Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - timing advance on a lightly built 350 (300 horsepower)
View Single Post
  #5 (permalink)  
Old 09-15-2011, 11:54 AM
cobalt327's Avatar
cobalt327 cobalt327 is offline
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Posts: 5,031
Wiki Edits: 1616

Thanks: 128
Thanked 616 Times in 565 Posts
Originally Posted by Ocean-Angler
street driver.. is this because I got the MSD without the vac. advance?
And the reason I did that, is because I found a good deal on a CRANE HI6-N ignition box, which required a very specific MSD or other dizzy, but the MSD version didnt have the vac. advance...
To start with, having no cam specs and not knowing what the real compression ratio is, along w/no idea (I'm guessing) what the quench distance is, there's gonna be a lot of guesstimating going on here...

Having a vacuum advance has far more advantages and basically no drawbacks on a street driven engine. It aids economy, it will allow a cooler running engine, at idle especially. It can help smooth the idle. Definitely a good thing to have.

I can put in the diff. springs, and the diff bushing and get the total timing in around there... really though? that low of RPM?
Basically, you want as much timing advance, as soon as possible- w/o the engine detonating at all. Detonation (pinging) will kill power the moment it begins and in severe cases will ruin an engine outright. To answer your question, no- 2800-3000 RPM is not to low of an RPM to bring the total in by. BUT, this will depend on a lot of things: vehicle weight, use, fuel octane rating, gear ratio, carb tuning, etc. There is no number that's correct for all engines. The numbers given are a starting point from where you will add and subtract timing as required to keep the engine out of detonation and making the best power.

Well the heads were stock with the 76 CC chambers. I had .35 thous. milled off them, so I factored that the main bearings are probably a little worn and instead of sayin 9.5 :1 I guess its .. 9.25 :1 ish...
First, there is no amount of main or rod bearing wear that will ever be great enough to cause a significant change in the compression ratio.

To compute the CR you need to know the head gasket and cylinder bore diameter, the stroke, the piston deck clearance (how far down the hole the piston is), the head gasket thickness, the piston volume and the chamber volume. If you don't know these figures, you're guessing and the difference could easily be more than a 12% variation.

The large chamber SBC heads are crappy flowing and the chambers are inefficient. Given that, the work you did may or may not have actually helped flow- w/o a flow bench, this is a crap shoot once you alter the stock port profile. Just cleaning up the ports and port matching the heads to the intake can help.

I seem to get that you didn't get a valve job done. And that means that likely the guides are also untouched. These two areas are wear points that have to be addressed on every used SBC OEM head I've ever seen. The guides always wear and are loose after being used for any real length of time. The seats being done correctly w/a multi-angle valve job and back cutting the valves will give you more flow increase at the lifts where it matters most, than most anything else a home porter could ever hope to accomplish unless the home porter has a lot of experience and/or has served under a pro.

He suggested in the cam, its a notch above stock, split duration.
What are the specs from the cam card?

Headers are 3/4 length. not full length, not block huggers.
Always use long tube headers any time they CAN be used. The shorter headers leave power on the table.

will be changing the stall to a serious billet machined 2600 Loose stall when I get the ignition system dialed in
I doubt seriously you need a billet torque converter! Use a good TC builder and get a TC that has a stall RPM that about matches the torque peak RPM of the engine, or slightly lower. That does not mean the TC will rev to the torque peak every time you pull away from a stop sign. It will mean that when there's traction and you mat the throttle, the TC will flash to where the engine is making the most torque for the best launch.

Last edited by cobalt327; 09-15-2011 at 12:03 PM.
Reply With Quote