Thunder
3/4 ton status
So what do all those stone age manifolds have to do with what we are talking about?????????
CK5
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Experience w/ HT383E Crate Engine
- Thread starter marv_springer
- Start date
So what do all those stone age manifolds have to do with what we are talking about?????????
MaxPF
1/2 ton status
My truck is TBI. The truck this was installed in was Central Port Injection. The truck I was planning to install this in will be CPI also.
What other reasons...?
Adjusted for a 25% loss thru the drive train, the magazine peak #'s are 275HP and 360 TQ.
So, 65 HP and 75 ft-lbs are still un-accounted for.
This quote bothers me too....
I read this to say that they baselined the stock [worn out] 255 hp Vortec 350 before and only got 14 HP and 14 ft-lb more w/ the 383...!!I think that's pathetic!
Marv
Well, the ads say "replace your stock 350 with a 340HP 435lb-ft HT383".. whoa... that is a bit misleading. They lead one to believe that you simply plop it in place of your stock 350 with no other mods and get all that extra power and TQ. I don't theeeenk so, Lucy.
The engine is identical to the regular HT383 except for the reluctor for the crank pick-up and a few other doo-dads needed for the swap into a Vortec truck. Now, the power and TQ figures obtained from the HT383 were with a dual-plane intake, 750CFM carb, headers, and a reasonably free-flowing exhaust. In the mag article they stuck it in a high-mileage truck with a stock intake, stock injectors, stock PCM programming, stock exhaust manifolds, stock exhaust with the original (and most likely partially plugged) cats and O2 sensors. The minimal power gain is hardly surprising. In order to get the numbers GM advertises one would need to do some extra mods. A good manifold-back exhaust would probably really wake the engine up. After that, it will need more fuel than the stock 19lb injectors can give. As others noted, you can't get bigger injectors for the Vortec manifold setup, so that leaves the only option being an aftermarket MPFI manifold, which is ridiculously easy to adapt to the Vortec wiring. This pretty much automatically implies a PCM reflash to give the motor the fuel curve it wants. The stock throttle body is probably adequate, as is the stock MAF. New O2 sensors would be a good idea if the existing ones have a lot of miles on them. Headers would also be needed to get the full power out of the motor, although I bet you can get most of tehe way with the stock manifolds (or better yet LT1 manifolds).
So, yeah the engine will make 340HP and 435lb-ft, but you gotta swap a whole lot more than just the engine to get it.
They look like replacements for the CPI setup...throttle body, the fuel rails, injectors, one of those intakes, no more CPI. 
And it looks like you can reuse the Vortec throttle body? Cool.
And it looks like you can reuse the Vortec throttle body? Cool.
MaxPF
1/2 ton status
Take a closer look, son. That is a MPFI manifold designed to take any throttle body that uses a standard square-bore mount. See the injector bosses in the runners? This manifold will let you use bigger injectors, and it flows much better than the stock piece.
Thunder
3/4 ton status
LOL I guess I should have looked a little closer and mabe acually read the descripions. I saw the square bore and just thought Carb.
But the problem is the CSFI. Unles you make very radical changes in the FI system (Like total retro fit MPFI like those manifolds are for ) CSFI just will not make the power needed for a 383. You can not use CSFI with those manifolds it wont work. CSFI really did not do all that good for early vortec 350s either.IMO
I would much rather have TBI than CSFI.
I'm gonna throw a wrench in this discussion...
If 14 ft/lbs is the gain, then WHERE does the gain occur. So far, as far as I can tell, we're hearing PEAK numbers here, which are obtained at WOT. So PEAK torque is only 14 lb/ft more than the stock motor. How often do you spend time at WOT at the peak torque RPM???
I'd really like to see the torque curves on both motors before making a judgment. There could be a large increase (much more than 14 lb/ft) at certain RPMs, most likely lower in the RPM range--which could be a beneficial or detrimental depending on the application.
If 14 ft/lbs is the gain, then WHERE does the gain occur. So far, as far as I can tell, we're hearing PEAK numbers here, which are obtained at WOT. So PEAK torque is only 14 lb/ft more than the stock motor. How often do you spend time at WOT at the peak torque RPM???
I'd really like to see the torque curves on both motors before making a judgment. There could be a large increase (much more than 14 lb/ft) at certain RPMs, most likely lower in the RPM range--which could be a beneficial or detrimental depending on the application.
I wouldn't be surprised if it's got better low RPM performance, but I can't help but think that article was simply a ploy for advertising dollars, which is why the important numbers weren't posted. Every other magazine that tests engines includes the RPM/power chart from typically 2-3000RPM to peak, or just beyond.
