Budman II

iTrader: (1)

Not sure if the L29 has a forged crank - pretty sure they are cast, but could be wrong. Yes, all of the Gen VI blocks have 4-bolt mains. One thing that you need to do that is critical to make these live in a boat - you need to replace the standard 11-lb oil bypass valve that is located in the filter pad with a 30-lb valve. Otherwise, the extra resistance from the external oil lines and cooler will cause the bypass to be activated and you will bypass the filter and cooler, and your bearings will be toast in short order. MANY non-marine Gen V/VI big blocks have been killed this way. There may also be a second bypass in the center oil return in the filter pad. Do a search on the general tech board on here for more info. This subject has been well covered.

If you can score a pair of Merc magnum factory roller cams as takeouts, you will have a pretty decent setup with the L29 heads. It would be an easy swap with the non-adjustable rocker arms, and you could probably re-use the lifters if they are rollers and in good shape.

I think most of the Gen VI 454s have provisions for a mechanical fuel pump (mine did), but the cam may not have the fuel pump lobe on it. You may be able to look up in there with a light to check for it.

If you are re-using the brackets from the Mark IV engines, you will have to drill out some of the bolt holes on your accessory brackets to 7/16" from 3/8", because the bolt holes in the heads are larger.

Budman II

iTrader: (1)

One last thing - I think the MK IV flywheel is balanced differently than the Gen V/IV. you might want to do some checking on this - it is a different part number due to GM going with the one-piece rear main and round crank flange. You can get the flywheels from Jegs for about $100 each.

Budman II

iTrader: (1)

Hopefully you know this now, but 38* total timing is probably what killed it. Most folks on this board don't venture past 36*.

If those engines were running good with no knocks, ticks, oil consumption, I would just pull the pans, check a few bearings, and run them as is to get you through the season. Then take your time and build two motors the right way over the winter - and get them tuned on a dyno this time.

dereknkathy

the cam i referenced in post 8 is a new 454 HO roller cam for 170 bucks. yes all gen 5 and 6 are 4 bolts. some L29 that were in heavy trucks have forged internals, they are called L21's. ..scarce. your 2 bolt gen 4 blocks are also fairly eaten away in the cooling passages. look how big the water pump holes are compared to when they were new...

downforce137

iTrader: (1)

im nearly positive gen5/6 do not have mechanical fuel pump provisions.. you also will not be able to use your original oil pans.

vintage chromoly

iTrader: (3)

The latest gm casting gen 6 does have a mechanical fuel pump provision.

dereknkathy

but the common heavy duty pickup truck motor that can be had in boneyards has no fuel pump mount.

Budman II

iTrader: (1)

And make sure you purchase the melanized gear to go with the billet cam. That includes the Merc Magnum cam. If you run the standard steel gear that you had on your 330's, you will chew up the distributor gear and possibly damage the gear on the cam, not to mention all the metal fragments you will send through the engine.

Budman II

iTrader: (1)

Check the casting number - I think the ones that end in 313 have the fuel pump pad. We had a pretty good size remanufacturer go out of business here locally a few years ago. He had dozens of 454 cores that he was liquidating. I went out there and looked at them - most of them were Gen V's, and those do not have the fuel pump provisions. But as I recall, nearly all of the Gen VI 454's that he had were equipped with the fuel pump pad. He said that the majority of those were warranty claims from GM for issues like oil consumption. They were a rebuilder for GM back in the day - the dealerships didn't always drop in a brand new GM engine on warranty claims - a good number of them were reman's.

hblair

You guys are a wealth of knowledge. Thanks for all the great information.
After taking everything into consideration, we have decided to reuse these mark IV blocks. Their condition is very good. There is zero rust scaling, and very little if any corrosion in the passages that I can see.

I finished tearing down the block that had the failure, and took it over to the machine shop this morning. I gave him the info on the scat kit I linked above. He thinks he can do better on the price and is going to check into that.
We will also go with the retro roller cam setup for these blocks. Also we're going to replace all the exhaust valves just to be sure and we'll be using these 049 heads. I've still gotta pull the port engine out and tear it down and get it over to the machinist. Hope to do that tomorrow, we'll see.

The L29 route just had a lot of variables and prolly other things we havent thought of (there always are).

Do you guys have opinions on what compression I oughta run? Any other ideas on cams? I'm thinking I'll be needing to run 850 cfm carbs. (gotta brand new set of Holley 750's
Thanks for your input fellas.