Retarding ign timing

[rocketracer380]

I’ve heard of racers pulling ignition timing on top end any benefit to doing this is it worth any hp is it better for mph and what type of gains should i expect how much should I pull out motor is a l88 with a roller cam in a 3000# car have gone 135 with mufflers my total timing was 24 total due to improper set up of crank trigger next time out same engine uncapped only mustered up 131 with 38 total 135 was with the wrong 1150 131 was achieved with a 1050 which in my opinion were way too big the general consensus is that the difference in mph was the result of the retarded ign timing but 4 mph is substantial gain and the car had 3 1/2 “ flow masters on it I would assume it would’ve picked up more uncapped engine combo as follows 12 1/2:1 comp std bore .725 comp roller factory stock gm round ports basically an l88 with a roller had big 2 1/4 primary’s

[1980RS]

Might help on an engine that makes big power, compression and camshaft but on my low compression I have retarded timing 6 degrees or more and have seen nothing at the track.

[steve cowan]

Might help on an engine that makes big power, compression and camshaft but on my low compression I have retarded timing 6 degrees or more and have seen nothing at the track.

Its been said that potential detonation can occur around peak torque, I have played with timing retard from 4500rpm -5500 rpm going down the track and also high speed retard where you can feel it lay over slightly with minimal change in et or mph.
Maybe we need to put timing into the engine at the big end ?? Maybe the timing is jumping around even with a crank trigger,
We are only seeing when the timing light goes off not when the mixture is firing or at least trying to fire

[novafornow]

I think that the only way that you will benefit is if you add more timing and then remove it in high. It has to do with the rate of acceleration.

[Biteme]

My thinking is that after peak torque the volumetric efficiency, and hence cylinder pressure drops, and also the time available for the flame to creat pressure is diminishing, so an engine will likely need more timing in this area of the rev range.

[BOOT]

I always thought it was kinda heat build up higher rpm/duration for advancing

Think sometimes for retarding it's a band-aid for a fuel system issue, as with many things you don't know unless you try and it may work for others n not for some.

[David Redszus]

My thinking is that after peak torque the volumetric efficiency, and hence cylinder pressure drops, and also the time available for the flame to creat pressure is diminishing, so an engine will likely need more timing in this area of the rev range.

At higher rpm, there is less time for combustion. But at higher rpm, the flame speed increases due to chamber
turbulence allowing the higher engine speeds.

At higher rpm, the combustion chamber/pistons, valves, etc, run hotter (more heat strokes per unit time), and we
retard ignition timing to reduce chamber temperature but increase exhaust gas temperature.

A major factor in determining ignition timing is the ignition delay period. Since the delay is a fixed period of
time, higher engine speeds require more advance to compensate.

All in all, ya gotta know when to hold em, know when to fold em, and know when to run.
And hope your engine simply wears out.
Gracefully.

[Tuner]

The trick of retard in high gear evolved in the type of drag racing where you could chill the engine between rounds, "go to the hose", so for each pass the cooling system and cylinder heads and intake are cold but the oil is warm.

I don't know about nowadays, but back in the day the rules said you have to have the fan and fan belt but didn't say the belt had to be in the pulleys at the end of the pass, so if it derailed, rolled over like a trained seal and jumped the groove, it was just a real shame the water pump didn't circulate the hot water to the radiator where it would heat the underhood carb intake air and slow the car.

We all know cool air intake makes more power but some stock class applications must use underhood air intake, so hot air from the radiator is a disadvantage. Some unfortunate folks might have had a misaligned alternator mounting which caused the belt to hop off at some high RPM, such as 5500 or so, and hang on the fan so it doesn't fall off the car, which would be a foul if something falls off the car onto the track.

With the arrangement of cold water in the cooling system and block and heads, the car is pushed to the burnout box, fired and rolled into the water where spinning the tires to clean the heat them derails the belt at the designated RPM so the water stops circulating, then stage immediately and make the pass.

Leaving the line with the heads cold wants perhaps 10 or 12 degrees more advance to have the best launch and 60 foot time, perhaps 44-46 degrees, then 7 or 8 seconds into the pass and in high gear when the heads are hot because of no water circulating and retarding to 34 degrees or so gives best MPH.

Such an arrangement would be reasonably appropriate for a 300 HP 327 or similar engine. Believe it or don't, 40-50 years ago we were doing this with dual points and a toggle switch. The Delco dual point distributors with D-112P points that adjust with a hex key Allen wrench made it easy to fine tune the timing split and the D-112P points would easily go past 8000 RPM with stability and accuracy.

Needless to say, this deal required strict maintenance, double checking with a timing light between rounds on race day and checking the distributor in a distributor machine between race days.

To get this timing split right and use an advance curve that added 1.5 deg per 1000 RPM through the power band was worth more than 1/2 second over a simple locked timing or the usual "all in at 2500". The scheme is outlined in Grumpy Jenkins Chevy Racing Engine book.

The fortune cookie said, "You will be fortunate to live in simple times."