I'm looking to build a 468 with some type of EFI. But there's a catch. I'm trying to do this as budget oriented as possible. I'm probably going to build my own intake manifold simular to a tunnel ram....only shorter than the Accel SuperRam so it'll fit under my hood. I need info on stuff like: what differasnt sizing does to plenum's, runners, etc. I know short runners are more HP & longer runners are more torque. I'm talking how differant runner diameters affect velocity and how a larger or smaller (and how to calulate just *what size* you need) plenum acts.

I also would like ideas on what type of controllers to look at. I'd like the idea of *get it tuned and forget it* as this will be strictly a street car. But it also needs the reliability of a stocker, along with the ease of finding replacements sensors, etc while on a roadtrip.

Please don't tell me to just buy this system (as in Accel SuperRam of Edelbrock's Pro-Flo) as in most cases these are way outta my budget or aren't really street systems. I'm not saying the ones listed aren't any good, I've just ruled them out for differant reasons.

I know you guys know more about EFI than anyone else I know and I'm looking to you guys for some help. Thanks! :hail:

 

I'm looking to build a 468 with some type of EFI.... \

Try doing a google search for tuned intake runners and plenum volume calculators. There is a ton of info out there some good some bad but you can get an idea.

I also would like ideas on what type of controllers to look at. I'd like the idea of *get it tuned and forget it* as this will be strictly a street car. But it also needs the reliability of a stocker, along with the ease of finding replacements sensors, etc while on a roadtrip.

Check out DIYPROM board and look for info on the stock 1227730 computer. With this system the limit is injector size for idle stability. The computer is fully hacked and easily programmable. It also has the parts availability and features such as baro correction and IAT sensing that allow you to set it and forget it.

HTH

John

 

Thanks for the info John. I was looking at the 90 - 92 SD ecm and I've been trying to find out what the limits to it are. I do all the research I can but normally only have 1 day a week to do much internet research as I drive a truck and don't have much time.

Again.....thanks for the info!

 

As 32V said, the issue with "how much HP" can the SD 7730 support centers around the fuel injectors. The problem is the stock ECMs use high impedence injectors. There are large injectors available to support high HP applications (though they get pricey), but as John said, you can only go so short on the idle (.9-1.1 ms is about as short as you can go, and for a stable idle probably 1.2-1.4 ms).

Now, a larger engine (with not too radical of a cam) to make the same HP as a smaller engine (with a more radical cam) is easier to control for idle, and therefore you can support a bit more HP. Generally 500-550 HP for a small block is point where you need to consider other alternatives. With a big block, you may be able to support an extra 50 HP and still maintain a reasonable idle PW.

But you are going to need some big injectors for those HPs.

Formula for Injector Size to HP is:

Injector Size x 2 x #Cylinders x %DutyCycle = HP.

 

how do you find the duty cycle of say a 24# accell injector? and by your formula thats what the capabilities of the injector are for example

24# injector * 2 * 8 (350) * .85 (85%) = 325HP (aprox) so this is what you would be limited to in HP by these particular injectors?

 

To find the Duty Cycle you need to have a scan tool capture of the injector pulse width.

At 6,000 rpm, you have 10 ms for 100% DC. Yes, you MAY SEE the ECM give a longer PW than 10 ms, but you can't get more than 10 ms of fuel since one revolution takes 10 ms @ 6,000 rpm. 80% DC would mean that @ 6,000 rpm, you injector PW was 8 ms.