i am tring to acheive 32 @ 4,000 timing.
My question is this if I can get that with initial and centrifical, should I lower the initial timing say from 12 to 10?
Thanks Guys,
Update:
I installed the garage door springs in the distributor. The throttle response is slower, as I expected going from in at 2,800 to 4,000.
It seems to have more torque and the rpm range seems to be extended.
I want to change the jetting before I dyno again.
I left initial at 12 for now.


[Modified by bud snyder, 2:49 PM 11/15/2001]

 

Your total timing is initial + centrifugal so one or the other will need to be changed. (An exception to that is if your centrifugal starts below the idle speed that you've set your initial at.) If you don't want to change your initial, your only option would be to change the amount of centrifugal in the distributor. As long as idle quality and off idle response are ok afterwards, it shouldn't hurt anything to reduce initial if that's what it takes to get your total where you want it.

 

Vetterodder,
Thanks for the info.
I remember that usually you try to set the initial timing as far advanced as possible on a Sb.
I will be using the heaviest spring in the MSD , which should be 20 @ 4,000. according to their graph.
I am also using these damn fast burn heads.
Thanks again,
Bud

 

Bud - I think your not looking at it correctly. The spring doesn't limit total mech advance. It just determines how slow or fast the advance curve comes in.

Depending on C/R and some other factors determines at what point you want you need total advance. The general rule is total advance at 28- 3200 rpm.

So you want to say start with 12 at idle and add 20 degrees of mech and all in at 3000 rpm. If your car rattles at light throttle cruising down the freeway at 70 mph is when you would use bigger springs to delay max advance.

 

gkull, Hi
I am sorry. I didn't supply you with enough information in my question.
I am under the impression that the advance stop bushing (blue) will stop the centrifugal @ 21 degrees on this MSD distributor. (It is actually 22) when we used the Sun machine.
These heads supposedly perform best at 32-34 @ 4000. If I need to get to 32 what should I do, what are my options? Just set initial timing @10? Just bag it at 34?
I am running 34 @ 2,800 with weights and springs only. I must be killing the heads performance with that timing, or they just ****.
Thanks for your help,
Bud

 

Bud - does it have a vacuum advance too, or is it just the mechanical?

 

71 coupe,
it has vacuum advance unit on it, but right now I have the line plugged with a ball bearing in the hose. It's a # 10 i think, which will add 20 at cruising. I'll leave it that way until I find the best timing for there heads and engine. I don't want anything to effect the setting at WOT.
Take care,
Bud

 

I really believe that you should set it for 10-12 initial and all total of 32 in by 3000 rpm. Then you still have 32@4000 and 32 at 5000. Stock hei's are often set at what is considered very slow and they are always total advance in the 3200-3600 range performance ignitions often run all in by 2800 or less.


If you have an adjustable vacuum advance set it for 4 degrees for starters. so you will have something like 36 total. then advance it in 2 degree increments until you get rattle cruising on the level freeway and then back it down.

 

gkull,
I don't know how to get that. from the graphs the closest I can get to what you suggest is what i had 32 @ 2,800. None of the spring combinations work.
Should I try a different spring company?
Please help.
Thanks,
Bud

spelling corrections


[Modified by bud snyder, 8:18 PM 11/15/2001]

 

Bud, what gkull said is right on. The springs control the rate of advance, not the amount. The bushing you use determines the amount of advance, not the rate. Sounds to me like you're already where you want to be. Are you yu having problems with pingng, surging, or otherwise?

 

:confused: :confused: :confused: What does slowing the advance curve have to do with making more torque & extending the rpm range???????

I need some educatin.

I understand that fast burns don't need as much total advance to make max power vs. standard head designs. But what does slowing down the advance rate have on the torque output??? If no detonation problems exist, then a slower rate would make less power, right? The extended rpm range thing is just as confusing. Can someone explain?

 

Vetterodder,
The car had less than expected test results on the dyno. I am searching everywhere I can think of to help the cause. I am searching for the best performance possible from these heads. If they(GM) are telling me 34 @ 4000 and I am running 34@ 2,800 I am assuming the first place to start is to set the timing @ 34-4000 and play with it from there. I only have three advance rates I can get with the springs supplied by MSD. The 34 total for right now is set in stone. This all may be all academic! The gains achieved by changing the advance rate may be so insignificant that it really didn't matter.
The car runs great, but facts are facts(dyno #s). I think that this engine combinition should do better, maybe not! We do start to get a slight sign of detonation at peak hp on 93 pump gas. That peak right now is only 5,300.

