383's and stock t.b.i ??

[bablazer73]

One of my buddies popped the moter in his 89 Z-71. I have another short block, but it needs a crank. He wants me to put the engine together with a stroker crank kit. No biggie as far as I care. My ?? is, what does he need to do to keep the stock E.F.I on the truck. He doesn't really have funds to upgrade much.

 

[4X4HIGH]

A 383 will require a larger TBI unit, larger injectors, and a chip burn. There is no way around it unless he wants to toast an engine.

 

[sweetk30]

http://www.tbichips.com/tbimods.htm brian has lots of info and great guy. do some good reading on there to get a good understanding on tbi needs.

 

[b454rat]

I ran a healthy TBI 406 on my old 90 GMC. Did nothing to the fuel/computer. Put 7500 miles on it, street and 4 1/2 hour road trips almost every weekend. Ran friggin awesome till the guy I sold it to smoking the tires around every corner blew the motor. Inless it's a real radical cam, the stock will work. Getting a custom tune will make it run up to it's full potential.

 

[eagle mark]

What's the cam specs on the 383 motor?

Does he have to pass smog in NY?

 

[bablazer73]

No build plan on cam specs yet. Trying to decide if it will work. No doubt it would be mild. Got a recomendation??

 

[b454rat]

I used Comp Cams Xtreme 268 in my 406. It had a noticable idle, and in a 383 it will be quite lumpy. I've had good results with Xtreme cams, maybe the 256 or smaller? Edelbrock Performer makes good look end torque....

 

[blackk5350]

A 383 will require a larger TBI unit, larger injectors, and a chip burn. There is no way around it unless he wants to toast an engine.

how will it toast your engine just wondering?

 

[4X4HIGH]

how will it toast your engine just wondering?

Because a 383 has a much different fuel requirement (larger displacement requires more fuel) and timing curve than a 350.

 

[blackk5350]

so if you dont give it enough fuel wont it just not run to full power? or will it blow up

 

[4X4HIGH]

so if you dont give it enough fuel wont it just not run to full power? or will it blow up

The engine will run lean and running an engine lean for a long enough period of time will kill the engine.

 

[vtblazer]

I picked up a chip from Brian for my 383 I have in my off road truck, no other mods were made than the chip.
Very mild cam, don't really know 'cause I didn't build it, neither did the guy I got it from.
Running old school vette 2.5" rams horn manifolds.

It made a huge difference with idle and helped lower end throttle response a lot.

Make note that my truck is a rock crawler and almost never sees RPM's above 3K, that's why I get away without running larger injectors.

Anything over 3K and you can tell the motor wants/needs bigger injectors (more fuel) as 4x4HIGH suggested.

 

[b454rat]

I'll try to explain it the best I can, I have a hard time sometimes. I think the motor would run fine at lower RPMs. Mine ran friggin awesome, actually think it had more ass than my Vortec 454 did at the time. But anyways, like VT said, at lower RPMs would be fine, getting in the upper RPM range might lean it out, or the fuel system couldn't keep up with the motor. After all, I have a 454 with a 600 edelbrock on it right now, I'm sure it won't go to 6000K very easily. And GM put a 2 barrell on a 396 in 69' Impala's. To a certain point the ECM will fatten up the mixture if it's lean, isn't that the beauty of fuel injection?

 

[Thunder]

If he keeps the stock TBI heads/ manifold. The stock stuff will feed it Ok. It wont make high RPM HP but it will be a torque monster. Use a very mild cam. Like a COMP 252 BH-11 or Melling MTC1
He will need to install an adjustable fuel pressure regulator to up the fuel pressure to keep it from going lean. 13- 14.5 psi.
A chip, injectors, bigger TB is the best way to go and highly recomended. But if you keep the build very mild with stock TBI heads. It will be fine with the stock TBI and and higher fuel pressure. you wont make the horsepower it is capable of. The TBI heads limit high RPM HP but build gobs of torque in a stroker motor. Plus it will get fairly good MPG.
I would at least install new injectors. I would not want to feed a 383 with a set of old worn injectors. A new set of 65 lb hr cop car flow matched injectors would feed that engine nicely.

 

[dyeager535]

To a certain point the ECM will fatten up the mixture if it's lean, isn't that the beauty of fuel injection?

