MIKER

For those who do not receive HotRod magazine, here is a summary of an interesting article about tweaking GM's HT383 crate motor.
Some of this may be useful reference material for forum members who are trying to decide on their upcoming engine combinations.

Advertised specs:
325 hp @ 4,500
415 lb-ft @ 3,500
"medium-rise GM dual-plane intake with EGR provisions"
Vortec heads
4-bolt mains
Hypereutectic pistons (9.1:1 compression)
Hydraulic roller cam. 196/207 duration @ .050 with .431/.451 lift.
Forged crank w/ 3.800" stroke.
Std 4.00" bore.

Step 1Initial Combination tested 338 hp @ 4,400 & 444 lb-ft @ 3,400
Headman Tork-Step Headers
Petronix Flame-Thrower HEI
Speed Demon Carb (625 cfm Road Demon) w/ jets at 70/76
Timing set to 34 degrees

Step 2 1.6:1 Roller Rockers 355 hp @ 4,700 & 452 lb-ft @ 3,500
Adding a set of Comp Cams Pro magnum 1.6:1 rollers gained 17 hp and 8.2 lb-ft at peak and didn't lose power anywhere in the curve.

Step 3 RPM Air Gap Intake 370 hp @ 4,600 & 466 lb-ft @ 3,700
Gained 15 hp and 14 lb-ft.

Step 4 Demon 750 Carb 379 hp @ 4,600 & 474 lb-ft @ 3,700
81/88 jetting.
Gained 9.4 hp and 7.7 lb-ft.

Step 5 Bigger Cam and thinner head gaskets 455 hp @ 5,600 & 493 lb-ft @ 4,200
Comp Cams XE282HR
230/236 duration @ .050 and .510/.520 (.544/,555 w/ 1.6:1 rockers) w/ 110 lobe separation angle. (The Vortec heads required valve guide modification for this swap due to lift) Swapping to thinner steel shim head gaskets bumped the compression ratio to 9.6:1. The larger cam gave up as much as 25 lb-ft of torque at every data point below 3,600 rpm. Also it formerly idled at 650 rpm and 19 inches of vacuum the new cam idled at 950 rpm and 12 inches of vacuum
Gained 76 hp and 19 lb-ft.

Step 6 Slippery Oil 463 hp @ 5,600 & 502 lb-ft @ 4,200
Changed from 10W30 dinosaur oil to Royal Purple's 5W30 street oil.
Gained 7 hp and 10 lb-ft.

They were so impressed with this oil that they're planning a full chassis-dyno test of Royal Purple products for the engine, trans, rearend, and wheel bearings.

SmokedTires

Thanks for the great post :) . Another printout to go into my folder :yesnod: .

MARKUS_P

17 HP because of roller rockers?? :eek:
Now I´ll buy them for sure......

Scooter70

Any idea what this motor might cost? 383 + intake + carb + cam + rockers = ?? $6grand?

Matt Gruber

i've mentioned this bargain several times. now you know why!
Markus- it is the switch to 1.6 ratio that makes most of the power

Alwyn678

Wow that was a cool article!!!!

Ganey

Agree w/ drives61.

That BB stroke really wanted more cam!

:cool:

MIKER

Ganey & Drives61,
Here is some additional info from the article that confirms what you are saying.

"Later on in the test, when we switched to a bigger camshaft, we tried a set of Comp's similar 1.5:1 rollers, thinking perhaps the new cam had enough lift to not need the help of 1.6:1 rockers. We were wrong: This engine preferred the 1.6:1 Pro Magnums every step of the way."

gkull

It's to bad they didn't try over a point more compression and some real aftermarket heads and a solid roller cam :yesnod:

I always did wonder about those 3.800 stroker cranks and what they were really used for.

Jenny

in the oil....they must have forgotten that they chose a lower viscosity?

