roller rocker cams

[P10DET]

Originally posted by manzano
Years ago, I worked in a shop with a couple of water brake dynos. Everyone there (including yours truly) thought the big number indicators reflected HP. Then, one day the repair guy came in, overheard one of us, and informed us that number was twist or torque. He was nice enough to share his knowledge of dynos with us, and I thanked him for it.

I was quite aware of this before.

Originally posted by manzano
I'm not sure why the redline was lowered. As I understand things, the roller rocker engines have a slightly more aggressive intake cam, the roller rockers (duh) and a lighter crank.

I would guess it was lowered because of increased valvetrain harmonics. The heavier weight (making an assumption here) of the roller rockers would increase the harmonics.

Originally posted by manzano
I wouldn't think the crank or rockers would be an issue at 7000, but maybe they eased up on the valve spring pressures a bit to reduce parasitic power loss at low RPMs.

The crank is not an issue, but indeed the rockers are. First, and once again, the issue with the SR20 vavletrain is harmonics. This causes the valves to float at high rpm and this in turn causes the rockers to fly off above 8000 rpm.

Originally posted by manzano
I bet JWT has checked the spring pressures, and could give you (anyone) the answer.

Indeed. That is where the information comes from regarding the valvetrain harmonics. I'm not sure how much I'm allowed to share, but I know in general terms what they discovered and how they came up with the info. I can say that the engineering that went into their cams and springs is on the same order of engineering that goes into F1 and Champ Car engines. This is no exaggeration either.

Originally posted by manzano
Bang-for-the-buck, you're right on target.

Yep. Bang-for-the-buck, the DPR heads suck wind. I'm not dissing DPR. All wacko head work does. They are more for someone who is crazy (like me) and wants to build an all-out NA engine.

Originally posted by manzano
Stick with headers, a cam, and maybe an intake, if you can find one that doesn't doesn't suck hot air, water, or both.

You pretty much don't have to worry about an intake under the hood. A number of folks have instrumented their cars and found the temps at the intake to be essentially at ambient once the car is at street speeds.

[P10DET]

Regarding the Dynojet dyno, I think I may have been right in the first place. I have to do some more research, but I think I have it.

Where T = torque, I = rotational inertia, and a = angular acceleration,

T=Ia

(a should be a lower case alpha, but I don't know this digithead stuff enough to reproduce it here, so I'll settle for a lower case a in italics)

Since I for the drum is known, and a is measured with data acquisition, T can be readily calculated. So far so good. The question is how we get to hp.

Well, since hp=TxN/5252 (where N = rpm), we simply plug in the figures for T and N. T was calculated as above. RPM is the rpm of the drum (not the engine of the car spinning the drum through the drivetrain). Therefore, since we know N and T at the drum through data acquisition, we can calculate the hp at the drum as well as the torque. Pretty clever, don't you think?

So, now we know the torque (and thus hp) being applied to the drum. What we cannot do is relate the torque and hp at the drum (and thus the wheels) to the rpm of the engine. So, we need to also collect the engine rpm data to plot the torque and hp as a function of engine rpm rather than the drum rpm.

So, there you are. My take on this after pondering for a day. I'm open for shooting holes in this and I'll be copying this to the SE-R Mailing List as well. I think this theory will hold up, but we'll see. If not, I'm sure we'll come away with additional insight.

[manzano]

Thanks for the head's up.

As for the steel shot, haven't those guys heard of walnut shells? I don't think I've ever left anything in an engine, but I did neglect to use Loctite on the flywheel bolts one time. Thankfully, it was the engine in my car.

I think I'll go where nobody has gone before (that I know of) , and get a Crower stroker kit, somewhere between 2.2 and 2.3 liter displacement.

I know some folks rant on about how you shouldn't mess with the bore/stroke ratio of an engine, but I don't think that will be an issue. That, along with a JWT cam, should be good for some good, streetable torque and hp. The funds are there, I am waiting on the warranty to run out.

Does anyone know if the JWT SE-R motor mounts fit a 2000 G20t?

Cheers

[A380Driver]

Do you get valve float about 7k in the SR20?

[P10DET]

Originally posted by manzano
As for the steel shot, haven't those guys heard of walnut shells?

For the record, I did not accuse DPR of leaving the shot in the head.

Originally posted by manzano
I think I'll go where nobody has gone before (that I know of) , and get a Crower stroker kit, somewhere between 2.2 and 2.3 liter displacement.

Unless you build it tomorrow, you won't be going where no one has been before. :right:

Originally posted by manzano
Does anyone know if the JWT SE-R motor mounts fit a 2000 G20t?

That I cannot help you with.

[P10DET]

Originally posted by A380Driver
Do you get valve float about 7k in the SR20?

I don't have information that detailed, but I think that is true. It's pretty slight though and not enough to throw the rockers.

The reason I know there is some very minor valve float going on is that the JWT valve springs by themselves will gain you a couple of hp.

