Team Chevelle banner
1 - 20 of 20 Posts

·
Registered
Joined
·
875 Posts
Discussion Starter · #1 ·
I need to purchase a few pieces to complete my 540. I''m thinking, ..better do it now, ... instead of waiting for, big time Obama promoted inflation to hit. It's distributor time, and I'd like to use vacuum advance with this street/strip engine. 10.5 to 1 -HR 252/255 w/.672/.629 lift. 110 LS. 1970 all steel Chevelle. I'm leaning towards a DUI, built to specs. Is there anything in my combo, that would make a vacuum advance distributor unpractical? Thanks
 

·
Registered
Joined
·
160 Posts
Pertronix Ignitor III

Pertronix Ignitor III w/vac. advance :thumbsup:


Billet, factory cap size, rev control, multi-spark.


Approx. 235-240 @ Jeg's.




Awesome piece & price! :yes:
 

·
Registered
Joined
·
1,916 Posts
Just make sure you limit the total advance to 36-38* at part throttle/high vacuum cruise with the vac advance. You may have to make a limiter plate to physically stop the Advance movement. Don't buy into that "you need 45-50* at cruise" BS or you'll rattle the headgaskets out of it.

I have my msd pro billet setup with 32* locked out and an additional 4.5* of vac advance(limited). 36.5* at cruise. 32* at wot. Works well.
 

·
In Memoriam
66 El Camino 57 Chevy pickup 2004 Tahoe
Joined
·
29,419 Posts
I'd shoot for a setup with 18 initial, 34-36 total mechanical and 15 vacuum. it may or may not ping at light throttle acceleration in high gear, if it does limit the vacuum to 10, see if that fixes it. different engines act differently, it depends on your specific combination of CR, cam, heads, rear gear, driving habits, altitude, etc.
 

·
Registered
Joined
·
13,426 Posts
Just make sure you limit the total advance to 36-38* at part throttle/high vacuum cruise with the vac advance. You may have to make a limiter plate to physically stop the Advance movement. Don't buy into that "you need 45-50* at cruise" BS or you'll rattle the headgaskets out of it.

I have my msd pro billet setup with 32* locked out and an additional 4.5* of vac advance(limited). 36.5* at cruise. 32* at wot. Works well.
How did you get to 4.5* vac advance?
 

·
Registered
Joined
·
1,916 Posts
How did you get to 4.5* vac advance?
Hey Joe, I just used the vac advance that came on the msd pro billet dizzy, it added like 18-20* advance, made a little limiting plate that would bolt down on top of the vac advance mounting screws and basically mechanically STOPs the vac advance arm in it's travel. This was trial and error. I kept measuring the vac advance with the timing light at around 2000rpms, then I kept cutting the length of my limiter plate once the advance was at 4*.....but after all was said and done, it ended up at 4.5* of vacuum. I have had it like this for about 2500-3000 miles now, I recheck it with the light and it is still consistant at 4.5* additional vac advance on top of my initial, which is locked out at 31-33* depending on the air...

The additional 4.5* of vac advance knocked 5* off of my freeway water temps at 3000rpms. No noticeable increase in fuel mileage though.
 

·
Registered
Joined
·
11,298 Posts
Giys,no need to make a vac adv limiter,heres cranes version pasted below avail from summit.

It took me approx 10 mins to install in the stock type point dist in my 396 ,its adj in i believe is 2 deg increments if memory serves me right.

The cam he's running in 540cubes should have enough int vacuum at idle/lower speeds for a vac adv to be helpfull.

I'd limit it to approx 10-12 deg max and try it on full int vac even at idle along with approx 18-20 deg base timing + mech adv in dist setup to give 18 deg mech adv @ the crank in by 2500-2600ish rpm for 36-38deg total.

With all timing in you would have approx 48-50 deg timing when at cruise whicvh is a little conservative.

If the vac adv doesnt seem to do well on full int vac (which i think it will) with running proper timing then try iy on ported for no vac @ idle.

This would be a good starting place for a street perf ign timing curve that will run decent off the bat,then you could try tweking the timing + - a few deg to see if the motor likes it or not from there.

Pasted below is the info for the vac adv limiter plate from Crane.

Dont know if it will fit HEI dist.