MIKER

I feel that a comparable engine could be built for less but here are the component prices from the article:
Step 1
GMPP HT383 crate engine $3895
Headman Tork-Step Hedders $200
Pertronix Flame-Thrower HEI $220
Speed Demon carb $300
Milodon claimer pan $100
Milodon oil-pump drive $14
Milodon oil-pump $40
Milodon pan baffle $5

Step 2
Comp Cams Pro Magnum 1.6:1 roller rockers $323

Step 3
Edelbrock RPM Air Gap Vortec $220

Step 4
750 Speed Demon, (mechanical secondaries) $440

Step 5
Comp XE282HR cam $240
Comp 1.43 springs $83
Comp retainers $60
Comp Viton seals $25
Machine Labor $75

Step 6
Royal Purple 5W30 $5/qt.

zwede

Re: 1.6 rockers...

A few years ago I did extensive dyno flogging on GEN2 LT1's. Got over 150 dyno runs on my 96 LT1 engine.

Found that 1.6 rockers are good for an easy 10-14 hp with the stock cam.

That's not to say 1.6 rockers will add power to any engine. It all comes down to what the heads flow at high lift vs the lift of the cam. 1.6 rockers will help just about any engine that runs a low-lift, stock style, cam.

Also found that full rollers are not worth much of anything. I can see the use of a roller tip to minimize valve stem wear. The roller trunnion is not neccessary unless you are running VERY high lift and heavy springs. Basically, solid roller territory.

I really like the Comp Cams Magnum roller tip rockers. Good quality and low price.

BTW after the 150 dyno runs I got the Lt1 from 290 hp stock (advertised 285) to 380hp. It still has the stock exhaust manifolds, and stock cam. No blower or NOS. The key on those is careful head work.

gkull

Mike - did it describe the stepped headers? Were they 1 5/8th to 1 3/4?

As to Jenny. When a motor is up to temp. The upper number is how the oil really is. Thin light weight oil 5w30 would help flow in a cold startup. I do believe most of the high dollar oils like Redline and others are superior. I just use synthetic with ER metal treatment in everything. Rearend - tranny - motor - power steering

MIKER

The intake swap caught my eye.
After seeing the results of using the Edelbrock RPM Airgap intake manifold (+15hp $ +14 lb-ft), it makes me sorry that I didn't make the effort to use one of them instead of the Edelbrock Performer w/EGR. I didn't want to worry about the hood clearance issue but I have an idea in mind that might work. I'll just have to save that mod for later.

mountainmotor

Quote by Ganey:
"That BB stroke really wanted more cam!"

Agree! That cam is way smaller than a 1989 305 TPI cam.

1.6 Rockers are just a Band Aid in this application just like when TPIS was doing it on the stock L98's

Tim H

I know adding 1.6 roller rockers makes plenty of power.
A couple of guys I know drag race and the first mod they do after there first run is add rollers and an electric fan and gain 3 tenths or more in the 1/8.
I have seen it several times and they swear by the rockers.
It worth taking off your heads and having them fitted with screw in studs,guide plates and the pushrod holes inlarged for the extra clearence.
Plus a thinner head gasket is the same as shaving .030 off the head if you need the compression bump.
Im going to go by that magizine as soon as I can.

Lt1er

I thought that the Price for the CC Pro Magnum rockers was high so I just looked it up in Jeg's It's nearly $ 65 high. They have them listed at $259.99 I'm running comp cams 1.6 roller tips because I couldn't justify the additional cost of full roller for a few hp.

MIKER

Gkull,
Here is what they had to say about the stepped headers:

"We wanted torque, so we chose Hedman's Tork-Step headers in an early Camaro design. The Tork-Step offerings propose to boost bottom end by using small, 1-1/2" inch tubing for the first several inches of each pipe, then stepping up to 1-5/8" tubing. Once our 383 made horsepower in the mid-400s, we tried a swap to regular 1-5/8 headers and ended up gaining a few horsepower while losing a few lb-ft of torque. As a result, the Tork-Steps remained on the engine for every dyno test in this story."

Captain Morgan

I have something to add about that Royal Purple oil. A friend of mine out in Utah races circle track and his dad owns the shop that sells a lot of the Legends cars. They put Royal Purple in a new diff and after a full season of racing, the gears still looked like new. That sold them on the stuff, they said they'd never seen anything like it. Now they use it in everything.

Paul 75 L82

Everyone need to take notice. Hod Rod, Checy High Performance and Car Craft all are showing Demon carb's on their motors. Its the wave of the future.