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1,620 Posts
Discussion Starter · #1 · (Edited)
Not really hypothetical, this engine exists it's just not mine.
Would this combination make a good motor for my 3500lbs Formula F206?
What would be the max RPM range?

GM 383 crate engine
Heads...Stock Vortec iron with 1.94/1.50 valves
Rockers...GM roller 1.6
Cam...GM Hot Cam P/N 24502586
Duration 218/228
Lift .525/.525 w/1.6 rocker
Lobe separation 112
Intake...Edelbrock Performer RPM Air Gap
Carb...750 Holley
Ignition...stock HEI

Dyno test
2500 412 196
2600 419 207
2700 425 218
2800 434 231
2900 442 244
3000 448 256
3100 425 266
3200 455 277
3300 460 289
3400 464 300
3500 466 310
3600 466 319
3700 465 327
3800 464 336
3900 462 343
4000 462 352
4100 463 362
4200 462 369
4300 459 376
4400 456 382
4500 453 388
4600 449 394
4700 446 399
4800 441 403
4900 436 406
5000 429 409
5100 423 411
5200 417 413
5300 410 414
5400 402 413
5500 396 415
5600 390 416
5700 376 409


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69,292 Posts
iggy,maybe I'm wrong but I never heard of a 383 from GM. I know Dodge had a 383....
GM did make a 283 small block

Is this a BB????? Looking at the cam specs ,are almost like the HP 500. But the engine RPM's are more like a small block.
Sounds like a good motor,but I am confused

Jump in guys,I may be waaaaaaaaay off.

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8,677 Posts
yep,,,Stu's got it,,,, it should make a nice boat motor since it has a nice flat torque curve. Heck with the HP #'s,,, torque is what gets ya there !!!!!

· Premium Member
13,815 Posts
The chart that Iggy is using is for a modified crate engine, notice the cam numbers.
A standard 383 has 325 hp @ 4500 rpm and 415 # torq at 3500 rpm.
Make a good street mtr for a lightweight car. :)

· Registered
1,620 Posts
Discussion Starter · #8 · (Edited)
You're right, it was modified beyond GM's original assembly.
Cam, rockers and intake were changed.
I thought this combo would make a good engine for my boat and wanted to know what rpm range would be best for it.

From GM Performance Parts

Specially tuned for torque, the all new HT 383 delivers great truck power in a small block package for your truck or street rod. With its 3.80" stroke and Vortec cylinder heads the HT 383 makes awesome torque, down low where you need it for towing or four wheeling off road. Peak torque is 435 ft.lbs at 4000 rpm, but the HT 383 makes over 400 ft.lbs. from 2500 to 4000 rpm. Developed with a roller cam, special heavy duty forged powdered metal connecting rods, "4340" forged crankshaft and hypereutectic pistons the HT 383 is designed to be worked. 340 horsepower at 4500 rpm doesn't hurt either. The HT 383 is an ideal replacement for any 1977 and older carbureted engine or off road application.

HT 383 Technical Information
Horsepower 340 @ 4500 RPM
Torque 435 @ 4000 RPM
Max. Recommended RPM 5000 RPM
Compression Ratio 9.1:1
Block 10105123 Four bolt main, cast iron
Crankshaft 12489436 Steel "4340"
Connecting Rods PM rods
Pistons High silicon aluminum with offset pins P/N 12489437
Piston Rings 12522848
Camshaft 14097395
Intake Manifold 12496820 Aluminum dual plane with/dual carb pad and EGR
Cylinder Heads 12558060 Vortec
Intake Valves 10241743 1.94"
Exhaust Valves 12550909 1.50"
Valve Springs 10212811
Rocker Arms 1.5 stamp steel
Valve Lash Zero
Spark Plugs R44LTS or Rapidfire #3
Fuel 87 Octane
Ignition Timing 32º total @ 4000 RPM with vacuum advance disconnected

· Premium Member
27,181 Posts
my basic question is this: is the a marine motor?

it's my understanding the marine engines are built differently than car engines. severe duty valves, coated water jackets etc..... designed to be run at 3500 rpm all day long....

I know my blower motor uses Inconel Severe Duty valves for instance.

- jeff

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1,620 Posts
Discussion Starter · #10 ·
Block, heads, crank, rods and pistons are identical to a street engine.
Brass core plugs are used in place of steel and intake manifolds are (usually) cast iron, intake and exhaust valves are changed to a severe duty type, a different cam and water circulation pump is used.
Beyond that there's really no difference.
The coolant passages are not coated to prevent corrosion. That's why Merc is now installing closed cooling systems on (most of) their engines .

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1,620 Posts
Discussion Starter · #12 ·
This is something I'll do in the near future.
I've been reading many books on marine performance as well as posts on several message boards including this one.
Before I think of dropping in that much HP/Torque I need to swap the drive from an Alpha to a Bravo. I don't think the Alpha would be happy running 466lbs of torque through it.
One step at a time.

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1,967 Posts
The cam I would use is a Crane #109831 222/230 Duration, 112 C/L .509/.528 Lift.

I have tried both the RPM and Air Gap version and couldnt tell the differance but the Torker II
got me up on plane quicker and with less bow rise than the afore mentioned dual planes.

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1,620 Posts
Discussion Starter · #15 ·
The engine I proposed is real and was featured in the august issue of Chevy High Performance. Article is titled "Twister, part III". The actual dyno sheet from Duttweiler Performance was copied direcly from the magazine, no horse power program was used.
They were using stock Vortec iron heads which have a max lift capability of about .420". When they switched to a CompCams XE282HR they had to modify the heads for the .525" lift.
The GM "HOT" cam is recommended in Dennis Moores book.
My current engine, 350MAG, pumps out 270 hp and gets me 58 mph on the GPS. A 176 horse increase would push my boat to....maybe...65 to 68?
68 could be a bit optimistic but I think it would be fast enough.
I know a guy with the same model Formula as mine (F-206 LS) but running a 502" BBC. He has serious trouble with chine walk at anything over 70 mph.
I don't think I want to get into controlability problems so I'd like to keep the speed under 70.

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1,967 Posts
Just suggesting a cam thats for marine use and an intake that seems to perform better than the other two and is cheeper in price. Asuming your article was for an automotive aplication. This info is not from an article but from a running boat test on what gave the most seat of the pants feel.

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1,620 Posts
Discussion Starter · #17 ·
Yes, the engine was meant for the street but the cam is acceptable for marine application.
In Dennis Moore's book Small Block Chevy Marine Performance he mentioned this cam as an upgrade to the stock 350 marine cam.

GM P/N 24502586
Hydraulic Roller (LT4 Hot Cam)
Rocker Ratio 1.5
Duration I:218, E:228
Lift (1.5 rocker) I:492, E:492
Lash Zero/Zero
LSA 112

Cost of engine package as tested in article was:
Engine 3699.00
Cam 210.00
Rockers 301.00
Intake 193.00
Carb 430.00

Total 4832.00 +/-

Sure beats the 10g's some people ask.

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42 Posts
With my 383 I built during the winter I now spin a 25" at 5300 rpm.. the old 270 hp 350 mag at best spun a 21" at 4500...

9.8:1 comp ratio
vortec heads
222/230 .543/.563 lift ( 1.6 rockers) 112 LSA
EMI exhaust
750 holley
rpm air gap intake
stock ignition

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1,620 Posts
Discussion Starter · #19 ·
Thanks Traviss.
Now that I see what prop and rpm your running I now have an idea what this engine would do.
Sounds like you have one stout sbc.
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