jmm98LS1

iTrader: (28)

Just want some opinions from you guys.
I've narrowed it down to the following retrofit roller cams for my 383 stroker:

XR282HR (230/236, .510"/.520" 110lsa)
XR288HR (236/242, .520"/.540" 110lsa)

Here's the motor:
383ci sbc, 4.030" bore
Scat 3.75" cast crank, forged I-beam 5.7" rods, KB hyper pistons
Vortec cyl heads, 1.94/1.5 valves, 64cc chamber, comp 918 springs
10.4:1 static compression
1.5 roller tip rockers
Edelbrock 750cfm carb
Performer RPM Air Gap intake
1 5/8" longtubes, 30" primaries, 3" collectors

I had a Desktop Dyno veteran run both cams on my motor, and I know it's just a computer run but he thinks these numbers should be fairly accurate. The smaller cam put out 380hp/470tq. The bigger cam put out 441hp/457tq. Here's the graphs:
XR282HR


XR288HR


The motor is replacing the 355 in my '85 silverado shortbed (in sig). It's got an M21 4spd and 3.42 gears. It's my daily driver (~150mi/week), but I could give two ***** about "driveability", a nasty idle is required. My dilemma: Monster lowend torque (and respectable hp) with the smaller cam, or awesome horsepower (and respectable tq) with the bigger cam. Which one would you pick?? Right now I'm thinking about choosing the bigger cam, and then advancing it 2-4 degrees to bring the powerband down a few hundred rpm. I'd like to shift this thing at 6000 since I didn't go the forged route. Fire away!!

Studytime

iTrader: (15)

Don't forget you picked up an extra 28 cubes with the bigger motor that are going to allow you to run more cam than you could in your old 355.

I wouldn't be afraid to spin it over 6K either. Some I-beams and a scat crank aren't going to be taxed too hard at your power level. Those vortec heads will keep it from revving too high with their smaller intake runners.

My vote is to go for the 236/244 camshaft. I think it'll fit your bill and will make driving the truck more fun if it's got better top end power. The extra stroke and the L31 heads will make it have torque down low.

Those desktop dyno numbers are skewed. That bigger cam isn't going to be worth 61hp by any stretch. It's likely that the power difference will be less than 15hp between those two camshafts.

Ben T.

1989GTA

How much lift can the valves have with the beehive springs? I would get a cam that would maximize the lift. I would also look into 1 3/4 inch headers if you have not bought the 1 5/8's already.

jmm98LS1

iTrader: (28)

The beehives are good to .600", but the vortec heads flow drops off around .550" so going over that won't do much good without port work & bigger valves. I've already got the 1 5/8" headers. I couldn't find any 1 3/4" to fit my application for less than $600......I scored the 1 5/8" in stainless for $230, and they should do fine for what I'm after I think.

jmm98LS1

iTrader: (28)

I was more concerned with piston speed with cast parts rather than power level. I've been told that 3500fpm is about as fast as you wanna spin cast cranks, and with a 5.7" rodded 383, that ends up being hair under 6000rpm. Am I way off base here? Scat rates this crank good to 500hp, but they don't say anything (that I've found) about rpm.

I'm beginning to think that too. Based on other combos I've been researching, the results for the bigger cam seem to be pretty close, but the horsepower figures for the smaller cam seem way low.....should be a smidge over 400.

Thanks for the input....keep em coming!!

Ryan02SS

iTrader: (3)

Real world flywheel numbers are probably going to be close to 400hp and 440tq flywheel with the larger cam. The stock Vortec's are not going to support much over that from what i've seen. For example a previous 383 with AFR 195's and solid roller 257/269 and Vic Jr made 498 and 442 on the dyno. I would choose the smaller cam if it were mine. More useable powerband, will still sound great and will more than likely achieve a better DCR. I would want more static compression for the larger cam.

Studytime

iTrader: (15)

That nodular steel crank should be tough enough even with a 3.75" stroke for over 6000 RPM. I wouldn't worry about it if it only happens occasionally. A local friend of mine had a cast eagle/scat crank in a 383 that routinely saw 6500 and went 11.0s at 125ish mph in a 3400 lb car. I'd mostly be worried about those pistons coming apart before the rods or crank.

I actually was working on a scat crank, scat 5.7" rod, hyperutectic piston 383 motor at work last week. It's a low-buck street motor for a cruiser. It has a small (plenum volume) single plane on it and a set of World Products S/R heads. Nothing special but probably a little better than a set of 882 heads not quite as nice as the Vortecs you are running. It's got a cam in it similar to the second one you listed. It's pretty close to your build.

It'll see over 6K on the dyno fwiw even with some economy pistons in it. A set of 1 3/4" headers will be bolted to it too, but besides those few small thigns pretty close to what you've got. It should go over 450 fwhp and hopefully make 465 ftlbs or better. Your motor should motivate your truck pretty well.

Have you clearanced your rods to not hit the cam yet?

Ben T.

jmm98LS1

iTrader: (28)

Thanks for the replies! I'm just having a hard time picking a 230/236 for a 383 when I've used similar duration cams in 350's & loved how they performed. Still undecided. Can anyone point me in the direction of a good DCR calculator?

Studytime: I'm still gathering parts, haven't started putting anything together yet.

chevydad

you did get the vortecs machined right?

jmm98LS1

iTrader: (28)

valve guides will be cut down to accept higher lift & new pc seals, that's all that's required to run 918's.

moge11

use the 236/242, or even the 242/248. You yourself said driveability is not an issue. Make that thing run.

WheelsUp84z

iTrader: (14)

I like the 288 cam (2nd one). Just based on the desktop dyno's alone, you can see the bigger cam makes a TON more horsepower, it makes little less torque, but you can see the torque curve doesnt fall off as rapidly as the smaller cam. 2nd one has my vote if those are the only 2 to choose from

chevy123

Call comp cams or crane cams and tell them what you got and what you are going to use the truck for. Don't rely on the desktop dyno. My friend built his engine from the desktop dyno and went with the cam that gave him the most and it did not perform that good. He called up comp cams and asked what was going on, and he had to big of a cam for his heads and compression. Bigger is not always better. Good luck.