87 Dizzy conversion?

[Stephen Carter]

What would it take to swap out from the stock dizzy, to something a little more tuner friendly?

I did a search but apparently my googlefu was weak the last couple of days and didn't find anything...

(as an aside, my truck was converted to carb instead of TBI, and the stock dizzy is running off the constant vacuum side of the edelbrock 750 [dunno if thats the right port or not})

Thank for any replies my friends!

 

[dyeager535]

What would it take to swap out from the stock dizzy, to something a little more tuner friendly?

I did a search but apparently my googlefu was weak the last couple of days and didn't find anything...

(as an aside, my truck was converted to carb instead of TBI, and the stock dizzy is running off the constant vacuum side of the edelbrock 750 [dunno if thats the right port or not})

Thank for any replies my friends!

They make weight/spring setups for the stock distributor. Been a long time, thought they were called recurving kits or something along those lines....ahh, here they are: http://www.summitracing.com/search?SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=hei curve

How does it run with advance hooked to manifold vacuum? If you don't need to deal with emissions, and the engine likes it, generally (authoritatively?) manifold vacuum is what you want to run.

There are persistent misconceptions about vacuum advance and ported vacuum...no less than GM engineers who worked designing these systems have stated that it was used SOLELY for emissions, the paper is out there somewhere. Vacuum drops when the engine is loaded, which does not effect mechanical advance but does affect vacuum advance. EFI engines run at ~20* at idle, and it's a heck of a lot smoother than 8*. Vacuum advance has minimal effect anywhere but cruise and idle, both where you normally want your highest advance.

The difficulty may come trying to run as much initial/mechanical/vacuum advance as can be used at cruise, while still maintaining a stable idle. You'd have to run all the numbers to see.

Someone has probably done a lot of work testing these things in a modern setup, I think it would be interesting to see if it's possible with a curve kit and adjustiable vacuum advance can, to get high idle advance, and still achieve good performance and cruise MPG.

 

[Stephen Carter]

They make weight/spring setups for the stock distributor. Been a long time, thought they were called recurving kits or something along those lines....ahh, here they are: http://www.summitracing.com/search?SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=hei curve

http://www.summitracing.com/search?SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=hei curve

Those parts state for non computer controlled HEI distributors, I'm guessing that's what is on the 87s?

How does it run with advance hooked to manifold vacuum? If you don't need to deal with emissions, and the engine likes it, generally (authoritatively?) manifold vacuum is what you want to run.

Actually runs pretty decent, I can get to highway speeds in relatively short order, considering the 35" tires, most likely stock gearing, and the over carbed engine (which may or may not be stock inside lol)

There are persistent misconceptions about vacuum advance and ported vacuum...no less than GM engineers who worked designing these systems have stated that it was used SOLELY for emissions, the paper is out there somewhere. Vacuum drops when the engine is loaded, which does not effect mechanical advance but does affect vacuum advance. EFI engines run at ~20* at idle, and it's a heck of a lot smoother than 8*. Vacuum advance has minimal effect anywhere but cruise and idle, both where you normally want your highest advance.

The difficulty may come trying to run as much initial/mechanical/vacuum advance as can be used at cruise, while still maintaining a stable idle. You'd have to run all the numbers to see.

Someone has probably done a lot of work testing these things in a modern setup, I think it would be interesting to see if it's possible with a curve kit and adjustiable vacuum advance can, to get high idle advance, and still achieve good performance and cruise MPG.

This is really my first vehicle in which I can actually adjust anything, I do have an 85 dodge aries with a dizzy, and all I can do with that is adjust base idle timing and the computer takes over. So my basic experience is null. Now if it was a fully computer controlled like an LSx based engine, I can toy with those all day long...

After the truck is fully warmed up, it does have a hiccup at idle (in gear only, which is strange) and on light throttle acceleration. Give it a bit more loud pedal and it seems to straighten up and fly right...

 

[dyeager535]

Those parts state for non computer controlled HEI distributors, I'm guessing that's what is on the 87s?

