[BAB]

Can someone explain where each of these vacuum sources are found (i.e above the throttle blades etc.)and how does it affect the characterics of the timing or car?

[BAB]

Can someone explain where each of these vacuum sources are found (i.e above the throttle blades etc.)and how does it affect the characterics of the timing or car?

[Big Mike]

Manifold vacuum is measured from under the throttle plate. It is typically used as a measure of engine load. High vacuum usually indicates a light load and a steady throttle position. Low vacuum indicates the throttle is open a great deal and the engine is under a load. "Fuel Economy" gauges use manifold vacuum to help you keep your foot off of the throttle and keep the vacuum level high and increasing your fuel mileage. One use of manifold vacuum includes: telling the vacuum modulator on an automatic transmission where to set pressures and shift points. Strong levels are usually held in "reserve" to increase the power brake booster's effectiveness and control doors in air conditioned vehicles. If you were to connect manifold vacuum to the distributor, it would advance the timing during periods of high vacuum and retard the timing during low levels of vacuum. Generally speaking, that would be the opposite of what you would desire. Retarding timing during throttle changes could create a hesitation or drop in power. However, certain emissions are affected by this arrangment and there are times when retarding the timing might reduce emissions at that time.
Ported vacuum is taken from just above the throttle plates when they are in a closed position. That means very little or no vacuum will be available when the throttle is closed. Uses for this vacuum source are used for by things that need to know when the throttle changes from idle. The most common usage wouldbe the vacuum advance for the distributor. As the throttle opens, a port in the throat of the carb gets uncovered and "signals" the port by applying vacuum to that port. It is not long lasting however. As the throttle continues to open past that port, the signal drops off to nothing. But the signal lasts long enough to advance timing or signal an emmisson control device such as a vapor canister or EGR valve. When used to advance the timing, the effect will aid in the engine to react to a throttle change more smoothly. Connecting this source of vacuum to a transmission modulator will cause a drop in line pressure and/or lower the shift point at an unacceptable point.
By the way, vacuum advance works in parallel with the centrifugal advance. The vacuum advance only works for a short period during throttle changes and is limited by the length of the slot in the advance unit. Centrifigual advance in controlled by RPM, weights, springs and a slot or other limiter.

[Kenth]

Vacuum advance ignition regulates timing depending on load on engine
Mechanical advance regulates timing depending on engine rpm´s.
At idle and cruise load on engine is low, vacuum signal high, fuel mixture lean and hard to ignite. This situation requires more ignition timing wich comes from the vacuum advance.
At WOT and high load on engine, vacuum signal is low, fuel mixture rich and easier ignited less ignition advance is required and as vacuum signal gets weaker vacuum advance retards the timing until the load get lighter then the vacuum advance comes back gradually.
The purpose of vacuum advance is to get your engine to run more effective, smoother, cooler and more economical.
You can tune your engine to run either ported or full manifold vacuum, use what your engine likes best, but use one.
I´m using full manifold vacuum to my vacuum advance canister, works great.
All early pre-emission (1968) Pontiacs used full manifold vacuum for the advance too.
Ported source were used on 1968 and later engines in various emission systems.

...........Kent

[BAB]

My understanding is that manifold vacuum always gives a little better idle however ported was prefered for driveabilty since it provided a little more timing during part throttle situations. There seems to be alot of different opinions .....which is why I thought I would ask the question. Thanks for the responses thus far.

[Cliff R]

This topic is kicked around quite a bit with many different opinions. As Kenth mentioned, use a vacuum advance, it is worth a couple more mpg's. Whether to use a manifold or ported source often boils down to personal preference. The only real difference between either one is that a manifold source will add timing at idle and when coasting. Any time you are cruising at light throttle they both operate the advance.

I frequently read where many will advocate using a manifold source to the advance. This adds in the amount of timing provided by the canister at idle PLUS the amount of initial advance as set by the distributor. In some cases this will help smooth out a "big" cam. For small or nearly stock cams there is no need to add any additional timing at idle in most cases.....but....it probably woln't hurt anything if you do. For "big" cams that end up with a really lumpy idle and low vacuum at idle adding in some additional timing by using manifold vacuum to the advance will help to smooth them out. However, with most stock canisters the timing can fall off when the engine is placed under load (put in gear for example) and it will falter and die out. This is exactly what happened on my own engine before the Rhoad's lifters were installed. The vacuum at idle (750rpm) fluctuated between 6-7". Even so the idle was stable and didn't change over 50 rpm in or out of gear. The initial timing was set at 10 degrees. When the vacuum advance was hooked up to a manifold source, the engine speed increased to about 1200rpm and idled much smoother. The throttle plates were lowered to get the rpm's back to 750rpm, all was fine. As soon as the engine was placed in gear it died out as the manifold vacuum fell to a point lower than the spring tension holding the advance. Installing Rhoad's lifters cured this problem, however, adding additional timing at idle just smooths things out and puts a slight "miss" into the engine. I prefer to hear the big cam and still enjoy a stable idle in and out of gear so no additional timing is added at idle speed.