Scott

============================================================

CRANE VAC ADV LIMITER PLATE PT # 99619-1 FOR GM V8 DIST
 

·
Registered
Joined
·
13,426 Posts
Scott, Ive ran both man vac advance and ported. My gripe with vac advance at idle (full manifold vac) is when stomping it right off idle, I do not like the loss of timing. I much prefer to limit mech advance to about 10* which let's me run that 26* initial/ 36* total for a clean crisp idle, and allows to instant throttle response. Vince had posted a pic showing a mech limiter screw installed on a HEI. I took this one step further and have mine set up with a nylon screw ( bought at the local HD) with the thoughts that the nylon will completely eliminate any potential to create a magnetic field. I do agree completely, there's absolutely no bonafide reason to only have 10-12* total timing at idle when it's so obvious how much better a tuned motor will idle once you get some timing in there. Just different approaches as to how you get that timing in there.
 

·
Registered
Joined
·
11,298 Posts
Scott, Ive ran both man vac advance and ported. My gripe with vac advance at idle (full manifold vac) is when stomping it right off idle, I do not like the loss of timing. I much prefer to limit mech advance to about 10* which let's me run that 26* initial/ 36* total for a clean crisp idle, and allows to instant throttle response. Vince had posted a pic showing a mech limiter screw installed on a HEI. I took this one step further and have mine set up with a nylon screw ( bought at the local HD) with the thoughts that the nylon will completely eliminate any potential to create a magnetic field. I do agree completely, there's absolutely no bonafide reason to only have 10-12* total timing at idle when it's so obvious how much better a tuned motor will idle once you get some timing in there. Just different approaches as to how you get that timing in there.
==================================================

Hi Joe,there's often more then 1 way to approach things and your's is a good one too.

Lord knows you sure know your way arround building & properly tuning good strong running bbc street motors which shows in your car's perf on the strip & informative posts here in T/C too.

I'm sure no matter which tune he decides to try 1st either one will run decent out of the box and he can dial in his setup to best perf from there.

Maybe your suggestion would be best for his 1st shot at it esp if he;s running auto trans.

Happy motoring.

Scott
 

·
Registered
Joined
·
875 Posts
Discussion Starter · #12 ·
Thanks guys, Joe, .... Just want to be sure that I correctly understand your suggestion. 26/initial, 10/mech, and 10/vac (ported vacuum). Total: 36, and at cruise 46. A few details I didn't mention, ... trans is a 4L80E, rear end will have 3.89's and heads are AFR 325's cnc optioned, .... if that needs to be taken into consideration. Thanks
 

·
Registered
Joined
·
13,426 Posts
Best comparison I can give you. I ran the same 26/36+10 vac on the 10.3/1 469" with both a 296/304, 236/244, .612/.632, 112LSA/107ICL cam and later a 297/300, 242/245, .650/.650, 111LSA/106ICL cam. Pump gas 92 octane, 93 octane when I could get it, no signs of detonation. We pulled the heads (Dart 310 alum) off the 469" for use on the new 540, so was able to do a good visual of the pistons and chambers, there was no signs of detonation. Carb was tuned for cruise AFR of no leaner than 13/1 with AFR at WOT of 11.5-11.8. Distributor is an out of the box DUI. Came with 24* mech advance. After a call to DUI, found out they do the same thing with the mech advance to limit it, install a screw. Took me a couple tries in/out to get it right, lot easier on a dist machine. Stock vac can on the DUI was replaced with the VC1852 ( 75-78 350/400 HD truck). Can starts at 7-9", full vac advance 5* (10* crank) at 12-14" vac. You can certainly install a vac advance limiter of some sort to further limit vac advance, but 10* seems to work. Think the reason the VC1852 works so well, not only does it only have 10* vac advance, but with needing 12-14" to fully deploy, it's only fully engaged at very low load. As soon as you get into it, timing backs off. Figure if you run a 6.5 PV, by the time the motor is into the PV, there's no vac advance there anyway.