Actually runs pretty decent, I can get to highway speeds in relatively short order, considering the 35" tires, most likely stock gearing, and the over carbed engine (which may or may not be stock inside lol)

This is really my first vehicle in which I can actually adjust anything, I do have an 85 dodge aries with a dizzy, and all I can do with that is adjust base idle timing and the computer takes over. So my basic experience is null. Now if it was a fully computer controlled like an LSx based engine, I can toy with those all day long...

After the truck is fully warmed up, it does have a hiccup at idle (in gear only, which is strange) and on light throttle acceleration. Give it a bit more loud pedal and it seems to straighten up and fly right...

Should actually be computer controlled of course, since it was TBI originally. If you've got the LSx experience, I say get rid of the carb garbage and go back to EFI.

Given that it has a vacuum advance, it's been swapped obviously.

I'm not going to be a whole lot more help unfortunately, I got out of carbs and won't be going back. I converted to the truck to EFI, and the car is going that way too. The amount of time spent monkeying with carbs and distributors can just as easily be spent monkeying with EFI. Except EFI does everything it can to stay running lol.

 

[Stephen Carter]

Ohh I'm tempted to swap to a 5.3 and 4l60e. But the current pay grade tells me no. Around here a salvage yard will sell a complete 5.3 with pcm and harness for 750$. But at this point, just trying to make this beast run and drive nicely...

 

[82355]

Was the TBI harness hacked when it was removed?

Martin

 

[Bent77]

I agree that time spent fussing with EFI yields more gains than the carb and vac advance.

Adjust the idle screws with a vac gauge and save for EFI

 

[Stephen Carter]

Was the TBI harness hacked when it was removed?

Martin

I believe so. So far I've seen not a trace of the TBI wiring in the engine bay. It may be tucked away some where but I doubt it. I've been looking at how this truck was modified before I got it, and it seems to be rather hack-ish, and not thought out properly.

 

[dyeager535]

I believe so. So far I've seen not a trace of the TBI wiring in the engine bay. It may be tucked away some where but I doubt it. I've been looking at how this truck was modified before I got it, and it seems to be rather hack-ish, and not thought out properly.

Which is 95% of the ones that have been touched, unfortunately. Probably a good candidate for the LS when you get the funds.

 

[Stephen Carter]

Sorry to resurrect, but i've been thinking about this more.

Does anyone know how the computer controls the timing? Or is it all in the curve set in the mechanicals of the dizzy?

The whole LS swap is in planning, but its going to take quite some time to get there.
I'm thinking going with a conventional dizzy and coil set up would simplify things a bit since this thing has been hacked and slashed harness wise, and allow me to enjoy the truck a bit more.

I'm thinking all I would need to do is go with a key on switched 12v source for the coil, ground, install new dizzy, time it @ 8*btdc (all sbcs i'm guessing) and then play with the mechanical advance springs etc?

 

[dyeager535]

You are talking ECM control I assume, since that is all there is outside of ESC, which is somewhat of a bastard. You talk about vacuum advance previous, so I'm somewhat confused why you are concerned with ECM control of ignition?

All of the GM OBD1 EFI I'm aware of operates pretty much the same way. Base idle is normally 0, but if anything above or below that, is added/subtracted to whatever the computer calcs, since the ECM has no idea what base timing is. Ignition module (in distributor) controls spark under 400RPM. Above that, ECM takes over and controls advance. It's more complex than that of course, but in general, spark timing is based on what the ECM sees as load on the engine, and RPM, and it has a lookup table that crosses the two. Things such as throttle position, knock sensor and engine temp are used to further fine tune the advance based on specific conditions.

Here's a screenshot of a typical SBC TBI truck application spark table:

 

[Stephen Carter]

You are talking ECM control I assume, since that is all there is outside of ESC, which is somewhat of a bastard. You talk about vacuum advance previous, so I'm somewhat confused why you are concerned with ECM control of ignition?

