Dyno Tuning - Expectations and Checklist

[REDSC400]

I hope to soon bring my Cobra to a chasis dyno tune shop here in Connecticut. Three years ago, I had the car on a chasis dyno machine to measure RWH. It was essentially a 3 pull event.

My hopes are to actually have the dyno tune shop help me with fine tuning the ignition, timing and carburetor using the chasis dyno as one of the tools to achieve a good tune.

To that end, does anyone have a sort of checklist that I and use as a talking document with the dyno technician?

I would imagine that a baseline and incremental adjustment steps would be necessary to dial in the best parameters.

If you have gone thru this with your Cobra FE engine, I would appreciate any and all feedback and thoughts. I would rather not be in a position of wishing I had thought of something to have done, after the fact.

Thanks in Advance....

[wtm442]

1) Do a tune up NOW. Plugs, cap and rotor.
2) Fill up the tank with premium.
3) Bring your vacuum gauge, timing light and carb parts with you (jets, cams, squirters).

Call the shop before hand and ask if they will provide what you are looking for - a dyno tune, and not just 3 pulls.

I would never make more than one change between pulls. If you make 2 or 3 changes (jets and timing, for example) and the HP does not change, it could be a big gain with one of the changes and an equal big loss with the other change.

[DavidNJ]

Ummm...Barry should chime in.

You should pick the shop to tune the car. They will either have or have access to a dyno. And should have the various jets, power valves, etc. for the tune. They should also have other tools, including a wide band O2 sensor coupled with the dyno.

Also talk with them about fuel. If you are pulling timing because of detonation, it is sometimes better to start with race gas and remove the detonation issue. Then, when the best settings are found, determine if detonation is an issue.

The other issue is weather dependent. I was just corresponding with someone who builds off-road racing engines, and temperature and altitude changes during a race apparently cause mixture issues that put extreme stresses on an engine. The weather on your tune day could be an issue.

I imagine Cobra owners in Arizona and Colorado have similar problems.

[REDSC400]

Thanks Warren and David, the dyno shop I am using is associated with the engine builder that built my engine some 14 years ago. I will double check to make sure he has all the necessary carb parts for my tune.

What does a wide band O2 sensor indicate? Lean or Rich fuel at speed?

I do not use the car for racing, just spirited cruising.

thanks

[stush]

Art,

Are you going to the shop in Danbury?

Stu

[REDSC400]

Hi Stu,
Yes to Jeffs next door to Danbury Competition Engines.
Perhaps next Friday, as I am taking the week off.
Should be fun.

Stu, a few of us are going up the Monroe CT cruise tonite (Friday) you game?
Art

[Power Surge]

Well, as a dyno shop owner myself, here's a few tips...

- Make sure the car is mechanically sound. The last thing the dyno shop wants to do, is chase down mechanical issues while trying to tune the car.

- Find out if they have the parts to tune the carb. I stock a full Holley jet selection, as well as the non-stick bowl gaskets and other assorted parts. If they don't have them, you'll need to bring them yourself.

- Make sure they tune the car in real world conditions. Don't tune the car with the air cleaner off, unless you plan to drive the car with the air cleaner off. Make sure they have a fan in front to simulate road wind and keep the car cool.

- Prep the car before going. Make sure you have the gas you want in the car. If you've never taken the bowls off the carb, get a set of the non-stick bowl and metering block gaskets, and pull it all apart yourself first. It takes almost an hour to pull it all apart and scrape the dang stock gaskets off. It's free if you do it yourself ahead of time. You'll pay for it if they have to do it on the dyno. Make sure you rear tires are at proper pressure, and equal.

- Make sure they pull the car in whatever gear is 1:1. That should be 4th gear, for both a toploader or a 5 speed trans.

That's pretty much the basics. How well they tune the car will depend on them. I've been flown to dyno shops all over the country for tuning by car clubs, and it still amazes me how clueless some of these places are. Just pay attention to what they do. If you have a decent knowledge of this stuff, you can easily see if they know what they are doing or not.

Hope this helps!

BTW, Stu, I have a question for you... was 4241 a single or dual carb motor originally?

[stush]

I would have been up for the cruise night in Monroe but we are on vacation. Another time. Let me know if you change your day at the dyno place. I may be a ble to swing by from work.

Stu

[HSSS427]

RedSC400 - Please post the results of your dyno session. Eager to pick up any tips and findings!
Thanks!

[Barry_R]

I am by no means a dyno expert - but I have participated in a few sessions from time to time. Do everything the other guys said. I have seen numerous times where repairs are being made on the dyno, where the guy showed up with 87 octane, and were they did not have any kind of plan.

Thats something not yet touched upon. The plan. You should have one. And you should pay for and get enough time to do the job without feeling rushed or like you need to come back again. You need to make two pulls for each variable to establish the direction for any change, and likely a third (or fourth, or more..) to verify the degree of change that delivers the best results. Those places that giev you three pulls are only good for bragging rights - you can't really learn anything meaningful in three pulls.

On a chassis dyno you are generally looking to "fix" two variables - fuel and timing. They are interrelated, and when one changes the other might want to change too.

My tendency is to start off with the timing in a "safe" spot and try to establish a smooth, predictable and reactive fuel curve. What that means is that when you change a jet by two steps the O2 sensor will show that change in the entire curve in a consistant fashion without bouncing lean or rich. This may require float level changes, fuel pressure changes, or on fussy carbs you could end up chasing around with air bleeds. 99 times out of 100 a bone stock Holley will be just fine - - other than being rich. We're not after best peak - or even best average numbers yet - - we just want to get the thing to respond predictably to changes.

Now you have a tuning baseline. Push the timing up and see what happens? Happy? Try more. Sad? Go the other way. You will find a happy spot - - lock things down and go back to fuel. Same drill - - but here you also have that O2 sensor to give you more directional data. Its nice to have - but as long as you don't hear bad things and the meter is not in some crazy 15:1 danger zone (safe ratios are usually in the mid-high 12:1 range) its more important to give the engine what it wants for average power. Peaks don't mean as much as does a nice linear curve. Go back to timing and fine tune/check that now - - your close or there

If you have time/gas/money left - - now is when you can play with other stuff to see "what if" - - pull the air cleaner and make a pull. Open the headers and make a pull. Don't optimize around the tweaked stuff - - use it as directional info for future plans (ie I really need to find a free-er flowing exhaust...).

Above all don't get too stressed out and have fun. Dyno time is cool.