90 7.4L upgrade?
 

I would like to do some mild upgrades to this engine. Was thinking about putting a mild modified cam and different lifters/rockers..... I take it that the current configuration is hydralic lifters? and non roller rockers? Anyone have some ideas for me for a cam and setup to get a couple more ponies out of her? I'm new at the engine stuff, but i want to get my hands dirty in it. thanks

Re: 90 7.4L upgrade?
 

You can put a cam in the range of about .550 lift and 230-240 at .050 in duration.You could mill the heads to bring up the compression.Head work [porting] is a decent power maker too.

Re: 90 7.4L upgrade?
 

what is stock lift and duration, doesn your second and third set of numbers refer to the lifters, or still the cam, any manufactures for the cam or lifers/rockers??

Re: 90 7.4L upgrade?
 

those would be duration numbers as measured at .050 and refer to the cam. that is how most cams are listed.

Have you ever installed a cam???

If you get a larger cam, depending on size, you may need new exhaust to prevent reversion.

Re: 90 7.4L upgrade?
 

BTW, with the upgade you might see a 50 hp gain which equals 3mph on the top end.

Re: 90 7.4L upgrade?
 

well, i'm only looking to spend around a thousand bucks, don't want such a wild cam that i have to change a bunch of other stuff, just looking to do the cam and maybe the lifters and rockers. No i haven't done it before, prolly won't do it either, will have my mechanic do it. Just askin some questions here. Where or who would i get the cam and parts from, do they sell the stuff as package deals at all??

Re: 90 7.4L upgrade?
 

Call Crane Cams or Competition cams and tell them what you want. I'd keep it 230 or less duration. You will need new springs unless your motor is a magnum then you could probably get 550 lift range as is.You'll need to check clearances to piston from valve and for spring bind. You could go to 1.8 ratio rockers too and get more lift from the cam without as much tradeoff in torque you'll have from a MUCH larger cam. Your stock ratio is 1.7. Go ahead and do it yourself,but get a good book"How to hotrod BBC" and read up over the summer then do it in the winter,,,,'cause you got some learnin' to do and summer is not the time for that. Maybe disassemble yourself and pay your Mech to show you how to assemble. But start reading before you get dirty :)

Re: 90 7.4L upgrade?
 

just got off the phone with mechanic, basically he highly advised me not too mess with the cam. He said as soon as i put a different cam in the idle will go up to be reliable, then i good take out the drive from engaging at that higher rpm's. Keep in mind i'm not looking for a huge lift, just a little something extra. He also said i would prolly not be able to get a skier out of the hole either with a cam mod. Any other opinions??

Re: 90 7.4L upgrade?
 

i have a bravo one drive, btw

Re: 90 7.4L upgrade?
 

The main restriction in the 7.4 are the peanut port heads. Their flow is limited at high rpm. The stock cam is conservative and is probably tuned to also to be limiting at high rpm. You'll need a cam + headwork to see any noticeable difference.
Gary

Re: 90 7.4L upgrade?
 

what about the higher idle rpm and beating on the drive issue?

Re: 90 7.4L upgrade?
 

Not true unless you go really big on the cam. Merc made the 454 in 330 (yours), 365, 400, and 420hp versions. None have high idle.

Re: 90 7.4L upgrade?
 

BTW, a big part of those other motors making more power, in addition to bigger ports and cams, is that they can spin to 5000-5200. Your cast crank will survive to 5000rpm if you dont abuse it. The valve springs wont like those rpm, so add that to your cam, lifter, springs, headwork upgrade too.
Gary

Re: 90 7.4L upgrade?
 

Not to jump off topic, but it somewhat pertains to this thread. It was mentioned earlier that he could go with 1.8 rockers. I have 420's or 425's with the lager rectangle I think 049 heads, or the HI Performnce chevy head. They have been pocket ported, and I was thinking of replacing the roller rockers, 1.7 Scorpions, to 1.8's. would I have to do much to use 1.8's and would it be beneficial. Or would it be pushing the HP up in the 55-5800 range where I wouldn't want to spin the engine at. By the way where is the peak power made in the 420's or 425's.

Re: 90 7.4L upgrade?
 

From that, I think if you share what your goals are that might help. If you end up making changes that add power, you could easily end up sacrificing low end torque for higher RPM and power and defeat the purpose you have your boat for. I'm going my the skier comment and making assumptions but knowing exaclty what you want to accomplish is the first step in making any modifications.

