351w Rebuild

Ha, ill leave that to you to tell him, do you have anyone that does interior, my latest quote was $1750 for everything minus the carpet

skicat wrote: John- your video is set to private. Can't watch the motor start up you are going to put in that off brand boat!

Greg, You will like it when you see who is driving it....

Try again

I ended up swapping the primary shaft, secondary shaft, linkages and throttle plates from the marine base to the auto base. I didn’t see any seals either. However, the magical labyrinth seal is still part of my Frankenstein carb, since the marine carb shaft is part of it.

A PCV valve is constant vacuum leak when its open. Typically, the manifold port is used for applications that need intermittant vacuum for very short periods of time. Like the brake booster or transmission modulator. PCV inputs are always located before the intake runners, so the leak can be distributed to all 8 cylinders. When you use the manifold port, the leak is isolated to one cylinder. I would think this would cause a lean condition on that one cylinder. Has anyone tried this?

If it works without problems, it’s definitely an easier solution than my carb base swap.

Here is a video of the start up last night, we got the cam broke in, now just to adjust the wiring and get it all fixed up and ready to drop in next week.
Start up video

Here's a picture of a shaft from an auto carb on the left and a marine one on the right. This is from a post in 2008 titled "I replaced the Pro-Tec system" that somebody started and I amazingly still had the picture on my computer

The marine one has 3 grooves at each end where it rides in the base plate. There are no seals of any kind that go in the grooves. I've had a number of them apart enough to see the shafts and every marine Holley was like this. There's really no reason to take the butterflies and shaft out, other than curiosity,it's a pain in the butt because the screws are staked and you have a good chance of screwing up the shaft threads taking the screws out or bending the shaft when you stake them again after they are back in place. Holley also says it is "slabbed" meaning that inboard of the innermost groove on each side only goes about halfway around and the rest (bottom part) is flat just like the part of the shaft that the butterflies hook to. Kinda hard to see this in the picture but that's how it is.

A SMART person would not do this, a curious one would and may or may not cause some engine damage if one of those butterfly screws fell into the engine while it was running cause it wasn't staked properly.


This pertains to let's say a 4160 from the 70's and 80's, don't know if there are any later model differences.

I'd call it magic about how they prevent leakage but I'd guess it works like a labyrinth seal. Somewhere on the internet there is a Holley explanation of how it works. I found it once and didn't save it.

Don't know when they started doing this to the marine carbs but they haven't always had the J tubes either. I had a 76 PCM 351 and the original carb new from the factory had no J tubes but did have the grooved, slabbed shafts. (List number 6576, it's hard to find this number in a Holley listing)

Maybe somebody will have a good scientific explanation why this works but that is how they were built(at least the ones I've had apart.)

I've heard that some newer ones have actual Teflon seals but that may have been an Edelbrock or Weber and I'm getting a little smarter and less curious so somebody else can look at that.


KenO (I'm curious, not smart)

I would counsel against going to an automotive baseplate. First there is a difference in the shaft sealing between an automotive baseplate and a marine baseplate.   When your float sticks and gas puddles on top of the butterflys you do not want the gas to pour out around those shafts onto your intake manifold. Second, you can quite easily locate a plug on that intake manifold that you can swap out for an elbow and give yourself someplace to hook up your pcv valve if you have clearance issues with the spacer in place (which I assume you will).

If you have clearance issues with the carb spacer you can replace the carb base with an Holley auto base (get rid of the carb spacer). There isn't anything marine about it, except that the input for the vacuum advance needs to be plugged. I did it when I ran a Holley with a Performer RPM intake.

Update: going to go fire it up tomorrow.

motor is getting built up as we speak, should the motor be put back in with the bell housing on the motor or trans?

Not sure I am as wise as cautious. Cant say I have hung a set off Aluminum Heads but have seen over the years many a cast Iron GT head crack at the water jackets above the head bolts. I think if I were to utilize aluminum heads I would find a set of aluminum logs and go that route... They look cooler anyway! Who knows depending how hard you run your boat the cast and aluminum heads may stand up! Then again!!!

Fl Inboards, i assume you would be the wise jody seal, what would the issue be of using the stock exhaust on aluminum heads?

IF i was to go Full Hydro cam what cam specs should i be looking at?

Yes, the tie bars are pricey (small block stuff might be a little closer to $400), but machining for a spider retainer and some stock (used) roller lifters would probably be a bit less $.

I disagree entirely on the potential of a roller... I would have agreed with you prior to going down both roads in 2 of my correct crafts. The reliability concerns are worth the extra cost alone, IMHO- but the power gains are real, and significant. Going roller on a LH engine is a no-brainer... And still worth the effort on a RH, though the cost goes up quite a bit.

I got the heads from a friend for a great price they are 60cc with 2.02 valves. If I was doing a stroker I would need at least $1500 for a heads alone that would flow enough. I have just that much total in this one. I do have a spare block laying around that I could build up piece by piece as funds allow. In these motors and the RPM's that we are turning roller cams don't mean that much more in power. You just need to be more selective with the hydro flat tap cams and use roller rockers. The link bar lifters that make it roller are around the $500 mark.