Hi guys.
It's nice to be back! After my heart troubles in the fall, I didn;t play with cars much, but here I am having fun with my slant again.
That's a real "boo/yay" as they say. The just completed project involved getting the timing curve set up for the turbo. I had to fill in the advance slot on the mechanical governor to limit the advance to just 12 degrees since I got serious preignition under boost conditions. This had kept me from really flogging the engine, as they say over, and over again in all the turbo literature engines will not stay together under boost/preignition conditions. That worked out well, but then I had to get a ported vacuum tap off the throttle body. The Buick TB has no such thing. Putting full time manifold vacuum to the advance was not acceptable. It raised the idle RPM too high. This required closing the throttle blades down to bring the idle down, which in turn would allow the engine to die, if for any reason the vacuum reading dropped off at idle,(a miss of any kind). This was particularly a problem under warm up conditions where the enrichment curve in the computer is steadily reducing the mixture as the temperature comes up. The resultant small retard in timing would further slow the engine down, resulting in more vacuum drop. This cycle spins the engine into a stall very promptly. I needed to get the vacuum advance unit out of the picture during idle.

After studying the old Holley 1 barrel, I could see that the ported vacuum tap enters the airstream just behind the edge of the throttle blade. It is covered until the throttle is kicked open a hair, at which point the tube is exposed to vacuum. I carefully plotted on the outside of the TB where the throttle blade rested against the inside of the TB bore, and drilled a #45 drill bit all the way through to the inside of the TB. The hole emerged just behind, and slightly above the closed throttle blade. When I say just above, I mean less than the diameter of the drill bit above. The bottom edge of the hole is hidden from view when the blade is closed. I then opened the hole with a .123 drill from the outside, being carefull to not go all the way through with the larger hole. I left the inside opening the smaller size. I then pressed in a 1/8" piece of brass tubing available at the local hobby shop, and reinforced the support for it on the outside of the TB with JB weld. It works like a charm. Now the vacuum advance sees no vacuum at idle. I can open the TB blades to get a stable, cleaner idle, and a miss in the engine for whatever reason does not effect the timing. The slant's idle is much more stable now. I haven't "flogged the engine yet, but taking 12 degrees out of total timing eliminated the preignition before, so this should do the trick.

It is really good to be back. I am looking forward to reading everyone's posts now, and hope I can help out some.

Sounds like we have another fabricator in the bunch.

It also sounds like you are making very good progress. Keep up the good work, I'll be looking for helpful tips on boost in another year or so after I have my car painted and have the new engine and transmission completed. (Honest, it's all just sitting in my basement waiting for 3 weeks of free time to put it all together)

Glad to see others are still forging ahead with the fancy stuff.

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1980 Aspen 225 super six

Welcome back Vader. I see you're "new". How did that happen? It was interested in reading your post because it is different than my experience. When I did the EFI conversion, and before I did the turbo, I had considered drilling a hole as you did but found that manifold vacuum worked fine and I never had a problem. When I installed the turbo I wanted to use the knock detector so I used the GM ECM to control ignition timing and the issue became mute. I'm running about 17 degrees of total timing and haven't experienced any detonation with 8# of boost. Are you using 93-octane? How much boost?
One problem that I have experienced is some detonation (not audible but on my knock gauge) when accelerating from a cruise of 65-70 MPH. This occurs even during mild acceleration when there is no boost, but only at speeds above 65 MPH. When I go full blast from a dead stop to 70 and beyond there is no detonation, only when I accelerate from a high cruise speed. I've been thinking of using some kind of high-speed retard that I can activate when on the highway, and toying with the idea of using the later dual pick-up distributor to implement it. One of the pick-up coils is slightly retarded from the other in that distributor.
Welcome back!
Bob D

Good show, Vader. Glad that port worked out. I'll do that on mine when I get home. I'd say 22-24 deg is the max at full advance, and 20 is probably more like it.

Bob, I would say that you don't need to worry about preignition under light throttle and no boost. It won't hurt anything until you get under a solid load. In fact, some newer cars run with slightly audible pinging under light load as the best mileage is on the edge of pinging.

Lou

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Home of Slant6-powered fun machines since 1988

Thanks for the tip Lou. I didn't know that. I'll still find it disconcerting when I see those knock gauge lights lighting up! I'm wondering how the newer cars keep the ECM from pulling back the timing when this knock occurs. I'm guessing that the knock detector circuit must be desensitized.
Bob D

They probably look at the MAP/MAF and see what load the engine is under.

You might check your vacuum readings when the pinging occurs. If it's above about 4"Hg and pinging lightly, then I think you're OK.