All of the GM OBD1 EFI I'm aware of operates pretty much the same way. Base idle is normally 0, but if anything above or below that, is added/subtracted to whatever the computer calcs, since the ECM has no idea what base timing is. Ignition module (in distributor) controls spark under 400RPM. Above that, ECM takes over and controls advance. It's more complex than that of course, but in general, spark timing is based on what the ECM sees as load on the engine, and RPM, and it has a lookup table that crosses the two. Things such as throttle position, knock sensor and engine temp are used to further fine tune the advance based on specific conditions.

And there is my problem. I do not know what sensors exactly the ECM uses in the stock TBI set up to calculate load (i'm assuming thats the top row on that graph). As I am missing TPS, MAP, etc since this truck was converted to a carb some time in the past. So I'm betting I'm not getting the computer based advance like I should be.

 

[dyeager535]

And there is my problem. I do not know what sensors exactly the ECM uses in the stock TBI set up to calculate load (i'm assuming thats the top row on that graph). As I am missing TPS, MAP, etc since this truck was converted to a carb some time in the past. So I'm betting I'm not getting the computer based advance like I should be.

Top row is input from the MAP sensor, correct.

If you have vacuum advance, you don't have a TBI/EFI distributor. I *think* some years of the ESC setup may have had vacuum advance, but they aren't real common. ESC was a standalone timing setup, used with a standard carb on the trucks only. Had a computer controlling it, with knock sensor and matching distributor.

If you do not have vacuum advance, then correct, you will be getting nothing for advance except whatever the base timing is set at. If the wiring is that butchered, I'm assuming they didn't leave the EFI distributor wiring in place.

Did they leave the under-dash wiring alone, or is that all butchered too? If they just cut up the engine bay side, getting the TBI specific wiring/components shouldn't be extremely difficult or costly, and you could just unplug the engine bay side of the fuse panel connector, replacing with one that hasn't been hacked up. Is the ECM/connectors under the dash still, behind the glove box?

 

[Stephen Carter]

I will have to check under dash, I just did a quick peek earlier and it looked relatively undisturbed. But I'll have to do a more complete check in the next day or so...

The distributor does have a vacuum advance on it. Which is connected.

 

[Blue85]

So it used to be TBI truck, then somebody converted to carb, but you still have the ECM? Without all the sensors running, the ECM CAN'T be used to control timing. If somebody happened to use the CCC setup to do the conversion, then there should be provisions for most sensors. But I've never heard of anybody swapping the computer carb in - only out.

There are aftermarket stand-alone ignition control setups, but I bet you could convert it back to normal TBI for the same money. If you still have the in-tank fuel pump and lines, the ECM and in-cab wiring, it could be a 1-day project after getting the top-end parts from a junkyard (or somebody on this site). Or as stated above, just tweak it and run it until it's engine swap time. Most trucks of this era like a lighter spring in the distributor, to bring the advance in a lower RPM. It's important to verify that the mechanical advance is actually working, as sometimes they get gummed up.

The ESC still uses vacuum advance and mechanical advance, as usual. You can't really set timing curves with that box, all it does it introduce some retard when knock is detected. It uses an ignition module with extra terminals to do this. Not worth swapping on, IMO.

 

[Blue85]

Just to clarify (this has all been stated above), '87 would have come stock with a fixed dizzy (no mechanical or vacuum advance), with timing controlled entirely by the ECM. Since yours has the can on it, somebody swapped an earlier dizzy on as part of the carb conversion.

How do you know it wasn't the entire engine that was swapped (Or for that matter, a body swap)?

Have you had a timing light on it? It would help to know what timing it's running at idle, off idle, etc. There could be a simple error like vacuum lines routed wrong, base timing off or stuck weights. Could be can of worms, though. The 80's carb motors had a complicated vacuum system with tons of hoses running all over. To start with a TBI engine and slap on a carb would require a lot of compromises and improvisation to get EGR, torque converter lockup, EVAP, etc. to work right. Even if you don't care about emissions, the carbs and distributors were set up to account for all of this stuff, plus A.I.R. and such. Many have done emissions systems deletes just to find some of these quirks. How about some pictures of the engine?

