Mythbusters - engine & dyno edition

[dieselgeek]

I was reminded of a conversation I had with a pro a few weeks back. He's done A LOT of dyno testing and put many internet "common knowledge" ideas to test. He's my age and we get along pretty well so we started sharing "things we've read that a lot of people believe that we have been unable to confirm"


The first one we talked about was "pulling timing in higher gears when your engine is accellerating more slowly will pick up MPH"

Well, to pick up MPH then you need to pick up power. And a DTS dyno lets you control the sweep rate (rate at which RPM increases). So we should totally be able to test this on their DTS dyno. They have MANY engines of all different power levels that are very repeatable and consistent - so, he tried it on a number of different applications - slow down the sweep rate to EXACTLY match the sweep rate that their Racepak data shows of a car making a pass down the track. Make a pull at the Low Gear sweep rate, then pull timing and make a pull at the High Gear sweep rate. The result? Max Power ALWAYS happens at the same Mean Best Timing number regardless if the engine is accellerating quickly (low gear) or slowly (high gear) or get this - STEADY STATE (engine not accelerating at all). He found that no matter if you're trying this on a stock 6.1 Hemi, or a mild supercharged pump gas big block chevy, or a stock eliminator 6.1 Hemi, or even a superstock altered Gen II hemi - the results are the same. This is a myth that's propagated it's way VERY far into the racing community. Lots of people refuse to believe the results. I bet we'll get that in some replies to this post.


I had to agree with him. I've made and programmed custom ignition controls, set up secondary maps based on gear, and the drag racers swear it's going to pick up mph, but I never once saw this happen at the track. "Must be some other problem" is what I usually hear.


Thoughts? comments? I have a few others we chatted about that he's tested in great detail - I'll save those for a little later :-)

[squirrel]

uhh....why would pulling timing in higher gears when the engine is accelerating more slowly, pick up MPH? That doesn't make sense. Do people believe that?

[TC]

You won't see me disputing the facts, I've had that opinion all along..........

[dieselgeek]

uhh....why would pulling timing in higher gears when the engine is accelerating more slowly, pick up MPH? That doesn't make sense. Do people believe that?

Hiding under a rock? that's one of the biggest beliefs of "top engine builders" racers, etc. There are ignition control systems out there that allow remapping of ignition in different gears. Some speculate that Pro Stock engine tuners/builders use this technique, others say it's done in Formula One. This is huge on the internet among racers - even the nostalgia fueler guys believe this.

[Ron Ward]

Scott, you mentioned timing vs. horsepower. Just out of curiosity, was there any effect on timing vs. torque through these sweeps?

Ron

[TC]

Hiding under a rock? that's one of the biggest beliefs of "top engine builders" racers, etc. There are ignition control systems out there that allow remapping of ignition in different gears. Some speculate that Pro Stock engine tuners/builders use this technique, others say it's done in Formula One. This is huge on the internet among racers - even the nostalgia fueler guys believe this.

I remember a rumor that was going around back in the day about the MSD adjustable timing control(the one with the knob), it was basically to the effect that while at cruise on the highway you could knock back your timing and get better gas mileage.......It was also said it made the motor run more efficiently.......If their's any truth to it I don't know, but I'm sure someone took this low rpm timing trick and figured it was going to work in the upper RPM's to.........

I do say a lot of what is spoken on the internet isn't the way they used to do it back in the day......I mean they were running 9's with locked out distributors, ported factory heads and 4 bbl carbs........It wasn't rocket science, though in today's world one would think it is........IMO tuning a motor for Max power output isn't really needed, if you want to go faster, build a better motor..........

[dieselgeek]

Scott, you mentioned timing vs. horsepower. Just out of curiosity, was there any effect on timing vs. torque through these sweeps?

None.

The dyno is actually measuring torque, then using a simple calculation to arrive at a Horsepower number. It would be mathematically impossible to change the torque at a given RPM without changing the HP. That was a great question though.

Torque will always equal (5252 x HP) / RPM.

Torque will also always equal HP at 5252 rpm too. That's a good way to know if your dyno is working properly or not.

[dieselgeek]

IMO tuning a motor for Max power output isn't really needed, if you want to go faster, build a better motor..........