An FYI, I ran the numbers for your motor. Using the seat timing of my cam as a baseline, adding in 10* for the intake side, your 10/5/1 CR will net a DCR of 7.39/1. We had my cam reground for install into the 540 I have assembled. It is now 297/304, 242/249, .650/.650, 112LSA/107 ICL.. CR and DCR for my 540 are 10.4 & 7.62. Like you I have alum heads which really helps control the combustion temps. Also run with a large capacity 2 row alum radiator, using the GM HD 7 blade clutch fan (HP robber, I know, but that's a tradeoff). Oh, my trans is a T400, 3.42 gears. Converter is/was a 9.5" 3000 stall, which I still need to have looked at, intent is to drop the conveter down to 2500 or so with the 540".

PS - Based on what I could find for advertised specs for crate 540's (Shafiroff, RM, Smedding), with the Dart 310 heads and the 242/249 cam, we figured my motor should come in at a conservative 650 hp at about 5800. Your motor is really stepping it up with the AFR 325's and the 10* added cam timing. I'd expect your's to well eclipse the 700 mark at about 6100-6200. Gotta love it.
 

·
Registered
Joined
·
875 Posts
Discussion Starter · #14 ·
Joe, Thanks again for the specific info. It sure helps. I'm hoping to be near, or over the 700hp mark, ... topped at 6200. And, your estimation is like a few others I've gotten. Yep, can't wait, and I'm gonna love it.
 

·
Premium Member
Joined
·
2,061 Posts
Joe, I was just wondering, I run full manifold vaccum and really while touching or hammering the throttle at idle, I don´t really notice any lack of performance due to the vacuum timing loss. Could you tell us some more about this ? Maybe I need to look into it.
On the other hand, I really notcied my idle was alot crisper running the 18 degrees full manifold vacuum + lower than ideal (18) intitial. Compared to before with the stock vacuum can, and messed up weights giving me 32 intitial and 26 total lol. (yeah you read that right :) Weights where stuck and vacuum can added 2-3 degrees only, and timing fell due to ecm retardation.
 

·
Registered
Joined
·
13,426 Posts
Remi, try this.

With a light connected, motor at idle, vac advance connected to manifold vacuum like you have it. Wack throttle while watching the tming, it will immediately retard to whatever the initial is. And, for a lot of applications [stock cam or mild cam upgrade with very little overlap ] maybe that works. I prefer to run as much initial as I can and limit total mechanical advance. Think about it this way. Motor doesn't idle clean with typical 8-10* initial timing (misfires, stumbles, rough idle, etc), so you add 12-16* (or more) of vac advance to clean up the idle. As soon as you mash the throttle off idle, you force the motor to operate under the condition of little advance, so for those couple seconds you force the motor into misfire. Thoughts are kinda simple, if the motor needs all that added timing to idle clean, then why force it run with what you know is not enough timing. Vince posted a pic , think it's a sticky on here, that shows a limiter screw installed, simple deal. Not sure it makes any difference, but I prefer to use either a stainless screw (which is non magnetic) or a nylon screw. Good luck.
 

·
Premium Member
Joined
·
2,061 Posts
Thanks Joe ! I agree with the running high intitial part, or lets say, I learnt it here from some of you guys very informative posts, tried on my car and it was great.
I need more intitial though, have a setup now and will try to get it right when the spring comes and my car has some of the parts in it that it needs to be driven. Like, engine, rear axle, springs, control arms, steering box... etc etc

I should have clearified it more, my initial question was why not run full manifold vacuum instead of ported ?
Stability at idle maybe ?
 

·
Registered
Joined
·
13,426 Posts
No need for man vac advance at idle if you set up the distributor to run as much initial timing as needed. FWIW, did some parts research recently. From what I could find, Mallory Hy-Fire has all the features built in. 10*'mech advance tming curve, switchable (low/high)vac advance range with 10* vac advance and multi-spark capability built in.
 

·
Premium Member
Joined
·
2,061 Posts
Thanks for clearing that up for me, so that´s what you guys discussed on last page, different ways to get to the same timing, I´m the slow one LOL.
 

·
Registered
Joined
·
13,426 Posts
One last thing, then I will back off. I should make one clarification. My preference for running as much mechanical timing probably more relative to a street/ strip car where you want that "hit" right off idle. Odds are the typical street cruiser that never sees the track will never know the difference either way. Important part is what Scott has been sharing for years, however you get there, just make sure you run plenty of timing at idle, your motor will love you for it.
 
1 - 20 of 20 Posts
Top