Valve Train, GM vs. Aftermarket
 

OK, my shopping list is getting shorter.
Thanks to everyone for the help

1999 7.4MPI conversion to a Carb. Engine that will hopefully make 400HP.

I have read Dennis Moore's book cover to cover a couple of time now, and I'm rereading about the valve train components.

My heads are at a machine shop being worked for bigger valves so it's time to decide what parts to by.

Keep in mind, I can't go too wild here do to my exhaust system. Stainless Marine manifolds with the short stainless risers for captain's call.

The least expensive way to go is to buy GM performance goodies:

- 454ho/502ho crate motor steel hydraulic roller camshaft 211°/230° duration, .511"/.540" lift, 112° lobe separation
- Double Valve Springs, Retainers, Locks and Seals to Match
- Reuse Non-adjustable Rockers and Shoulder Bolts

Cost would be under $300

Aftermarket Option:

- Crower, Crane, or Other Manufacturer, hydraulic roller camshaft with 222°/229°, .540"/.560", 114°
- New Lifters ???
- Springs, Retainers, Locks, Seals to Match
- Extra Machining may be required ???
- Conversions Rocker Studs
- Roller Rockers

Cost would be $800 to $1200

Will the extra $$ be worth it ???

I like your first option except for the camshaft selection. Go with the 502/502 camshaft instead. The stock roller lifters, pushrods and non adjustable rockers will work fine with this camshaft too. The GM dual valvesprings will work well with that valvetrain and cam.
Should get you to 400 horsepower and be very reliable.
Sincerely
Dennis Moore

Not enough lift. And lift is what will force you to go to aftermarket valve train components.

Watch your piston to valve clearance on the non-gm cam. These pistons are not notched. I'm running the 454HO cam you are thinking about, and it makes loads of torque, but poops out over 4K. I also would go with the 502/502 cam. Change the springs, and run the stock non-adjustable setup.

OK Guys,

If the 454HO cam is not enough, then I guess the best upgrade for the money is the ZZ502/502 cam.

Spec. 224°/234°, .527"/.544", 110°

GM has two different double springs listed, one has 110lbs seat pressure, the other 140lbs.
Which should I use?

The Guys at both CP Performance and Stainless Marine have told me that I can not use a captain's call system with this cam. Too much exhaust duration and overlap.
Are they being too conservative ?
Has anybody used captain's call with this cam?
I don't want to suck water into my engine.

Should I scrap the captains call and use mufflers ?
If so, I will need the longer riser, right ?

Thanks for the help!

Use the 140lb spring. That's the one GM uses with the crate 502/502. Their springs,retainers,seals,etc are all available from www.competitionproducts.com really cheap. They buy mercruisers stuff when they turn 502's into HP500's. Can't say about the reversion issue, cause the friend that I know that's using it has Teague switchables. Pretty mild cam tho, I think you'd be fine.

I am running comp cams, 226/234 @.050 with .547/.564 lift on 111 lsa with 4 degrees advance. No problem with stock mercruiser manifolds and imco ss risers. You may be crossing the line with the 110 lsa, but it is close. I run 125# seat pressures with no trouble.

BT :cool:

Hey Pat,make sure they port under the valve seats,called the pockets!!! Tripps

Jack/Budah-Would you mind posting the @.050 overlap numbers on the Crane 741 and the 502/502 "junk" cam? Is there a new unknown lobe design that allows a cam with more duration to actually have less applicable overlap even with 2 degrees difference in LSA?

OK Guys,

While we are still debating which camshaft I should use, I did take your advise BUDAH. I bought some good double valve springs 128lbs @1.880", 0.670" max lift. The retainers and lock I bought are the 10° version.

Back to the cam:
I spoke to Crane about the 731, and they told me that I can not use my stock lifters, too much lift. I can use the 721, but the last time I asked you guys, You told me it was kind of mild.
Madmax also brought up a good point about a cam with more lift than the GM. Will there be a clearance problem with the L-29 pistons?

Thanks for the help everyone.

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

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

:D

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.

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.......!

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

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

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

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. :D

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. ;)

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.

