Do you guys think that one of Holley's 4bbl TBIs (combined with the right intake manifold and adapter plate of course) is a good mod to be done for higher hp and tq? Or is it better to stick with a 2bbl setup and save the money for other mods?

 

The 4bbl units are for larger displacment motors or motors where the 2bbl units become a restriction. The 4bbl units are usually used on engines making 400+ hp. Unless you have something scary, stay with the 2bbl unit.

 

^^^ Exactly what he said.

 

And you'll cook the injector drivers right off the circuit board if you try and wire the injectors up. Either that or you'll give them half the voltage. So you'd need an extra injector driver board to do it right. Then you'll have a HARD time getting the thing to idle UNLESS you use the smallest injectors. But when you've done all that you'd be wishing you hadn't wasted all that time. Dont' get me wrong, some people can do it and have done it, it just takes a lot of work.
Do a search, you'll see this topic isn't new.

 

I ordered one yesterday. I have read about everybodies experiences here and on a few of the truck forums and I have decided to give it a go. My 383 appears to be choked by the 2" TB's I have on there now. I plan to use the drivers from a spare ecm that I have laying about..
I dunno for sure that it will work ok, but I'm prepared to try.

 

Have a read of these links. I got them from the "New to TBI......" sticky at the top of this forum..

https://www.thirdgen.org/techbb2/sho...holley+and+4bbl

https://www.thirdgen.org/techbb2/sho...holley+and+4bbl

https://www.thirdgen.org/techbb2/sho...holley+and+4bbl

https://www.thirdgen.org/techbb2/sho...holley+and+4bbl

https://www.thirdgen.org/techbb2/sho...holley+and+4bbl

https://www.thirdgen.org/techbb2/sho...holley+and+4bbl


This one is also worth a read:

http://www.454ss.com/Articles_new/tweek/TweekTB.asp

 

Can we say source coding? Id keep the second set of bores closed and injectors off untill I needed them. Using one of the unused outputs on the 8746, like the AC drive, would allow one to turn the extra driver on and off. The bpw will also need to be changed once the extra injectors come online. I tested this on the bench but I have no reason to buy a 4 bbl yet.

 

As far as the holley stuff, the only thing I dont like about their tbis is the crappy castings. Theyre thin and have lots of hairline fractures. I bet if I dropped my holley or overtightened it, it would shatter.

 

Cool! I'd like love to try it out. The only thing that might be a pain is getting the AFR not to spike when you switch and then being able to have logical code for the switching. I'm almost inclined to think that the 2nd set of injectors should always be on but they should be at a very low pulse width, the lowest, which can be adjusted in with the injector constant. Then have them increase pulse width after the primary set has dead headed at a set duty cycle of say 80%. This way all of the opening throttle butterflys will have fuel flowing for better (not great) distribution). I know that's a lot of thinking out loud so I'm not expecting a reply.

 

Turning on outputs is easy enough. Just load up the address for the controller, flip a bit, and save it. Im switching one output at 38,400 baud so they can turn on and off fast enough. As for the afrs when a switch occurs, I have no idea exctly what would happen. Might have to maybe filter the bpw or something.

 

The newest 900cfm TBI package (including thier commander ecm) from holley has a progressive linkage and doesn't turn on the 2nd pair of injectors till a tunable xx% TPS.

I will be using a 16168625 PCM. I will first try to get it working well with all 4 injectors working together.

This PCM has 2 VE tables, one is full size, the other is called 'closed throttle VE' and operates up to 1800rpm. The TPS % where it switches from the main table to the 'closed throttle' table is adjustable.

If I find too much fuel at idle with all 4 injectors firing, I may be able to use an op amp on the tps voltage to switch a pair of injectors off under say 10% TPS and switch to the closed thottle VE table at the same time..
It may be difficult to get the transition to be smooth, but its worth trying before I rip the 4bbl back off..

 

How much did you pay for your 4bbl unit, Ben?

 

I am in Australia, so the info is not gonna be of much help to you...
I bought it used for $295, thats about $210 US.....
If i don't suceeed in making it work, it will end up on ebay... If it works out ok, i'll consider upgrading the pod and injectors to the newer type.
Ben..

 

Those older injectors are junk as you probably already know. Delhpi makes those same replacement mopar injectors. I wonder if theyve made any updates to them to make the injectors work properly.

 

Yeah I have read that the injectors are junk.
Hopefully it will work well enough to give me the confidence to blow some more $$ on the upgraded pod and injectors.

 

Today I installed my holley 4bbl tbi.
With a bit of tuning I managed to get it idling better than it did before with the X-Ram and 2" TB's..
Man those holley injectors can dump some fuel if you need them to!
I haven't driven it yet as I haven't even made up brackets to connect the throttle, cruise and TV cables. My biggest concern with this thing was if i was going to be able to get it to idle nicely, so I didn't even bother hooking up the cables.
Now that the idle tuning was successful, I'll finish the job.
Lookin' good so far.

 

you are light years ahead of me. i spoke to holley rep at nhra and it seemed like a great plan with sequential opening of the fly's. i bet you will like the result. did you retain the xram manifold or(SY1) ? how is clearance to hood (c4)?

 

Hi Ron,
The used holley I bought is an older model with butterflies that all open at the same time. My biggest concern was if i could get it to idle properly with all 4 injectors, but it was a piece of cake. I changed the BPW to my new calculated value, then tweaked it from there till the WB said it was idling at the ARF it should be. I multiplied the AE tables by 0.6 as any small blip of the throttle dumped gallons of fuel into the manifold.. and I also had to reduce the proportion gain tables a bit to steady out the idle. Its now more stable (speed and afr) than the x-ram even was, and i think its picked up a bit of vacuum also. I'm willing to bet that the cold running is ALOT better also, but I'll have to wait till the job is finished before i can comment on that.

I am using the x-ram's wieand base with a 1" open spacer. This puts the filter mounting ring at the same height as where they were with the x-ram. I have a spare factory air filter housing that i hope to modify to fit, so it looks stock and retains the cold air setup.

It's gotto work better than the x-ram huh? ;-)

I know this is similar to what you are doing, so I will keep you posted.