markiemyster

OK This is where I prove how little I know.

The crate engine I purchased came with a MSD HEI distributor but it was not set up for a mechanical tach. I called Jegs and told them what I needed and they sent me one with a mechanical tach but also a vacuum advance. It say for Corvettes on the box.
I was just going through the installation information that came with the engine and it says that if I run a vacuum advance the warranty is void.

Can I just plug the end of the vacuum tube on the distributor? Can you get a distributor with tach drive but not vacuum?
I know these are probably very elementary questions to most of you but it's all new to me.

Thanks, Mark

wmf62

yes, you can just plug it/cap it and it will act just like a regular distributor without vacuum advance.
Bill

markiemyster

Thanks Bill.

That's good to hear

62Jeff

I'm curious Bill, will a distributor set up for a vacuum advance, have the right mechanical advance when the vacuum is excluded?

I would GUESS but do not know, that the advance curve for a mechnical advance-only distributor would normally look different than the curve for a distributor set up with a vacuum advance.

buns

I'd like to know which crate motor you bought, and their reasoning for this.

mikem350

Remember if not using the vac advance the engine will run hotter, have poorer mileage and maybe less throttle response.

The mfg is probably worried about reliability if too much vac advance causes detonation or needs a particular spark curve. At any rate you should try to match the curve they recommend!!

wmf62

the mechanical advance is independent of the vacuum advance, the vacuum advance is an additive to the mechanical. purely mechanical distributors, including intial timing on the balancer, usually have no more than approx 34 degrees total advance, whereas a vacuum distributor might have a total of approx 51, BUT that last 17ish degrees is solely from the vacuum can and is accomplished by the vacuum can rotating the whole plate that the points sit on. the mechanical advance is solely a function of the weights and springs on the top of the distributor shaft.

any distributor needs to be curved for the specific engine it is installed in, both mechanically and vacuum, and total.
Bill

62Jeff

Bill, thanks for the quick reply.

I have many more questions that I can't resolve in my head, but there's no point taking the OP's thread off on a tangent.

markiemyster

Bill,

Should I see if MSD sells a distributor with a tach drive but not vacuum?
Would that change anything?

Thanks, Mark

Buns,
This is the link to the thread that explains the engine project and what I bought
http://forums.corvetteforum.com/c1-a...-pictures.html

skids

MSD's 8454 dist has no vac adv, but you need an ignition box. Have you considered maybe a Mallory Unilite, if you don't want to use a box? Neither of these are HEI however.

skids

www.performancedistributors.com has a HEI tach drive mech adv dist. $419.00

markiemyster

Skids,

I have a MSD 6A that I bought with the new distributor.

skids

Your MSD should have came with a vacuum advance lockout kit. You could use that if you don't want to run vac adv. IMHO, I would keep your dist and use it. My feeling is the general consensus here will tell you to use vac adv, and dial the dist in according to what the engine needs. I converted over to MSD with vac adv, after using a mech adv only Unilite, had the car on the dyno, and now I'm happy!

wmf62

Mark
it all comes down to cost, whatever you can get the 'cheapest' (and with good quality). aesthetically, a no-vacuum distributor might look better without the can hanging unused, but it will be no different mechanically than one without the can; BUT there may come a day when you might want to use vacuum advance (after the warranty period is up), as there are many positive benefits to using it.

if you're worried about the mechanical advance curve, then most anything you get will have a generic mechanical curve and would have to be checked and possibly tweaked with new springs and/or weights.
Bill

redred65cpe

I think the warranty not being valid with vacuum advance is bogus. I would think that street driving would be compromised somewhat with no vacuum advance. I wouldn't be surprised if the vacuum advance unit on the distributor is adjustable. Does it have a "hex sided snout" instead of round? Adjustable vacuum advance units make dialing in timing curves much easier. If it were me, I'd use it.

larry

Frankie the Fink

I don't see you winning on this one - if you run the engine with a vacuum distrib (even if you plug it) the company could be SOBs and claim the warranty is void. After all, how do they know it was plugged/locked out when a problem occurred ?

Which means you either run the original mech-only distrib full time...or stick it back in to get a warranty fix if you've been running the vacuum distrib (plugged or not). So why not run the vacuum anyway and get all the benefits ?

I'd be questioning the engine company on this anyway...

If you DO decide to go with a mech-only, tach drive distrib then do NOT install the vacuum version so that Jegs will take it back - no questions asked...

66since71

I'm having a hard time understanding why they (JEGS and Blueprint) would not want a vacuum advance on a street engine? From customer satisfaction (part throttle response and fuel economy), to durability (dillution) and a handful of reasons in between. Did JEGS say why vacuum advance voids the warranty?

Harry

midyearvette

this must be due to the fact that more folks do not know how to time their engines with today's un leaded fuels. to un properly time an engine AND also use a vc, could be un kind to the mill. i have written many posts on this timing subject on this forum until im blue in the face, i don't like being blue mainly because it is a ford color, so ill just say this....this vc cannister argument falls into two distinct and stubborn camps,those that swear by it and those who dont...im in the latter camp....usually the folks who like vc, haven't taken the time to set up strictly mec. advance the proper way....there are sooo many pieces written pro vc and many are laughable....so im not going to open this can of worms any more.......it's all about today's fuels......

wmf62

ahhh, you forgot 'Petty Blue'...
Bill

Frankie the Fink

That's silly - you can botch up a motor with a bad timing setup regardless of the spark advance technology.

Hell, the Model-Ts would get holes knocked in the pistons if the driver didn't set the manual spark advance properly....no vacuum advance in those days!