The TCC lockup issue is an interesting topic, though. How is that set up?

 

[Stephen Carter]

Just to clarify (this has all been stated above), '87 would have come stock with a fixed dizzy (no mechanical or vacuum advance), with timing controlled entirely by the ECM. Since yours has the can on it, somebody swapped an earlier dizzy on as part of the carb conversion.

How do you know it wasn't the entire engine that was swapped (Or for that matter, a body swap)?

It is entirely possible that the motor was swapped, the more I think about it, the more likely that scenario is the one I'm dealing with.
I don't think it was body swapped, as the body mounts look original, the the bolts don't look like they have been hit with any sort of tooling.

Have you had a timing light on it? It would help to know what timing it's running at idle, off idle, etc. There could be a simple error like vacuum lines routed wrong, base timing off or stuck weights. Could be can of worms, though. The 80's carb motors had a complicated vacuum system with tons of hoses running all over.

From what I can tell, there are 3 vacuum lines LOL, PCV, one from carb to brake booster, and one to the vacuum canister on the dizzy

To start with a TBI engine and slap on a carb would require a lot of compromises and improvisation to get EGR, torque converter lockup, EVAP, etc. to work right. Even if you don't care about emissions, the carbs and distributors were set up to account for all of this stuff, plus A.I.R. and such. Many have done emissions systems deletes just to find some of these quirks. How about some pictures of the engine?

The TCC lockup issue is an interesting topic, though. How is that set up?

I have exactly ZERO clue about the TCC lockup, I was told that the transmission was rebuilt, which stands to reason, as its not nearly as dirty as the rest of the motor lol.

I did forget to mention that its an edelbrock 1407 carb (750cfm, way too big for this motor).

I took some pictures if there's anything you want to see specifically I can try to get some tomorrow.

 

[Blue85]

That does look like the 87-only belt setup. The grommet behind the tranny dipstick is where the harness should be. Those are the TBI valve covers. Is the manifold casting 14101074? It really is possible they just swapped the intake, distributor and carb and started over on vacuum lines. It's not unheard of for somebody to give up on fixing their fuel injection woes, just to jump into a bunch of carb woes.

It looks like you still have the fuel pump relay and there's no signs of a mechanical fuel pump, so it's likely you still have an in-tank electric. That's probably what the regulator on the side is doing - knocking the pressure down to carb levels.

Don't see the vacuum switch for proper TCC lockup. Since it's probably the original TBI 700R-4, it's expecting a lockup signal from the ECM. They may have just wired it to the brake switch so you get lockup all the time in 4th gear. There are also aftermarket lockup controllers. Can you get a picture of the throttle linkage? I think I see a TV cable in there, but can't see how it's tied to the throttle.

 

[Stephen Carter]

That does look like the 87-only belt setup. The grommet behind the tranny dipstick is where the harness should be. Those are the TBI valve covers. Is the manifold casting 14101074? It really is possible they just swapped the intake, distributor and carb and started over on vacuum lines. It's not unheard of for somebody to give up on fixing their fuel injection woes, just to jump into a bunch of carb woes.

The kid I got it from said the guy he got it from couldn't get it started, and it was running an aftermarket fuel pump (holley i think?) and he put a regulator on it, set it at 2psi and left it at that and it ran. I've since adjusted the carb, set fuel pressure to a reasonable 5psi (by the gauge on the regulator), seemed to pick up a lot better.

I will this weekend (woo for 5 day weekend!), hook up my timing light and see what I have at idle and off idle. It does look like an older HEI dizzy since i've taken a long look at it, so maybe the non- computer controllled advance kit listed above may work out so I can maybe squeak out an extra mpg outta the beast lol!

 

[Blue85]

Yes, a standard HEI curve kit should fit that.