Cam suggestions for 383 build
 

I would like a custom ground but is out of the budget. The boat is a 98 glastron gs205 and weighs 2600 lbs dry. We will be doing a little fishing and skiing both. It also has a Volvo penta sx duo prop out drive. Plans are to run exhaust out the stock leg. I'd like to make as much torque as I can with this set up. The heads on this 383 are 23degree EQ heads with 180cc intake runners with with both intake and exhaust runners ported and 64cc fast burn combustion chambers and compression at 9.3. Any ideas? I don't want to worry about reversion but do want a strong cam.

Cams that I have looked at are Lunati voodoo hyd roller 20080721 and Comp cams extreme 270xm. Would either be strong out of the hole all the way to 5500 rpm and free of water reversion problems?

Lunati 20080721 (Formerly Part Number 60121) Chevrolet Small Block LT1, LT4, & 1987-Present Hydraulic Roller Voodoo Camshaft RPM Range 1800 - 6000 Lift .515"/.530" [email protected] 219/227 LSA/IAC 112/106
Strong power increase in mildly modified engines with excellent throttle response. Will work with stock converter in 383+ c.i.. Likes 2000 RPM converter in 350 or less c.i. applications. Likes 3.23-3.73 gearing. Largest choice for inboard/outboard marine applications. Has noticeable idle and likes headers.

Voodoo: Lunati's Voodoo series of camshafts deliver more area under the curve than any other series of camshafts. This means more throttle response, quicker acceleration, more vacuum and better efficiency. These factors, combined with maximum horsepower and torque, make Voodoo camshafts the perfect choice for a wide range of high performance applications.

RPM Range: 1800 - 6000
Lift with 1.6 Rocker: .515"/.530"
Duration @ .050": 219/227
Advertised Duration: 270/278
LSA/IAC: 112/106

The cam change may not do much with the stock exhaust, the 270XM in my brothers 383 crapped out at 5000 rpm. You might look at the 276 XM.

That's what im afraid of. I like the advertised 6000 rpm of the lunati cam but not at the cost of water reversion. I think the 276 xm would force me to buy headers.

I built twin 355 Vortecs two years ago with the comp XM 264 Roller.Here are my results:

SuperFlow
Dynomometers and Flow Benches
SF-902S

355 MARINE CHEVROLET Result Summary Date 12-20-2012 1:46 PM Temp 80 Deg F. RH 74%

RPM TQ* HP*
2600 399 198
2800 408 218
3000 421 240
3200 430 262
3400 436 282
3600 440 302
3800 444 321
4000 448 341
4200 451 361
4400 450 377
4600 443 388
4800 438 401
5000 431 410
5200 421 416
5400 409 421
5600 396 422
5800 373 411
Max 452 422
Avg 426 339

* Test Exhaust 1.5" Diameter Dyno Tester Supplied Headers.

355-cid VORTEC SPECS

Bore / Stroke / CID: 4.030 / 3.48 / 355 cid
Compression: 9.4:1
Block: GM factory four-bolt 350 L-31 VORTEC
Crank: SCAT forged-steel PN 1101-11133
Pistons: Probe forged (PN 130212334-030)
Rods: Probe (PN 1201-10062) 5.7"
Rings: Total Seal Moly
Bearings: Clevite
Gaskets: Mr. Gasket and GMPP
Cam: COMP Cams (XM264HR) 212/218 at .050, .488/.495 lift, 110 LS
Lifters: COMP (PN 875-16)
Chain: COMP (PN 2100)
Pushrods: COMP (PN 7372-16)
Rockers: COMP 1.5:1 (PN 1417-16)
Heads: GMPP Vortec (Scoggin-Dickey PN SD8060A)
Manifold: Edelbrock Performer RPM Air Gap (PN 7516)
Carb: Demon (PN 1402010VE)
Distributor: Davis Unified Ignition DUI-7000
Spark Plugs: Autolite AR103
Oil System: Milodon HV (pan PN 31505)

I am running stock Mercruiser OEM Exhaust with y pipes in the boat so I'm loosing power on the top for sure. running 1.5 Ratio Bravo I's with 23" Mirage I have all the power and torque I can use. i have no reversion issues and make BIG TQ numbers down low.

