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90 7.4L upgrade?

Old 04-05-2005, 10:49 AM
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Default Re: 90 7.4L upgrade?

Gary: I think you're right, the 330 to 300 rating was just a change from crank to propshaft HP. But I thought that GM started using the peanut port on truck engines in that same time period, so that's what Merc got. I have seen 330 engines on a '78 Scarab and they had regular oval port heads.

The regular oval port heads have more potential to make HP, but with the small cam in these engines there probably wasn't much difference in HP.
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Old 04-05-2005, 11:09 AM
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Default Re: 90 7.4L upgrade?

I think you're right about 70s/early 80s 330TRS. I had large ovals on a 79 boat. But I also know most 80s 330s (including an 81 I had) and later 7.4s had peanut ports.
Too bad about the change. IMHO those small ovals were better than rectangular for most 454 applications.
Gary
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Old 04-05-2005, 10:40 PM
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Default Re: 90 7.4L upgrade?

so can i get away with just dong some head work, or do i need to compliment it with cam work as well. I'm up in wisconsin, any ideas who does this type of work?
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Old 04-06-2005, 12:14 AM
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Default Re: 90 7.4L upgrade?

If your budget is around a $1000 and you are going to have someone else do the labor, then you don't have many options. The only thing you might try is some 1.8 roller rockers. They "might" be good 20hp and 1mph. Get a full tuneup and keep it reliable.

Next get your prop labbed. it sthe bang for the buck. You might see a 2mph gain.
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Old 04-06-2005, 01:24 PM
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Default Re: 90 7.4L upgrade?

Griff,
could you please elaborate on the 1.8 rollers. I have Merc 420's (large rectangle port with bowl porting) and have been wondering about doing this. Or are the cams in my 420's to large for me to do this. I have seen some 1.72 rollers rockers but I wanted to try the 1.8's.

Jason
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Old 04-06-2005, 07:23 PM
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Default Re: 90 7.4L upgrade?

High ratio rockers will increase lift. Your .050" duration numbers may increase 2 degrees. There is a chance that you will need to grind a little off the pushrod slots in the heads for proper clearance. Probably not, but you'd better check.

A true cam swap will give far better results than just changing to high ratio rockers.

oval and peanut head 454's made about the same power. The peanut port heads do cry uncle before the ovals if you plan to mod the motor.
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Old 04-06-2005, 10:41 PM
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Default Re: 90 7.4L upgrade?

So basically, i'm looking at doing a head job, putting a different cam in, and rolle rockers. Anyone know of a good place to send the heads around my area. Btw, i was researching the book stores to get a good book to learn more about this, i would like to tackle this project over the snow covered winter next year, motor has to be pulled to do the coupler anyways.
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Old 04-07-2005, 08:52 AM
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Default Re: 90 7.4L upgrade?

I don't think for your budget you are going to be happy with the results. If you can squeeze around $1700 out of the wallet you will be much happier.

As some have pointed out the later model GM heads had intake ports that are very small. I don't know of any aftermarket intakes that line up good with the OEM peanut ports. For the best bang for the buck you need to get a set of 049's BBC heads, an Edelbrock Air Gap or RPM Performer Oval port intake and a cam / lifter change to hyd rollers. This would net you the largest increase $/HP. Then in the future if you want to go bigger you can add a 4.25" stroke crank and build yourself a 496CID engine and have a package capable of 500HP.

Chris
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Old 04-07-2005, 09:24 AM
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Default Re: 90 7.4L upgrade?

Listen to CStraub, I have been through this. I am on my third complete modification of a stock 330HP engine. You can take the peanuts port heads and install larger valves, pocket port them and gasket match and get a matching peanut port intake. With a mild cam upgrade, my engine had great low and mid range throttle response. The peanuts can be made to work. However that will not be enough for you. Like Straub said, you will then need to go to a head that can ultimately flow better. You either should resign yourself to spend more money, or leave it alone. There is just no free lunch on boat engines.
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Old 04-07-2005, 09:30 AM
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Default Re: 90 7.4L upgrade?

Cloudmaster,
This thread brings back memories of my first boat in 1994, which was a 1990 Baja 210 ESS with a 7.4L. I basically did what cstraub is recommending, which will cost more than $1000. I got a set of 049 heads that were fitted with 2.19" intake valves and 1.88 exhausts with a match ported oval port Holley Strip Dominator intake with a 750 CFM double pumper. I picked up these parts for $1200 bucks. I then got some Rewarder Headers which were about $1500. I went with an Erson hydraulic flat tappet cam 228/235 @ .050" on a 112+4 and new lifters for another $100. I was very happy with the performance of this motor. It had great low and mid range power, more than enough to pull skiers. I ran a custom 26" Spinelli 3 blade prop, which I turned 4700 RPM in stock form for 65 MPH on radar. After the mods I turned the same 26" pitch prop 5400 RPM for 75 MPH on radar. The hood on the 210 will need to be modified for exhaust and intake changes as it is a very tight fit with the BBC. Be careful, this stuff is very addictive as I had 3 more engines in that boat over the 10 years I owned it, always looking for more. I eventually put a 2" shortie drive on and ran a pretty nasty solid roller 496" high compression motor for some pretty good speeds for the boat. Have fun and good luck!

Craig
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