ptuomov

Diameter = 1.8 inches -> Area = (1.8 inches / 2)^2 * pi = 2.54 square inches

mark kibort

I dont remember this! (but I certainly believe it) I know that your first 6.4L only made about 370rwhp, (I think I posted the graph from your catalogue), but that was on a stock S4 system, kind of like what I did with only a set of GT like cams If I remember correctly. 360rwhp for a stock S4! Well, there is more proof that it can be done. by the way, we all ran on keiths dyno and it was a dynojet 248e. I used it in sacramento, Devek had it at it dynodays and it was a good check of power reality. . I remember using it when all the mods of my 84 got it from 170rwhp to 243rwhp with euro intake, cams, RRFRs, headers, exhaust, etc.

mark kibort

where on the engine could there be ports this small! Of course the area has to be in the 2.3-5sq' range. diameters are in the 1.8 range.

maybe the number came from the valve size, but there are two of them per intake and exhaust .(i.e 37mm would equal about 1.5sq")

pi*r^2

IcemanG17

BMEP brings up some interesting comparos......

Just for comparison....my M3 makes a rated 103.5hp/L but is more like 110hp/L in reality....so using the stock rated torque of 295ftlbs.....that makes a max BMEP of only 182psi which is plausible....

Which is quite similar to dennis's 362ftlbs (wheel torque) or 180.7 psi BMEP...but his actual torque would be higher more like 425ftlbs using the standard 85% loss calculation or around 212 psi BMEP...which is quite high....so I would say the actual drivetrain loss is LESS than we think...if his loss 90% then it makes 402ftlbs or 200.7psi BMEP....high but possibe....

Looking at larger stroker style 928 motors.....Simards 427 makes 500ftlbs which ends up with a wheel torque BMEP of 176.6psi BMEP and at 90% of 196psi BMEP...also possible.....

Louies motor at 534ftlbs is harder to explain using BMEP....since he's about 396.5 cubic inches....his BMEP is off the charts....203psi BMEP using wheel torque and 225psi BMEP at 90% (594ftlbs)...but it does it...again and again.....Louies motor probably is the most dyno tested and proven 928 engine out there......

BC

Exactly. Testing, Testing, Testing. And alot of smart decisions. And dyno testing testing testing. And short runners on Louie's motor.

The design of the motor can be done many different ways. Its what happens when its together and how/who is doing the tuning that matters.

mark kibort

Does BMEP have to use data at max torque or max HP? I was using figures at max HP. seems silly to use max torque values, as you could get a long stroke engine to make big peak torque, but no real power.

ptuomov

A couple of points after some research.

First, one can make a crude adjustment for turbocharging by multiplying BMEP by atmospheric pressure / (atmoshpheric pressure + boost). This will make turbo engines look like they suck in terms of efficiency, but they kinda do with their low compression ratios and overly rich charges. There's a long thread on this in one of the RL turbo forums, I think 993 turbo.

Second, it is much, much easier to make high BMEP at low rpm than at high rpm. That's because of frictions mostly. So F1 making the same BMEP as 18000 rpm as Nascar at 9000 rpm is a different level of achievement, no matter what the fans of pushrods, restrictor plates, carburators, and two valve cylinder heads say.

Third, all three 928 engines listed here are individually tuned engines. They all make high (dynojet or mustang or whatever) rwhp BMEP. It's all consistent with my theory and the OBVIOUS evidence in this thread that engine specific tuning is (a) REALLY important and (b) often the CHEAPEST source of additional ponies (and BMEP).

ptuomov

My software predicts the BMEP at each rpm.

I think that if you are looking to use BMEP as a bull**** detector, pick the maximum torque rpm value and compare that. As Greg Gray points out, often the claimed results end up beating expensive purpose built machines and imply even with a perfect burn a volumetric efficiency number that is implausible.

slate blue

By Mark Kibort

Mark, you certainly make some pretty big statements You have experience in this area to back this up I hope? Do yourself a favour and go back to those links I provided, it took a long time to find suitable material as this topic is not widely advertised/distributed. Read Motoman, then come back and make the same statement.

On my stroker 2V engine the valve size is 2.10" and the port average CSA is 2.19 sq". The valve has an area of 3.465 sq" and the port opening is in the region of 1.7 sq". So that tiny port flows around 290 cfm at 0.500" . The standard 928 S4 port flows around 300 cfm @ 0.500" but is in the 2.42 sq range. For a if you had a 104 mm bore and say the capacity of a GTS and a rev limit of 6,800 rpm which port is better and why?

Greg

mark kibort

Greg, I never knew that pi r^2 was such a big statement. .