We tune a lot of different engines here delivered to us from folks having LOTS of idle issues. In almost all cases, the cure is NOT in the distributor, as they have chosen a cam that is a tad big for the static compression ratio of the engine. We go after the carb instead. Once the idle system in the carb is brought up to par things are fine even at relatively low initial timing settings. It usually becomes a matter of personal preference at this point as to what source to use for the advance and how much additional timing to add with it. We have found that it is not necessary to add much more than about 8-12 degrees of timing at cruise on engines with well chosen parts. Anything done during rebuilding/upgrading to increase combustion efficiency will usually mandate less total timing and less additional timing needed at light throttle.

In any case, as mentioned, experiment with your combination to decide how much timing the engine wants under various conditions and what source it prefers to be used for the vacuum advance. For engines set up here we seldom if ever use manifold vacuum to the advance, mostly because additional timing at idle is not needed AND we LOVE to hear the lumpity sound from the cam!.....Cliff

[buwalda]

Ditto what Kenth said.

My understanding is that Pontiac went from full manifold vacuum advance to ported vacuum advance for emission reasons, NOT because ported was better.

To those running a big cam & 10-12 initial timing, try this simple test: with your engine warmed up [ & in Drive if auto ], loosen your dist clamp & slowly advance the dist [ clockwise ]. The idle speed will increase & idle quality will become smoother. End of test.

This will now allow the throttle blade opening to be reduced & the idle mixture screws will be more sensitive to adjustmnent.

Don't be surprised if you find the timing for the above test to be well over 20 degrees! A hot engine will be unlikely to crank with this much timing, so the best bet is to use vacuum advance hooked to full manifold vacuum. As the stock vacuum advance can may have too stiff a spring to operate reliably with your 'big' cam, the Crane adjustable unit will work wonders. My 455 gains about 2" of vacuum with vacuum advance & a whole lot smoother & dependable idle. Not to mention cooler running, better throttle response & mileage.

[Cliff R]

We've done LOTS of testing in this area thru the years. I can't qualify the running cooler part. Troubled engines we've tuned here just kept on running hot no matter how much or what source was used to add timing to them. As for mileage we've never noticed any significant gains at cruise using manifold vacuumm for the advance over a well located "strong" ported source. If the ported source is located just above the throttle plates you will have the amount of timing from the advance added at light throttle cruise the same as it would be if a manifold vacuum source were used. Same for throttle response, quick heavy throttle response is a product of the mechanical curve and has little if anything to do with the vacuum advance as they don't add any timing at low vacuum. For light throttle response, again, a well located ported source will add the timing in with the slightest of throttle movement and provide excellent off idle smoothness. What it really boils down to is personal preference. For engines sporting well chosen cam specs for the static compression ratio there is no need to have a lot of timing at idle speed. For the big cammed engines they typically want a higher initial setting. We've went after the carb instead of raising the initial timing off the scale to get them to idle correctly.....Cliff

[can_am4me]

It sure is great to see this topic discussed by people who know what they are talking about. It is amazing to me the number of so called "professionals" who can not even tell you the basic function of the vacuum advance. I know guys in this hobby who think it is purely an emmission device, and must be disconnected. FOOLS!

[buwalda]

Quote on page 12 of the Edelbrock EPS Carburetor Series owner's manual:
"If the engine has a fairly radical cam it may require an excessive amount of throttle opening and/or have low vacuum levels. Either condition can lead to poor levels of adjustability & erratic idles.
. Another fix for the above condition is to run as MUCH SPARK ADVANCE AS POSSIBLE AT IDLE. If the dist. is fitted with vacuum advance, connect it directly to MANIFOLD vacuum. If you are not able to employ vacuum advance for some reason, then the mech. curve should have a low limit, which will allow you to use PLENTY of INITIAL spark advance".

End of quote.

It goes on to recommend a weaker step up spring if the above does not help.
Kenth gives an excellent explanation of the benefits of vacuum advance. I cannot understand why anyone would use ported vacuum advance, when full manifold vacuum advance gives additional improvements over ported vacuum when using a big cam.

[Cliff R]

I sit on the other side of the fence. I can't see why anyone would want to add a bunch of timing at idle to a street/strip engine when it is quite easy and highly successful to tune them to run at or close to stock initial timing specifications?

Even though my opinions vary from most of what I read, we continue to tune and set up strong running street/strip engines, many don't even use a vacuum advance, and when we do use one about 8-12 degrees is added via ported vacuum to help milage a tad at part throttle cruise.

