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Old 02-27-2011, 05:41 PM
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TBI to Carb swap..distributor question

I am doing a TBI to Carb swap on a 92 chevy 350. I found a carb intake for the engine that fits. I know that the engines from 74 - 86 is different from the 87-95. Will a HEI distributor from the 74-86 fit my 92? I know I will have to change the gear on it to fit the cam, but is the shaft long enough to connect with the oil pump rod?

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Old 02-27-2011, 06:01 PM
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You won't have to change the distributor gear. Just put in a Chevy HEI. You can also use the 86 and earlier intake if you file the center intake bolt holes larger.
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Old 02-27-2011, 08:43 PM
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Does your 350 have a roller cam? if so, you have to change the gear, but yup, the distributor fits right in. no problems, Steal the power from it from the wire at the TBI COil.
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Old 03-01-2011, 04:35 AM
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Quote:
Originally Posted by jsmartdothan
Will a HEI distributor from the 74-86 fit my 92?
Yes, the distributors used during those years will fit your engine perfectly.

But- you have to be sure the distributor is for use w/o the CCC computer. This means the distributor needs to have both a vacuum and mechanical advance built into it.

There were many cars made from '81-'86 that are not correct for what you are doing, so just be sure the distributor is a "stand alone" HEI and not for use w/a computer. Trucks through '86 may have the right distributor, but not all of them will be correct.

Again- you need an HEI w/BOTH vacuum AND mechanical (springs and weights under the cap) advance built into the distributor.

If you happen across an HEI w/an "extra" 4 wire connector on it, and it has both mechanical and vacuum advance, you can still use it. Just splice the green and black wires on the distributor side. This will bypass the electronic spark controller.

Last edited by cobalt327; 03-01-2011 at 04:42 AM.
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Old 03-01-2011, 04:57 AM
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if the tbi is coming out and you have a 700r4 the swap is vary easy.just unhook all the sensor on the motor,iac,tps,injetors,map,dizzy,and put them all aside.all you need to get is a throttle linkage/tv bracket to hookup your tv cable and throttle linkage .hook up a hot wire to the dizzy and the white to the tach.and a mr gaskets AFR to drop the fuel presure down to 5 to 9psi .the pump in your car/truck now runs about 13psi so theres no need for a EFI fuel presure regulator.you can get away with just a carb FPR with a return.but still don't start cutting all the wires just neatly wrap them up and set them aside this way you still can use the OD without going into the wires
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Old 01-03-2013, 07:58 PM
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TBI to CARB Distributor

First just a little back ground, I was CARB and went TBI, won't go into the details.

Decided to switch back to test something with the CARB, but did not want to pull the Computer or Distributor.

Interesting Fact, if you leave the computer connected the the TBI Distributor, Remove only the, TPS, INJECTOR Wiring and IAC.

The idiot light on the dash will turn on, but the car will run and timing will work from the computer with a default curve thats been programed into the computer's "Limp home mode" which works pretty close.

If you have a digital timing light check the curve while all those are unplugged and the carb is installed.

Want to save some cash on the fuel system, pick up a brass tee fitting for $1.69 and an 8psi cracking check valve with a stainless or brass seat $24.00

I'm sure to get a lot of negitive post on the above about how this won't work, however been running like this for a while, tested fuel pressure under all loads with a gauge in the car, perfect 8psi will full flow to the return line unrestricted. And timing checked many many times to be sure.
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Old 04-10-2013, 10:47 AM
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Check valve

Quote:
Originally Posted by edecisions View Post
First just a little back ground, I was CARB and went TBI, won't go into the details.

Decided to switch back to test something with the CARB, but did not want to pull the Computer or Distributor.

Interesting Fact, if you leave the computer connected the the TBI Distributor, Remove only the, TPS, INJECTOR Wiring and IAC.

The idiot light on the dash will turn on, but the car will run and timing will work from the computer with a default curve thats been programed into the computer's "Limp home mode" which works pretty close.

If you have a digital timing light check the curve while all those are unplugged and the carb is installed.

Want to save some cash on the fuel system, pick up a brass tee fitting for $1.69 and an 8psi cracking check valve with a stainless or brass seat $24.00

I'm sure to get a lot of negitive post on the above about how this won't work, however been running like this for a while, tested fuel pressure under all loads with a gauge in the car, perfect 8psi will full flow to the return line unrestricted. And timing checked many many times to be sure.
I see where it would work but if it fails you lose a very expensive carb! for a $100.00 savings just my opinion.
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Old 04-10-2013, 10:59 AM
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Instead of going through all of that headache just swap your ECU. keep your TBI, keep your dizzy, keep your fuel system, and greatly improve tunability.

