Procharger experts needed
 

7.4 MPI with a 5 psi pulley and blow-by. Tearing it down now and I am planning forged pistons. What ratio would you reccomend and where can I get them.? I also plan larger rod bolts into the stock forged rods. What should I do with the valves? Thanks for your response

Re: Procharger experts needed
 

A little more info would be helpful. Depending on the gas you can get on the water and whether it's intercooled, you could go as high as 9.5 to 1. If all you have is 87 octane and no intercooler, stick to 8.5 to 1. Less compression and more boost will make more hp. If you have any idea that you might want to change pulleys in the future, stay with the lower compression. If you have the 3/8 bolt rods, don't machine them for larger bolts. That will just weaken the rod cap. Replace them with the best 3/8 bolts you can get. ARP Wavelock or equivelent. Valves in a supercharged engine should alway be top quality. Manley or Ferria stainless intakes and inconel exhaust. Get a good valve job from a person who knows what they're doing like Jim Valako aka Jim V here on the board. Use 2.25 intakes and 1.88 exhausts.

Re: Procharger experts needed
 

Thanks for your respose. I can only plan on the lowest grade of gas. I plan to stay with the 5 PSI pulley. The stock comp ratio is 9+/1. I have knock sensors. I do not believe I have had any pre-ignition; however I also have weak cylinders.Where can I go for piston selection. Thank you Bob

Re: Procharger experts needed
 

www.flatlanderracing.com has a good selection and good prices. Try the SRP's. Stock forgings that Merc used to use gave 8.8 to 1. That should work ok. I think I'd run 89 octane though.

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If you use the small dome pistons .020 or .030 oversize, without decking the block and use the .042 thick Fel-Pro teflon head gasket, you'll end up at 8.8 to 1. The flat tops will be below 8 to 1 and thats not good for what you want to do.

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This is good info. keep it coming. I am upgrading my 454 mags in a few weeks. Going with PC after freshining the motors.

Re: Procharger experts needed
 

Change the heads don't spend the $$ to modify them.
The L-29 heads are no good for superchager engines, probably why your engine has failed. The point of the heart shaped cumbustion chamber gets red hot and melts holes in the pistons.
I would suggest a set of Edelbrock or Worldproducts large ovals when you rebuild.
Good Luck!

Re: Procharger experts needed
 

The 7.4MPI has 100cc heads, 9:1 with flat tops. Dome pistons will hit the point of the heart shaped chamber.
Like I said in my earlier post, I would suggest different heads.
The MPI intake should bolt up to any large oval head.

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My bad, Didn't realize that engine used vortech style heads. My piston advice is only good for open chamber heads. Thanks for the correction.

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I would like to keep my heads but I will look into the heads you suggested. If I keep my heads I guess what you are saying is that new valves, perhaps larger will be wasted compaired to the cost/benefit of the larger port heads and you also state my plennum will still work.

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The Edelbrocks are a good deal when you consider they come with the inconel exhausts and good intakes. Valves for your existing heads are going to cost 500.00 alone. Then you have to think about seat work and valve guides. Aluminum transfers heat better which helps to control detonation also.

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I had a set of L-29 heads modified with new better valves, springs, port work... Cost me like $900.
I won't go down that road again... :rolleyes:
Yes, your intake will bolt on aftermarket large oval heads.
I spoke to Tyler Crocket at length about the L-29 engines a few weeks back as I'm rebuilding one this winter. So I have another suggestion for you. I bought a GenVI 454/502 mag cam from him to replace the cam as well.
It has about the same lift but more duration and will work well with the MPI. I think the $100 is worth and extra 30HP. Probably more than 30HP with the supercharger.

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I have a set of 2000 502 mag mpi heads with about 150 hours on them. The heads are complete, the motor ran fine so there is no damage to them. I also have the rocker arms, keepers, and valve covers, cam and lifters that I could package with the heads. Pm me if you are interested.

I decided to go with a set of Canfield heads, a custom ground cam and some roller rockers. Like I said there was nothing wrong with the parts I took off.

Re: Procharger experts needed
 

I don't believe that the GM large oval intake on a 7.4MPI will work on rectangular port heads.

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You're right, he'd need to get a new intake. The heads would be that much better than stock though.

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Just a question here...Is this a 1997 or so 330 hp MPI or a 98 or later 310 MPI.
Only the 310 had the Vortech head where as the 1997 330hp version had the peanut ports with a Mag rectangular intake bolted on it.
Dave

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That's a wierd combination.

Re: Procharger experts needed
 

Agreed :eek:

Both the 454MAG MPI and the 7.4L had the same MPI intake (805233A6). Nice mismatch; rectangular ports feeding into peanut ports.
The 7.4LX was the new 20hp less Vortech motor in 1998.

Very weird indeed...
Dave

Re: Procharger experts needed
 

I'm quite sure he has the newer L-29 engine, we've talked before about it...
To bad, if he had the wacky combo, a set of used rec port heads would be a great way to go...

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Sorry I have not responded sooner. My wife and I went off to San Francisco for a get away. The motor is a 1998 7.4MPI with L-29 heads. The edelbrock large oval heads sound good. How much and where? Will this up-grade effect my piston selection. Should I aim for 8.5/1, 8.9/1???

Re: Procharger experts needed
 

Edelbrock has lots of dealers. Maybe check their web page for one local to you.
Make sure you buy the marine heads; they are anodized and have the lager, better quality valves. 1400-$1500 per set.
I believe the large ovals have a 110cc cumbustion chamber so with flat top pistons you'll end up around 8.5:1.