Going from FI to Carb, What to do?

[1HI4x4]

Well after lots of reasearch, head scratching, I have settled in on my repower plans for the winter. I was going to install a 12 valve Cummins, but after all the research, bracketry needs, mounts ect. I have determined that I am going to stay gasoline. I'm going to be building a big block (490 maybe 502) and running a carb(Demon/Holley). I thought about going with a Ramjet FI but engine builder tells me big torque at low RPM's come from carbs. I'm looking for somewhere in the 600-650 ftlbs of torque range at under 3000 rpms for the new motor. The question I have is what's the best way to keep my 4L80E, buy a stand alone computer, or is there a way to keep the ECM from the TBI setup? Anyone done this?

[VileZambonie]

What is your factory set up? Is it already a bigblock? You can keep the stock computer but you will need the primary input sensors still.

[1HI4x4]

It's a 5.7 Throttle Body, I'm going to a big block carb motor, won't I need the imputs from the motor in the stock ECM for the tranny to work?

[eventhorizon66]

Aside from the fuel systems used.  600-650 ft lbs at or below 3000 rpm is a tall order for a NA 490-502.  You might consider just building a positive displacement blown 383 or 400.  Magnason and Whipple make an efficient lysholm-style blower that is up to the task of 600 ft lbs in a well built 383.  Or you could just shoot for 750-850 ft lbs and build a blown 454/489.

Another idea, if you require a NA big block, is a Caddy motor.  This one looks like a nice little turn key: http://www.cadillacperformanceparts.com/index.php?option=com_content&task=view&id=19&Itemid=62

[1HI4x4]

My engine builder had one on the dyno the other day that made 635ft.Lbs. at 2850 rpms, it was a 502ci, it had a quadrajunk on it. So I know it can be done, truck has to be very streetable. I don't care about the HP number, I need big torque, I do alot of towing. I don't tow at 4000 rpm's.

[eventhorizon66]

Cool.  Hope you don't mind sharing the specs on the engine you end up with.  That motor must have had some efficient heads.  And I think you just shed some light on the carb you should run.  Why not a Quadrajunk?  They're great for towing.

You can defintely adapt a TPS sensor to the carb.  HAULIN IT just did this in his hot rod.  He also used a Baumann TCM to run a 4L60E.  Maybe he'll chime in here.

[VileZambonie]

If this is a towing rig, why not run a TBI big Block? You can use a factory harness, ECM and sensors. All you need to do is get a new chip.

[1HI4x4]

If this is a towing rig, why not run a TBI big Block? You can use a factory harness, ECM and sensors. All you need to do is get a new chip.

I don't think I can get a TBI to produce the numbers I'm looking for.

[Captkaos]

The engine builder is incorrect as far as EFI goes.  A TBI and/or ramjet is what makes torque at low RPMs, people swap to carbs to get high HP/rpm numbers.  The tunned runners help make low RPM torque  The Ramjet 502 makes 502 horsepower and 565 lb.-ft. of torque, and it has over 500 lb.-ft. of torque available from 2200 rpm on up.

They guys on 454SS.com have some good tips on making power out of the TBI setup.

I would put the 502 in with the current ECM and chip it, upgrade the pump and the injectors/TBI with more flow and you should be close.

[eventhorizon66]

I agree with Capt.  If there is one place that carbs will always lag behind EFI, it's low rpm / low throttle conditions.  I've never heard/read anything to the contrary.

But everyone's got opinions and they're all different.  At some point, you've just got to find somebody you trust and stick with what they say.  That is if you lack the experience to make your own decisions.

[1HI4x4]

I suggested A Ram Jet Set-up to him and he said that would be a good choice, but he was no fan of TBI. That's when the converstion went to carbs on an old style dual plane intake, ported to match the heads.