I've done a little bit of research about doing a LT1 EFI to carb conversion, but would like to find out more from the apparently very small number of you that have actually done it. As of right now I got my buddy's SBC edelbrock single plane intake (don't know too much about it but it has a very low overall height and looks like it'll outflow the hell out of my ported LT1 intake) and a holley 650cfm double pumper (i'm pretty sure he even has a low pressure fpr laying around I could just have) just sitting in my garage and if it'll work I can buy them from him for around $100-150 (He put a big block into his chevelle and has no use for them anymore).

First off, will the intake ports line up with the head ports exactly? Secondly, where could I find a schematic for the bolt pattern that will need to be drilled into the SBC intake manifold? (from what i've read all you need to do is drill new holes to match the gen 2 SBC heads?) I also want to minimize the amount of cutting to the cowl area, it seems to be pretty unlikely that i'll be able to just drop in a conventional distributor without doing some cutting, so atleast for now will I be able to still use the optispark... Is it possible to use the ECM just to run timing on the opti and just get rid of the all the fuel tables? If so, (with the short rise intake) will the carb be able to clear the cowl area without cutting? What about the fuel lines, what fabrication needs to down there with the intake and return line? I'm looking for some elaborate details on this entire process and anything anyone else can think of that needs to be done would be quite useful. Also if anyone knows of any websites with some more information in regards to running a carb''d setup on Fbody please let me know about them, because I haven't been able to find anything about this and I really want get a indepth idea of what I might be getting myself into.

 

First off whats the reason for the switch?I ran my fuel injection all the way into the 9's so performance wise its up to the task unless your making unreal power.Besides that injection is much better suited for a street driven car as far as throttle responce and ease of maintainance is concerned.I have a carb on mine now but its a dominator on a 1st gen 420 ci sb and only because I couldnt afford a stand alone ignition system and converted EFI single plane otherwise mine would still be injected.

 

Well, for now I am just pondering the idea and try to get an idea what is involved with the switch over. I can't seem to find too much about it online, so I thought i'd post on here with hopes that someone that has either done the swap on a fbody or knows a bit about it will chime in.

 

anyone?

 

Do a search on it on here, if you cant find enough info on single plane intakes just e-mail me.

Bret

 

I did a bit of reading up off the search and but still have some of the same questions.. I can't seem to find to much about these:

1. Pretty much most of the people on here that did the actual conversion seems to have just bought the GM carb conversion intake manifold, I know of this already, BUT couldn't find too much about the actual conversion process of a single plane intake like the one laying in my garage.. I did manage to find one thread about this where someone was saying that it was easier to match the holes in the heads for the intake due to something with the primaries.. I don't want to pull the heads off and match the holes on the intake. IS IT POSSIBLE TO DRILL THE HOLES INTO THE INTAKE TO MATCH THE STOCK INTAKE?? ALSO, THE INTAKE PORTS ON THE STOCK INTAKE APPEAR TO BE IN THE SAME PLACES AS THE SBC1 PORTS, WILL THEY LINE UP?.. If so, I don't quite understand why it would be difficult to drill the new holes into the SBC1 intake?

2. Also, (kindof still relating to the single plane intake) it appears with that GM duel plane intake you have to cut the cowl area some, but with the single plane intake (which sits lower), IS IT STILL NECCESARY TO CUT THE COWL AREA (assuming I can run the opti for igntion)??


3. Everyone seems to just pull out the opti remove it, block off the hole and just run a MSD ignition and Distibutor after cutting the cowl area, but the stock ECM is retained to run the guages in the car, AC, etc. IF THE STOCK ECM IS RETAINED COULDN'T I STILL USE THE STOCK OPTI FOR NOW?? The signals from the opti sensors (lo-res/hi-res) would still be there, so it sounds like it would still work, BUT WOULD THE FACT THAT NONE OF THE SENSORS (map, iat, ect..) WILL BE HOOKED UP, WHICH WOULD MESS UP THE FUEL ALSO MESS UP THE TIMNG OR CAN ALL THE FUEL TABLES AND SENSORS JUST BE "TUNED" OUT (I don't know too much about programing a ECM as you can probably tell.)

