weaz4200

iTrader: (2)

Question for the guys who have done the L03 305 LT1 cam swap, ditched the fuel injection and went carbureted. Where did you end up with timing? Initial/total and vacumm advance/ ported/manifold?


I have a 305 in my 92.

Lt1 cam
081 heads
Street dominator dual plane
600 cfm vac secondary holley
72 jets/6.5 power valve/red pump cam/31 squirter/long yellow spring on secondary
Mallory fuel regulator set to 6 psi
Stock pump in tank
R43ts plugs

Stock 700r4/converter. Stock rear/gear. Stock tire.

I get 20 in of vac @ idle
The HEI has 20 degrees of mechanical and 8 degrees from the vacuum canister.

Right now timing is 17 initial plus 8 vacuum advance from manifold.

Its runs alright but wont roast a tire at all.. plus it pulls good to 4K rpm then flat lines after..

Wanna hear opinions. Timing? Spark? Fuel?

thanks.

Fast355

iTrader: (2)

37° total is too much advance for those heads. Pull it back to 14° initial for 34° total. If you want to roast the tires you need a S10 torque converter and 3.73 gears. That cam and head combination should pull well to atleast 5,500 rpm provided the valve springs are not worn out and the cam is correctly timed.

weaz4200

iTrader: (2)

I'm confident the cam is installed correctly.. maybe the valve springs are worn.

I dont mean roast in the sense of a race car.. I just meant I cant even slightly smoke them compared to the way the stock 305 was factory.. if i floor it from a dead stop it wont even chirp the tire.

so 14 initial and 34 would be all in at 3000 rpm with the distributor springs i currently have.

where does vacumm advance come into play? I have an adjustable canister which allows from 8-25 degrees vacuum advance. Do I use it at all? If so how much would you think to start with? Manifold or ported?

Thanks.

Fast355

iTrader: (2)

I would work on trying to bring your timing advance in more quickly if you can. I am assuming you are running 2 medium weight springs at the moment. I would try one medium, one light spring. That should bring the timing in by about 2,600 rpm. As for your vacuum advance, I would shoot for about 48* total at 3,000 rpm with no load. If you are getting full mechanical advance of 34* by 2,600 rpm, that means you need 14* of vacuum advance. I prefer manifold vacuum. With 14* initial and no mechanical advance at idle, you should be 28* at idle at that point. You will need to make a couple full load, full throttle pulls and read the plugs to make sure you do not see signs of engine damaging detonation or lean running.

weaz4200

iTrader: (2)

I'm running the lightest black springs in the kit I have. I believe it's the 929G kit.. I do have 2 distributors though. 1 in car and other spare. So I have 3 sets of weights to look at.. I'm not sure if theres a weight difference between them but I'll weigh them.

Now. If for whatever reason the weights are same and dont help to get all in at 2600.. then is there a recurve kit you recommend that has lighter springs?


how does that work? Can you adjust vacuum advance based on rpm? Explain please.

okay. I checked yesterday and my adjustable canister gives me an adjustment of 10-25 degrees to use.

Thanks.

Fast355

iTrader: (2)

Total advance is a combination of

Initial + Centrifical + Vacuum

At WOT you do not have enough vacuum to activate the vacuum advance so it is Initial + Centrifical.

weaz4200

iTrader: (2)

I understand that. What Im unclear on is... Then with vacuum advance shoot for 48 total at 3000 with no load.

that I dont get.. after I set eveything.. do I rev it to 3K rpm in park and see if I get 48 degrees? Or does it just fall where it falls? How do I verify 48 @3000?

thanks.

Fast355

iTrader: (2)

You can verify it with a dial back timing light by holding it at a point above where the mechanical advance is fully advanced. It was more of a point of reference than anything. Some engines tolerate more or less advance and no two are the exact same, but I have run a very similar combination and that is where I ended up with the best results.

I have a Vortec 305 with a Lunati 268 cam in a 1999 Tahoe. The main spark table is setup to give the equivalent of 20° initial, 12° mechanical by 2,600 and 10° vacuum by 10 in/hg.

NoEmissions84TA

iTrader: (1)

The only advance curve kit you should buy is made by Moroso. Their weights are glass hard.
The cheap ones have soft weights and will wear in a short period of time, causing you to
pull your hair out trying to figure out why your engine is behaving in a strange manner.

weaz4200

iTrader: (2)

Gotcha. Thanks. I'll see what happens when it try what you said.

kit# 72300?