Hotdog1958

I just bolted in a new, LS 364/440 - it has flat-top pistons with 10.9:1 compression -.500/.500" lift cam, Holley 770 street avenger carb in my 69' Camaro. Brand new, crate motor from GM performance.

With a Trimec 5 speed manual trans,
In 4th gear on fwy @ 70 mph is about 3000 rpm,
In 5th gear @ 70 mph is about 2000 rpm

Problem is I'm getting pre-detonation when I step on it.

Today, I heard it maybe the carb? I've been told its starving it of fuel, and my carb choice was not correct?

I don't want to damage the engine, it sure doesn't sound good and I can't be doing it any favors.

Any suggestions and direction would sure be appreciated.

Pop N Wood

iTrader: (1)

Typically that is caused by poor quality (low octane) gas, going lean, or too much ignition timing. It can also be things like hot spots or casting flash in a combustion chamber, but most likely it is in your tune.

So run 93 octane gas, and check for vacuum leaks. I assume you have the GMPP single plane intake that comes with that motor? Then tell us what timing curve you are using (pill number or custom curve), if you have a MAP sensor hooked up, and what you did to tune the carb.

That vac secondary street avenger should work just fine, but may need to be dialed in a bit.

Hotdog1958

I was questioning the octane.. I've run about 3 tanks thru so far (only about 300 miles on the engine) 1) with Shell 92 octane, and the last 2 were chevron. Not sure where to get 93 octane, what about a booster?

I have the MAP ignition. I started with the Number 1 module, and have gone up 2 times, now at the 3 sensor.. (i think I have 6 total)

I really have not tuned the carb.. as i'm pretty much a layman in that area. I can bolt things together, but havn't the experience re-jetting and such.

speedtigger

iTrader: (16)

Sorry to be a stickler, but just so we are on the same page, the term is either pre-ignition or detonation.

^^^This is it. It is almost certainly in your tune. Establish a safe timing curve first, then go after your A/F ratio.

There is, however, one more variable that comes to mind. That is your engine may have air trapped in the cooling system allowing the heads or upper cylinders to overheat. Check to make sure you coolant bleed in your heads are plumbed properly AND ARE FLOWING. Mine were plugged up with junk when I got my motor and had to be drilled out to get them flowing. But, my motor was used.

Pump gas premium should be more than enough octane for your combo.

The modules suck. I hope you have the MSD box and not the Edelbrock turd. The MSD is fully adjustable, the Edelbrock is not.

If you have the MSD set your total timing above 1000 RPM to a flat 26 degrees and try that. You can increase the timing later if the car likes it after you have the fuel and cooling all dialed in.

Pop N Wood

iTrader: (1)

I think we have 93 octane in my area, so if the premium in your area is 92 then that is good. I have the exact same motor and trans in my car btw. I run a 750 DP with mechanical secondaries though.

Yeah, start out with one of the lower numbered pills and get your carb dialed in. Do yourself a huge favor and get a wideband O2 sensor. Absolutely invaluable to tune with. In fact, if you tune without one you are either really really good or just guessing.

Double check for vac leaks first, a quick google search will tell you how. Make sure all the vac and PCV ports are properly plugged. You might have a gasket leak or clogged jet/air bleed in the carb too. Is it new or used?

How did you set your idle mixture screws? With a vacuum gauge? Float level? Sure your fuel system is flowing OK? You need to step through all the basics with a new build.

If you want to dart board and see if you get lucky, go up two sizes on your main jets. Make sure you keep good records of everything you do so you can get back to stock configuration should you go the wrong way.

The stunningman

iTrader: (47)

Stick shifts are harder to tune than autos due to the direct load instead of the build-up slip of a stall.

Like speedtigger said if you havethe edelbrock box... Give up. Do yourself a favor and get the MSD so you can actually tune it.