Camshaft for 350
 

I am in the process of replacing the 350/260 engine in my scorpion 230. The engine I am replacing it with was built by a local machine shop, I was told it would have a conservative 350+ hp.(@ 5000RPM) I was just wondering on your take on it. The engine has 9:1 compression 4 bolt stock bottom, (heads) 2.02/1.60 valves with 3 angle blended bowls unshrouded valves and a 30 deg. backcut on valves, cleaned up runners, gasket matched and pinned studs. Weiend stealth air gap intake ( has roughed up runners for better fuel atomization) gasket matched with 2 inch spacer and a holley 600 spread bore carb with stub stack. The cam specs are 262/272 adv duration, 204/214 @ .050, lift 420/442 and a lobe seperation of 112. Stock omc exhaust (for now) with warmed over and smoothed runners and thru hulls. I am concerned with cam. Is it enough to get me to the 350+ hp mark and with a ls of 112 will this give me probs. with water reversion. A lot of the cams I read about are at 114. Any input would be greatly appreciated. Thanks

IMHO your cam should work pretty good as far as in a boat but as far as making 350 hp with that cam and stock exhaust manifolds I highly doubt your going to be anywhere close to that unless you have some really killer heads, I'm thinking more like 275-280, RM builder might chime in with his wisdom, Smitty

I hope I have more than a 15 hp gain over a stock 260 hp merc with 8.5:1 low rise cast intake and carb with a stock heads (76cc 1.94/1.50 single angle valve job) and a cam of 202/214 dur and 395/404 lift. I have alot of time and money into it. Thanks

Go with the lt4 hot cam from gm, it will wake it up and you can run it with stock exhaust

The camshaft you chose is less powerfull/smaller than the stock marine camshaft.
You will need at least 218/224 degrees of duration @.050 lift to get close to 350 horsepower.
The camshaft used in the 350/350 horsepower 1969 Corvette engine had 224/224 degrees of duration @ .050 lift.
For best performance install a camshaft with 110 degrees of LSA (lobe sep angle).
Dennis Moore

I won't have to worry about water reversion with that cam. I thought I had to stay around a 112 or 114 LSA to avoid this.
Again thanks for all the great info.

I agree, cam is REAL small and I would be surprised if it made 300 hp especially with stock manifolds. In the old days I would have bought a cam from Ultradyne for it with numbers like this (IF exhaust was going to be upgraded but stock heads were kept))
276/286 112 .454/.454 221/230 Biggest cam for stock-style spring. Excellent in 350-400 size engines. Largest cam with power brakes. 1500-6000
I really liked that grind and ran it in motors with mild compression with good luck, that cam with 882 heads ran away from my zz4 350/350 hp crate engine in the same vehicle
Today however I would just call RMBUILDER and buy what he reccomends as he optimizes these set-ups. If your motors already done and ready to go in though I would say just run it and enjoy your boat, it just won't make quite ass much as you were hoping for, Smitty

Thanks for all the info. How do I get a hold of RMBUILDER

Comp Cams makes a small block (and BBC) "Maximum Marine Camshaft".....it is the maximum camshaft reccomended for marine use, Im assuming without risking reversion....you may want to check it out.

He's actually in Rochester, 585-654-8583

I ran twin TP 174s (from memory) years ago before going to the HOT roller cam and fast burn heads. Close to Artics suggestion....typically described as an "RV cam" in the books.. .457 lift int & exh, .269/.269 /112
Used stock exhaust and corvette Al heads with 1.94 valves.
peak 357 HP at 5500, 341 ftlbs...according to GM (crate motor)...

Lane

Question?
 

What type of cyl heads are do you have? Vortecs 12558060 - SD8060A would be the way to go.

112 ls should be fine with that cam and exhaust but it may be good to increase the idle speed just a bit to insure against reversion

I would recommend a Comp Cams XM270HR paired with the vortices which would put you around that HP.

