CANADIANOLDS

This engine was built for my sons 23 foot inboard boat that he picked up with a cracked block. Someone didn’t drain the water then stored it outside in the winter. He picked up a short block that was out of a 95 firebird. He later got some used aluminum pro-comp heads cheap because the guides were shot.

The 92 to 97 LT1/LT4 is the oddball red headed step child in the SBC line of engines. The block and heads are specific and can only be used with each other.

it’s reverse cooling and has different deck cooling passage than any other SBC. It also has a cam driven water pump and cam driven front mount distributor. Hydraulic roller cam, it’s own cast aluminum or plastic timing chain cover .

the heads have a goofy bolt pattern so intake choice is very limited.

they use a decent Mahle piston with narrow rings and are flat top with reliefs. They use a dummy shaft at the rear to drive the oil pump.

To use gen I heads on the gen II block the two big water passages on each upper corner of the deck need to be plugged and new oil drain slots need to be cut in the deck as the heads have different oil drainage into the valley.

The two holes in the timing cover that drive the water pump and the distributor also need plugging. Then a stock single roller chain is used ,, a double roller won’t fit under the cover.

The are 4 water pump passages in the front of the block that are also split into an upper and lower feed for the reverse cooling and a huge oddball water pump. the casting that separates the upper and lower holes is removed all the way back into the block. spacers were made with a stock location hole in them to block the big lower hole and allow a stock gen I pump to be used.

the big holes in the deck are the same size as a 1” pipe thread so they get tapped. 4 1” iron pipe plugs are installed with loose fit and JB weld to just slightly below the deck surface and then levelled off with JB. 24 hrs later the JB is filed level with the deck

We used gen one steel shim gaskets to bump compression a bit. A gen I single plane and the original marine Carter carb rejeted. The stick marine distributor from the old engine was used

the short block was cleaned, reused the same bearings, rings and lifters. Comp cams hyd roller with 218 int at .050 was used..XR270HR-10

68post

Slick ! Sure would be a head scratcher when first seeing it. Any issues since ?
I've seen LT1 heads on a gen1 also.
These blocks are reported to have pretty thick cyl walls.

Lonnies Performance

Excellent fabrication but my question is why not modify the heads to fit the block?
Then you retain the reverse flow cooing. That was the best part of this engine.

You then run a standard SBC intake & distributor, keep the factory water pump & lose the horrible Optispark distributor.

On the last one I did, I converted to an LS1 style ECM with individual coils so no distributor was required.

I messed with these engines for years & still have a new set of fully CNC ported LT4 heads & intake.

Here's a carb style intake modified to replace the factory one that was on my supercharged 383 LT1

CANADIANOLDS

It runs fantastic. Boat does a true 65 mph. He sold it and the new owner loves it.

CANADIANOLDS

It would have been more difficult to modify the heads to fit the block. Those 4 huge holes in the deck can’t be transferred onto the head. It wouldn’t work because the head gasket is way to different as well.

We did use a stock water pump, got rid of the opti spark and went with genn1 intake and distributor.

can’t run reverse cooling in this boat anyway