Today, a customer drove about 140 miles here from Pittsburgh just to have us fine tune his fresh 400, 10 to 1 CR Olds 442 engine. His engine builder had installed a 221/230/110 Comp Cam and he was having LOTS of troubles with it. At least 4 others tried to set it up for him before we got it. It showed up with a stock (remanufactured) points distributor sporting a 25 degree advance canister hooked to manifold vacuum. It idled smooth as a sewing machine, not the first hint of lope from the moderate sized cam....and DIED as soon as it was placed in gear if the idle speed was set below about 1000rpm. It also died out instantly if the A/C compressor came on. Despite my best efforts to get it to idle via manifold vacuum the change from free idle speed to loaded in gear was far too great for my liking, even after I reduced the amount of movemet from the advance to 12 degrees.

As delivered here, the initial timing was at 12 degrees, total about 38, plus the 25 degrees from the advance. The carb mixture screws were nearly seated but had little effect at any position until just before seating them. During the test drive the engine had a slight ping at full throttle when heavily loaded and a LOT of ping at any part throttle operation.

The initial timing was set back to 8 degrees, the vacuum advance slot shortened to add 12 degrees, hooked to a ported source, carb mixture screws backed out to 2 3/4 turns where they had full effect if moved any further in. The engine now idled with a nice "lope", but very stable. It only changed about 50 rpm when placed in gear. With the new lower total mechanical setting of 34 degrees and adding in another 12 with the vacuum advance at cruise the Old's 400 now runs at all rpm and any condition without any audible detonation.

The owner commented on how much better the engine sounded at idle and loved the almost no change in rpm from in and out of gear. He was now quite happy with his new Comp "high performance" cam and loved the lumpity, lumpity sound. We then went into a long discussion about how many different opinions he had recieved on how to tune his new engine and the list of friends that had tried to help him set it up. Our conversation drifted into talking about this particular post. He couldn't understand why someone would want to add a bunch of timing at idle and smooth out the engine so you couldn't even tell there was a "big" cam in it? I simply told him that there are a LOT of ways to set one of these engines up and it is always best to expiriement with each combination to find out what it wants and what works best......Cliff

[dutch injun]

Cliff, so all you did was reduce initial timing and backed out the idle mixture screws some more? Why could´nt the ´other guys´ have done that? Is there something you´re not tellin? What was the change in idle vacuum? Not trying to be suspicious ,but I have a similar situation. Big cam that wo´nt pull vacuum unless it´s waay advanced at idle.
Also Demon Carburation says to increase initial to 20/25 degrees with a big cam, so that´s what I did, but if there´s better ways it must be more than just fiddling with mixture screws?

[Cliff R]

We did a bit more than just reduce the initial timing. This engine, at near 10 to 1 static compression ratio DID NOT want a lot of timing from the vacuum advance AND did not want much initial advance as it was experiencing difficult hot restarts at the 12 degree BTDC static setting. It pinged HARD at any attempt to drive the car at light throttle due to the canister adding in 25 degrees of timing to the already 12 degree initial setting PLUS what was added by the mechanical advance as the engine speed increased.

If those tuning the engine had any clue about changing or modifying the vacuum advance to only supply about 10-12 additional degrees of timing, they would have had much better success with their tuning efforts. I was able to get the engine to run just fine using a manifold source for the advance once the amount of timing added by the canister was reduced...but...I did not particularly like the drop in rpm when a slight load was placed on the engine. By using a ported source (no additional advance added at idle) the throttle plates could be opened a bit further, making for a more stable idle in and out of gear with almost no change in rpm's when placed in gear. Of course I could have purchased an adjustable vacuum advance unit and went on to tune it for using a manifold source and set the spring tension where the low reading at idle would not be overcome and reduce the timing when the load was placed on the engine....but....again...why? The engine sounds much better with a slight lope in it and we were quite pleased with the end result.

As mentioned previously, experiment with each combination and use what works the best or more to your own liking. I'm not selling here or advocating one particular way over the other for ALL applications. We tune carbs lots of carbs here to work with poorly chosen components. This is almost always where the troubles start, WAY TOO MUCH cam for the static CR of the engine and/or trying to use a carb that is not capable of supplying enough idle fuel at lower than normal vacuum readings at idle speed. I don't consider running the initial timing up over 20 and even near 30-35 degrees BTDC at idle THE cure for this scenario. Just an opinion based on over 2 decades of tuning high performance street and strip engines.......Cliff

