74 replies to this topic

[ls2lxhatch]

I am glad you have posted the sheets as they explain what is going on. You where half right when you thought that the 1200 ft-lbs needed to be divided by the diff ratio.

I suspect that the 1200 ft-lbs figure you saw and the figures on the dyno sheet is the raw torque figure measured at the roller which is affected by the gearbox, diff and tyre and dyno roller diameter.

A dyno measures torque and RPM. HP is calculated from the torque and RPM using the formulae.

HP = ( Torque * RPM ) / 5252
Torque = (5252 x HP ) / RPM

How Dynos Work

Dynamometer

Consider an engine that produces 200 ft-lbs at 5000 RPM which is 190.4 HP.

Then we put a 2:1 gearbox on that engine and measure the output at the shaft. We get 400 ft-lbs at 2500 RPM which is (400 ft-lbs * 200 RPM) / 5252 = 190.4 hp.

We know the engine is actually reving at 5000 RPM we can work out the torque the engine is producing (5252 x 190.4 Hp) / 5000 RPM = 200 ft-lbs.

Edited by ls2lxhatch, 26 September 2010 - 08:44 PM.

[ls2lxhatch]

Yes, the 1200 ft-lb is as correct as the 3000 Nm (2212 ft-lbs) figure that the 81 kW Patrol produced.

It find it difficult to understand why a dyno operator would choose to plot this torque figure as it is basically useless for gearbox choice or engine comparison. The figure clearly is not engine torque.

To compare engines and select an appropriate strength gearbox you need to know what the engine torque is. The Patrol dyno shows 3000 Nm (2212 ft-lbs) @ 2200 RPM with around 70 kW (94 HP). Surely you don�t think that the Patrol is making 2212 ft-lbs of engine torque. We know that engine torque in ft-lbs = ( 5252 x HP ) / RPM. Therefore the Patrol engine torque without allowing for drive train loss is 5252 x 94 HP / 2200 RPM = 224 ft-lbs.

Based on the Raceme�s dyno results you were looking for a gearbox that could handle 1200 ft-lbs. This indicates you mistakenly believe that Raceme's engine is producing around 1050 ft-lbs to 1200 ft-lbs of engine torque. You also think that that Raceme�s engine is producing more torque than Litre8, the CAPA VE Ute Vortec 409 ci and Rorym�s 355.

I have been looking at G-Force Racing who make spur dog ring, helical dog ring and helical synchronised gears for about 5000 dollars. They look pretty tough but are only rated at 600 ft.lbs of torque which is a bit concerning considering last time i saw on the dyno i was making about 1200 ft.lbs of torque.

As i said it didnt make 1200, it made more like 1050 with an ultra restrictive exhaust and a slipping clutch, one of which has been fixed and the other is getting looked at, hence were just looking at something a bit higher.

Why is it so hard to believe? at 10psi its effectively a 8 litre engine with very high volumetric efficiency, 355 is only 5.7, even assuming R's engine would have been making 100% volumetric efficiency at the top of the torque curve due to the modifications he did to it.

All I have said the whole time is that I don�t think you need a gearbox capable of handling 1200 ft-lbs of torque because I don�t believe the engine is producing 1200 ft-lbs of torque.

[ls2lxhatch]

I think you will have no problems producing more than 400 ft-lbs once you have sorted out a few issues. Based on Rorym's 335 ci 411 ft-lbs, you would think that 600 ft-lbs would be around the upper limit that you could expect with 10 psi boost. Therefore a gearbox that handles up to 600 ft-lbs should be suitable.

For peace of mind, give COME racing a call and ask them what sort of torque you can expect from your combination and any future plans you have for the engine.

[76lxhatch]

But I know the lockup function SHOULD be used- something to do with preventing overheating when in overdrive.

Sorry to wade in late on the discussion, but doesn't that only apply when a lockup converter is installed? I.e. if you don't want the lockup, you buy a standard design converter and all is well?

[76lxhatch]

I thought the lock up was electric for some reason, most likely wrong though.

Yes, electric controlled - easy done on any injected engine as all the ECUs have provision for it. Its basically only a switch, I've also heard of people simply using a manual toggle when running behind a carbed engine but that seems a bit rough

edit: it has just occurred to me that the lockup converter issue is probably the same as street driving with a high stall converter - driving too far at speeds where the converter is not fully engaged causes them to overheat, and this may occur with tall gearing (such as the standard Commodore 3.08:1 diff) and the overdrive ratio? The converter clutch would solve this problem, but assuming that you have done your normal homework with regard to stall rpm and cruising speed I guess you wouldn't need it

Edited by 76lxhatch, 28 September 2010 - 08:39 PM.

[76lxhatch]

i am wondering if the older 304 computers controlled the auto through the bcm (body control module).

Nope its not that complex, all done by the ECM/PCM. The good thing about doing it properly is that you get a lot more fine control (which you can really just set and forget) - minimum speed, unlock delay, etc etc which all help to make it work well while being reasonably unnoticeable to the driver.

The BCM introduced in VRs controls the security system along with a number of the controls and systems not related to the engine. If you have a PCM designed to work with a BCM all you need to do is disable the security in the tune and you have everything you need to run the engine and trans.

[BENN0]

Im coming in a little late here, but if you prefer manuals im not sure why you want to convert to an auto?
You have stated that the car is a difficult to drive with the current setup. Why not invest some effort and money into a suitable clutch? There are clutches availabe that are light on the pedal, yet can handle plenty of torque. There are guys running blown VE's getting around with manuals and they are no problem to drive every day. I dont see why you could not have a clutch made to suit your requirements. It will not be cheap, but will still cost less than converting to an auto.

If you are set on converting to an auto, then a properly set up (correct combination convertor and lock up setup) 4L80E will be nice and smooth to drive. But will sap more power than a manual and most likley will be heavier. I would not reccomend a full auto arrangement though. A nice firm shift kit (with a decent convertor) will be just as quick, but still offer some comfort.

P.S Roller dynos measure Tractive Effort at the wheels (in NM or ft/lbs) not engine torque. To convert this tractive effort to engine torque you need to consider the tyre size, diff ratio and gearbox ratio used..... Tractive effort is a value much higher than that of engine torque (using the same units)