Your limiting factor is not the fact that it is a stock exhaust manifold, or worrying about reversion, but rather trying to exhaust out the outdrive. That is your choke point. The Lunati cam would likely work but not trying to push it out the prop. Keep the LSA wider as you go up in cam size and utilize thru-hull exhaust with the stock manifolds and risers. Crower has some nice hyd roller cams that would work too. Don't pick a cam that makes peak power at 6000 rpm as you will likely never see that in a boat. Some drives don't like that.

Target an LSA in the 112-114 degree range.

FWIW, I'm running a cam nearly equivalent to the 276XM, stock exhaust with thru-hull and no reversion.

True. Many 383's and 350's out there with the Comp 270 HR extreme marine. Performance heads and Most afmkt exhaust.

218/224 at .050" on a 112LSA.

Top usuable rpm in boats 5k for 383's and 5200 or so for 350's.

Great all round cam though. Makes real good power with good heads.

Gm LT4 hotcam

Sprink, looking at your dyno readout, something just didn't look right. That motor had a peak torque RPM of a bigger cam and continued making power higher than the cam listed should. That cam should have had peak torque at 39-4100 tops and ran out of steam at 5200. Your dyno guy might have screwed you because those dyno numbers are exactly the same as this one listed in Popular hot rodding. http://www.popularhotrodding.com/eng...ec/index1.html . Not saying you don't have a good set of motors, just wanted to point that anomaly out.

So what are you implying? That two nearly identical engines one built in 2006 and the other in 2012 can not yield the exact same results? :lolhit: :lolhit: :lolhit:

The details in this case do not point to shenanigans by sprink's builder.

Looks to me that a good recipe was copied. Where was the magazine engine built?

I just saw this and really don't care .But since you ask ,I would say no ...You never get identical results on two of the same motors. In play land yes .In the real world ,no ..

Why is a custom ground cam out of the budget? I've had a couple done recently for less than I could get a comp from jegs.

Found this on Comps site, http://www.compcams.com/v002/Pages/394/XR264HR-10.aspx

Through headers

Just wanted to show their findings on RPM and power range.

That's what I was thinking. Cam motion did my cam for my drag car for just north of 300.

Why do you say that? Just curious. Why the arbitrary rpm limit?

Not a arbitrary limit. The rpms I stated are where the boat will run fastest. Will run out of 'steam' past that.
So, with the XM270HR it will run fastest near 5k with a 383 and 5200 or so in a 350. Both having decent aftmk't heads (vortecs included) and exhaust.

That's real life results.

edit in: if you want to run faster and at a higher rpm you will need more cam.

AC Crooks - you are correct about the HP and that smaller (212/218) comp cams. I know you know your small blocks and that proves it. GMPP's 425HP motor uses better cylinder heads and 383 cid's and a larger 222/230 HR cam. As a note, Their Vortec single plane added 20hp over the highrise dual plane to get it to the 425.

also,edelbrock's catalog shows the hp/tq for their heads,cam and intake.plus he like to have his cams make some vacuum.

Could always install a $700 slob cam and ruin the party and get out of boating.

I don't think that a good recipe was copied and resulted in near identical numbers. The motor in PHR had a bigger cam. I think the guy selling them just gave him a bill of goods regarding the dyno numbers. Those HP an Torque numbers are what I would expect from a 383 with the cam Sprink is using. I'm just saying hey look at this, to much of a coincidence.

A lot of useful information from all of you, thanks. Is your engine loud all the time? I'd love to hear the engine loud but not all the time. I'm pretty green on terminology but could I run a cam like the 276 comp and quiet the engine when wanted or is that getting into a lot of expense? I need to get this project done before my 12 and 14 year olds are grown. My old job is gone that let me spend what ever I wanted on toys and I'm tempted to buy a mild hyd roller just to get it done and get everyone out fishing and skiing. It just seems a shame as well built as the motor is.

