The dyno may compensate for the gearing, but.................

You're also spinning up the flywheel and 2 wheels (plus everything in between) which the dyno can't compensate for because it has no idea of the mass's and inertia of all those pieces..........

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

My dyno operator does all pulls in second gear, but the sheets do show mph.
Will

The one time I was on a dyno, they had me do my pulls in 2nd gear as well. Did not shift to 3rd. I need to dig the printout out and look it over some more.

Brian

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Flyin' Brian

74 Duster, 225, rear-mounted blow through turbo at 12psi boost, street/strip car
"Sixy Beast"

I have wondered about this very subject for years. Very interesting discussion. I certainly can see Billdeman's point. It seems as if the entire drive train effects rear wheel HP. Why not gear ratio as well? It is rear wheel HP after all. It might be fair to say one conclusion you could draw from this discussion is that it is questionable to compare dyno readings from different set ups. They would have their greatest value in comparing readings for tuning purposes on the same set-up. Do a pull; tune; do another pull; compare. But for two people to compare dyno sheets done in different gears on different dynos? I don't know about that.

Lobster, I am delighted the turbo is working. It seems like you have picked a good cam. I probably should have consulted with the slant forum for my cam selection instead of the cam grinder. I think my cam was what made it so pre-inition prone. Stay away from complex electronics in your ignition. That seemed to be another downfall of my set up. I was trying to fix the cam problem with electronic timing control. It never worked right as a result. It seems you are headed down the right path. Keep us posted.

Sam

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Yes I'm learning from this thread too. It looks like my understanding of the gears and horse power were wrong.

Couple thoughts about pre ignition/detonation... PSI, the shop that tuned the car on the dyno was super concerned about detonation and spark suppression. When I called to set the appointment they grilled me with a lot of questions and had me make some changes.

Per their request I replace the plugs with 6's (heat range) and gapped them at 30. I also hooked my fuel pressure regulator to vacuum. Now my fuel pressure is relative to vacuum or boost. Otherwise the mixture could lean out under boost.

The distributor is still set at 10 advance with no pre ignition.

Sadly I have not been driving. We are having the coldest weather in years, which is probably not what most of you would consider cold. But I don't want to change my oil and thermostat, so I wait...

Cheers,
Barnaby

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These ones go to eleven...

I think some of the tech articles presented in the link below may be of interest for those following this thread. The articles are written by Stewart Sandersen, some on his own and some from the Fast Ford Magazine in UK. Even though many have a Ford focus, the general tech info is always interesting, there are lots of info on turbos, EFI mapping, and also on dynos...

http://www.motorsport-developments.co.uk/stus.html

Enjoy.

Olaf

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Aspenized

In all honesty, a chassis dyno is a tuning tool. The numbers you get are just that, numbers. They can vary widely depending on how the software is set up or even who is operating it. General rule of thumb is 15-18% loss at the wheels.

Mike used to make all pulls in the highest gear the motor could pull.

The one where I worked was a Dynojet. It did record RPM as well as MPH and time. MPH was figured by how many revolutions the drum made in X amount of time. A dyno really needs an A/F meter on it too to be of any use.

Gearing will affect readings, but not as much as you'd think. Torque converter will tend to skew the numbers more than gearing, especially if it happens to be a loose one.

So, don't get too wound up in pure numbers off a chassis dyno. They may be good for bragging rights, but the only real numbers that count are the ones on a time card from the track. The lights there don't lie.

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Official Cookie and Mater Tormentor.

Is that 10 advance initial, with some centrifigal, and some vacuum advance? What is your total at WOT and 2000 rpm? Is this EFI? Do I remember you saying it was throttle body? When I first met Lou, his '64 had TBI, and it seemed to work very well. Your 220 hp is a good first dyno result. Mine was 180, with a miserable tune, by a guy who did not know what he was doing.He was supposed to be tuning it. It would hardly drive home, but showed 180 RWHP on the dyno.

My car has been sitting as well. We have had miserable weather here in the North East. Not as bad as you guys in the north central part of the country, but too bad to drive a classic RWD hobby car. I was going to make this transmission change a mid winter project, but since I have not been, and likely will not be driving it soon, I might as well start pulling the manual tranny stuff out soon. Hang in there. Spring is coming. Nine days from the Winter equinox and counting.
Sam

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