General Category > Quadrajet Carb Talk and Tips

350 having detonation problems.

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Greasy Harley:
I actually loaned my distributor to a friend that needed to get his truck running.
As soon as I get it back, I will experiment with different timing.
I have been doing a lot of reading about tbi heads, swirl port heads, compression ratios, quench, cams, etc.
I will try to tune it before I throw more money at it. I'll update this post when I know something.
Thanks for all the help

-Russ

tayto:
keep us posted. my engine is currently a short block with no oil pan or timing cover on and i won't be getting around to reassembling it for another month. if a cam change is in order then would be easier to do it now before i button everything up. i have a 2 piece timing cover and LSx style lifter trays, so changing a cam in situation will be easy. remove rad, waterpump, rockers, crank pulley, rotate engine twice and pull cam. dont need to remove intake or oil pan (in theory)

tayto:
BTW what octane are you running? 87?

Cliff Ruggles:
I have been doing a lot of reading about tbi heads, swirl port heads, compression ratios, quench, cams, etc.

The more things you do to make the engine efficient the LESS timing and fuel it will need to make optimum power.  Less octane as well.

There are quite a few "players" in the deal, static compression ratio, shape of the piston tops, combustion chamber shape, cam size and timing, intake/exhaust efficiency, quench distance (the big player), engine temps, etc.

These days we shoot for .035" quench distance and never over .040" for any reason.  We also run high compression ratios than most folks do.  Like many other things associated with this hobby folks continue to regurgitate old/outdated information.

The proverbial "brick-wall" of 9.5 to 1 for pump gas is at the top of the list.

Inaccurate information in other areas that make the list are "upgrading" to a double roller timing chain (the stock Morse type is at least twice as strong), high volume/high pressure oil pumps (they just cost power and reduce timing chain/distributor gear life and can shear the drive shaft).

Another big myth is upgrading to a bug-zapping ignition system.  Stock type points will make the same power as HEI's if not a tad more (natural high rpm timing retard) and last 25-30,000 miles without issue.

In recent years I've yanked out and round-filed more Petronix units than I can count, and not a big fan of MSD stuff either.  It works OK, but NEVER takes a chit when you are in front of Jegs or Summit stores.

Anyhow, I'd tune the combo so it doesn't ping even if you are ending up with at or slightly less than 30 degrees total timing.  Avoid light springs and goofy weights in the distributor, a timing curve starting right off idle and all in around 2800-3200rpm's is adequate.  Use vacuum advance and be conservative until you find the ideal amount to add at light engine load.

Most well thought out engine combo's I build or tune here will like about 10-14 degrees initial timing, 18-20 mechanical, and 10-15 from the vacuum unit.  I seldom use manifold vacuum to the advance and never try to "crutch" a lumpy idle with a ton of initial timing.

A very well though out engine build isn't going to like, want or respond well to tons of timing at idle speed, I don't care what the "guru's" tell you on the Forums........Cliff

Greasy Harley:
So, I finally got back around to working on my truck.
Here's what I know;
I reinstalled the MSD street fire dizzy. (might swap that out later, we'll see)
I set the initial timing to 4* without vac-adv
mechanical came in at 25*
set the vacuum advance for an extra 10*
and my timing at idle jumped to 15* with vac-adv attached

Seems happy, idles smooth, decent torque, starts easy.
Probably not 100% dialed in, but it is a solid starting point.My truck runs great with the original cam and heads, No parts swapping required
There is no pinging and it has decent power. I'm gonna leave it here, at least until the engine is broke in.

This has been a learning experience, and I have had to admit that I might not understand timing and combustion quite as well as I thought I did. (I know a little more now though ;)  )
I'm glad I listened before I started swapping parts.

Thanks for all the help,
-Russ

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