I don't have the $300 or $400 I was quoted to go that route. The comp 270xm roller I can get for $259. Not sure about the 276 comp but it looks like if I were to go that route that I will have to sink more into an exhaust I had not counted on.

Do you have flo sheet on those heads? I'd like to compare to the 180cc EQ performance heads I went with. When you say y pipes are you saying tru hull or out the prop? I almost went with vortec heads then decided on the EQ 180cc with 64cc intake runners. They used molds of ported ports on these heads. The intake to exhaust flow ratio is real good on these heads and should make excellent torque . I bought the stroker crank on ebay for $270. It's a kellog forged and nitride treated crank. A guy in Oklahoma went to the auction at the Mercruiser plant when they shut down and bought about 30 brand new stroker cranks for scrap price then turned around and sold them on ebay. They were all big and small block chevy cranks still new in the boxes. He really had no idea what these cranks were worth. I should have bought 4 or 5 at that price.

I went with 5.85 Oliver connecting rods and RaceTec forged d dish pistons with valve reliefs for up to 570 lift cam. The deck was cut down with the pistons .005 in the hole.Compression comes out at 9.3.1.This is a link to the heads I bought except the ones in the link are a bigger version of what I have.http://www.ebay.com/itm/Cast-Iron-cy...056b0a&vxp=mtr

The EQ Heads are very good. Will make a little more power than stock Vortecs.

I hope so. I've read a few articles on engine builds where they were used and made real good torque. I had talked to a well known head porter who was familiar with them and he encouraged me to go with them over EQ's vortec heads which are pretty good also. The EQ performance heads look very much like a ported Dart head right out of the box for a lot less money and are much thicker than some of GM's crack prone heads. They are a quality casting.

FYI:
I did a top end on a high hour 350 Mag (260HP) in a 20ft boat (really 19ft) and about 2800lbs.
218/224 at .050" / 113LSA Comp Extreme EFI HR cam
180cc heads
Weiand Air Strike (like the Eddy Air Gap)
650 Vac BG Carb
Eddie Marine Exhaust Manifolds (already on boat)
Merc Alpha Outdrive

15mph increase was result. NO BS. I'm intimate with that boat. LOL.

It's also an animal planing if at WOT - so....that needs to be held back to take care of outdrive.

Reason why I mention above is that you have same size and near same weight boat + a bigger engine. Heads are pretty much the same performance wise.

So, even if you go a little smaller on cam, it should still be an animal compared to whatever was stock. Just remember what we said top rpm will be as far as best speed. That 212 at .050" cam from Comp will probably be 4600 rpm.

Interesting setup, it's similar to what I put together in some aspects.

Anyone care to guess what it will make? Below are specs;

Bore / Stroke / CID: 4.030 / 3.48 / 355 cid
Compression: 10.2:1
Block: GM factory four-bolt 350
Crank: GM Forged/Balanced
Pistons: SRP flat top
Rods: Eagle I-Beam 5.7"
Rings: JE
Bearings: Clevite
Gaskets: Cometic
Cam: Bullet Cams (CHS284/292HR112+4), DUR @ .050 230/238, .530/.530, LSA 112, INT C/L 108
Lifters: GM Dog Bone Roller
Chain: Cloyes Billet
Pushrods: Smith Bro's
Rockers: Pro Magnum 1.5:1
Heads: Edelbrock E-Tec 200
Manifold: Mercruiser HIgh Rise Dual-Plane with 2" spacer
Fuel: MEFI 1, 90mm Throttle Body
Distributor: Merc.
Oil System: Melling HV
Exhaust: Stainless Marine, long tails

http://youtu.be/9RlLV8QBbCk

Any time you truthfully reveal what you have done...there are always critics. Bottom line...all things considered I'm happy with what I have and it performs very well.

