HI, the reason I am putting this in the TPI section is it has to do with a TPI question, This is the delima. I have filled out all the information that I have ie. THE HEAD FLOW / CAMS SPECS and misc, but when it comes to intakes it gives me several options, and one of those is a TPI, but there is the question. When you pick the TPI it really limits the power range, I know because of the ability to flow, but it doese not take into consideration of a moded TPI that will flow better than the stock unit, like a set of SLP RUNNERS, very much moded plenum and base. I have used the DESKTOP many times on carbed engines and as long as you have the correct info put in it always seemed to be real close when we dynoed the engines on the real thing. I an effort to get some more realistic numbers do you think that a selection of the dual plenum or open plenum may be more in line with a highly moded TPI set up, just currious if anyone has run into this problem? THANKS for your help and any suggestions.

 

Come on, I know someone has to have pondered this question, and knows what kind of numbers a moded TPI can flow in relation to a carbed intake. Like maybe a dual plane performer or say a open plenum race victor jr ect. I have seen in this forum where some of you have the TPI flowing enough to pull past 6 grand pretty easy. Thanks for your help....

 

Is there an option of selecting fuel injection from the menu(there was on early version of the program)? The problem is that the TPI runners are so much longer than a typical intake that comparing the two in terms of torque production is like apples and oranges. The thing about the TPI, and EFI in general is the area it produces under the curve, before the torque peak. This can be 20-30 lbs/ft more than a carb and intake at lower speeds, even though peak power numbers on the carb combo could be the same, or even slightly more. You'll probably still get a reasonable estimate of the engine's potential in terms of HP and torque, because what the program is doing is evaluating the size and efficiency of the air pump, which is all an engine is. This is determined more by engine size, compression ratio, cylinder head design, and camshaft profile. If the intaqke and exhaust are totally out of whack you are going to choke the thing, and not get close to the estimated numbers, but to do that you'd have to do something really foolish like run a single plane intake on a near stock 305, or a dual plane on a sprint car engine.

Keep in mind that torque is real and measurable, but horsepower is just mathematically determined based on torque and engine speed.

 

Thanks for the response TKO, yes I understand that HP is a byproduct of torque and engine speed. That is why I was wondering about the increase in air flow that a larger intake would have on the effect of the engine. What I was trying to compare was I guess is the CFM flow rate of a moded TPI to a larger carbed intake, So being that a stock TPI is highly restrictive in air flow as to say a RACE VICTOR JR, I was just currious about how close on the DESK TOP that would be. The DESK TOP does offer a TPI selection among the others, but it seems for sure that it is configured in the stock set up, that being said the increase in air flow of a highly modded TPI would effect the air pumping action like a larger intake, I know the runner length is drasticaly changed but would the increased amout of airflow make the TPI seem larger like say at least a good flowing DUAL PLANE, that would make the engine a more efficiant pump especially at a higher RPM and therfore generate more HP in the upper range. I know its going to move the power band around some but thats O.K. because im trying to kill off some low end power. I had a lot of success from tunnel ram engines to big block spray set ups on the DESKTOP but have never had to use the TPI selection. So please give me your oppinon on that... I appreciate you input THANKS

 

The TPI, even modified is much closer to a dual plane. Stock TPIs have runners about 12" long. Single planes are about 4-5" and dual planes are more like 8-10". The plenum volume will be much larger, but this isn't really important. A carb engien can't have too much plenum area, because it would just cause the fuel to fall out of suspension and puddle. A TPI just moves air, so it can store as much as it wants, to a point.

 

I've always used "Sequential Fuel Injection" when dealing with a modified TPI like you describe.

 

THANKS TKO, so you think that a dual plane would be more like a moded TPI, actually I think TPI total runner length is more like 22 inches because the runners are at least 8-10 by them selves, but thanks for your opinion. Also thanks KEVIN91Z, so the numbers you use on SFI are numbers that seem to work out for your estimations. Have you any real world numbers that help to show that this is a close analysis. Like have you dynoed any of the combos that you have done on DESKTOP to see how close they are. Most of mine come out to about 2-3% when we get good info to put in. and temp/baro corrections. THANKS

 

I read somewhere that if you include the runner in the head (intake port) that the runners in a TPI are about 22" long. If you subtract roughly 4" for the head port, and the consider that most modified TPIs are running siamesed or semi-siamesed runners that probably cuts you down to about 12" of dedicated intake runner.

I've always seen that the numbers generated tend to be very accurate with good information, cam timing particularly. If anything I usually am 5-10 HP to the good over the estimate from the program.

 

Right, with my SLP siamese setup I figure the total length of the runners are about 12 inches long. Around 7 for the intake manifold and the 5 inside the head. Just about what the LS1 motors are. My dyno graph reflects it.

 

I've noticed my Desktop Dyno 2000 is really close on its horsepower figures, but way off on its torque figures. I've tested it on both my engine configurations, and it was within 5 horsepower at the flywheel, calculated. But what it says for my flywheel torque is what I get at the rear wheels.