Texas is correct, even with bigger valves and minor porting the stock heads pale in comparison to vortecs and the nice thing is they are cheap and a fast way to gain 20-40 hp!

Heres what Comp Cams says about their Extreme Marine Cams.....

Comp Cams 'Xtreme Marine' Hydraulic Flat Tappet Camshafts
A Unique Cam for Marine Applications
If you're heading to the great outdoors, Comp Cams offers camshafts designed specifically for marine applications where low idle speeds are necessary and where restrictive exhausts require special cams that work well against wet exhaust system back pressure. These unique camshafts generate an extremely wide powerband, offering the low-end torque needed to jerk skiers up quickly and the high-end power needed for maximum performance. Also, Comp's larger camshafts are engineered for engines with less restrictive exhausts and drives that will tolerate higher idle speeds. An excellent choice for jet boats or power boats.

heres the list.....from the Jeg's catalouge

Chevy 262-400ci Small Block 1955-98
249-12-232-3
Xtreme Marine™ Hydraulic Flat Tappet Camshaft
Lift .447/.462
Duration 256/262
RPM Range 1000-5000
More info on Comp Cams 12-232-3
$129.99
Ships
in 6 days


249-12-236-3
Xtreme Marine XM262H Hydraulic Flat Tappet Camshaft Only
Lift: .462''/.477''
Duration: 262°/268°
RPM Range: 1300-5500

More info on Comp Cams 12-236-3
$129.99
Ships
in 6 days


249-12-240-4
Xtreme Marine™ Hydraulic Flat Tappet Camshaft
Lift .480"/.489"
Duration 270/286
RPM Range 1600-5800
More info on Comp Cams 12-240-4
$139.99
Ships
in 6 days

249-12-244-4
Xtreme Marine™ Hydraulic Flat Tappet Camshaft
Lift .498"/.500"
Duration 278/292
RPM Range 2000-6200
More info on Comp Cams 12-244-4
$139.99
Ships
in 6 days

249-12-248-4
Xtreme Marine™ Hydraulic Flat Tappet Camshaft
Lift .516"/.522"
Duration 290/306
RPM Range 2500-6500
More info on Comp Cams 12-248-4
$139.99
Ships
in 6 days


249-12-318-4
COMP Cams Xtreme Marine Hydraulic Flat Camshaft
Lift .464"/.464"
Duration 268/276
RPM Range 2400-5400
More info on Comp Cams 12-318-4
$139.99
Ships
in 6 days

249-12-324-4
COMP Cams Xtreme Marine Hydraulic Flat Camshaft
Lift .483"/.483"
Duration 280/280
RPM Range 2600-5700
More info on Comp Cams 12-324-4
$139.99
Ships
in 6 days


249-CL12-232-3
Xtreme Marine XM256H Hydraulic Flat Tappet Camshaft & Lifter Kit
Lift: .447''/.462''
Duration: 256°/262°
RPM Range: 1000-5000

More info on Comp Cams CL12-232-3
$199.99
Ships
Today


249-CL12-236-3
Xtreme Marine XM262H Hydraulic Flat Tappet Camshaft & Lifter Kit
Lift: .462''/.477''
Duration: 262°/268°
RPM Range: 1300-5500

More info on Comp Cams CL12-236-3
$199.99
Ships
Today


249-CL12-240-4
Xtreme Marine XM270H Hydraulic Flat Tappet Camshaft & Lifter Kit
Lift: .480''/.489''
Duration: 270°/286°
RPM Range: 1600-5800

More info on Comp Cams CL12-240-4
$205.99
Ships
in 6 days


249-CL12-244-4
Xtreme Marine XM278H Hydraulic Flat Tappet Camshaft & Lifter Kit
Lift: .498''/.500''
Duration: 278°/292°
RPM Range: 2000-6200

