I have noticed with the new motor now that I have some seat time with it I am getting what seems to be some knock. Very hard to hear over the exhaust but now with the top up it sure sounds like it. I did not think I would get into knock with this big of a cam 252/260 @ .050 duration. My old motor the stock LT1 bottom end with a supposed 9 to1 pistons and a cam of 248 @ .050 I could run crap gas and not get it to detonate. Now I have more compression, a true 10.4 to 1 and with this cam I am just getting a slight bit of knock. Right now the timing is at 36 degrees total and I might back it down to 32 or 34 to see what happens. Or I might run some Octane boost. It has been a while since I bought some boost. What is a decent brand if I need it?

 

Is 10.4:1 your static cr? When you get detonation you must retard the timing. As far as octane boost is concerned, I'm not too sure which work, most OTC products raise the octane by a few tenths.
I posted a two part question back in February asking the question why todays vette (11.00:1 cr) can run on pump gas and why the older vehicles detonate and about octane boost. You can buy toluene from the hardware store and mix it with the feul you have. The thread has also formulas as to how much toluene to add to the feul and the octane ratings.

 

Here is some more info. http://forums.corvetteforum.com/show....php?t=1487527

 

Am I getting old, or was that Deja Vu? Am I seeing double?

Good question about the newer engines and higher compression ratios running OK on today's gas. I guess that the ethanol in the gas isn't helping our older cars much, and that the newer cars computers can adjust themselves for these conditions?

I have heard of a place where you can buy racing fuel, but it costs plenty.

 

Octane boosters are for the most part useless. The can will say "1 can to a tank raises your octane 3 points!!!" That is not 93 octane to 96 octane. That is 93 octane to 93.3 octane. And if you use toluene DON"T GET IT ON THE PAINT!!!It will trash it before you can blink.

 

simple how it is done - computerized ignition systems! if it detects detonation it automatically retards the timing back. The computer can adjust the system instantly and constantly.

on the other hand my stock original '65 L76 is 11:1CR and it runs fine on pump hi-test 93 octane with no detonation issues with timing at 36º.

 

Gordonm, are you running a vacuum advance ?

 

Gordon, I agree with 63Mako. The octane boosters you find at PepBoys, etc are useless and nothing but snake oil. At best they increase octane rating by tenths of a points, not the full points that the labels lead you to believe.

if you are at 36º total timing now and are detonating I'd lower the timing 2º at a time until it stops. If your knocking is only slight when under heavy load it will probably only take 2º, maybe 4º, to eliminate it.

 

No I'm not running it now.

 

Back off the timing, make sure it's detonation you are hearing, take a close look at a plug or two

 

Your hearing knock,how about pinging?

 

Not exactly sure. It is only happening on hard throttle in the upper rpms. The AF ratio is good but with a cam of this duration I thought it would bleed off enough cylinder pressure. I'll have to back off the timing and seewhat happens. The weather is crappy here today so it will have to wait a day or so.

 

The best solution would be to run higher octane gas. A mixture of pump gas with race gas or aviation gas would do the trick. Your big cam DOES bleed off compression at lower RPM's but the longer duration is intended to enhance volumetric efficiency at high RPM's. That is, the intake valve closes later in order to take advantage of the momentum of the air and fuel entering the cylinders. If you have to run on pump gas, try retarding the timing a bit. You will be sacraficing some power, though, and that is why you built your motor the way you did in the first place. When you go to the track, advance timing and run good gas to take full advantage of your setup.

I've never had good luck with the Octane boosters that are commercially available. A friend of mine bought some TEL lead booster from a guy advertizing in Hemmings Motor News that he swears works, but I'd always had the best results buying aviation gas at the local airport. Haven't done this in a while so don't know if they've regulated this any more than they used to. It used to be that you could just carry a couple of 5 gallon cans up to the pumps and they'd fill them up.

 

I've had great success with a product called octane supreme 130,I believe it was known as lead suprem 130 a few years ago.It's the only one that really worked for me.