.

ptuomov

This is the answer to the BMEP "puzzle."