Lou

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Home of Slant6-powered fun machines since 1988

Thanks for the welcome mat. I am listed as new, because I just offically joined, even though I have been participating for years. I think 17 degrees total advance is why you are not experienceing any serious problems with pre-ignition under load. Prior to recurving my distrbutor, I had 35 degrees advance, total, and that was just too much. If I retarded the initial setting to TDC, it would run WOT just fine, but idled very poorly, and died every once in awhile. You are using the GM ECU, and the GM knock sensor, which should keep you out of any big trouble. I assume the map sensor is feeding the ECU information about boost conditions, and the Buick GN programing is likely designed to retard the timing only under boost conditions and pre-ignition. My guess is the mixture gets just a little lean on you when eccelerating between 65 and 70 under light throttle. I have the same knock gauge in my car that you do, thanks to your advice, and I "see" inaudible knock now only under light acceleration in warm up mode. I don;t worry about it at all. It goes away completely once the engine arms up. I am using the Mega Squirt ECU, thanks to Dart 270's able assistance. It's fuel map is nice, but the version I currently have does not have a spark control. If it did, it would be possible to completely tailor the spark curve to the exact needs of this engine.

Bob, did you ever install the Idle Air Control? If so, that would explain your success with the manifold vacuum at the distributor. By the way, is your centrifigal advance still active? Do you run the vacuum advance, or does the Buick ECU handle that? Have you ever considered going to a programable ECU of some kind? They take a little work to get tuned in right, but I think they are worth the effort. There were more than few times when I went crying to either Lou, or the Mega Squirt web site for help, but in the long run am glad I went that way. They are getting ready to release an ad-on module for ignition control, and that is in the works for the future here.

One more thing Bob, I took both mufflers off as you advised, and got another easy 700 RPM out of her. She pulls strong to 5200 RPM now, whereas before, while it could get to 5200 RPM, it was clear that shifting at 4500 ws better. She just seemed to poop out above 4500. Now she races right up to 5200 strong. I suppose it could go higher, but I am told these guys stay together longer if you keep the RPM down, and don;t try to spin them up real high. Now she has no mufflers at all: just straight pipes. She is a little loud, but not offensive. Sounds kind of like a 70's Jag. Thanks for the tip.

Relating to your exhaust point, Sam and Bob. Cameron Tilley's turbo car has 3.5" (you read that right) from the tubo housing back, and he said it makes a huge difference, even over 2.5". He also runs a HUGE intercooler, about 18" square and 2.5-3" deep, and that also made a huge difference.

Lou

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Home of Slant6-powered fun machines since 1988

Knock gauge? How do I build one?

Vader,
I initially used the IAC but eliminated it a few years ago because it seemed to sometimes have a mind of its own. I like the idle much better without it but then I only drive this car in the summer. Now that I have the turbo with the ECM controlling the ignition timing I've eliminated both the vacuum and mechanical advances in the distributor.
I'm sure the MS is good technology but I'm quite happy with the way my set-up runs. I like the MAF with its ability to keep things in tune, the knock retard capability, and the idea that I can carry a spare (cheap) ECM.
If you want to tone down the exhaust try the Monza tips. They will mellow it and take the harshness out, and I doubt it would hurt your performance.
Craig,
A knock detection gage can be purchased from Casper Electronics ( www.casperelectronics.com , P/N 102001, $69). Instead of the gage you could make your own knock detection indicator if you prefer. This is described in an article entitled "How to Build a Smart Knock Detector for Less Than $20" that can be found at http://www.turbobuicknewsletter.com/bon ... onus1.html. You'll also have to get a knock detector and Electronic Spark Control (ESC) module from a junk yard. The detector that you want has a ¼-20 stud that will screw right into the top of the SL6 block. These are found on later GM engines. The earlier ones had a ¼ NPT stud and would have to be adapted to ¼-20 to screw into the SL6 block. I found that the best place to install the knock detector was in one of the ¼-20 tapped holes on the top of the block. These are the tapped holes normally used to attach a bracket when pulling the engine. If you get the later knock detector the stud will fit in this tapped hole. It is important that the knock detector be torque into the block at 14 ft-lbs.
Bob D

Bob,
Are you using a stock turbo buick ecm or did you get a custom chip burned?

Actually I'm using an '85 ECM with a stock chip from a naturally aspirated '85 GM 3.8L engine with my turbo. The turbo ECM is sequential, and although it would default to batch fire in the absence of a cam position sensor, it had a miss at high RPM. I tried a few of these so I'm convinced that the problem was related to the default mode. To my amazement the stock naturally aspirated batch fire ECM worked perfectly as long as I used the turbo MAF sensor and larger turbo injectors. This really demonstrates the versatility of the MAF system in my opinion.
Bob D