Ok, I'm finally crawling out from lurker mode. Thanks to everyone here for all the help so far in all the old threads.

I'm doing my own version of 330 on roids and have probably read through 200 old threads over the last month. The one problem I'm still having is cam selection. I've seen so many different recommendations, and many of them don't have cam specs.

Here's what I'm building:

496 Stroker for a 260 Powerquest
Forged Pistons 9.5:1
Roller Cam
L29 heads (For fast burn and ability to run higher compression on same octane)
496 HO Exhaust
Edelbrock air gap dual plane
750 or 800 Holley

My desired outcome:
Increase maximum efficient cruising speed
Keep close to factory idle (I do a lot of meneuvering in tight conditions)
Avoid reversion
Peak power at 5500rpm (Hopefully around 475hp)
Durability (I don't want valvetrain problems due to high lift or heavy spring pressures)

With the mixture motion from the L29's, the increased displacement, and the change to a roller cam, I should be able to bump up the cam considerably without killing my idle and getting into reversion problems, but the question is, how much?

I've had several people suggest CompCams 270HR with 218/[email protected] and .51 lift, but several others have said I'd be way undercaming a 496 with that cam.

Anyone run a similar combination and have a roller cam they really like?

Thanks

What are you shooting for for max RPM?
Have the L29's been ported?
What kind of lift and seat pressure have the heads been set up for?

475hp at 5500rpm for a 496cid at 9.5:1 is no sweat. In fact 500hp at 5000rpm will be easy, using good cyl heads

Tough part may be your cyl head choice, if left stock.
L29 flow numbers at 28"H20 :

Lift-----Intake-----Exhaust
.100----63---------49
.200----121--------91
.300----165-------120
.400----198-------133
.500----226-------140
.600----242-------142

Talk to JimV here on the board about what should be done to those heads to support max power at 5500rpm and weigh the $$$ vs a better aftmkt head. He can help you there too.

Also, if your goal is just 475hp, and since you can make this at a much lower rpm than 5500, this will support your 'valvetrain dependability' by not having to rev as high.

I don't have the heads yet. I've got a line on a pair of stock heads as well as a pair of slightly reworked heads with stainless valves. I'm holding off on a decision until I decide on a cam.

Problem with porting the L29 heads is that most people end up killing the mixture motion in the process, which negates the value of using them. I did some of the intial developement work on these heads years ago at GM, and they really are light years ahead of the oval ports in terms of cyl/cyl consistancy and combustion efficiency. My guess is that given my conservative HP goals, I'll gain more in cruising speed and efficiency than I'll loose in top speed. Given that this boat is already a handfull on a good chop, I'm not sure I want to see anything over 70mph, which I should be able to get with 475hp. Let me know if you think I'm going to lose more with these heads than I think I am.

Thanks

I would choose heads and then let the camshaft be last. I don't know what the runner volume is on these L29 nor cross sectional area. I'm a firm believer in not over heading a boat engine for the simple fact we don't have the luxury of gear changes and or clutches/stall converters to bring the engine into its power.

I don't think your goals are out of reach especially since you are looking for midrange punch, my concern is the CID and the crosssection of the head compatability. Moving air for 454 running down the highway at 2800 rpm is no sweat. Moving air for a 496 at 4000 rpm maybe a different story.

This is kinda ruff, but good for knowledge when putting a combo together.

I used an equation that helps us see if we are in the ballpark for valve lift vs head flow vs CID vs peak hp rpm.

Using 454cid with cfm I posted above for these heads:
.500 lift cam = 4283 rpm
.600 lift cam = 4587 rpm

Using 496cid with the cfm I posted above I get:
.500 lift cam = 3921 rpm.
.600 lift cam = 4199 rpm.

Again, this is taking flow of head, cid of engine, lift of cam, to come out with what rpm your peak hp SHOULD (not will) for best effeciency, etc. Basically, before head becomes a good sized restriction.

So, just using it as a 'tool' we can see that the parts selction doesn't marry that well together. Pretty close though for a 330HP 454 - as Merc used it.

==================
Anyway - I could be talking out my 'azz' since I actually have no hands on experience with these heads and just threw out mathmatics which I do use but don't heavily rely on. Not too mention - these are flow figures I copied from Scoggin-Dickey, so since not mine I can't vouch how accurate they are.

BTW: Thumbs up for being a part of the development team. That's super cool in my book.

I like to look at engine component selection "holistically". I agree one of the biggest mistakes people make when putting together an engine is selecting any one component that's way over done for the rest of the engine: too big a cam, huge heads, too much carb, etc.

I'm still flexible on head choice, but at this point, short of spending $$$$ on aluminum heads, the L29's seems the best compromise for the goals I'm shooting for. Now what kind of work do I want to put into them is another question.

Thanks again for all the help. Keep it coming.

PS. I'm sure someone is getting ready to chime in with "just buy a crate motor". I'm still looking for this mythical cheap crate motor everyone is talking about (in every post about similar topics). For what I'm looking for, i'd have to spend an extra $3k for an equivalent crate motor, and it still wouldn't be what I really want. This is my first marine motor build-up, but I've done plenty of auto and bike motors, so I really do know what I'm getting into. Yes, sometimes a motor buildup goes bad (usually when you use a cheap machine shop), but when it goes good, it's REALLY good, and you get that extra bit of pride everytime you hit the throttle.

you may want to go to www.racejunk.com and see if you can find a set of Oval Merlins. Bang for the buck these will make any 496 run. This may be more "bang for the buck" in the long run.

