Need cam selection advice... SBC
 

I'm going to be changing the cam in my 383 to something a little wilder to make up for the difference in displacement over what Comp recommends. The current cam is a Xtreme Marine 262H with these specs:

XM262H 262*/268* Adv dur, 218*/224*.050 dur, .462/.477, 112* LOA

Comp advises that this is the biggest that one should use with an I/O. The rest of the cams listed in that line are designed with a jet in mind. My builder thinks it's too mild for the displacement and that there is definitely some hidden useable power to be found there. Due to the set budget requirements set forth by "the one who must be obeyed," I cannot go the roller route which was what I had planned originally.

I will definitely be going with Comp as I can get a sweet deal on anything that I get through them (through the shop).

With the first motor that I had built it made 390hp and 450 ft lbs of torque. 400 ft lbs was on tap from 2500 RPM and on. We did not dyno the replacement, but I'm told that it should put out as much if not more power than the first since the bottom end was straightened out. All of this was with a 385 CID, 9.8:1, ported Vortec heads, and the above listed cam. The boat was on plane by roughly 2k RPM (not even breaking a sweat).

What do you folks think? Suggestions? What about reversion with bigger cams... any threshold? I use Marine Power center-riser manifolds with 4" risers which are not extended. They do seem to exit water a little farther down the pike though than the old three inchers did.

Oh, the boat is a 23.5 ft cuddy... I guess more like a runabout than anything. Weight is 3415 dry and holds about 80 gallons of fuel, no water and an Alpha One drive.

Thanks!

I saw the other cam post farther down the line. With the 262H I do not see any problems with reversion using the manifolds that I have now. I boat in salt and semi salt water and as such I think that cast iron manifolds will be the best for my situation (God help me if I mention needing to buy a new set of stainless manifolds and risers).

With that said... please go on. :D

for a Idea..I am going to run the Crane roller cam #109831. 222/230 at .050 duration...509/528 lift....112 LSA
I choose this one and to get a peice of mind I called crane and they set me up with the same one I had choose.

383
4340 eagle crank
H beam eagle stroker rods
forged full floating dished srp pistons 9.9:1
edelbrock air gap intake
750 holley w/1" spacer
vortec heads, 7/16 screw in studs, with guideplates.
Crane full roller valvetrain

stock exhaust so far.. running outta money :(


This thing is built like brick ****house :D :D

it is going in a 18.5' powerplay tippin the scales at 3000 lbs. with a alpha..

There is one more cam above this, they say this is the biggest one to be used in a marine motor. it is crane #119641... 234/242 .050 duration.... 539/558 lift on a 112 LSA..

I just read a little more info and I am going to run the 1.6 roller rockers. so my cam will be ..222/230... .543/.563 lift at a 112 LSA..

Tom, I'll bet that the reason that Comp Cam said that cam is the biggest for I/O's is not because of the lift or reversion, but because of the idle. Remember that alpha of yours needs a momentary "stall" to get out of gear. If you go with something too wild you might start stalling out when youre trying to shift out of gear. Also make sure you have enough clearance to the pistons. My guy was saying youre okay until you get up around .520 then you may need reliefs or dishes to get the clearance. But I also had the blocks and heads decked.

Now are you going to end up like me with a boat all torn apart over the summer. ;) Mine is finally in one piece. My wife is already asking how all the other projects are going to get done if the boats in the water this year. I told her what projects! :D

I think I'm good with the valve-to-piston clearance. The stall issue is something I didn't think about though. I guess I'll have to keep in mind the idle characteristics and such.

I'm not going to have a dead boat this summer! :D I'll have it running before the spring thaw and as soon as the river water starts warming up we'll be out there.