[manzano]

Re: shot - I consciously did not ask you to finger anyone - that is your business.

As for the stroker, I don't mind being second. I can grind the block if I find any interference there, but it will be nice for someone else to discover other issues such as oil pan clearance, etc. I'm not looking for mega HP numbers, just 'bout 150 hp and 150 lb/ft torque at the (drive) wheels.

Life does suck sometimes, but it's part of the game.

[manzano]

George,

Regarding that dyno thingy that won't die, the roller rpm has no correlation to engine speed. If a dyno is reporting HP without monitoring engine speed, it would be assuming a fixed drive ratio and outside tire circumference.

If you could input drive ratio (for whatever gear you use for the pull) and tire size for each different car, yes, the dyno could calculate HP without engine speed input, no problem.

Without that info fed into the dyno, it would be a 'one size fits all' ratio, which would not be accurate.

To illustrate, get two identically prepared rear-drive (for simplicity sake) cars and outfit one with a 2.06 rear-end ratio, the other with 4.11 gears.

Now, do a dyno pull for both, 2nd gear, no engine speed input. Without knowing engine speed, the car with the 4.11 gear is gonna kick the others' tail. The 4.11 jumps off the rollers, while the taller geared heap takes forever to make the pull.

Hook up the engine speed, and you'll see that both vehicles have identical torque curves.

That's the best example I can think of

Cheers

[P10DET]

Originally posted by manzano
Regarding that dyno thingy that won't die, the roller rpm has no correlation to engine speed. If a dyno is reporting HP without monitoring engine speed, it would be assuming a fixed drive ratio and outside tire circumference.

Nope. This is 100% incorrect. That I'm quite sure of. If you look at the second link you provided, you will find they used an inertial dyno hooked up directly to the engine. The rpm being measured is in essence the rpm of the drum (since it's hooked directly to the engine).

Originally posted by manzano
Hook up the engine speed, and you'll see that both vehicles have identical torque curves.

Nope. Not even close. Now you are assuming that the Dynojet measures engine torque. It does not. It measures torque to the wheels and with different gear ratios comes different torque multiplications.

[manzano]

George,

We've been referring to roller dynamometers, which have no relationship between engine speed and roller speed.

Here's THE link: http://www.idavette.net/hib/dynojet/index.htm

After reading all the info, uh, I can with certainty say

I was wrong about a couple of things.

I was oversimplifying, and underestimated the ingenuity of Dynojets. Dynojets can indeed measure hp, but do require engine speed input to factor out gear ratios.

If I knew how, I'd insert one of the 'poke myself in the eye' thingys.

anyway, read away. It's good stuff....

cheers

[manzano]

So, in closing....

The Dynojet brand of dynamometer can determine the current horsepower of a vehicle without knowing its engine speed based on, uh, here it is from Dynojet:

*** Start ****
During manufacturing, Dynojet Research figures the mass equivalent of each pair of drums to four places and bearing drag to five places. Those proprietary figures are figured into the computation the dyno computer makes. If the mass equivalent of the drums is known, the drum bearing drag is known and the rate at which a vehicle’s drive wheels accelerate the drums is accurately measured; then the "thrust force," in pounds, at the rear wheels can be computed with a high degree of accuracy.
*** End ***

So you run your car on the dyno at a steady engine speed, and it says: '150' HP.

What the Dynojet doesn't know is if the car on the dyno making 150 horses is an 8 cylinder loafing at 2000 rpm's or a 2 liter 4 cyl screaming at 7000 rpm's.

So it uses engine speed to factor out gearing. In other words, it can calculate torque at the wheels by comparing roller speed to engine speed. One little calculation to factor out gearing, and it knows wheel torque.

So now it can plot the points for HP and torque, and draw the nice little curves.

Hope I got it right this time. Crow tastes like crap. :bloatted:

Manz

[manzano]

Oops,

Sorry for the extra 't'

[P10DET]

Originally posted by manzano
So you run your car on the dyno at a steady engine speed, and it says: '150' HP.

Actually, on a Dynoject, you don't run at a steady engine speed, but rather run it up through the rev range.

Originally posted by manzano
So it uses engine speed to factor out gearing. In other words, it can calculate torque at the wheels by comparing roller speed to engine speed. One little calculation to factor out gearing, and it knows wheel torque.

Oh so close. Someone sent me a private e-mail from another list that I think hit the nail on the head. While T at the drum can be determined, and hp at the drum can be determined......

HP at the drum is the same as hp at the wheels. But, the rpm of the wheels is different from the rpm of the drum. So..... the speed sensor actually figures out the rpm of the wheels and calculates torque at the wheel. Whew. What an exercise. I'm a geek. No doubt.

Originally posted by manzano
Crow tastes like crap. :bloatted:

It goes down better with Shiner Bock. Trust me (it would be rude at this point to ask me how I know).

If you can't get Shiner Bock, you'll just have to make do with some inferior beer.