Cam and engine Gurus.. Need a blessing or condemning

[Friscoboater]

I have just ordered my Engine and I have to make a cam decision. I am trying to get the most torque out of this engine. So can you look at this cam and tell me what you think.

Here is what I have.

350 that is stock with 8.5:1 and 194 heads.
Edelbrock performer intake
Quadrajet
New log style manifolds going through the y pipe and dumping at the gimble

The cam I purchased is a Comp Cams Xtreme Marine XM262H.

The specs are

Duration at .050/ Int= 218 Exhaust = 224
Duration Seat to seat = Int 262 Exhaust 268
Lift Int .462 Exhaust .477

power range 1300 to 5500 but the peak will be a 4500.

Is this too big of a cam? According to desktop dyno it gives the best torque in the family of cams. Around 420 Lbs @2500.

Are my log style manifolds going to be a problem, and will an alpha handle that torque?

They are installing high lift Valve Springs for me.

Thanks for the help guys.

 

[HVAC Cruiser]

Re: Cam and engine Gurus.. Need a blessing or condemning

Hey Frisco, when I ran the software for your engine I came up with 379 fp with the 262 cam

You might want to look at the 256 I think it might suite you better

Wait for some others to chime in but you might be over caming the engine a little with the 262

Hope that helps some

 

[Friscoboater]

Re: Cam and engine Gurus.. Need a blessing or condemning

I had the intake wrong. My number syncing with yours now. Now the XM256H has a better toque curve. 400.3... CRAP!!!!

 

[HVAC Cruiser]

Re: Cam and engine Gurus.. Need a blessing or condemning

I had the intake wrong. My number syncing with yours now. Now the XM256H has a better toque curve. 400.3... CRAP!!!!

Sorry to be the bearer of bad news, when I looked at your # they didn't look right, so I ran them so see. I am actually building a 383 and I am going to use the 256 its a real nice cam. when running low compression you don't want to put to much cam in her.
I noticed you are going to use the log style exhausts, any reason for not switching over to center style 4" Your engine might breath better with them

 

[Friscoboater]

Re: Cam and engine Gurus.. Need a blessing or condemning

Right now it is not in the budget. The logs are new and I cannot bring my self to spend 1600 for a conversion.

 

[HVAC Cruiser]

Re: Cam and engine Gurus.. Need a blessing or condemning

Right now it is not in the budget. The logs are new and I cannot bring my self to spend 1600 for a conversion.

I know how that feels, but you can get the GLM Manifolds complete with the 4" risers gaskets and studs for $385. My risers were bad and that's actually what toasted my engine so I searched out the best deal I could

 

[Friscoboater]

Re: Cam and engine Gurus.. Need a blessing or condemning

that is just for the risers. You still need to get all the accessory brackets and the hoses and pipe to adapt to the old y pipe.

 

[HVAC Cruiser]

Re: Cam and engine Gurus.. Need a blessing or condemning

that is just for the risers. You still need to get all the accessory brackets and the hoses and pipe to adapt to the old y pipe.

True, that's just the Manifold and Risers I had a 3" center exhaust to begin with so for me it was just the elbows. all the brackets stayed the same

 

[Friscoboater]

Re: Cam and engine Gurus.. Need a blessing or condemning

I am tired of trying to figure this out. I cancelled the order from jegs and I will just have the engine builder do RV cam. Keep it stock and reliable.

 

[wca_tim]

Re: Cam and engine Gurus.. Need a blessing or condemning

the 256 cam would be about perfect...

I run th 270 version in a 383 and it's a mild cam in that engine. nix on the rv cam you'll be happier with the 256 imho

 

[system-f]

Re: Cam and engine Gurus.. Need a blessing or condemning

Keep it stock and reliable.

x eleventy billion!

 

[wca_tim]

Re: Cam and engine Gurus.. Need a blessing or condemning

Sorry to disagree with the last poster, but cam design has come quite a ways and the comp xm series is every bit as good a product as any "factory" rv or factory cam. period.

There are several important differences in a marine cam. The xm cams and other marine designed cams and have a split duration - the exhaust duration is longer than the intake duration which means the exhaust is open longer than the intake to account for the poor design of marine exhaust manifolds and relatively restrictive marine exhaust systems.

In addition, the 256 cam would be a VERY safe choice for your engine, would be every bit as reliable as a factory or "rv" cam and would make a little more power without any sacrifice in fuel economy (read more distance traveled per dollar - maybe subtle, but could be measurable). It'll give you a little higher valve lift as well. especially coupled with 1.6 ratio rocker arms, that cam will make a decent bit more power than a "stock" cam (often the comp cams engineers will tell you to run 1.6 ratio rocker arms... the lobe profiles can definately handle it with the spring pressures they spec for their cams).

If you're interested in reading more and comparing the specifications of factory version marine cams with the cams you're looking at send me a pm with an email address and I'll send you some interesting reading...

to help you think about it, the merc factory hydraulic flat tappet marine cam has the following specifications

duration at 50: 200 intake, 212 exhaust
valve lift with 1.5: ratio rocker arms: .400 intake: .410 exhaust
lobe centerlines: 108 atdc, 112 btdc
Lobe seperation angle 110.

merc factory hydraulic roller cam (much more modern design):

duration at 50 197 intake, 207 exhaust
valve lift with 1.5: ratio rocker arms: .430 intake: .450 exhaust
lobe centerlines: 106 atdc intake , 112 btdc exhaust
Lobe seperation angle 109.