[skipp65]

cliff,did you change the mechanical advance weights or springs? and how do you modify the vacuum advance without an adjustable can,or is thata trade secret? and how do you check how much vacuum advance you have-ck timing with it unhooked and then hook it to manifold vacuum and check again?seems like you took a lot of timing out-didnt that make it loose power? sorry about so many ?s but i am going through this scenario right now and thought i was doing good by setting initial at 19-20.car idles at 750 in gear,idle screws have full adj.ported advance.starts good when hot and with 9.5 cr doesnt ping during hard accel,but i would like to hear more of the cam

[tininjun67]

a note for you racers that are still running manifold vacuum to the distributor. If there is anyone doing that. If the engine builds vacuum at the upper rpm's, (and it will) you will be advancing the timing. I found this out with an 850 and a 930cfm carb. The little 400 was doing some serious breathing. I disconnected the dist. and gained 2 tenths and 2 mph. This on a car that was already running 11.80's. That was the cheapest 2 tenths I ever got. Maybe the most expensive learning curve though. Anyway, I'll have to give the ported side a shot. There are some good arguments for it. Nice work Cliff.

[Cliff R]

There were 3 issues to deal with for this particular combination. First, the 12 degree initial advance setting was causing difficult hot restarts. Second, pinging HARD at any light throttle driving, third some audible detonation at heavy full throttle. Scenario 1 and 3 mandated less initial timing to cure the hot difficult restart and audible detonation at full throttle/heavy load. This was easy, just lower the initial timing back to 8 degrees which also lowers the total timing from 38 back to 34. This move cured both issues. The distributor weights/springs and mechanical curve were acceptable so nothing was done there.

Next I went after the 25 degree vacuum canister. It was removed from the distributor, clamped in a vise and a spot of weld was added via the MIG welder to fill most of the slot in front of the arm. Then a 3/16" round file was used to refile the slot so a .110" drill bit would just slide between the arm and the stop. This reduced the amount of vacuum advance added by the canister from 25 degrees down to about 12.

After the canister was modified it was hooked up to manifold vacuum while watching he marks with a timing light to verify the amount of timing added. We made several attempts to tune leaving it hooked up to manifold vacuum. Having the intial 8 plus another 12 degrees from the advance had the initial timing at 20 degrees. It actually worked pretty good other that the idle was dead smooth and the throttle plates were nearly closed and mixture screws nearly seated. The engine rpm's fell off quite a bit when the trans was placed in gear due to the heavy load from the stock torque converter. A bit too much for my liking so we moved the vacuum source to a ported one and then re-adjusted the carb. With the throttle plates further open and the mixture screws backed out more we found almost no change between in and out of gear. The engine also developed a nice "lope". The owner test drove the car for about 15 minutes, came back with a BIG smile on his face, paid the bill and left.

Keep in mind when reading this post that the Old's 400 was topped with one of our custom calibrated late model q-jets sporting the correct idle calibration for the application based on the static compression ratio and cam .050" duration. It had enough bypass air to idle at lower vacuum readings without nozzle drip combined with plenty of idle fuel and full control of it......Cliff

[skipp65]

thanks cliff,ive read a lot of your posts on here and learn somthing from most of them-you ever think of writing a tuning book

[cujo]

Cliff wrote "This is exactly what happened on my own engine before the Rhoad's lifters were installed." What was the difference between the Rhoad's lifters and the ones you removed?

[Cliff R]

Cujo, I was using the HT951-R lifters in the 455 until one of them pounded out a clip and it went thru the engine. Luckily no damage was done other than it got chewed up by the distributor gear and a peice of it got into the cam bearing.

I had a set of Rhoad's lifters on the shelf so decided to install them. Before the Rhoad's were added the vacuum at 750 rpm was around 8-9" and dropped about 1" when place in gear. The idle speed was steady at 700rpm in gear, but pretty rough. I had about 12" of vacuum at 1000rpm. I would also note that any attempt to use manifold vacuum to the advance raised vacuum at idle and mandated lowering the idle speed some. When the trans was placed in gear the engine immediately died due to the vacuum falling below the spring tension in the advance unit. It is adjustable, but I'm not fond of lowering the spring tension that low.

Adding the Rhoad's lifters raised the vacuum reading about 2" at every rpm in and out of gear. The engine still has a slight "lope" at idle, but is much smoother. I can use either ported or manifold vacuum to the advance and it works fine. Except, I love to hear the cam so no additional advance is added at idle speed. I still get all of the advance right off idle via a good ported vacuum source so fuel economy and off idle smoothness are the same.

The Rhoad's lifters didn't provide any improvements as far as ET and MPH but make the car much easier to stage in the lights, so I did see some benefits. The reason I'm not seeing any ET improvement is due to the converter stalling at near 3400rpm, the Rhoad's lifters are well "pumped up" by then and functioning like stock lifters......Cliff

[Kenth]

TIMING AND VACUUM ADVANCE 101

The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.

The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.

At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).

When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.

The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.

Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.

What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.

For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.

...........Kent