At least that's my opinion. :evilb:

Re: 90 7.4L upgrade?
 

If you do much of a cam upgrade at all, the rocker arms may be suspect. Depending on your particular parts, you may have the lower grade rockers. They are prone to excessive wear at the pushrod with higher spring tension and extended lift.

The gains you will get from what you describe here will be minimal in my opinion. You will change the sound a little and make the ultimately reliable 454/330 less reliable. Maybe gain a couple of mph if you are very lucky. Maybe ! Cam changes for this motor make more power at higher RPM.

Personally, I would add a safer for the engine, better and lighter exhaust system, maybe a better flowing flame arrestor, upgrade the oil in the motor and drive and call it a day. You'll get similar performance results but INCREASE your overall reliability instead of decreasing it.

Just a thought.

Re: 90 7.4L upgrade?
 

WARNING: You are about to take the first step onto a slippery slope; the need for speed is a disease! I had a 1990 boat with a 7.4L so I can tell you exactly what I did and how it performed. It's also how I got hooked. :evilb:

It's no use changing just the cam. You need a better intake, at least port your heads and change the cam and lifters. I basically copied the 454 Magnum. I used the stock Qjet with richer secondary rods, and Edelbrock Performer - O intake and a Speed Pro cam that had the same specs as the 454 Magnum cam (224 @ 0.050", 0.510 lift with stock rockers). Staying with this lift meant I didn't have to change the springs, but I checked them for tension and coil bind first. I don't know if 1.8 rockers would help. If I was going to use them anywhere on the engine it would be the exhaust side due to the single pattern cam and stock exhaust manifolds. But now exhaust lift is 0.540" so check the springs again.

I had the heads pocket ported and valve job done by a professional and matched the intake ports to the intake manifold myself. (That's a lot of cast iron to remove and you will only do it once!)

In stock form the boat went 60 mph spinning a 21 Mirage prop at 5000 RPM. Modified I could spin a 23 Mirage at 5000 RPM for a 5 mph gain. This confirms that the changes turned the 300 HP 7.4L into a 365. This is the easiest HP you will ever get in a boat, after that you really need to start thinking about better parts.

Do a search on "330 on steriods" and you will find a bunch of stuff about turning your engine into 400 HP. Better heads are the key to that.

P.S. There was no discernible effect on idle quality or speed or bottom end power. Your mechanic is thinking about the effect of much bigger cams.

Tom

Re: 90 7.4L upgrade?
 

i didn't know my boat was 330hp, thought the pshp was only 300, mine is on a baja 210 ess btw

Re: 90 7.4L upgrade?
 

Your engine is only 300 HP. But the previous model had better heads and was called 330. That thread has good info if you switch to regular oval port heads instead of the panut port heads that you have now.

Re: 90 7.4L upgrade?
 

Hmmm, I thought they just rebadged the peanut port engines from 330 flywheel hp (330 TRS) to 300 shaft hp (7.4L) in the mid/late 80s.
Gary

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.

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

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?

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.

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

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.

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.

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

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.

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

Re: 90 7.4L upgrade?
 

Cloudmaster,
On www.hotboats.com there is a set of 049's Fresh for $400 + freight. That is a good deal.

Chris

Re: 90 7.4L upgrade?
 

the link doesn't work........when you say 049's, what r u referring to, is that a manufacturer? Also, someone suggested labbing my prob. If i was to lab my 25 pitch miragae, would it be toast the first time i hit a rock or something. Can it still be rebuilt?

Re: 90 7.4L upgrade?
 

049 is the last digits of the Chevrolet part number of that head. It is a GM Head. It is very similiar to a Chevrolet 781 head. These are the open chamber large oval port heads. They are a great marine head because the runner sizes are large enough for the volumn of flow you will need but not too large as to lower the velocity of flow like the rectangle port heads. They are good for moderate performace upgrades. If you were going for the maximum amount of flow you would choose the rectangle port heads.

Re: 90 7.4L upgrade?
 

But, make sure they have the 1.88 exhausts and 2.19 intakes and hardened seats for the exhausts or you will be putting a lot more money into them. These heads dont really add much without the bigger valves.

Re: 90 7.4L upgrade?
 

Why couldn't i give my current heads to a good machinist and have them reworked to match the intake or a port and polish or something, then get a mild cam and roller rockers to compliment the head work? Is doing this gonna do anything for me, or make things worse??