I was just stating measurements of intake ports and valve sizes Ive measured. I forgot what you mentioned regarding port area, but I thought you said 1.8sq". that would be a port diameter of near 1.5". I dont think we have any of those.

Hey, technically, you are way over my head here and Ill be the first to admit it. Interesting stuff, but all I was referencing to was dyno and track performance differences that seem to be inline with most dyno runs and weights for cars Ive competed against.

thanks for the links though and I will try and find time to read them. seriously, it is interesting and to me its all kind of black magic .

as far as the port size and flow rates. Yes, Ive seen some big ports that flow less than small ports when well designed. I think what you are getting at is the benefits of the graduation of the port diameters as the flow hits the valves in regards to flow speeds . Ill read the links.

mk

slate blue

By Mark Kibort

If somebody has a gun, please shoot Mark K for me, if you can't find him shoot me instead, put me out of my misery This is the last post I will waste my time on since you have no understanding of it and are just posting rubbish. Stop trying to defend the indefensible.

The engine that Marc T is referring to develops BMEP at peak power of (if we use 420 hp as the flywheel figure) 162 psi, the engine this thread is about is at least in the 190 psi range (close to 200 psi) whether is high or low in that range is neither here nor there. Those engines are miles apart as far peak BMEP goes, my engine calculates at 170 psi and is also fairly stock apart from an elaborate exhaust system and optimized intake.

As far as BMEP goes use the peak torque and peak hp numbers, generally peak hp is used more.

By Ptoumov
This is very true.

Greg

slate blue

By Mark Kibort

Alright I take back the bit about shooting either one of us.

Greg

mark kibort

put down the ego hat and step away from the computer!

Listen, the engines are not that far apart. Did you see the dyno runs? there is a 10-15hp noise fluctuation at the end of the dyno run. Dennis' peak hp is around 6000rpm and its near 375ish rwhp, a scant 15hp over what Marc T. saw with his 5 liter mentioned here, and with NO tuning. hey, did you notice that dennis' ran the same hp before the tuning?

Its a discussion Greg. You are implying that the engines are not making as much HP as they clearly have made. Is 15% the numbrer? as I mentioned, if it is for 330hp, it might only be 13% at 375hp, due to some of the losses being fixed.

slate blue

By Mark Kibort

When I don't know something or I am unsure, I don't take definite positions, most of the time I am happy to go with the flow and people who know me will back that up. I certainly never challenge somebody on a topic I no very little about. You on the other hand take a completely different tact and from others have said it is not the first time. The worst offence you commit is when you put it out there like it is fact when you admit you know very little about it. Why do it? Just to confuse others or is there ego on you side of the keyboard? Lighten Francis it was a joke anyway.

As I said in a previous post the more I know (knowledge gained) the more I realize what i don't know, this engine building stuff is so so complicated. An example, I am slowing accumulating parts for a 4 V engine, I have the Carrillo forced oiled pin rods with the Carr bolts (rated 295,000 psi) I have the Mahle box bridge pistons, less than 400 grams ultra lite and strong, I needed to get some wrist pins, well there were some new Ti ones available with DLC coating, the plan was to have the rods brass bushed.

So I thought, with the forced oiling and the brass bushing and the dlc on the Ti pins which are very light (70 grams) and good for the high revs and high power levels (around 8,400) rpm and therefor reduce the loads on the crank so that I may be able to run the smaller main journals I am investigating.

What could go wrong???? Well what could go wrong, I ring the maker of the pins and they said you wont believe this but the forced oiling creates little holes in the Ti pin. We don't know why but it has happened a number of times. We strongly recommend against it. I accept the advice.

Readers can draw their own conclusions.

Greg

P.S Edit, I wrote these posts when and i still do have a terrible headache/migrane, seeing those posts MK just pissed me off at the time, so if I over reacted I apologize.

ptuomov

Not that I am an expert or anything, but just a novice playing with the numbers a bit. I would say that your 2V head has the potential of making more average power than the stock S4 head between say 4000 rpm and 6800 rpm without a compromise in the top end, if the intake runners, cams, compression ratio and the headers are just exactly perfect.

You can get
- intake resonance tuning to give you a high intake port pressure at the intake valve opening
- a low pressure during the overlap in the cylinder
- some temporary overscavenging of mixture to the headers which is then pushed back into the cylinder with the perfectly timed exhaust reversion wave
- finally a big inertia effect from the fast air speed at the late intake valve closing

(All read from a book, not that I've done any of this.)

When all this plays in concert together over a reasonable rev range, you'll make a lot of torque, BMEP, VE, and power.

However, there's a lot of uncertainty especially about the top end with an engine like this. The air speed might get too high and the whole thing choke. The resonances might be off. Changing a muffler might kill 20 horses. etc.

I am very interested in seeing how much power those heads make in your combo.