Re: Ok guys new idea... EFI need help
 

The corvette servo will make it shift harder from 1st to 2nd and 3rd to 4th. The servo applies the band in 2nd and 4th gear.

Re: Ok guys new idea... EFI need help
 

You know that ALL Quadrajets are capable of flowing about 800 cfm? The same carb is used on a 231 Buick V6 as a Cad. 500. Each carb is tuned for the size of engine it came on and there is a stop that limits how far the throttle blades can open thus limiting airflow. The Qjet from the 231 will not work well on the 500 and vice vesa. Telling him to throw the Qjet in the trash is not good advice in my opinion.
First, you need to make sure the truck is tuned up. Cap, rotor, plugs, wires, fuel and air filters. Most of the time, the coil is fine and does not need to be replaced. Then move on to tuning the carb.
Also, you need to check your gearing. 4.10 gears is not helping the fuel mileage any. If you wanted to switch to fuel injection there is a good thread on here covering TBI swaps.
http://67-72chevytrucks.com/vboard/s...d.php?t=352321

Re: Ok guys new idea... EFI need help
 

i think it has 3.73 in the rear end the qjet carb is really old and ima put the new heads from my uncle a new intake and a new edelbrock carb is 600cfm the right amount for my truck?

Re: Ok guys new idea... EFI need help
 

It is very possible there is a problem in the vacuum control system that the truck 700R4's use for lockup control so the converter is not locking up like it should in 4th. This would drop your mileage a little.

Re: Ok guys new idea... EFI need help
 

The big valve heads will only worsen your mileage. Bigger valves = more air flow = more fuel consumption, end of story.

You can do very well with the heads you have with a good truck cam, intake & carb.

I would suggest this cam

http://www.summitracing.com/parts/CCA-12-234-2/

I put it into my old 81 K20 and even with no overdrive it would manage 16 mpg when with the stock cam it only got 12. With your overdrive and the lock-up functioning you should have no problem getting better mileage than that.

The Performer EPS intake and 1406 Edelbrock are just right with this cam too.

Re: Ok guys new idea... EFI need help
 

If you know how to work on Rochesters they are great carbs. But they are very hard to tune. I've only known one person that could and he died a long time ago. The money spent on that could be spent on a new carb.

Re: Ok guys new idea... EFI need help
 

You are completely wrong here. The converter only locks up in 4th gear and at a preset mph or vacuum level. It does not lock up in any other gear and if it had never worked since he owned the truck (which is highly likely with the lousy vacuum control system in the trucks) then he would never know it didn't work.

On the countless 700R4 vehicles I have owned they drop a very noticeable 300-400 rpm when the converter locks up. It feels like a shift into another gear.

Re: Ok guys new idea... EFI need help
 

The reason I said that is because that's what the tranny guys told me when mine slipped. After they replaced the converter it went away. The slipping was very noticeable. I guess they could have been wrong too, but that doesn't explain why they fixed it.

Re: Ok guys new idea... EFI need help
 

Your converter was damaged and not functioning right.

If the lockup system is not operational then the trans will still work perfectly fine running around town but the converter just won't lock up when you hit the threshold speed.

The vacuum control module the trucks use is prone to failure and I have had to replace three on different square body trucks I have owned to get the lockup feature working again.

Re: Ok guys new idea... EFI need help
 

I know I'm a little late to this thread and it sounds like your going to keep your carb, but look at this kit:

http://www.professional-products.com/EFI_3.php

I helped a friend drop a new 400 in his '69 camaro, he has this kit on it. After he put about 600 miles on the car and got it dialed in, so it could self learn we went for a ride. We went up through the mountians here, and back almost 200 miles round trip. Tank was full when we left and he topped it back off before we came back to my house. Calculated out to 17.2 mpg. This motor has 500 hp and over 520 ft-lbs. It also has a tremce tko 600 and a moser 3.42 geared rear end and he was not being easy on it. This setup has the potential to give more MPG just crusing on the highway.

Here is the video of it on the dyno, with the specs in the comments. While these types of setups are expensive, they will deliever the MPG. This engine would probably be doing good to get 10 with a carb........


The car is a blast too by the way!! :D

Re: Ok guys new idea... EFI need help
 

Yea i was looking at that kit but i think its cheaper just to stay with a nice new intake carb and the heads

Re: Ok guys new idea... EFI need help
 

It all comes down to how much power you are wanting to make when it comes to an EFI swap and the cost involved.

For under 300 hp you can get away with a stock GM TBI setup by just upping the fuel pressure. Relatively easy to tune with a modified engine but you can also just drop in the drivetrain from an 87-91 Suburban and be done with it.

With a bored out TBI setup like the 670 cfm Holley or the aftermarket bored out GM parts you can make even more power with just minor mods to the programming.

Much beyond 350 hp will take more air flow & fuel and requires a big jump in cost to something like the FAST system or you could run dual TBI units on a dual quad intake. You can run a modified GM ECM to run dual TBI units. Dynamic EFI has done a great job with this capability.

You would have far less into it than the FAST system costs and most everything in your system could be sourced at the local auto parts store when something eventually breaks.

You could also just start off with the Dynamic EFI ECM and only run a single TBI unit on your stock intake then save up your money for the dual quad intake and another TBI unit if the power level isn't what you want.

The Dynamic EFI ECM will even run E85 fuel too. Pretty nice product.

http://www.dynamicefi.com/

I plan on using one on my 68 Camaro when I convert it to EFI.