Langadorf

If I have to retard my timing 7* to avoid engine knock on pump gas, how much horsepower am I losing (assuming I start around 500HP)? Is there some formula to determine approximate losses?

Matt Gruber

a popular question best answered on the dyno.
you go there on pump gas, do a pull, switch to race gas, advance it 7, and you get the answer.
Dyno tuning tips in my sig. link.

69 N.O.X. RATT

On my motor (454) with 450 rwhp and 470 rwt, 2 degrees cost my 3 pds tq and 7 hp. I pulled the timing out from 36 to 34 to see what it would cost me when I shot a little N20 into the motor

Larry B.

I keep seeing this "retard the timing"topic posted.... Actually it is MUCH better to limit the total timing rather than retard the initial. Retarding the initial serves no purpose other than loss of throttle response, hotter running. By limiting the total with a limit bushing in the distributor, you retain all of the low end power and drivability AND get rid of the pinging.. Of course you do still loose some horsepower but that's unavoidable.

Vetterodder

Actually, it's best to optimize BOTH initial and total, and also everything in between. Optimizing initial is great if you only idle. Once past idle, more timing isn't just desirable, it's very necessary. Though most of us don't spend much time at high rpm, I don't think that many would be eager to give up the serious power losses that would result from reducing total timing in order to have "optimum" initial timing. Recurving the advance curve allows us to "have our cake and eat it too".

Your "11.7" cr is way too high for pump gas and, without reducing it, I think your only option is race fuel. Personally, I'd swap pistons for a lower cr. The power you would gain by being able to run optimum timing would be several time what was lost by the lower cr. While some computer controlled engines may be able to do pump gas with high cr's, they do it by serverly cutting back on timing when they detect knock.

Jason, how much power you are giving up by reducing your timing depends one how much you are reducing TOTAL timing by. If you have a 500 hp (at peak) engine and you reduce advance by 7º from what was optimum, I 'd guess that you are giving up about 50hp. What's the point of paying extra bucks for a more powerful engine if, 1, it isn't fun to drive, and, 2, it can't make the power that you paid for in the real world?

The Dude

It's probably best not to time a retard. The important thing is that he or she tried REAL HARD. And graham crackers. YAY!

Larry B.

I had to take 10 deg. off of the total AND cannot run any vacuum advance. To accomplish that by retarding the initial would have meant 18deg ATDC initial . But that's a BB.....


[Modified by silvervetteman, 5:24 AM 3/18/2003]