Competition cams XM256H:

duration at 50: 212 intake, 218 exhaust
valve lift with 1.5: ratio rocker arms: .447 intake: .462 exhaust
lobe centerlines: 110 atdc intake, 114 btdc
Lobe seperation angle 112.

you listed the 262 cam specs in your original post...

comp cams web page describes the 262 grind as: Hydraulic-Biggest cam for inboard/outboard, good mid-range with excellent response, noticeable idle. it would probably get by for reversion - probably - with your manifolds, and would have a bit of a lope at idle. the 256 will be a very safe choice...

and the 256 grind as: Good for inboard/outboard pleasure boat, skiing and good economy.

the 256 was designed for your aplication and has been used in a TON of boats...

If you were building a 383, the 262 would run about the same in a 383 as the 256 does in a 350...fyi

Note that you should not use your stock valve springs, and you should make sure to check your valve train geometry as well... If you are still stuck, send me a pm with your email. I'll scan some pages out of a book on marine engine performance for you. Hope this is helpful... Not an expert, but have some experience and do my homework when making choices like this. Cheers

ps. drive is fine and don't know about your manifolds. I wich you had been doing this last summer - I'd have given you the complete later exhaust system with all the brackets, hoses and y-pipe for the cost of shipping. I wound up putting them on the curb for the scavengers to take for recycle... along with heads, etc... Good luck with your engine

 

[Friscoboater]

Re: Cam and engine Gurus.. Need a blessing or condemning

Thanks for the help Tim. That post really helped me out.

 

[Friscoboater]

Re: Cam and engine Gurus.. Need a blessing or condemning

I just wish I could find someone that has used either of those cams and let me know what to expect. Some many people have got me scared about the log style manifolds.

 

[funk6294]

Re: Cam and engine Gurus.. Need a blessing or condemning

Call comp cams and talk to the guys there and explain your set up. Since they have done a considerable amount of R&D to come up with these grinds they will be best able to tell you what to expect.

 

[Friscoboater]

Re: Cam and engine Gurus.. Need a blessing or condemning

I did speak with them. they Told me to put in the XM270H. That cam is even bigger.

 

[wca_tim]

Re: Cam and engine Gurus.. Need a blessing or condemning

the 270 is too big and will give you reversion. A lot of times the people you get on the phone at comp cams don't know anything - especially about boats.

I currently have an xm270 in a 383 and it has a significant lope to it - it would probably be too much for gneral use 350 in a multi use kind of boat.

The 262 would sound about like the 270 in my boat (can see what that sound like on the utube vid below, granted the engine is far from stock in other areas, but that should give you a sens eof what a 262 will be like in your boat...).

the 256 will not cause reversion and will be well mannered in your boat.

try doing some searches in this forum... I'm certain that a number of folks on here have used them. They've been around for a good while and are made to work with factory exhaust and drives - almost no overlap (is what causes rough idle, etc...).

 

[Friscoboater]

Re: Cam and engine Gurus.. Need a blessing or condemning

I thought I did a search, but did not come up with anything. I just did one again and came up with lots. Funny.

Thanks for the help on all this. I think I am going to call the builder tomorrow and have him give me a price on flat top pistons. You boat sounds great by the way. How is your hole shot?

A question about reversion. Is it the danger of sucking in lake water from the prop or the waste water from the engine?

 

[wca_tim]

Re: Cam and engine Gurus.. Need a blessing or condemning

holeshot? it's light, it'll pretty much stand up on end out of the hole if it's not trimmed in really far and the tabs aren't down. pulling a big slalom skier out of the water, 2-3 adults in the boat takes about half throttle...

why flat top pistons?

duh.. I looked back above. know you're on a tight budget - been there before. depending on which heads and pistons you have, you might be able to bring compression up and gain more by spending that money on a pair of vortec heads. Presumably the builder would deck the block to give you a tight quench (important in avoiding detonation and lets you run more compression without detonating). I'm running iron heads at a little over 10:1 compression on pump gas with no problems. vortecs would be fine doing the same and flow very well at the same time.

OH, look up some posts by mkos. his engine was a budget build and has a gm lt1 "hot cam" in it I believe. makes good power for what he spent on it.

 

[Friscoboater]

Re: Cam and engine Gurus.. Need a blessing or condemning

Thanks a ton for the info. My thinking was that the flat top pistons will take me to about 9.75:1 with a stock early 80s iron head. Am I correct in thinking this?

Take a look at this guys boat.

His block has a few goodies in it, but what got me was the cam, and he is using stock manifolds.

HERCLC4A $119.99

Chet Herbert Cams has been grinding cams since 1949. Performance, high quality and a low price. Everything you want in a performance cam and more. Cams for your tow rig, street performance, street-strip or race. If you need assistance picking out a cam please call our tech line at (704)435-0095.

Excellent low to mid range. Good idle, daily performer. 9.5:1 suggested.

RPM Range: 1800-6200Advertised Duration: 280/290Duration @ .050: 220/230Lift: .467/.480Lobe Center: 110c

Here is the boat idling

http://www.youtube.com/watch?v=-kr7LE4FcSg