 

nunus,
I don't know the answers to your questions. I wish I did!
I was stating an observation on the short test drive I made after changing the advance rate. This engine peaks at 5,300, but it seemed strong past that point yesterday.

 

Gkull - Thanks for all of the ignition advice :D
My Mallory Comp 9000 has an adjustable vac advance. It seems like it would lose it's adjustment after a coupe of weeks (it starts to back out & give more advance) Ever have this problem? Other than buying a new vac advance, is there a way I can fix this? :cheers:

 

I also have Mallory dist. and it seems to me I replaced the original with the Crane Cams adjustable. But don't quote me on that. I don't see anyway to fix the threaded allen from moving inside the canister.

I'm going to take mine into Mallory and they do free recurve. I'm in the same boat as Mr. Snyder with fast burn technology heads. Mine are Dart, but they recommend 32 max degrees. so at this time I have just been running low initial to end up with 32 degrees and I have 6 vac and all in at 3200.

All high initial really does is smooths out the idle. But with 6 mech and 6 vacuum it's okay but not as nice as 16-18 degrees at idle.

 

gkull,
You were right on with the timing setting you suggested. My last spring change seems to be the best. 32@ 3,200.

Good luck with your timimg adjustment. 6 initial must require a little finesse starting out from a stop.

Thank you for all your help with all my questions,
Bud

 

Bud, if it's top end hp reading is the only concern, then the curve or when it peaks doesn't matter as long as total advance is all in by that rpm. The benefit of bringing in the advance earlier is that it helps to build more torque at lower rpms. Unless it creates problems, there is no good reason not to bring in advance sooner than most stock distributors do. Changing the advance rate will only affect the power output up to the rpm that total is reached. The fast burn style head's preference for less total advance is well documented but what is optimum may vary depending on other factors such as cr and cam timing also. If your budget allows, take more time on the dyno and try different amounts of advance. It sounds to me like you're already at or near optimum timing and those missing ponies might be found in jetting or elsewhere.

Is it possible that you aren't really missing any ponies? It's easy to start with an expectation based upon some advertised gross ratings (or what you think a certain combination will make) and underestimate the differences between gross/net/rearwheel. The standard deduction (15% or whatever) for rear wheel power vs flywheel assumes a comparison between net, not gross, flywheel hp. For example, a factory engine may have a 300 hp net rating as installed in a car from the factory but that same engine might be advertised at 350 gross hp when sold as a crate engine. If you were to run the factory car on a chassis dyno with it's 300 net hp engine and then replaced that engine with the 350 gross hp crate engine, the rwhp rating would be about the same.

 

gkull, I wound up "overlapping" my advance and it's worked out great. When I installed an MSD distributor I wanted to use it's lightest springs but they started advance at 750 rpm and I idle at 850. I always set my timing at total anyway and the end result gave me 10ş @ 750 and 13ş at 850. Upon start up, my starter only has to crank against 10ş but I get the benefit of more timing at idle and off idle.

 

Vetterodder,
I don't fully know the charisticsof the fast burn heads. If it is only important that the total advance is 32 degrees, then I put everyone through this for nothing.
I made dyno runs when I had the old 275 dual engergy cam in the engine. 241 @ about 5,300. I had a full throttle problem also. Car ran Ok
New dyno run with 274 XE cam & throttle 265.8 @ 5,300. UP 27.3 HP torque up 12.1 Lbs. The car runs great! It just seems to run better through the entire rpm range than the WOT dyno results are. It sure feels like more than 27 hp gain. Note: I used the same dyno for both test runs. The wires and plugs were perfect on the Sun machine, overlayed looked like one set. A/R peaked at 14.5, not bad. I changed secondaries from 78 to 80 which should be about perfect.
Is it the best this engine can do? Maybe! I am well pleased with the car and it is a pleasure to drive. I have driven it more since the last mods and the cam change than i did since 1980.
Thanks for all your help, take care.
Bud

 

Vetterodder,
I forgot to reply to your suggestion to try more dyno runs. I had planned to do so next week, and acually change the springs between runs(2) which will give me a run at all three settings.
I am delaying that. Mr gkull and I have been discussing what I can do to extend my rpms past my previous 5,300 with a spring change. I just haven't decided if it is that inportant for a car that just runs around the streets.
Truth be known the odds of getting to a red light and having something willing and able to engage in a liitle sport in the other lane are very slim! Man I long for the good old days. (60's)
bud