OBD1 can not, and will not fix too small of an injector issue.

The reason is this: The O2 sensor is designed to keep the engine at peak *emissions* operating AF ratio. During acceleration/heavy load the O2 sensor is IGNORED. That means the ECM has no idea if the engine is running lean or rich. The O2 sensor is massively misunderstood. 14.7:1 AFR is NOT the AFR to make power. It's the emissions AFR. Guess what? The stock O2 sensor is ONLY accurate at 14.7:1 AFR!

How then, does GM keep the engines from destroying themselves by running lean under load? Very simple. They do it the same way that warmup is done. They use *preprogrammed* timing and fueling maps for the *STOCK* engine. This means that GM spent the time to datalog the motors under most any driving conditions they could imagine, and preloaded the ECM with this data. If you swap motors, injectors, mess with timing, ANY of that, without tuning, you are seriously hampering, and perhaps damaging, your engine.

At "heavy" throttle positions, in ANYTHING other than the stock, GM motor, the engine is NOT getting the right fueling or timing, period.

burt4x4 had his EFI setup dynoed, check the link in my next post below.

While driving like an old man will certainly help a mis-tuned situation, there is no way around the fact that engine damage is right there. Anyone who has driven a motor with a vacuum gauge hooked up, understands that babying the pedal doesn't reduce the load on the engine much when its starting from a stop, or pulling a hill, etc., which is exactly when TBI/TPI is ignoring the O2 sensor.

 

[bablazer73]

Thanks for all the great info guys!! I am not sure what his overall budget is at this time. I know he plans to keep the stock exaust (has cat back,but stock manifolds.) The cam choice will most likely be under 270 duration. Sounds like he's gonna have to step up and do T.B.I, larger injector and the chip. If it doesn't look like he can spend the money, I'll try and talk him down and just do a 350 for him.

 

[y5mgisi]

subscribed for the good info.

 

[dyeager535]

For those that haven't seen it, here is burt4x4's post.

http://coloradok5.com/forums/showthread.php?t=163920&highlight=dyno

I will edit my above post, I thought he was running stock stuff, but he was not. Regardless, it's the same deal. That is why people "cheat" by upping the fuel pressure to the injectors, however that screws up the computers calculations as well, since it "knows" the lbs/hour rating of the injectors at a given (stock) fuel pressure. When you change fuel pressure, the ECM tries to compensate, which it will, but only up to a point.

 

[bigblock72]

There is only one right way to do this. I think with the amount of money that is going to be invested in this project it's pretty much mandatory to do it right from the beginning.

You're a little vague on the combination so I'm going to make a lot of assumptions here. Adding a stroker crank ups the compression at least a half a point so the spark maps have to be just right. The increased displacement means increased fuel then if you add a bigger cam, headers, intake etc.,etc. I didn't get into better heads which can add even more compression and more power so as you can see you're way out what the stock chip is programmed to do and possibly the injectors depending on what combination you go with.

The right way to do this requires a chip to be burned and some careful datalogging, period!!!! If you can't, won't or don't do this then build a stock motor you'll be happier in the end. If you're combination makes more than about 260-280 horse then you'll need bigger injectors, period. If you run it lean the motor will not last long nor will it make any more power than a stock motor. I don't understand why someone would spend 2-3 grand on a motor and try and use the stock stuff when doing it right would only cost an additional 200-400 dollars.

I don't mean to sound like an arrogant know it all PITA but I see and fix these same problems and it ALWAYS ends up costing people more than if they would have just done it right in the first place. Once the correct steps are taken your 383 will live a long prosperous life and will more than return the investment.

When you pick your cam keep the duration under 215 degrees (@ .050") on the intake and the lobe seperation at least 112-114 degrees. Any more duration or narrower LSA it will very difficult to get a stable idle.

 

[4X4HIGH]

I built a very healthy full roller 350 and put almost 5K into the engine build. I'm running a 454 TBI unit with 95 lb/hr injectors with a high pressure fuel pump and an 18 psi spring in the regulator and a custom chip from Brian at TBIchips.com. I couldn't be happier with the end result. This engine is making 400hp and 510 ft/tq. The torque is a nice flat curve from 2000-3500 rpm and the HP is at 4000 rpm.