[Stan Weiss]

Originally Posted by Skip Fix

My question on chassis dynos is since your rear gear ratio multiplies TQ why does that not affect it?

Skip,
Unlike an engine dyno which measures torque, a chassis dyno calculates torque from a number of measured factors and the math does workout.

Stan

[Skip Fix]

I guess Stan but the rollers are loaded and it takes TQ to turn them. The chassis dyno guys I have talked have said a loose convertor can affect it, as well as slicks growing with rpm.

[Stan Weiss]

Originally Posted by Skip Fix

I guess Stan but the rollers are loaded and it takes TQ to turn them. The chassis dyno guys I have talked have said a loose convertor can affect it, as well as slicks growing with rpm.

Skip,
It has been awhile since I talking with someone about a roller chassis dyno. What I was told was, yes those things did make a difference but not as much as it would seem. A dyno test in 3rd gear (1:1) and 2nd gear (1.48:1) were not the same but there was no where near a 148% gain in torque and HP. Thing might have changed or I could have been given bad information,

Stan

[PAUL K]

Originally Posted by Stan Weiss

Skip,
It has been awhile since I talking with someone about a roller chassis dyno. What I was told was, yes those things did make a difference but not as much as it would seem. A dyno test in 3rd gear (1:1) and 2nd gear (1.48:1) were not the same but there was no where near a 148% gain in torque and HP. Thing might have changed or I could have been given bad information,

Stan

We tested one of my cars with a 446 engine on a chassis dyno. When testing in third gear it took a long time to pull to 7,400 because of the 3:50 gear. We tried a back to back pull in second gear and there wasn't a noticeable difference in the data. We finished the session using second gear. But the "instructions" for the Mustang dyno said to use a 1:1 gear.

[Formulajones]

Just to give you an example as to how wildly HP numbers can vary going from an engine dyno to chassis dyno, since we've had a few we did that very thing with.

Dad's engine in particular made 724hp on Tony Bischoff's engine dyno (flywheel) I'm very certain those numbers are real, Tony doesn't fudge things or run a happy dyno. If it makes that power you can feel comfortable it's legit.

After finally getting the car setup to run properly (trans/converter/rear gear) at a 4129 lbs. race weight it's gone 10.60's at 128 mph with a very soft 60 foot. So yeah, at that weight, the HP is there.

So he decided to put it on a Dyno-Jet chassis dyno for giggles. Kevin runs this particular dyno and is used for all of the Nascar SW tour series teams that have to run spec engines to make sure someone isn't playing with the rules. For what it's worth he assured me it's a very accurate and repeatable dyno. It has to be or Nascar wouldn't approve it's use.

He made 5 or 6 back to back runs and every run was 505-510 HP to the rear tire. That's a pretty dramatic difference from flywheel to tire.

That's with a very snug Hughes converter that drives tight, and I didn't lock it for the runs. The trans is a 4L80E, Heavy steel 1000hp driveshaft, 12 bolt rear with 3.42 gears, and the heavy steel wheels.

That's more than the 15-18% driveline loss you often hear chassis dyno guys throw around, and I've run into this same scenario with other cars as well. So I don't buy into the whole math formula of this much power equals such and such at the flywheel. I told Kevin what it made at the flywheel on an engine dyno and that we were looking at a 30% difference, and he was not surprised with that at all.

Just goes to show it's not a perfect formula trying to figure all that out. I was told things like aluminum wheels, aluminum driveshaft, and other lightened parts like that would increase RWHP so there are things that can change the numbers around a bit. Not every car is going to be the same result.

[AG]

Using Hp calculators and an ET of 10.65, Hp is 675. It is also 675 Hp by the mph which is unusual they are the same.

[Verdoro 68]

Out of curiosity, how much power do accessories and belts eat up? I'd think those could compound on a chassis dyno in street trim and take up a few hp. Seems like many engine dynos run no accessories and an electric water pump.

[Formulajones]

Originally Posted by AG

Using Hp calculators and an ET of 10.65, Hp is 675. It is also 675 Hp by the mph which is unusual they are the same.

Yeah I feel a lot of those formulas are skewed a bit too. There are a lot of them out there and not many agree on each other lol

What I can tell you is I feel there is a pinch more mph in the car with more tuning and for sure I know there is ET because he's chicken footing the car at the starting line and only going 1.74 60 foot and the car has gone 1.40's in the 60

[Formulajones]

Originally Posted by Verdoro 68

Out of curiosity, how much power do accessories and belts eat up? I'd think those could compound on a chassis dyno in street trim and take up a few hp. Seems like many engine dynos run no accessories and an electric water pump.

Correct, and the difference would vary greatly on a per car basis.
For instance under drive pulleys and things of that nature will change the numbers. Every car is different, that's why you can't just put a percent on it and say it makes such and such at the flywheel based on chassis dyno numbers

[Stan Weiss]

Originally Posted by Formulajones

Yeah I feel a lot of those formulas are skewed a bit too. There are a lot of them out there and not many agree on each other lol

What I can tell you is I feel there is a pinch more mph in the car with more tuning and for sure I know there is ET because he's chicken footing the car at the starting line and only going 1.74 60 foot and the car has gone 1.40's in the 60

The formulas are just a general / close guesstimate. One major factor they lack is aerodynamic drag. You run a low et and a higher MPH with the same engine in a corvette than you will with it in a mini van.

