Sonic30ss

Pat,
Dump that Captins call and put those pipes right out the transom, I want to hear that puppie sing when we pass
Who is doing your head work??
Do they have a Serdi machine, if not see me Sat. I'll set you up with a great shop.
Joe

Madmax

The crane 731 will hit the pistons on the intake side for sure, and prob the exhaust.

The 721 will be close, very close. Most likely the exhaust would be fine, but the intake ??? It would HAVE to be measured and verified.

While I agree, the 731 would be a better choice, the 502/502 will drop in with stock lifters, rockers, etc, without fly cutting your pistons. I don't think the 721 would be more powerful than the 502/502 cam. I'm not endorsing it, cause I know everyone says to not run it, all i'm saying is that it will drop in with very minimal cost.

Just for fun, I plugged all 3 in desktop dyno...... the 502/502 came out on top. hmmmmm

MAG502NUM

This really is one of the better threads in a while. Jack-Not flaming, honest, but somtimes you might be a little on the subjective side, which is OK, but you never seem to want to discuss any further once you make a statement.

Madmax

Hey Budah.! no offense taken...., it's just a forum baby.!

I measured when I put the 454HO cam in (.511, .540). It had plenty on the exhaust side, but the intake was getting close...i can't remember the exact #'s it's been a while....

these motors have flat top pistons with no reliefs in them, and they are cast/hyperuetectic, so 1 smackaroo, and it'd be new motor time.......

measure to be sure....... if the 731 fits....run it, it would be a great cam...!

Btw Budah....i think i'm gonna try the AFR heads.....the specs look great.! thanks for the info.......!

Dennis Moore

I guess we should all get a kick out of the arguments between a 110 and 112 degree lobe sep angle.

I've never seen so much fuss over two camshaft/four crankshaft degrees of duration before.
The only time the comparison can be made is with identical spec camshafts. If one camshaft has 4 degrees more or less intake or exhaust duration than the other the point is moot.

I think some people - with just enough knowledge about camshafts to be dangerous- have it stuck in their minds that 110 degrees or less of LSA is bad, no matter how small the camshafts duration is!

A small duration camshaft will have less overlap than a large duration camshaft and therefore the LSA can be made smaller without any problems.

The problem with water ingestion into the engine has more to do with intake manifold vacuum than anything else. It is the intake vacuum that pulls water back into the cylinder during valve overlap. A dual plane intake manifold with a small plenum will have more vacuum than a single plane intake manifold with an open plenum. Water ingestion is the most prevalent at high intake manifold vacuum (throttle closed and engine at an idle). A marine engine has very little manifold vacuum once the throttle is opened. Most will have zero at wide open throttle.

Dennis Moore

Pat McPherson

I may have the camshaft.

Lunati now makes a number of Gen VI cams too.

Part # 54847 218°/226°, .534"/.544", 112° Sep.

or for an extra $20 they will grind the next bigger on a 112° Sep. angle rather than 110°

Part # 54848 112+2 220°/230°, .535"/.545", 112°

What do ya think?

It's not the "junk" GM cam.
There should be no clearance issues.
I can use my captain's call risers.
I can use my lifters and...
I my even be able to use my stock non-adjust rockers.

Hey Madmax,
Do mind running these though your computer? I'm hoping for 400HP.

Tripps,
I copied the pages out of Dennis Moore's book for the machine shop. They told me they know what to do.

Joe,
Glen at GCR is doing the work.
No, he does not have a Serti Machine. He has a small 2 man shop, but builds lots of race engines. He just finished a pair of 540s for Ocean Performance. I'm confident he will do the job right.
See you tomorrow after the Poker Run.

By the way guys,
I am converting a Volvo 7.4MPI not a Merc.
Same base engine though, 7400 Vortec, also known as L-29

Dennis Moore

It was a 509 MPI EFI Mercruiser that made 495 horsepower at 5000 rpm and 625 ft. lbs. of torque @2500 rpm. It used the 502/502 camshaft, stock valve springs and lifters and J+E 9.5:1 pistons. The stock rectangle port heads, non adjustable rocker arms and IMCO exhaust manifolds. The MEFI was reprogrammed and the fuel rail had an adjustable fuel pressure regulator. The injectors were stock.

I think the controversy over four degrees of camshaft duration is getting a little heated here (the difference between 110 and 112 LSA is four crankshaft degrees). Nobody seems to mention that advancing the intake lobe centerline by four degrees is a pretty common tactic to increase low speed torque. This not only closes the intake valve four degrees sooner (for an increase in cranking compression) but also opens the intake valve four degrees earlier (increasing the possibility of water ingestion with an earlier exposure of intake vacuum to the exhaust system).

But then again, maybe we ought to change the subject. I am finished.
Sincerely
Dennis Moore

Pat McPherson

Hey Guys,

I had no intension of creating such a controversy. I guess i will wait a week or two before I ask which carb I should use.

Anyway, I have only rebuilt a few engines in my day, this being my second big block to tinker with, so I do appreciate all of the great input.

My boat is a relatively light 24' Superboat that does 65mph GPS any day of the week and I have seen 67 once or twice. While my wife and all of my friends tell me to leave the thing alone, that is just not me. My goal is to see 70+ on my GPS. I believe 400HP will do it for me.

I am running muffler inserts now with the stock cast iron exhaust. I purchased Stainless Marine Manifolds with the short stainless riser for captains call. I saved the Y pipe from the 24 Pantera I sold, so I am only the diverters away from completing my exhaust system.
I think I would rather spend the $$ on diverters than a high dollar set of mufflers. Besides, Joe wants to hear her sing, and with a flip of a switch she will be singing straight out her 4" pipes.

In conclusion:
I desided to spent the extra for the springs retainers and locks per Glen my machinist who has seen allot of broken GM stuff.
If I go with a GM cam I will use the more mild OH cam not the zz502. Mr. Moore has made a good argument for zz502 being a desent cam for a marine engine, but he did not say I could use it with captain's call. I am thinking not.
BUDAH, I am not going to use the crane 731 either. I don't want to get into any clearance questions or buy new push rods.
If it is going to be an after market cam, then likely a custom grind from Crower or Lunati.

Thanks again for everone's help.

Pat McPherson

Hey Fastech,
I was out running around with a 24LS today. Nice boats those Formulas.
A 24' Superboat will go well over the 70 mark with a 454mag, the newer stepped hull version is rumored to hit 75.
400HP should do it.

Pat McPherson

Hey Fastech, I don't think the step pad hull 24' superboat is 5mph faster, maybe 2mph.
Jo at Pantera has told me a step on such a small boat will do nothing. The boat will trim past the step. I can say, with the hammer down, there is not much boat in the water.
I have run along side JMK406 and we are pretty close, he has me, but not by much. His boat is a 2002 with the 320HP/6.2. The boat is a little lighter with a small block and Merc. claims the 6.2 has more power than the 7.4. Next year I don't think we will be so close.