GCD1962

I just bought a HEI tach drive for Corvettes from All-Ignition

http://www.all-ignition.com/

$120 + shipping (fast shipping). I haven't had a chance to install it as yet, but it appears to be very well made (and made in U.S.). I sure the components are the same that others are selling for twice (or more) the price.

midyearvette

that's true and we agree but just imagine a bad timing set-up along with a bad vac. set up!!......i just came from jegs to buy some head gaskets and asked a tech there about this policy and he stated that true jegs is tired of melted pistons and bad timing set ups and too much advance on their crate engines especially when a vac. adv. is used. hey what ever works for you is alright for me, it's just most do not comprehend what advance is for and all the data that has been sent in this forum is staggering for such a simple form of technology....jmho

Ironcross

Normally performance engines do not need or use a VC can whether street or strip. Where the poor gas mileage and overheating issues come from I have no idea. Because its a non issue and wrong.

midyearvette

......i said it before and ill say it again....vacuum advance is for weenie cars!........jmho

mrruffhouser

My '61 runs great on it's dual point, mechanical advance (no vac.) distributor that's been in it as far as I know, from day one. What's the fear of a non-vac. setup? Yes, you need to set it up correctly with max. advance @34 degrees.

markiemyster

Thanks guys for all your input, I quess

Think I'll just return the MSD 8572 (tach and vac) and get a MSD 8571 (tach but no vac)
The engine came with a MSD 8360

midyearvette

..GO FOR IT!!, i knew you didn't have a weenie car........LOL

Ironcross

Heres my A990 Hemi, and below that is my LS7 and L88 Chevys. No VC`s are used or are necessary for any condition some have incorrectly spoken about. However it may be from their lack of familarity with the high performance engines of the 1960`s

C2Driver

My ZZ4 runs great without a vacuum can. No overheating or gas mileage issues. Acceleration is
amazing, with no lag when I hit it. Just instant torque.





- Pat

69427

Nonsense. Every engine, regardless of its performance capability, has a cylinder density/residual EGR/burnrate curve. Running the same absolute timing advance at light loads as heavy loads causes the combustion thermal efficiency to decrease significantly, producing a crappy idle, overheating, hotter exhaust valves, and poorer fuel economy. Running without a vacuum advance went out in the sixties (along with roadhugging weight).
I run a vacuum advance unit on my street/track (road course, not short quarter mile jaunts) 427, and the extra advance cleans up the idle quality, reduces dieseling at shutdown, and improves the gas mileage/throttle response on these reasonably unsophisticated cars.

69427

Does this look like the underpinnings of a weenie car? C4 suspension, Wilwood brakes, coilovers, 5 spd transmission, and 427 w/aluminum heads (to be replaced with the ZL-1 currently under construction). And yes, the vacuum advance will be hooked up again.

Ironcross

Those that dont agree should read my post again. I said "normally" they are not used with HP engines. I think a real ZL1 {part of that old 60`s stuff} is nothing more than a lightweight L88 that in those Corvettes that ran circle track or that other type 'cross country or something' against the Ford Cobras and didn`t use a VC. It dont suggest you cant use one, its just not necessary or they would be on all the L88`s and ZL1`s too.

As to mileage and overheating, C1 Vettes with FI never used one and mileage with my 61 FI piece got a even 20 MPG with a 4.11 axle at freeway and above speeds. Its operating temperature was 180 in Miamis heat and idle was perfect. And talk about acceleration, The 61 was close to fantastic on the street whether that was appropriate or not. And as a NHRA National Champion I do know the difference between fast and slow.

There I think I covered all the issues from my perspective with ZERO so called related problems stated that happens with out one. My 62 FI piece dont overheat either. Another Miami Vette.

And finally, I knew this would bring this post to life again.

66since71

Could not have said it better.. and so do the guys at Chevy who developed the ZZ series engines!

I am also sure however, that you can build and drive an exciting car without vacuum advance... but it could be better!

Harry

Maybe I don't agree on the overheating and hotter exhaust valves part now that I re-read it, it runs effectively rich without the compensation, not lean. Otherwise...

DansYellow66

My 2 cents. My car has an old school 427 set up originally with an all mechanical advance distributor, 12:1 pistons, 256/266 duration cam @ .050 inch, aluminum rectangular port heads, L-88 intake, big rods, etc. It ran like a bear this way but was barely streetable. Trying to get the thing started and keeping it running long enough to warm up in cool weather especially, was a chore. In summer the temp gage would creep up to the 3/4 hash mark on the gage at the slightest hint of traffic. I put on a stock (except jetting) 427/425 Holley that helped a little. I finally pulled out the Accell distributor and put in an old Magpulse distributor with vacuum and finally a VC-1810 vacuum can with full time vacuum source. I would never go back. This change alone - the VC-1810 can - dropped my warmest gage temperatures back to between the first and second (mid-point) hash marks on the temp gage. I can prime the carb on a cold start through the fuel bowl vent, hit the key and now it actually will run on fast idle without dying once (still quite dramatic in trying to idle however).

BUT - I did develop a miss at cruise from an over-advanced condition. I suspect this is a trend with today's fuel and the additional vacuum advance at light throttle sets the mixture off too advanced of TDC and causes it to kick back or miss - basically a form of pre-ignition. You wouldn't think this could harm the engine at light throttle but it's certainly unsettling to be cruising along with the engine missing or bucking several times a second at least. I suspect that may be the reason for the warranty disclaimer by Jeg. I cured this by building a stop for the vacuum can to limit the amount of vacuum advance by about half. Even that amount makes the motor much easier to live with and it cruises clean without a miss now.

Dan

JohnZ

Well, you can add that "tech" to the list of folks who simply don't understand vacuum advance. Nobody ever melted pistons due to vacuum advance - it drops out when you put your foot in it. It's simply ignorant to attribute engine failures to vacuum advance, and just plain stupid to say they'll void the warranty if you use vacuum advance.

buns

First they tell you to unhook it, then they tell you not to use it?

69427

It doesn't matter if you agree or not. It's simple combustion physics (or chemistry, if you like). Running retarded timing, which is what you're doing without a load-variable timing system (vacuum advance) results in higher exhaust gas temperatures, and higher exh valve temps. Never a good thing. The retarded timing also causes the burning mixture to be exposed to a larger surface area of the cylinder walls, resulting in a greater heat transfer into the coolant. The heat (gas) you paid for is supposed to be used to make horsepower, not boil water.
Regarding your rich and lean comment, I have no idea what you are referring to. We are discussing spark timing, not carburetor calibrations.

markiemyster

This is a cut and paste from their web site

High Performance Engine Technical Tips
Get expert advice on your high performance stroker & crate engine applications

Vacuum advance and Timing of Blueprint Performance Engines

(June 05, 2007)

Warning: Do not use vacuum advance when installing Blueprint Crate Engines. Using vacuum advance will void the warranty.

Refer to the Blueprint Installation Manual for all timing specifications.

Timing is critical to ensure the longetivity of the engine. Do not exceed recommended specifications

66since71

Mike, your explanation seems to make sense, if all of the mixture is burned. My rich/lean remark was based on my understanding that less than optimum advance results in incomplete burning. If that were the case then incomplete burn is effectively a "rich mixture". But, I learn a little more about this stuff every day. Thanks for the feedback. In any case, I still agree with you on the need for vacuum advance.

Harry

buns

I would call them and ask them what the differance is between their engines, and the other 3 gazillion small block chevys running vacuum advance.

If you don't, I will.