 

TPi "runner length" varies. total runner length to a cylinder would have to include the plenum to be compared to a carb intake. calculating a carb intake runner, you would be calculating the distance from under the carb to the clinder, so for TPI, from the TB to a cylinder. - at rpm the plenum is not holding any air to dump into the runners, therefore its is part of the runners. That would be why so many people say anything from 17-22 inches. #1 cylinder would be short, #8 on the other hand...

 

What do you mean by that?

 

the program shows what it should be at the flywheel, he means the program said his torque should be 400, but in actuality he has 400 at the wheels, not at the flywheel.

 

He should have a lot more than 400 ft-lbs at the wheels unless he has 1:1 gears.

 

more than 400 ftlbs at the wheels? what's his combo? that's a lot of torque for mouse.

 

If he's got 400 ft-lbs at the flywheel he should have around 1,200 ft-lbs at the rear wheels, depending on gearing.

 

umm i was 400 as an example, not what he really has, i was just explaining what he meant

 

Some of our cars are making over 400rwtq.Check out the graph

It's my car. Dyno Don post it for me.

 

That's not rear wheel torque, that's flywheel torque measured at the rear wheels.

 

That graph is REAR WHEEL TORQUE AND HORSEPOWER!

 

Rear wheel horspower yes, rear wheel torque, no. The dyno has used the linear speed of the edge of the tire and the engine RPM to estimate the total torque multiplication of the system, and is using it to infer the flywheel torque, which is displayed on the graph. Although many people wrongly call it "rear wheel torque" because of how the measurement was taken, that's not what it is.

 

I disagree. Vincent is correct. The torque measurement was taken from the rear wheels on the dyno. The Horsepower is calculated from torque. There is loss in the drive train.

 

If you were to change your gears from 2.73 to 4.11, would you see a corresponding difference in the torque figures on the dyno?

 

I know us guys hate to read directions but if you look under the user manual there is a whole section on TPI. It says:
The Tuned-Port Injection Induction menu selection models a stock TPI. However,
a wide range of aftermarket parts have been developed for the TPI system,
including enlarged and/or Siamesed runners, improved manifold bases, high-fl ow
throttle bodies, and sensor/electronic modifi cations. These higher fl ow systems are
often best modeled with the Standard-Flow Single-Plane choice for small-runner
systems or the High-Flow Single Plane model for large-runner packages.
Roy

 

Rear Wheel Torque and Horsepower on a chassis dyno are corrected numbers. They have to factor in the gearing in the system, and yes, you are seeing the numbers after driveline loss. For example, a stock WRX puts out 227 horsepower at the flywheel, but on the chassis dyno you will see numbers in the 180 range. Essentialy you are losing 47 horsepower through the driveline due to friction and the power consumed by rotating weight. This isn't the MEASURED number at the wheels. That would be the flywheel number times the gearing minus the driveline loss, and yes different rear gear ratios would affect the MEASURED numbers. Running the car with the trans in different gears would have a similar affect, since the overall gear ratio is being changed. The printout or readout you get is a corrected number. The goal of the chassis dyno is to give you an idea of what you are making at the flywheel, which is why they adjust the figures instead of saying you are making 1,600 lbs/ft, because at the flywheel you are making 400 and simply have a 4.30 rear gear and some amount of frictional loss.

I also don't think you can count the plenum in runner length. One reason is that in a V8 engine two cylinders are sucking off the common plenum at the same time, as they are both on the intake stroke. Another is that plenum volume has more to do with RPM potential than torque, because the plenum is essentially a storage chamber for air, or air and fuel. Engines with a higher RPM potential need more plenum volume to supply enough air or air & fuel at higher RPMS to keep from starving the engine and forcing a lean condition, or effectively limiting engine speed because the engine just can't rev any higher regardless of throttle angle becuase it just can't breathe (the plenum volume has acted as a sort of throttle stop). You could use a huge plenum chamber on a short runner intake and it won't bolster low end torque. You could also reduce plenum volume on a long runner engine and it won't improve RPM potential. Runner length is the runner of each cylinder from either the back of the intake valve or the head mating surface to the point where the runner diverges into the plenum. The starting point is a matter of how you wish to compare different intakes, but most serious enigne builders would start at the backside of the valve.

 

Thanks FASTMAX, that was the response I was looking for, I appreciate that you are intelligent enough to look at the directions....LOL. That would have been all crazy for me to do that......Have a great day...

 

To FastMax and Others. It would depend on which version of desktop dyno you are running. The latest versions do indeed cover TPI better as you stated.

I'm using the High Flow single plain because of my "highly modified" TPI. We are talking around 260 to 270 cfm for the manifold and I will know for sure when I get it flowed. The Edelbrock manifold is Extrude Honed. The runners are siamesed so they have to flow more than that. I'm comming up with some pretty impressive numbers not normally associated with TPI.

I also plugged in the LS1 manifold and I could see that was not quite correct. I already have higher torque numbers than shown without my future mods. The single plain manifold does indeed seem to be more in line with my modified TPI going by the real dyno runs I have.