Sure. I'll take a stab it.

It will be much faster if you're wife is driving it.

Loud is a relative term. Several factors come into play with 'loudness' in my boat. If the bimini top is up the boat is perceived to be louder inside the boat since the sound waves are bouncing off the water, up and into the bimini top reflected inside. Obviously the true dB reading aft of the boat remains virtually unchanged. I don't have readings for the current motor, but stock Merc 350 Mag with Rex Marine Sound Selector system was about 82 dB at idle, cutouts closed and if I remember about 86 dB with the cutouts open. New motor has more bark, but I haven't pulled the meter out to measure it and I only have straight through hull.

I can, and have run inline silencers and they do cut the dB by about 6-8 but also choke down the top end rpm by 300-500 so I almost always leave them out. With a milder cam you may not have that problem. There are several exhaust cut-out systems available which can also give you some sound options, but they should be avoided when cams get more aggressive since the butterfly valves diverting the exhaust down the Y-pipe when running closed can exacerbate potential reversion issues with performance cams. They also add expense. $600-800 just for the system, not including additional exhaust hose, thru hull tips, and the labor required to cut the holes.

To answer your question, I would be hesitant to run the Comp 276 with a diverter type exhaust system.

Definitely faster when the wife drives it. After all, this one is hers.

That does sound like my boat. The 305 was missing when I bought the boat but most everything was still in it. I guess for the time being i'll look for a cam that is a step above what would have been in a 5.7 I can swap later if I still want. What kind of HP is a sx cobra duo prop good for? Am I going the wrong direction again thinking about comps XM270 ? Advertised at 5200rpm or is it doable through the stock leg?

Exactly. As long as your happy that's all that counts.

Is this cam doable in my 383 exhausting through the stock leg and would it actually reach the advertised rpm? What kind of hp and tq numbers could I expect from it?

Lunati 20080720 (Formerly Part Number 60120) Chevrolet Small Block LT1, LT4, & 1987-Present Hydraulic Roller Voodoo Camshaft RPM Range 1600 - 5600 Lift .507"/.515" [email protected] 211/219 LSA/IAC 112/106
Excellent choice for stock to mildly modified engines, works well with OEM style injection, great inboard/outboard marine cam for economy and sking. Good mileage and torque increase.



RPM Range: 1600 - 5600
Lift with 1.6 Rocker: .507"/.515"
Duration @ .050": 211/219
Advertised Duration: 262/270
LSA/IAC: 112/106
Valve Lash: Hyd/Hyd
Cam & Lifter Kit: 20080720LK
Complete Kit: 20080720K
Lifters: 72910-16
Springs: 73943-16
Retainers: 75742-16
Locks: 77003-16
Valve Spring Kit: 73943K1
Valve Seals: 78501-16
Timing Set: 93026
Pushrods: 5040-16
Rocker Arms: 85340-16

38
You will likely incur pumping losses (both intake and exhaust) that will inhibit you from reaching 5600 RPM. It will be beneficial to address your exhaust lobe due to the downstream restriction the log manifolds present. The displacement has increased ~9% from the original spec, increasing the spent charge proportionally. I would suggest increasing intake duration, reducing your exhaust bias (from the new intake lobe) to: (1º-4º) It will also benefit you to pay close attention to your ECL.

Bob

If I give ya a hundred down would you help make this problem go away rmbuilder?:D

Or suggest an off the shelf cam that will let me get the most from this 383 that I can exhausting through the stock leg?

I have been offered a brand new hyd roller cam and roller lifters a long with new roller rocker arms, chain and gears. valve springs push rods from a 325 HP 5.7 mercruiser that is being reworked for opposite rotation. He is asking $375 for everything. I can't hardly turn that down. Will my 383 gain or lose running that hyd roller cam? Pretty sure he said it was a duel pattern cam. He also said the cam is a 5,000rpm cam. Everything is for my same year engine, a 98.