More info on Comp Cams CL12-244-4
$205.99
Ships
in 6 days

249-SK12-232-3
Xtreme Marine™ 256H Hydraulic Flat Tappet Camshaft Small Kit
Lift: .447/.462
Duration: 256/262
RPM Range: 1000-5000
More info on Comp Cams SK12-232-3
$225.99
Ships
in 6 days


249-SK12-236-3
Xtreme Marine XM262H Hydraulic Flat Tappet Small Kit
Lift: .462''/.477''
Duration: 262°/268°
RPM Range: 1300-5500
More info on Comp Cams SK12-236-3
$225.99
Ships
in 6 days

249-SK12-240-4
Xtreme Marine XM270H Hydraulic Flat Tappet Camshaft Small Kit
Lift: .480''/.489''
Duration: 270°/286°
RPM Range: 1600-5800
More info on Comp Cams SK12-240-4
$229.99
Ships
in 6 days

249-SK12-244-4
Xtreme Marine XM278H Hydraulic Flat Tappet Camshaft Small Kit
Lift: .498''/.500''
Duration: 278°/292°
RPM Range: 2000-6200
More info on Comp Cams SK12-244-4
$229.99
Ships
in 6 days

249-SK12-248-4
Xtreme Marine™ XM290H Hydraulic Flat Tappet Camshaft Small Kit
Lift: .516"/.522"
Duration: 290/306
RPM Range: 2500-6500
More info on Comp Cams SK12-248-4
$232.99

They are wrong. Sorry.

As DMoore suggested 218/224 at .050" with 112LSA , and another person on the HotCam (218,228) , will get you close or just over depending on the heads used.
These (Comp Cams + GM Hot Cam) have been run in tons of marine small blocks and believe it or not they stop pulling at 5200rpm on 5.7's.

Fact, not theory.

As mentioned, Bob Madera is a great resource + cam supplier to help you get to your goals.

So over the weekend I was looking for a set of vortec heads and came across a vortec long block which I ended up purchasing from a friend. I am just going to shelve the other motor. It is a fresh motor with flat tops and it is suppose to be 9.2:1 compression eith the stock roller cam setup. So now my question is, I would like to obtain between 350- 400 hp. Is it possible and what cam, intake and exhaust to run. I would like to keep the roller setup and have plans to upgrade the exhaust. I appreciate all the responses and am learning a lot about .

Best thing you can do is find a copy of Dennis Moore's book "Small-Block Chevy Marine Performance". It'll answer a lot of your questions.

Suggestion
 

Cyl Heads. Vortecs 12558060 - SD8060A
Intake. edelbrock RPM Air Gap
Camshaft Comp Cams XM270 HR
Exhaust. Dana, Stainless Marine or if on budget GLM Aluminium.

Make sure at minimum that good rod bolts (ARP) are used for higher RPMs.

Yes this combo should put HP approx 350HP but not much more.

If mor power is needed you may want to go with 383 rotating assembly.

Just my opinion THX

350 horsepower is doable (on pump gas) but you will need to twist the engine at least to 5200-5500 rpm. 400 horsepower is doable (on pump gas) but you will need to twist the engine to 5700-5900 rpm.
You will need a camshaft that works at high rpm but will give up a little torque at low rpm.
Are you prepared for the increased noise of your engine at the higher rpm?
The reduction of torque at low engine speeds?
How about the extra noise of thru-the-transom exhaust?

Most people have an unrealistic idea about a pump gas 350making 400 horsepower at 4800 rpm. The only way that happens is with a supercharger and premium fuel.

By all means modify the engine for more performance but set your goals a little lower. 325 horsepower @ 5000 rpm is very doable with a 350 on pump gas.
Dennis Moore

What type of cam profile should I be looking for to be in the 325-350 hp range.

Thanks for all the great info.

I suggest contacting Comp Cams and telling them you want a camshaft with the above specs and a 110 LSA.This will get you 325 -330 horsepower @ 5000 rpm with a smooth running engine and acceptable fuel economy.
Dennis Moore

what do you think of some of the newer Marine cams I listed from Comp??