For the average hotrodder I feel the same way. Freiburger says the same thing about his bonneville engines, run them at 75% of potential or overbuild them by 25%...

But there are a whole lotta stock eliminator, superstock, and pro stock engine builders who do not think this way!

[Matt Cramer]

Glad to see someone put that to the test; I've even heard of things like "top end retard boxes", and it's interesting to hear that those are mostly just shooting yourself in the foot.

I know a lot of sport bikes use different spark tables for different gears, but I suspect that's to help keep it rubber side down in the lower gears.

[JeffMcKC]

Scott I like doing it, and Pro Stocks do it. The reasoning is several things. I do what ETs best. Using more timing in low gear than even shows best power on a dyno will launch a car better, but in high gear it starts to have too much timing, and kicking the piston back. Now figure in also combustion chamber temps and latent heat.
DG lets say you’re at the perfect temp on the line, and at 60', how much heat does the chamber see at the end, do you need to start the fire at the same place to get it to end at the right time?
When you’re reading the timing mark on a Plug, I see that as Combustion timing not ign timing and you have seen why. If you want that mark to stay in the same place all the way down the track as the temps go up, it has to be pulled back or fuel changed. Jakes red car has more ign timing in it than came off the dyno, and the ET picked up on it on the bottom end but killed mph, then pulled it in the upper rpm range and the mph came back. Don’t confuse the the why pulling, sometimes its adding then bringing it back to the dynos timing, think of it as over timing, also we do it on gears but its also controlled as rpm as with anything lots of combos to get what ETs best.

This is why we dont race dynos, they have there place, but finding what ETs best is not the place.

[JeffMcKC]

For the average hotrodder I feel the same way. Freiburger says the same thing about his bonneville engines, run them at 75% of potential or overbuild them by 25%...

But there are a whole lotta stock eliminator, superstock, and pro stock engine builders who do not think this way!

They cant someone will always make 115% VE

[BBR]

I always thought it was a pump gas trick to ward off high load/down track detonation.

[dieselgeek]

Scott I like doing it, and Pro Stocks do it. The reasoning is several things. I do what ETs best. Using more timing in low gear than even shows best power on a dyno will launch a car better, but in high gear it starts to have too much timing, and kicking the piston back. Now figure in also combustion chamber temps and latent heat.
DG lets say you’re at the perfect temp on the line, and at 60', how much heat does the chamber see at the end, do you need to start the fire at the same place to get it to end at the right time?
When you’re reading the timing mark on a Plug, I see that as Combustion timing not ign timing and you have seen why. If you want that mark to stay in the same place all the way down the track as the temps go up, it has to be pulled back or fuel changed. Jakes red car has more ign timing in it than came off the dyno, and the ET picked up on it on the bottom end but killed mph, then pulled it in the upper rpm range and the mph came back. Don’t confuse the the why pulling, sometimes its adding then bringing it back to the dynos timing, think of it as over timing, also we do it on gears but its also controlled as rpm as with anything lots of combos to get what ETs best.

This is why we dont race dynos, they have there place, but finding what ETs best is not the place.

I hate to have to say it, but my opinion will remain: Power is Power. Also, I am not so sure that Pro Stockers pull timing on the big end. David is involved with a number of pro stock teams and says that the rumor is strictly BS.

Too much timing reduces power - ask anyone who uses an engine dyno. Too little timing loses power. If you want max power all the time, you run the same timing, period. I'll change my opinion when I see different. In the end, it's all about having fun anyways so, no hard feelings! ;-)

[JeffMcKC]

Never is on my end Scott, sounds like we need to take my junk to Toms and baseline it. Then to the track and move timing up in low and down in second and high see what we do in real life. Return my call LOL I got some questions, I knew you when I got call backs LOL

[JeffMcKC]

question scott if a turbo car makes max power at the salt flats at 40 lbs boost and 30* timing do you run 30* timing for 4 miles because the 15 second dyno pull says it made the most power there or does the heat come into play so you have to cut it back as temps raise to keep the same power as at the start of the run.

We need 100% power "Giving it all she has Captain" says Engineer Scott full thrusters and all that to set the Record for the whole run.