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. :D

Do MPI motors have lots of vacuum at idle and therefore might be more susceptible to reversion??

An MPI motor (like a Mercruiser with tuned port injection) has a huge amount of plenum volume between the throttle butterfly and the intake valve. Intake manifold vacuum is much lower because of this.

On the other hand, the new small block EFI's, with the dual plane intake manifolds, have a very small plenum similar to a carb.

I have always wondered why Mercruiser used the Dart single plane intake manifold and not a high performance dual plane intake manifold on the 500 HP carb engine. I would be willing to bet that a modern dual plane would make the 500 HP carb engine more powerful at all rpm ranges.
I suspect that the engine didn't make more horsepower with the single plane but, because of the open plenum and lower manifold vacuum at idle, the engine sucked less water into the cylinders at low speeds (during valve overlap).
Do you think Mercruiser High Performance was smart enough to understand why it caused less water ingestion?
Sincerely
Dennis Moore

You'll have to excuse me, Jack. I'm taking every opportunity to gather information so that SOME DAY I can perhaps feel confident about having some build-up configuration done on my 454 Mag MPI (yes, w/o swapping for a carb).

So far, I've got:

Cam: Crane 168731
Springs, retainers, locks, etc: Isky
Rocker studs: ARP
Rockers: Comp Cam Pro Magnum
Heads: worked over stock (or maybe Dart Iron Eagle if I can get comfortable that I won't have valvetrain geometry problems)
ECU re-programming?? Who the hell knows.

I got all of this just from listening to you guys debate and drawing my own conclusions. Am I dangerous or what??

Dennis, not sure where I remember reading this, but what i remember was mercruiser went with the single plane because they thought it was worth losing a lil low end torque in order to achieve better cylinder balance. Supposedly they determined balance was better than having more low end torque and having some cylinders running lean/richer than others.........

just my 2 cents...... like i said, can't remember where i read that.:confused:

Jack, were you able to dyno those motors? Were they 454 or 502?

Pat:

If you aren't too impatient, I am about to water test a pair of 454 HOs that I changed the cams out using the 502/502 cams. I have been waiting for some tranny coolers to come in, and they are supposed to be here tomorrow. If they do, I'll be on the h2o by this weekend. I have cranked the motors, and they sounded great, but the real test will be on the water with the GPS.

KS30

KaamaScarab30,
My engine mods. are a Winter project.
Please let us know how she runs.

Wow, you guys are getting steamed!

Overlap is overlap, whether it comes from tight LSA and shorter duration, or wider LSA and longer duration.

Max had a good point on checking valve to piston clearance on the lo-po 7.4L. I did a Gen V 7.4L a few years ago and discovered that installing larger valves (going from the stock 2.06" intake to 2.19") created a clearance problem. The heads (peanut ports) were also milled .020. The pistons had a small notch with a radius to match the 2.06 valves. When I mocked up the motor with the new larger intake valves, I discovered that the valve head extended beyond the radius of the notch, which, even with a relatively small cam (218/222, 112), reduced the v/p clearance to dangerous levels. I had to cut the notch on a larger radius. I also cut the notches deeper while I was at it. The exhaust valve clearance is generally excessive to begin with so a bigger cam will not cause any problems on that side.

Also, valve to piston clearance is most affected (on the intake) by cam changes that in one way or another start the intake valve opening sooner. That could be by more duration, tighter LSA or simply advancing the existing camshaft. A trial and error test that I did showed that for every degree the intake opening point was advanced, the intake valve to piston clearance was reduced by .005".

Rich

I'm running the GM cam zz 502/502 no problems.I made my choise from Dennis Moore's book and I'm glad I did.:cool:

HeyGuys,
There is an engine builder, bobl, that posted on a previous thread about mods. he did to a L-29 7.4MPI.
He said he installed larger valves and a different cam into one of these engines.
Anybody know him?
Maybe we could get him to comment....:)

Fastech how about page 123 on the closing ramp. Chevrolet uses a slow closing flank to very carefully set the valve down on it's seat.To me that it where my reliabilty would come in.True my choice was also based on my merlin oval ports and not haveing to change any of the valve train.:cool: James