Smitty

iTrader: (1)

Dyno,
Couldn't agree with you more but remember he is dealing with a STOCK bottom end here!!!

I have a 2 bolt main small block that I run to 6500 but as you said good machine work!!! My engine is all balanced as an assembly and revs beautifully!!!!

dyno

Oh! I thought we were going to open her up!!!!

Madmax

DonMan:

I went the same route you have gone and picked up an honest 6mph. Note however, this was switching from peanut port heads to the vortec heads. I would guess the simple cam and intake swap would be significantly less. I used the Edelbrock performer RPM, 454HO cam instead of the 502/502 cam, Gil exhaust, Vortec heads, K&N filter. Changed the ignition module from the stock 454 to a 454mag (Thunderbolt V) to reset the rev limiter to 5050rpm. I will be really curious as to how it runs with the 502/502 cam. Actually, i will be even more curious to see if it clears the pistons (check it!). Mine has a nice lumpy idle, but doesn't pull on the top end quite like i expected. Low end from 2500-4000 is phenominal. I would guess what most have said here, that the cam will be 2 much for the heads. You will have some fun getting the cam to work anyway. You will need to replace the stock valve rotators with spacers on the intake and exhaust. The intake guides for some reason are bigger, so you'll hafta drill out the spacers. The springs will then drop right on (with the proper seals and retainers). You'll prob hafta screw around with shimming them to achieve the right pressures. Stock valvetrain will work fine.

Carb-wise, i'm running a stock Mercruiser/Carter/Weber/AFB. I'm still playing with jetting, so I can't really help ya too much for a baseline. I'm currently running 107 jets on the primary and secondarys with a 68/42 primary rod. Install a 5" spring for the metering rods, or you'll be beating your head on the dash trying to figure out why it doesn't run. The cam won't pull enough vacumn to keep the metering rods pulled down into the jets, so it just dumps fuel and drowns the engine out.

I hope you have luck with the cam, and if it does work out, i'll prob be switching. I've been waiting for someone to try it. You are definately goin the right route getting rid of the MPI for small time mods.

To wrap this long saga up, i'm now looking for a 174 blower, so maybe what everyone is telling you is correct. Leave the fulie and put a blower on........

DanB

You wont have any clearance issues with that cam..but check it anyway. Make sure the springs are setup right!!!! and for piece of mind I would switch over to adjustable rockers. Easy to do and cheap. The Air gap works good..I got one on mine. Mallory makes a marine pump cheaper and better then holley. Mine is 4 years old and still puts out 8lbs a full throttle. And you dont need a regulator. Id go with a Holley carb. But thats a personal prefrence. I understand them..I dont an AFB
Dan

dyno

Dan what Mallory pump are you running????And yes its still cold as a ***** up here!and no I cant come down there......yet! maybe in Feb. or March.....I'm working on it!

bobl

The 310 HP MPI 7.4 is the Vortec engine. The heads are actually very good. Just have larger valves installed and a good bowl blend and they will support well over 400 HP. I would use a much smaller cam though. That's only a 454. You want to build peak HP right around 5000-5100 to keep the engine alive. The heads will breath well, you don't need a big cam. The MPI is a problem. Changing to the carb will get you where you want to be. As long as you design the engine to make a lot of torque and keep it at those RPM it will live just fine. If you go over about .550 lift you'll have to flycut the pistons. That 502 cam will be pretty tight. I like something around 216/220 on 110 degree LSA for that package.

Vinny P

I would not be looking to get too much more power from this motor. Remember, the bottom end has cast parts.

SeaRay Jim

DonMan,

I see Bobl already replied to you, and that you're in Texas too. Bob has mine in his shop right now (7.4 MPI) working on it.

You see the name of Bob's shop in his sig (near Lake Travis). I brought mine down from the DFW area. If you want someone to do it right, give him a call. Once the parts are all back and machine work is done, you'll be able to get an idea of what gains to expect once mines done; a case study if you will. How restrictive is the GM MPI on our's, we'll see.

There are good options for staying with EFI as well going carb; we're reserving options for mine once we see what we get. It all depends on what you want, how you'll run it and how much $$ you want to sink into it. Ouch, bad choice of words. How about "...how much $$ you want to "invest" in it."

Give Bob a call.

88 MACH 1

Been running mine all summer with the Merlin. No problems and lots of power. I'm in fresh water too, was recommended to me to use the brass inserts because of aluminum and water combo. Not sure why but when you are talking to someone with experience, I usually go with there opinions. Later, 88 Mach 1

Madmax

BobL:

not to step on any toes here , as far as i know, larger valves can't be installed in vortec heads. If you look at the chamber, you'll see what i mean. The heart-shaped design, doesn't really allow for any increase. Maybe some head experts can jump in here and disprove me. I'd love to get some bigger valves in there.!