 

Yes, but your problem is that the holes will overlap and you can't get the intake to #1 seal up in the lifter valley, = vacuum leak, and #2 there will be no place for the bolt head to clamp to on half of the holes. If you ever look at one of the single planes I do I weld up the intake flanges where the bolt holes used to be and then convert the intake manifold over for the LT1 bolt pattern. They are in different spots AND at a different angle which means you also need to figure out a way to give the underside of the bolt head and washer a place to clamp evenly.

No depending on what you run for a elbow/TB setup. If you ran a carb, it's going to need to be cut.

Yes.

No you need all of those sensors to make it work, that's why you talk to someone who has done this before, that's why I suggested that. There are 4 vacuum fittings you will need(opti, FPR etc.) and a place for the IAC, the MAP and a PCV to get it all working.

Bret

 

Thanks for all the help it cleared up a lot.

How much do you generally charge to just weld up the old holes and drill out the new ones for the LT1 bolt pattern? (don't need to convert anything for fuel injection)

 

wait distributor? i thought Lt1s had no cam gear to drive a distributor?

EDIT: NEW LT1's that is, like the 90's ones

 

I don't know.. I thought you just pulled out the oil pump drive and could drop in a regular distributor?

 

Yep you can do that.

E-mail me if you need specific info on the intakes.

Bret

 

Get ready for a fun job...I just got done hooking everything up right now, went to fire it a boom...no go. I'll have to mess with it next week. With the GM dual plane carb intake manifold you dont need to cut the cowl to fit it. If you running an air breather (i'm not because its a drag car) your going to have to cut the cowl. If you using an MSD dist. your going to have to cut the cowl. If your installing a dist. mounted in the rear you going to need to drop the motor. Your going to need to cut the cowl anyway if you use an msd because the plug ends don't fit. Theres no way around it...your going to cut the cowl.

I'm not sure how others on here set there stuff up but you'll need to pressure regulators if your using the stock one. I just completly redid the whole fuel system. You'll also need a carb (duh), throttle cable, throttle bracket, hold down for the distibutor, misc. fittings for the fuel system, new plug wires, msd box, the list goes on brother.

 

I hit a little snag in my big block conversion because I'm waiting for motor plates, but, to help you with a couple of things.....

I did not retain the computer so can't help you with that but in terms of the distributor I bought a "crab style" MSD dist and it fits under the cowl. Depending on your intake it is the carb that makes it necessary to cut away the edge of the cowl, just in front of the windshield.

As far as the fuel lines I have read a lot of guys that use a regulator to regulate down the pressure. I am changing the lines over to standard lines.

I basically have read a lot here on the site and that's where most of my research took place.

Good luck!

 

I have mine running (BRE EFI Super Vic) and it wasn't a simple bolt on thats for sure. With the Super Vic and the Wilson Elbow milled as far as possible, I still needed to cut the cowl for clearance. Maybe about 3/4" back and 4" wide. Now with a Carb, it almost looks like you would have to lose the wipers for clearance but I can't say for sure about the intake you are looking at using.

You will need to drill and tap new holes into the heads though. The center two holes on each side will not line up. You can't just drill the holes to match the LT1 pattern because you will never get a bolt through there. You could feasibly drill and tap the heads while on the engine since you aren't drilling into water, it is just material hanging out in space. With a drill jig and tapping block it probably wouldn't be all that bad. Just make sure you really seal up the lifter valley and clean up all of the chips carefully. I guess if I were that far I would just pull the heads and do it the right way, but it would probably work if absolutely necessary.

I chose the EFI route for tunability and driveability in changing conditions. The car does surprisingly well for the massive throttle opening (90mm) and has very good road manners so far. I would strongly suggest going the EFI route if you are going to drive the car on the street since you can get away without any significant cutting and still retain the stock computer and just modify the wiring harness for the new TPS and IAC.

 

i have a carbed lt1 in my s-10 and i have a edelbrock 600 on the gmpp carbed intake and an msd distributor. but i pulled all my electronics out. its a time consuming project but at will be worth it when all said and done. good luck. matt