122bhp at the flywheel, only 82 at the wheels - drag?

[dunclentdr]

Have had an early style head fitted on my S1 along with a set of 40DCOE02 carbs, it is a very original car so keeping in with that.

Lots of time on the rolling road today (Aldon) and it is now running well again.

Power data is:-

122bhp at 6370rpm
107.5lb-ft torque at 5235rpm

but - only 82bhp at the wheels which seems a much higher drag than might be expected.

Does anyone have advice on whether this is higher than should be expected and, if so, possible causes?

Thanks

David

[Chancer]

You have 82bhp at the wheels, the other figure is the flattering probably made up estimate of flywheel BHP to please the Max-Power yoofs and to make sure that customers arent dissapointed and come back.

Back in the late 90s there was a Rolling road guy who never advertised and you could not even get to see except by recommendation of a current Customer, he was brilliant at set up and getting the most from every engine, racers would often have to wait a whole season for session with him.

He refused to ever talk flywheel BHP as he knew how much bull5h1t was out there (and the manufacturers are the worst) he used before and after rear Wheel BHP and for most racers it ultimate BHP was traded off for a good torque curve and driveability, those that hassled him because they really wanted his estimate of flywheel BHP to brag about did not get it and could never get another session with him.

As for your losses, without getting in to what % they may be, the most important ones are sticky tyres and doing a power run in anything but direct drive top gear.

[el-saturn]

it's just a simple addition: which includes mainly friction: dr-shaft, wheel bearings, cv joints etc AND if you ask me there's another deamon to look in to - that's way too much imo sandy switching to a petronics after 35yrs this weekend: from a 25Dsomething cheers (actually drinking an italian sample, so i'm cheering myself!)

[rgh0]

82hp at the wheels is about normal for a standard cam early head S1 especially if done in say third gear.

The 122hp estimate of flywheel power based on that is wrong. You should have around 100 to 105 hp and that lines up pretty well with the 82hp measured at the wheels.

cheers
Rohan

[dunclentdr]

Thanks - it's a QED rebuilt head on 360 cams so was hoping for a little more...

[el-saturn]

....i'd also say 20hp loss: regardless of actual engine power of course! i'd say cv joints add another 5! sandy

[Mick6186]

Are you saying that cv joints drain more power than donuts. If so I'll stay with rubber,
Mick

[rgh0]

Thanks - it's a QED rebuilt head on 360 cams so was hoping for a little more...

OK as its not a standard S1 engine. A few questions to help determine probable HP with a S1 die cast head (i assume that is what it still as) and QED 360 cams.

1. Are valves sprint size or standard size
2. What carb chokes and jetting do you have
3. What ignition curve do you have
4. What exhaust system do you have
5. What compression ratio do you have
6. Are you still using the standard mechanical cooling fan and is it two bladed or 4 bladed version
7. What did the dyno tune person do to the car ?
8. What gear was the rolling road done in
9. What tyres are you using and what tyre pressure was the rolling road done at.
10. Has the block been bored oversize

You should have more than 100 - 105 hp that a standard S1 engine puts out and more than 82HP at the wheels with the QED 360 cams but the rest of the engine needs to be setup to work properly with the cam to get the extra.

cheers
Rohan

[dunclentdr]

Thanks Rohan

You may remember the car, Jeff Rowse owned it and I have tried to add the finishing touch via adding an early head.

Here's my best go at answers to your questions:-

1. Are valves sprint size or standard size - Sprint
2. What carb chokes and jetting do you have - 40DCOE02 carbs, 33mm chokes, 120 mains, 170 airs
3. What ignition curve do you have - runs Ignitor II
4. What exhaust system do you have - think it is standard
5. What compression ratio do you have - don't know!!
6. Are you still using the standard mechanical cooling fan and is it two bladed or 4 bladed version - yes, 4 blades
7. What did the dyno tune person do to the car ? - just set up the new carbs for me
8. What gear was the rolling road done in - 4th
9. What tyres are you using and what tyre pressure was the rolling road done at. - standard 155 Yokohama, need to check pressures!!

Any help welcomed.

David
10. Has the block been bored oversize

[rgh0]

A well tuned in good condition big valve sprint cam engine will give around 95 to 100 hp at the rear wheels. Maybe a bit more depending on how the test is done

So we are looking for why your engine does not give that and only 82 hp or around 20 hp less at the rear wheels apart from accuracy of the dyno itself.

Items I can see are

1. 4 bladed mechanical fan about 3 hp
2. Standard cast 4 to 1 exhaust versus 4:2:1 extractors and standard S1 tail pipe and muffler versus straight through design of later units about 6 hp
3. Unknown advance curve, could be anything but lets say 5 hp for un-optimised advance for the fuel your using
4. Smaller inlet tracts and ports with original dia cast head even if sprint valve fitted compared to later heads approx 3 hp
5. Lower compression ratio of standard head versus big vlave head approx 3 hp
6. Standard tyre pressures on test which are pretty low and lead to higher losses, could be anything but lets say 5 hp.

So its not hard to get down to the measured wheel hp versus what you could have expected. How much of the above you change in search of more rear wheel power depends on how original you want to keep the car.

The other issue is the type of rolling road dyno used and its accuracy. If its an acceleration flywheel dyno ( as many are these days) versus a steady state brake dyno then the maximum power reading is a very short transient measurement under acceleration and may not be be representative of true steady state maximum power. i have never used one of these acceleration dynos and i don't really understand how they allow for the car engine and transmission rotating mass slowing acceleration versus the dyno flywheel rotating mass.

cheers
Rohan

[dunclentdr]

Thanks Rohan

I think a new exhaust at some point and removal of the fan may be the right steps - if that can give me 10% extra without affecting the originality too much would be nice.

David

[Grizzly]

I found the Rotoflex couplings / Cv make a hell of a difference, i had my Sprint dyno'd last summer and i had 24% Trans loss on Rotoflex's (i queried this and the dyno operator had thought my brakes were binding but they weren't on closer inspection) on the second attempt at Christmas with only a set of kelvedon Cv shafts and reduced droop shocks i was getting 18% trans loss.

So read what you will into that.

[prezoom]

I was reading a post about using a chassis dyno on another site yesterday. It was pointed out by a dyno operator the importance of getting both rear wheels in line with the roller. A degree or so off, and you will induce additional drag, which will influence (reduce) the recorded horsepower. He also demonstrated to the vehicle owner by cranking the ratchet tie down straps down one more click, the vehicle gained 2 horsepower. I learn something every day.

Just where do you place the tie down straps on the rear of an Elan or Plus2 when doing a rolling road?

[GuyC]

David, Grizzly,

I had my +2 dyno'd last year and had a similar experience to you both. It is a recently rebuilt, standard engine tuned on a rolling road and then dyno'd at 114BHP with about 84BHP at the wheels. The dyno operator was surprised at the rolling resistance and said it was higher than he expected compared to similar classics. We use him regularly for different cars and his performance figures are always fairly average, so don't believe he's one to make his over-read. I have what looks to be quite an old UJ / rotoflex driveshaft setup so I suspect that to be a contributor, if I go to CV joints I will be interested in doing another dyno run!

[pauljones]

I too have cv joints on mine, i also have EFI, eletric fans, tubular manifold and i believe sprint size valves. A 3.54 diff too
Ages ago i posted my dyno curves, which i can no longer see, 84.7bhp at wheels if memory serves correctly. I did want a little more to be honest but as it happens its a great car to drive and a quick drop to 3rd gives a wonderfull sound and gives me a smile, as well as a safe pass.
Should be simmilar to yours.