Are you sure those flow numbers aren't for the old L-29? I think there was an L29 years ago that was a real pig. I do know that out of the box, the new L29 head should flow a little better than stock oval ports on the intake, and significantly better on the exhaust. I don't have the flow numbers myself, and my budies that are still at GM are out of town, so I'll have to get back to you with the "official" flow numbers.

Thanks

29 yr old 'Lucy' from dateonline.com ? Yes, she was.

Different forum though.

Seriosuly, it could be - it's the only flow #'s I have in my notes from these heads. Again, from Scoggin-Dickey in their catalog. I have no 'confirmed info' on them.

There are some great sources here (not me, sorry) that will probably help you more. It's Friday and all my customers are headed to the racetracks, the water, or jail probably, so here I sit sputtering my lips...I mean fingers.

Many good members here that can really help. Hopefully they'll chime in.

SB,
Your numbers are the same as mine out of some GM High Performance literature I have. This L29 head is described as a large oval port design that flows better then any other oval. We must note though these numbers I am sure are with a stock valve job and a 2.065" intake valve.

bcarpman,
I was recently involved in a project with a base engine consisting of a Mercruiser 330/454. The owner wanted a cam/head (the peanuts had to go) swap that would net a 100 HP gain. One of the options consisted of a swap to the L-29 Vortec heads.

As SB pointed out the raw (box) flow numbers for this head are not particularly strong, however the overall design is superior to the early ovals. The opportunity was available to have the bare heads sent to a member of this board (HayJay) that works in the cylinder head department at Katech. The heads were not fully ported, however the flow improvement from the modifications was impressive. The Merlin was slightly stronger mid-lift but the L-29 carries nearly 30 CC less intake with a smaller CSA and easily stays with the Merlin on top.. Attached is the flow graph, both intake and exhaust, comparing the:
Stock Vortec L-29
GM 049 Oval
Merlin Oval
Katech/HayJay Modified L-29

The flow values were measured at Katech @ 28” and I am confident they are valid. Buying the heads bare, performing the above modifications, SS Intakes and Inconel exhaust, and a spring/retainer package that matches the cam profile, could be a very cost effective option, easily capable of exceeding your target power goal. I wasn’t a believer in these heads initially, but with some modifications they respond well and definitely have a place in moderate performance applications.

Bob

Yes, I've worked with Katech before, and I'm sure their data is trustworthy. I haven't talked to anyone there in a long time, and I'm not sure who "HayJay" is. Hopefully he'll chime in. This would be an option I'd like to persue.

Seeing you are from MI, give Tyler Crockett a call. He is the guru !!! Dave

http://www.crockettmarineengines.com/

Send me over an email and I will pass along the contact information with the data.
Bob

Can I swing a vote to some Brodix Race Rite Oval's or if you can wait some AFR ovals ? They should help your cause other than some outdrive torque breakage. LOL.

Just playin. Kind of. Not really. Sort of.

Thanks for the reference Bob.

bcarpman.....It sounds like you know what you're getting into and with your history at GM, it sounds like you know what you're looking for.

The build that Bob is talking about was successful in a few different ways. First, the owner's set of "peanut port" heads originally on the engine, had been grossly mishandled and poorly prepared. The valvejobs leaked terribly and they were built with mis-matched components. A real mess. So to start, just bolting on a set of well prepared heads made a big difference. Second, I think Bob recommended a very good cam for the application and created a strong running package. Third, the 18cc difference in chamber volume increased the compression ratio by about 1 point, from about 8:1 to 9:1. I am a firm believer in compression making power (when it's applicable), not just good airflow.

I didn't have a chance to measure the port volume on these heads after I ported them, but the work was just in the bowl area and would not have increased the volume by much. It worked well with this 454 and I think it would work well for good low to mid range power on a 496.

You can contact me through Bob or you can send me a PM and we can discuss this option if you're interested. I'd be happy to work with you on your project.

Jason

Question? In ref to the GM 049 head castings as referenced in the graph....are those 049's modified with any bowl/pocket porting or short side radius work or larger valves----OR are those just BONE STOCK untouched 049's with stock 2.06" intake valves/1.72" exhausts??? Just curious thanks.

Well, although I started out looking for cam suggestions, I ended up with a lot of good cyl head advice.

However, in that time, I've also gotten some good cam advice, and have decided I'm looking for an HP500 cam. It's 230/236 @.050 and .570 lift on 114LSA. It should obviously be good for 500 HP and should also idle decent.

I found one for sale that is a "regrind". I'm a little hesitant about that, and would rather find a "takeout". Anyone know anything about reground roller cams? Or does anyone have a takeout for sale?

thanks

Merc 500EFI
Crane Grind#HR-292-2S-14 IG
292,298 at .004” Lift with 1.7 rocker .598” , .610”
230, 236 at .050”
ICL 109 , ECL 119
LSA 114


======================

Merc HP500 Carb
Crane Grind#HR-284-2S-10IG
Adv 284, 292 at .004” Lift with 1.7 .576 / .598
At .050” 222, 230
ICL 105, ECL 115
LSA 110