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I am building a zz502 for my jet boat and I have a set of 454 mpi heads does any body know if these heads will support a 6000 rpm motor
 

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E-7 Sheepdog (ret)
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Head casting numbers?
 

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Head Casting # 10141279 They Came Of A 10hr 2000 Merc Mpi Engine As Far As I Can Tell They Are Identical To The Vortec 7400 Heads
 

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It's what we do
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The key question is are they from a 7.4 MPI or 454 Mag MPI? Mercruiser listed their engines this way and all engines with "454" are Mags with rectangle port heads and 118 cc chambers. These heads will support the rpm's you are asking for. The only Merc engines that said "454 Mag" that did not have rect port heads were the ones use in 1986 to 1988 with the Alpha package.
From memory the heads you have are closed chamber about 100 cc and a little larger oval intake port that the "small ones".
You will get lots of people saying use them. They would not be my choice for a 502 that runs 6000.
 

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E-7 Sheepdog (ret)
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Head Casting # 10141279 They Came Of A 10hr 2000 Merc Mpi Engine As Far As I Can Tell They Are Identical To The Vortec 7400 Heads
10141279...96-up...oval..CLOSED.."Vortec 7400", 100cc chambers

Being the large oval port heads, I wouldn't try to feed a 6-grand spinning 502 with them, They could do it with a good deal of porting work, but I'd want to start with something bigger for that much RPM in that many CID.

According to one site, they have the best flowing ex. ports of a BB Chevy head, that's not a lot of help tho if the intake won't let enough in.
 

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When I converted my jet from an Olds to the BBC I picked up a Gen-V BBC that had those heads on it for really cheap. Supposedly it had been freshened up. I just wanted to get it on the water without going through the motor and had asked on a few other sites what these heads flowed with no answers. I searched high and low and still never came up with an answer so I just put them aside.

There are a few things to notice right off the bat about these heads.

#1 They have bastard rocker arm studs ( puny shaft dia.) that are for the self centering stock rockers. If you want to use any other rockers other then stock you need a kit from Crane cams. (about $200) The pads for the studs are also higher or lower ( can't remember) then all the other heads.

#2 The intakes have that "ramp" to increase swirl. I have no idea how much this impedes the flow but I know on the SBC it is a flow killer.

#3 the valves are the 2.07 int. and small exh.

#4 the castings are really thin. They crack easily around the head bolt pads on the outside.

My evaluation of them was that by the time you got them up to speed one would have alot more $$ then they are worth invested for very little gains. I had a set of 781 and just used them.

IMO they could hardly support a 454 above 5k let alone a 502 at 6k rpms.

If anybody has some real flow numbers for these heads I would be interested to see what the intakes flow.

R.B.
 

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E-7 Sheepdog (ret)
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Well, in digging arround the web, I find SOME references that connect that head as the "L29" head, which was a truck head, with arround 230cc intake ports, which is NOT a good thing for this aplication.

L-29 flow I found looks like this, with no port volume listed:
Lift ---- Int----Ex

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

That's less than a typical set of '049's or 781's will flow.

My ported '049's are a touch better than a set of rectangle 990's (just because the numbers are easy to paste).

Lift ---- Int----Ex
.050 -- 31.8 -- 26.1
.100 -- 67.2 -- 56.8
.200 - 146.3 - 113
.300 - 221.9 - 147.0
.400 - 270.7 - 176.6
.450 - 277.0 - 189.8
.500 - 283.4 - 198.6
.550 - 291.8 - 201.9
.600 - 297.0 - 203.0
.650 - 297.0 . 204.1

Go for a better set of heads (ie, bigger) than those, unless you really have to make some use of them.
 

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Boat Nut
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I am building a zz502 for my jet boat and I have a set of 454 mpi heads does any body know if these heads will support a 6000 rpm motor
I had the same heads, from a ZZ502 on my 540, it pulled to 6200 on a B impeller. I would suggest having the valve guides checked, as they run a bit tight for marine use. I upgraded to Inconel exhaust valves before I ever ran them. I put 8 seasons on them, never has an issue, no evidence of corossion in the water passages. I sent them out for rework this year, I opened them up to rectangle port, easy to do, lots of metal to allow this. I then sent them out for valve job, and flowing. got a call from the flow guy, and asked why I stopped on the port job, I said I never felt comfortable going any further. They said they could make even for improvement dropping in from the pockets, and again opening up the runners. I told them have at it, said I wanted the most out of them. I wound up with 2.30 intakes up from 2.25, with 1.88 exhaust. The flow numbers on a 4.25" sleeve were excellent, 395 int. and 292 ex. still with great velocity in the runner. I will find out what thy do next season. Here is a before and after of the rectangle port match, but I don't have any pictures taken since the flow work.
 

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Discussion Starter #9
I am still mixed but after looking at the flow numbers and playing around on comps camquest it looks like i will have to try and find some better heads of do alot of port work
 

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Well, in digging arround the web, I find SOME references that connect that head as the "L29" head, which was a truck headquote]

Thats pretty much what I gathered at the time. The L-29 is what I remember them being refrenced as. It's about time some flowed a set. :D
 
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