I think they are fine but they are also flat lifter cams. If you have a roller cam engine I strongly suggest you install a roller camshaft/lifters for better durability.
Maximum camshaft for a 350 would be 224/230 intake/exhaust duration @ .050 with a 110 LSA but you will need to twist the engine to 5200-5500 RPM for maximum performance. You might get 350 horsepower with this camshaft...
Dennis Moore

LSA 110 or 112
 

Dennis,

I have always thought that 112 LSA was the safest to avoid reversion?

Unless you run long risers to dump the water as far back in the exhaust flow.

Just wondering

I'm just wondering if you are the same guy that wrote the books on marine performance engines?

Sounds like him with his cam info and rpm ranges.

Very good books Dennis !

I may not agree with everything you say/recommend/etc cam wise / power wise / etc but your books are really well done. Very good resources for most everyone. Wholly crap are they worth alot now since publishing has ceased.

That said, for shelf cams, the Hot Cam and Comp XM270HR (I'd rather the XM) have been time proven for power, idle, mileage, etc,etc for everyday driving 5.7's with Vortec and other typical performance heads. They idle great and pull to 5000-5200rpm.
383's will need a little more cam, like the 224,230 that DM mentions. Or bigger of course if a 'more juiced' build. More power than the typicals, a wise call would be to RMBuilder.

I experimented a little a few years ago and installed the Comp XM EFI cam with 218,224" at .050" , .575 lift, 113LSA on bone stock '91 Merc 5.7L , and installed BrodixIK180 heads/w beehives, etc,etc. 52-55 (55 was best)stockmph, 65-68mph
(68.1 was best) after. Idle like stock, brutal acceleration out of hole, and very good top end. Both Engine Versions used Eddie Marine exhaust.

Experimentation was really just the 113LSA. Normally I'm like Dennis where I like the tighter LSA's on small blocks, but I've found with good heads we don't have to run our chances of poorer idle, reversion chances, etc, etc that a tighter LSA will give. I still would not go wider than 112LSA for pretty much anybuild. Of course if building 'all out' we throw all compromises out the window and give the motor everything it needs. Alpha's need not apply. LOL.

Anyhow, if anyone wants to hang (online) with a big group of smaller deep vee I/O boats with single small block engines from 50mph's to 80+mph's, send me a PM and I'll direct you to where they are. Never any BS (weird I know) and always willing to help (with actual experiences) when they are around.

I can't send pm's. So where is this hangout ?I swear I have been everywhere online lol. Run a lil 185xlt powerplay w/ 13.1 428 abc/ alpha ss.

Thanks!

I am going to give rmbuilder a call to see what he recomends for a cam. I am going to stick with the roller setup because I am using the whole vortec block not just the heads. I will post his reply.

Now if you aren't Tdaddy shoot me dead. LOL.

You already hang out there and you're pretty much on top.

"It's a small block nation" - Tdaddy

- CFM (SB here)

Well **** I guess I know where your talking about lol

Of course the issue is not really LSA but valve overlap between the exhaust closing and the intake opening.
With smaller duration camshafts you will have the SAME AMOUNT OF OVERLAP with a tighter LSA (108 degrees LSA for instance) as a larger duration camshaft with a wider LSA (112 degrees LSA). A smaller duration camshaft with a tighter LSA will be as powerful (or more powerful) than a large duration camshaft and a wider LSA. They will both have the same amount of overlap but the smaller cam will close the intake valve sooner and create more cylinder pressure at low speeds.

Really the point is silly because how much effect can 2-4 degrees of difference in crankshaft rotation have on the effect of the camshaft on an engine?
NOT MUCH!!

I only suggest that smaller camshafts with a tighter LSA will be as powerful as a larger camshaft with a wider LSA.
Dennis

So did u right the books? If so was wondering if you knew how to find a copy, they are almost non existent

I want to hang
 

can you please direct me