Stan

[Stan Weiss]

Has anyone used a hub dyno? It takes tire growth and tire slippage out of the picture.

Stan

[AG]

Originally Posted by Formulajones

Yeah I feel a lot of those formulas are skewed a bit too. There are a lot of them out there and not many agree on each other lol

What I can tell you is I feel there is a pinch more mph in the car with more tuning and for sure I know there is ET because he's chicken footing the car at the starting line and only going 1.74 60 foot and the car has gone 1.40's in the 60

I use the same two equations that calculate Hp by ET and mph and calculate it myself. They are of course an estimate (generated from lots of empirical data) but I find they are useful to calculate differences in your own car's performance with changes that are made.
1.40s 60' is smoking, is that with the same converter that is in the car now?

[Formulajones]

Originally Posted by AG

I use the same two equations that calculate Hp by ET and mph and calculate it myself. They are of course an estimate (generated from lots of empirical data) but I find they are useful to calculate differences in your own car's performance with changes that are made.
1.40s 60' is smoking, is that with the same converter that is in the car now?

Yes

I was stumped and wondered why it wasn't pulling it's usual wheelie until I pulled the datalog and found he didn't reach full throttle until 2.1 seconds into the run lol

[Tom Vaught]

Originally Posted by Stan Weiss

The formulas are just a general / close guesstimate. One major factor they lack is aerodynamic drag. You run a low et and a higher MPH with the same engine in a corvette than you will with it in a mini van.

Stan

Agree, Stan and unless you have accurate "Frontal Area" and "Coefficient of Drag" numbers (from a Lockheed type wind tunnel), you are just using swags.

Guesstimate is a good word.

And you really need to do Track Testing as well as Wind Tunnel Testing at the correct weight and ride heights.

Tom V.

[Skippy597]

Originally Posted by steve25

Cliff, just so we are all on the same page here, the OP combo uses 1968 1/2 RA2 heads, so D port intakes , round port Exh.
Only a bowl blend was done on them.

If I had to take a educated guess I would say that in terms of peak Intake flow he might have 215 to 220 cfm @ 550" lift.
Don't know what might of happened to his flow numbers below 300" lift because there easy to screw up and end up with less then stock.

Exh wise if a bowl blend was done he likely picked up a lot at peak lift and if he was to slap headers on would be over scavenging due to the high flow ratio and the duel pattern Cam used.

Hey Steve,
Can you elaborate a little more on your thoughts on when a single pattern cam is preferred? At what flow ratio? I have heard and read this before but then they tested this on engine masters and made more power with a dual pattern cam. Just curious on some additional thoughts from you on the subject.

[Skip Fix]

Round port exhausts flow 85% on my RAIV heads with the larger RAIV ports whereas the RAII have a smaller D port intake port that flows less so your exhaust is already outflowing your small D port intake and does not need the extra exhaust duration.

I'll bet the Engine Master's test did not test a motor with a head that has 80+% exhaust flow, much less 85%.

FWIW my RAIV motor ran better with a "reverse split" cam-4 cams in it no other changes and most of the RAIV round port exhaust stocker and Super Stockers use a single pattern cam.

[steve25]

A lot of what’s needed for a intake to exh ratio is in part put in place actually by the motors compression ratio.

Once you get up to the 10 to 11 to 1 range, a over all 75% ratio is all that’s needed most times.

Please note like I just posted this is the over all ratio by averaging your numbers in the range of valve lift you will have.

Above 11 to 1 in what we will assume is a race only motor a number of 65% works.
As you drop down below 10 to 1 there is still a lot of unused gases left in the bore once the piston has dropped down to BDC.

In these cases and especially if exh manifolds are used you want the valve job , the valve and the valve bowl shape to produce the highest amount of LOW lift flow that can be had.

This is where flow testing is indispensable unless you really have a good grasp on what your looking at from many years of porting work under your belt .

This will blow down the cylinder faster and take good advantage of doing that at a time when the exh runner is not saturated with the gases due to the rising piston.

In other words get a lot of the needed job done before the piston even starts the exh stroke cycle.

Dropping this gas pressure as fast as possible also means the other moving pistons are not using as much of there motion energy to pump out these gases in other cylinders when exh stroke does start.

I dont know, that’s the best I can explain it right off the top of my head.

[Skippy597]

Thanks guys.
Not trying to Hijack the thread from the OP, I can PM you steve if you'd rather do that. On the engine masters test I dont recall if they listed the flow numbers but it was a excellent flowing aftermarket head and Schneider cams was recommending a single pattern since the exh flow was so good. But in the test they literally gained everywhere with the dual pattern cam.

So is the theory that your trying to keep the higher cylinder pressures with a single pattern and since the exh flow is so good that you dont need it to be open longer than the intake and also since you have the cylinder pressure pushing the gasses out, its more efficient that the intake pull. Is this understanding correct?

[Skippy597]

And to add, what is the benefit of a single vs dual pattern cam in theory?

Also just rewatched the episode of engine masters and he doesnt give flwo numbers but mentions that Keith at schneider cams recommends single pattern for engines with a 80% flow ratio, so I would assume that since he issusggesting it for the einge that it is near or at that.

[steve25]

When it comes to a motor that's more in the race built vein those better results with the duel pattern Cam where more likely due to the better placement of where the overlap phase was now taking place and the timing events on either end of that phase that better met the motors needs.