You can even modify your stock ECU if that's the route you want to take. It makes MUCH more sense in most cases- and the total cost is less.
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Old 04-10-2013, 08:58 PM
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TBI to CARB

Your right, there are times that you want TBI, but there are also times that a CARB is just better for the old engine.

I've been running now for allmost a year on my Holley, I have my o2 Gauge in the car still and with the CARB its reading better than the TBI at all speeds, it responds faster to changes than TBI, I'm still running the TBI fuel pump in the tank. I can swap back to TBI in about 15min because everthing is in place, when I feel like it, the Carb will leave a 30foot track from the tire from a dead stop. The TBI will chirp the tires when it feels like it.

The one change I did make was I put a 4.5 PSI regulator at the Tee fitting going to the CARB for the reason stated above in the prior post, I did not have any problems but I worried about a clogged return line flooding the engine so I put in the regulator to prevent damage.
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Old 04-10-2013, 09:19 PM
How fast is fast enough?
 
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I'm going to assume your tbi unit was not tuned? As for changes I have yet to find a carb that takes into account air temp, knock, coolant temp, etc.

Carbs can work real well but they never will have the ease of tuning nor the instantaneous adaptability that efi has. There's a reason gm made the switch about 40 years ago.
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Old 04-10-2013, 09:38 PM
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"I'm going to assume your tbi unit was not tuned? As for changes I have yet to find a carb that takes into account air temp, knock, coolant temp, etc.

Carbs can work real well but they never will have the ease of tuning nor the instantaneous adaptability that efi has. There's a reason gm made the switch about 40 years ago. "

The TBI was tuned perfect, Had it checked several times, the origional TBI computers were slow to process changes, and your right Carbs take more effort to tune, but when setup correctly do as well.

The main reason GM made the switch was for SMOG not performance as it was mandated by the goverment, I grew up at that time, and I remember how bad all the cars were in performance and power when they made the switch.

In 1986 California still required smog to be in working order on a 67 Camaro, to meet the rules at that time a Smog kit had to be added to a 67 camaro, the change at that time was to set the timing to 0 BTC, and plug the vacuum advance, and to place a small sticker on the driver window or dash.

I still remember driving my Camaro away from the smog shop, soon as I got home I put it all back like it was.

Not all changes are for performance, most are to comply with the new smog laws. IMO
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Old 04-11-2013, 07:23 AM
How fast is fast enough?
 
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Quote:
Originally Posted by edecisions View Post
"I'm going to assume your tbi unit was not tuned? As for changes I have yet to find a carb that takes into account air temp, knock, coolant temp, etc.

Carbs can work real well but they never will have the ease of tuning nor the instantaneous adaptability that efi has. There's a reason gm made the switch about 40 years ago. "

The TBI was tuned perfect, Had it checked several times, the origional TBI computers were slow to process changes, and your right Carbs take more effort to tune, but when setup correctly do as well.

The main reason GM made the switch was for SMOG not performance as it was mandated by the goverment, I grew up at that time, and I remember how bad all the cars were in performance and power when they made the switch.

In 1986 California still required smog to be in working order on a 67 Camaro, to meet the rules at that time a Smog kit had to be added to a 67 camaro, the change at that time was to set the timing to 0 BTC, and plug the vacuum advance, and to place a small sticker on the driver window or dash.

I still remember driving my Camaro away from the smog shop, soon as I got home I put it all back like it was.

Not all changes are for performance, most are to comply with the new smog laws. IMO
Its really bothersome when people don't realize that many devices that lower emissions ALSO increase performance.

How do you think EFI helps emissions- by providing more accurate fuel metering under varied conditions. More accurate fuel metering... now what would that have to do with performance?

Carbs and mechanical distributors can work well enough right after you tune them properly- but as soon as ANYTHING changes they need to be retuned. "anything" can refer to different gas, different temp, different barometric pressure, hell even a different oil can affect it.

God knows a TBI unit isn't perfect, but it is an advancement from carbs, particularly on a street vehicle that will see ever changing conditions.
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Old 04-11-2013, 07:27 AM
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were going way of subject for this orgional post, but thanks for playing, johney tell him what he's won....
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