There is a lot of vacuum from the engine at idle speed, it's in the intake manifold BELOW the carb butterflies. That is the vacuum source for all things related to the 'car' not the motor. Things like power brakes and vacuum motors that operate the heater controls, or flip up the head lights on some cars. Generally speaking there is about 20 inches of vacuum available. ABOVE the carb butterflies, depending on how your carb is ported, there is no vacuum available until you open the throttle slightly.

Didn't/doesn't Edelbrock sell a water injection kit? Seems to me I remember one...

WOW!!! :JEKYLHYDE Lots of "old school" thinking here :D Yes the newer cars (1987 is "new" to me) that have turbo's and stock computer systems can really benefit from methonal . Turn up the boost with pump gas and the car will fly. My daughter has a Buick Grand National with a V6 turbo (STOP LAUGHING !!!) that she runs pump gas with methonal injected in the plenum. This is her summer beater like you guys have your "summer" Cobra's. She DRIVES the car anywhere and everywhere. Races at the drags then continues up to the lake for the rest of the weekend a few hours away. Oh the car runs around 18#s of boost with no methonal.. 25#+ with methonal that equals to a 9.94 @ 138 in street trim in a heavy 3660# brick. :D NO I haven't tried it on a naturally aspirated car BUT if any of you guys have a supercharger or turbo it's def worth looking into :cool:

So diddn't put the old vacume advance dist to the test did ya Ex. Some buy em some build em, Some just talk.

jimmymac, not sure what the question is...

I'ver hooked mine up with both intake vacuum and ported carb vacuum and not run it all. Currently I'm running intake vacuum, primarily to address the 'run on' condition as I like to set my idle speed around 1000 rpm, which is kinda high.

Bear in mind not ALL carb ports are the same. Some provide intake vacuum, others are ported above the butterflies. Easy to tell, the engine speeds up at idle, or not.

MSD can provide the theoritcal specs for the vacuum advance, something like 10 degrees advance at 15 inches of vacuum, etc. etc. I've found the specs actually can vary quit a bit in the real world. My advance unit starts to advance around 10 inches, all though, MSD says it is more like 15.

Ex, I'm also not sure what Jimmymac is trying to say...earlier in the thread he said this:

Do you really believe there's a vacume advance distributor out there? Are you aware of the full meaning?

then this:

Try pulling the vac line off the from the carb. Hook up your timing light. start it.check timing. put a vac on dist, check timing again!!!

then this:

So diddn't put the old vacume advance dist to the test did ya Ex. Some buy em some build em, Some just talk.

I think he thinks a vacuum distributor doesn't advance the timing when it receives a vacuum signal? Jimmy, it doesn't wound like you know what you're talking about. I have done exactly what you described, and the timing DOES advance when you add vacuum to the can...what are you trying to say? I'm sure Ernie has done the same thing, and he's probably forgotten more than you know about motors...tell us clearly what you think happens when a distributor with a vacuum advance can operates normally.

I've verified both vacuum timing schemes: ported and manifold.

GM HEI distributors from late '70s till computer control took over utilized manifold vacuum advance. You had full advance until you got into the throttle, then as manifold vacuum dropped off, the timing retarded, decreasing the chances of spark knock. Verified with a timing light on a 1977 Chevy 1/2 ton pickup with 305 small block.

Earlier, before emissions became a concern, most manufacturers used ported vaccum (as used by Excaliber here). Increasing airflow through the carb causes increasing ported vacuum via the venturi effect, slowly pulling in more & more vacuum advance. Verified with a timing light on an '81 Jeep 258 six and a '66 Mustang 289. Sort of tough to do, because it CANNOT be checked with the vehicle sitting still and opening the throttle. The engine MUST be under load to create the necessary airflow in the carb venturis required to create ported vacuum.

For one of the best descriptions of various timing schemes (including switching from ported to manifold vacuum, delaying advance, etc.), try to find a Petersen's book on carburetion & ignition from back in the mid 70's. You'd be amazed at some of the methods that were used in the pre-computer days.

Oh, and regarding German fighters... Would water/methanol injection be justified in a Cobra if you had a BMW on your tail?:D

I have not been able to pull the vacume on my engine to operate a excel vac dist. with the dual plane intake. I know the tunnel wedge will have less vacume. Till I slam the throttle shut at 7500. Iv'e never had a hesitation or lack of low speed power! the car weighs 3440. I'm running a 1970 model excell dual point that I converted to stock ford electronic pieces. Its a 11.75 to 1 engine. Mr Partrige from south of Menphis Tn cut the cam for the car. It loves all the advance I throw at it about 40 winter 38 summer. All in by 3000. Question is wouldn't a light car use more advance sooner? the carbs are tuned for lean cruize and a little fat wide open.

I think you mean "Accel" distributor? There is very little vacuum available when the throttle is pretty wide open, it is virtually zero vacuum at WOT (wide open throttle). A 'lumpy' cam profile is the main reason for a low vacuum signal. At idle it may well be 10" of vacuum or even less. Thats why some guys cannot use a Power Brake vacuum booster and are forced to go with some types of mechanic hydrualic power brake booster (often called 'juice brakes'). Vacuum advance is extremly difficult to 'feel' or 'sense', it comes and goes based on throttle position. While on MOST cars it will improve mpg during steady CRUISE rpm, you will not 'feel' this, you have to 'measure' it with careful mpg calculations.

IF your cruise rpm 'inches of vacuum' is BELOW the threshold of the distributors vacuum advance unit requirements, you will get ZERO benefit from it's use. Vacuum advance starts at 15" and your cruise vacuum signal is 10", equals no benefit. Of course when you CLOSE the throttle vacuum goes WAY HIGH, perhaps 20" and you get full advance. Which again has virtually no impact on mpg or performance when the throttle is closed.

SOME vacuum advance units can be adjusted for a lower signal AND 'total advance' they introduce, most cannot be adjusted. You need a good vacuum gauge to determine your cruise, idle, full throttle and closed throttle vacuum signal. Use a LONG hose and place the gauge on the windshield (use tape perhaps) or in the cockpit and note the readings. Compare the cruise vacuum signal to the specs on your Accel distributor to determine if your 'in the ball park'. Check to see if the Accel distributor can be modified for the vacuum signal strength required.

Your right, Accel! The distributor I modified Is a Echlin Remember the good ones? Im cammed up to the limit for the street. So no vacuum. But why does it run like a bat outta hell with full advance all in by 3000? Havent checked down here at sea level. At 5000ft I got 13 mpg with 3.90 gears!

Basically engines really like advanced timing, early and lots of it. BUT, you gotta feed it in carefully, ideally right to the very limit of detonation. Thats why modern engines have knock sensors and computer control to deal with the timing.

I have a knock sensor. I have MSD adj.timing control. Ready to put water/meth inj. and a two stage NO2 for 4th and 4thover pull. 4th over figures at a 3.05 gear. Maybe I hope to be able to run some pump gas again.

Just wondering why you want to run water to ??? we ran a turbo car both ways .. Ran better with straight methonal :MECOOL:

It would be great to be able to cruize on pump gas again. If water will do it great if not . Ill try a mix. no supercharger