Thanks on the stall issue though... I totally forgot about that part of the equation. I would have been pissed if every time I had to shift the engine died! :rolleyes:

TomZ- I know you're going CompCams and have a stroker- this is what I came up with for my 355's and they work great ( a little lumpy on the non-stroker but no problems with the Alphas and their shift interruptor)-would work great on a stroker motor as well. I've always had good luck with Iskendarian Cams. This a little similar to the 280H?
Isky Dual Pattern MegaCam
270 intake, 280 exhaust
221 intake, 232 exhaust @ .050
.465 lift intake, .485 exhaust
112 degree lobe center
Running Comp Magnum Rockers 1.6 on intake only for a intake lift of .498"
All in all it's a pretty impressive marine grind. No reversion problems at all either on EMI Thunder exhaust.
Jim

[ 02-10-2002: Message edited by: jafo ]

That's the same cam I was running in my 355 a while back. I thought it was a bit much for the 355 and the heavy boat BUT the motor was also a bit worn out as well so that might have been part of it.

Do you have a grind number for that one? If not I'll just look it up when I get the chance.

Thanks!

The grind number is an Isky 281-12.

:D

TomZ- The tired motor may have been some your problem-I used them on complete OH's. It's an aggressive grind for a 355, but the torque still comes in at a low RPM and stays with it on up. The 1.6's on the intake help as well.
It probably is more suited for a stroker, but I really like these cams. My 355's are in a VERY heavy boat as well ('86 Formula 242LS), but I have the advantage of two engines. I'm sure Comp can match it up or grind something for you very similar. :)
Jim

TomZ,
I've been reading about building 383/400ci motors and there has been a consistent warning about rod to cam clearances. That is with the 5.7" rod of course. Have you had this problem or how did you avoid it? How big a cam can you go before encountering it?
Thanks Chuck

for the rod to cam clearances, you can have a small base circle cam ground, or have the rods stroker clearanced... you need a minunum of .050" between the two.. I am buying the eagle h beam 3D rods that are already clearanced for a 3.8" stroke.

The rods were clearanced to work with the block and a reasonably sized cam. Because the motor was built with a marine-type cam in mind the clearance issue is not as big a deal as it would have been had this been going into a car... where I would have been running a very BIG cam and more compression to crest the 500 HP mark ...so it should not be an issue. The motor is not in the boat at the moment so I can easily check the clearance and I will, though I don't see any problem with a cam that is still below .500" lift, which is where I plan to be. If I do find a problem I'll switch to smaller base-circle grind which will definitely clear it up (though cost will be greater).

Good point though. :D

Now... I wonder how they do it with the new HT383s that GM is producing? They use a 4" bore with a 3.80" stroke to reach 383 CID. There was an article on it in Hot Rod or Car Craft this month. Guess I'll have to see what they used in terms of a different cam and the effects on rod/cam clearance (this motor uses a 5.7 rod as well).

Tom

I didn't have problems with my cam/rod clearance, but when I put in a new crank into one engine I had to clearance the block for the counterweight. That kind of suprised me.

I've got that issue of Hot Rod here in front of me.

There's no mention of any clearance work on the block or rods.

The cam in the engine as supplied by GM is 196/207 @ .050 duration with .431/.451 lift, LSA not specified.
Peak HP: 338.1 @ 4400 and peak torge: 444.3 @ 3400 using a 625cfm carb and hedders.

Swapped carb for 750cfm, 1.6 ratio rockers, RPM Air Gap intake and Comp Cams XE282HR (230/236 dur, .510/.520 lift, 110 LSA) and a thinner head gasket raising comp ration from 9.1 to 9.6.
Peak HP: 455.3 @ 5600 and peak torque: 493.0 @ 4200.

Sound lik a good deal for a little extra work.

After all the work they changed the oil over to Royal Purple.
Peak HP: 463.1 @ 5600 and peak toeque: 502.9 @ 4200

[ 02-12-2002: Message edited by: Iggy ]

Ahhh... the benefits of a roller. If I didn't have to come up with $1400 in Fed taxes this year I might have gone that way instead. (Homer Simpson voince on) Stupid IRS...

How much would a 2* drop in lobe separation angle effect reversion? I was looking into some of the split pattern Xtreme Energy cams (basically a 270/280 type grind) but all of the automotive grinds are based around a 110* LSA. I think there was something on it in the Dennis Moore book but I can't find it right now (buried in the office).

Any thoughts?

ttt

Found the book... 109* according to Dennis Moore is the sweet spot. Anything shorter is looking for trouble with reversion and driveability.

