Looking for help with new distributor.....HELP!!

[goingballistic]

I'm in the final stages of the rebuild. Got an MSD distributor via Summit today and was installing it and noticed that the tach drive is mechanical.

Being this is an 81, there is no provision for a mechanical tach drive, I am assuming it is electrical connection via the 4 pin plug from the dist to the computer in the car.

So the question is this. What distributor does one use. I don't want to place a new tach nor connect mechanical to the tach, I'd like to use the electical connections to the tach to avoid mods to the original tach or dash board.

Any one got any suggestions. The distributor I bought was an MSD-8572 "chevy Corvette with tach drive" I had no idea it was mechanical drive. If anyone has a part number, manufacturer etc, it would be greatly appreciated, I'm desperately trying to get to the dyno in two weeks and if I miss the date, I'm off for another month until I can reshedule...............HELP!!!!!!!!!!

Thanks.

 

[pgtr]

Hate to say it but that's probably not the unit you wanted. "Tach drive" is the mechanical cable driven tach provision used on Corvettes til '75. I suppose you can make it work by hooking up your tach to the coil or something but... MSD has others that might be better for a 75+ C3s including an HEI clone and standard style distributors (8360? 8361?). I strongly suggest sticking with the vacuum can equipped models for street applications. I presume Summit will exchange it for you?

good luck,

 

[Jack]

Are you /were you planning to run an MSD box? Pretty sure The distributor you have MUST use a box.
JACK:gap

 

[goingballistic]

Thanks, I'm not worried about them exchanging it, they are pretty good about that, the problem I have is that I have no idea what distributor to order.

I really have no intentions of using the on board computer, the motor is punched out to 388 and 10.6:1 CR. The distributor has the vaccuum advance but I really don't want to go to mech tach drive, so I'm looking to see if someone makes a drive that drops in that I can feed to the tach, I'm expecting that one doesn't exist as I think the wires feed the computer with a pulse that then feeds the computer and updates the tach, so I suspect that that any off the shelf wont work.

I'm willing to put a distributor in that connects to an external tach meter ( I'd rather not do this but if that's the only option?) that I have to mount in the car but I'd prefer to use the original if possible, I'm fearful that no one makes an of the shelf that feeds the tach directly, I suspect it HAS to go through the computer and like I said I'm not using that with the new motor.

Any one???????????

 

[Jack]

I just checked ... 8572 is wrong one ... it does require a separate MSD box (at least $160)... the box will drive you elec tach but requires a lot of extra wiring.

MSD 8365 would have been the correct stand alone distributor to drive your tach ... and by pass factory comp/ECU ... probably about $300-$350

I have complete brand new Accel stand alone HEI that will do same ... half the price.
JACK:gap

 

[bossvette]

Does your origional distributor have a vacuum advance or is it controlled by the computer. There are basically two versions of the HEI the early non computer and the later computer type. The later style did come in both a small cap and large(coil in cap) style.
If your origional distributor has a vacuum can and is not controlled by the computer a generic chevy MSD will work the tach signal will be taken from a wire on the MSD box you do not need the "tach drive" distributor that is for earlier Vettes with mechanical distributors.

 

[bossvette]

just saw your latest post my 76 has a brown wire that drives the tach and it connects to the HEI don't know for sure about an 81 but you should be able to use any replacement HEI that is pre computer and take the computer out of the picture for engine control.

 

[goingballistic]

I just checked ... 8572 is wrong one ... it does require a separate MSD box (at least $160)... the box will drive you elec tach but requires a lot of extra wiring.

MSD 8365 would have been the correct stand alone distributor to drive your tach ... and by pass factory comp/ECU ... probably about $300-$350

I have complete brand new Accel stand alone HEI that will do same ... half the price.
JACK:gap

Jack thanks and also the rest of you for the help. It's always the little things that seem to get you in a rebuild and for the love of me are eating up more time than I ever imagined.

Jack, you're right, I looked into that last night. In talking to Summit, apparently they have no idea what they are doing and for that matter neither do I !

I appreciate the offer but I'm going to send the one I bought back and exchange it for the part number you supplied. I looked into that one and your right, it's the one I should have bought in the first place. I actully thought about buying the box and wiring it all up so I could have more control of the timing, the more I look at it the more it appears to be a major hassle to do. I'd like to stick with MSD as I've always had good luck with them, again thanks for the offer.

Thanks again for everyone responding, I might make this Dyno yet !

 

[Jack]

8365 offers just as much "control of the timing" as 8572 w/box. You'll probably like 8365. Don't hesitate to ask questions here at CAC ... lotsa good folks willing to offer help/opinion. G'luck w/ dyno etc.
JACK:gap
-edit- Roller cam in new motor? ... if not, no problem ... If so, check w/cam maker if the distributor's gear is proper metalurgical match to gear on cam ... it can really matter.

 

[bossvette]

-edit- Roller cam in new motor? ... if not, no problem ... If so, check w/cam maker if the distributor's gear is proper metalurgical match to gear on cam ... it can really matter.

Yes it does make a difference I found out the hard way check with the cam manufacturer to see what type of gear you need or you will be chasing gremlins after a while.

 

[Bob Chadwick]

I've got the 8365. A nice set up that will allow you a lot of control over your timing curve with very little effort.