Now I jus thave to choose a grind.

I'm going to run the Xtreme Energy XE-274-H. These are the specs:

Adv- 274*/286*, 230*/236* @ .050, Lft- .487/.490, 110* LSA

Any thoughts? Anyone have a desktop dyno that they could run the numbers through? 383 CID, 10.1:1, Vortec heads (not sure of what the numbers are but they have 2.02/1.60 and a fair amount of porting), Performer Vortec, 750 CFM quadrajetc, center-riser manifolds (Barr, better than the Mercs).

Thanks!
Tom

Tom, I'll run it tonight. I'll insert your cam against my engine and look for the changes. It should be pretty close to yours since we're running almost the same except for heads and cubes. It will get you into the ball park. You can compare the increases or decreases against your numbers on the engine you dyno'd. The big thing would be the flow of the heads, I have info on stock Vortec's but not ported with 2.02's

Thanks Jeff!

I think the head flow is equivalent to the GM Fast Burn... I had all of this documented here at home but my computer crashed and I I lost it all. 230/170 @ .500 seems to ring a bell.

I'm eager to see what you come up with... I've read about some 355 combos with less compression and a notch down on the camshaft work out to somewhere in the low 400 hp range. I think I'm going to have a real drive buster here. ;)

Thanks!
Tom

Tom I ran the numbers last night. I used a 383 with 750 CFM carb, dual plane intake, and flat tappet hydraulic lifters. I found the numbers on a vortec head but the valves are the 1.94/1.5 but I'm able to adjust the valve size. Since you have your heads ported we'll see how close thes numbers are.


Your Extreme Marine Cam: 2000-172 HP/ 450 Torque, 2500 217/455, 3000 262/458, 3500 305/458, 4000 339/445, 4500 361/422, 5000 363/381.

Extreme Energy Cam: 2000-159/417, 2500 206/433, 3000 252/441, 3500 299/449, 4000 343/451, 4500 380/443, 5000 401/421.

It looks like its a good cam for the upper revs. Althought there is still a ton of torque down low it gives up a fair amount to the extreme marine. The extreme marines torque is flat as a board all the way up until it gets almost to its max operating rpm. Where the EE doesn't start to drop off until later. I guess is all in where you typically run at. Hope this helps.

Wow, that's a major slide in torque when comparing the two.

Since the boat is heavier than a comparable go-fast and since I'll be spinning a bigger prop maybe I should stick with the 262 or maybe up it one notch in the marine category?

Could you run these numbers for me? This is Comp's XM-270-H which is the next rung on the ladder.

270*/276*, 226*/236* @ .050, .480"/.489", 112* LSA

I guess I'd like to see the flat torque curve with a little more horsepower. I would rather not have to beat the crap out of the motor to get up on plane and keep it there. If the other cams are requiring that then I'll stick to what I have for now. How do you tihnk one of the other cams would run (XE-274 and the XM-270)?

Any suggestions?

Thanks!

Tom here are your numbers.

2000 162 hp/426 ft/lbs.
2500 207 hp/434 ft/lbs
3000 251/439
3500 297/446
4000 340/447
4500 375/438
5000 398/417

Looks like is a wash between the two.

I figured as much...

Do you think that the more aggressive cam will be driveable? I think I'll stick to it and give it a try (nothing to put another cam in it if I need to).

Here's a thought... maybe the lower torque of the more aggressive cam will help to save the drive from major destruction? Yeah that's it! ;)

Anything has to be better than the old 355 was so I guess it'll do. ;)

Lower torque?, I hate to tell you your alpha is going to hate you anyway.:D Youre idle is probably going to suffer, but like you said switching the cams is no big deal. Looking at all the numbers, such as overlaps and IVO EVO, and that kind of stuff, it isn't too far off the Exteme Marine. So I would think it would behave similar.

But you have to admit, that Extreme Marine is a pretty good cam, down low. Cams are cheap. Someone should invent a break away coupler. If you get close to toasting a drive, it gives first.

39 days and the cover comes off.:cool: