1971 LT-1 Engine rebuild Suggestions
1971 LT-1 engine (3.70 rear end),all matching numbers but throws oil out exhaust and has 90K miles. Had valve seals replaced 1K miles ago--no change. Looking at staying pretty stock with solid flat tappet lifters, minor boring to clean up cylinder walls, minor polishing and porting, increasing compression to 9.5:1, new parts except rods (if they are ok) and crank. Also thinking of going with a slightly different cam from the original (#3972182 with 242I/254E, valve lift 459I/485E & 114 degrees separation)---someone suggested 109 degrees separation type cam. Also should I stick with the original oil pump and if so should I rebuild it. Any suggestions/input appreciated since I have never had an engine rebuilt. Thank you.
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Re: 1971 LT-1 Engine rebuild Suggestions
Paul, all I can tell you is to make very sure they don't try to convince you to have the block "decked" it's seldom necessary and you will loose the all important stamp pad numbers.
regards
Roy -
Re: 1971 LT-1 Engine rebuild Suggestions
Paul,
You could do a leak down test before you take the engine apart to see if the air leaks past the rings or valves. If you absolutely need to overhaul My suggestion is to use the stock solid lifter camshaft. The oil pump can be cleaned and check end clearance and reused. Don't lower the compression, you could actually use the 1970 style pistons with the dome to get a little more compression.Comment
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Re: 1971 LT-1 Engine rebuild Suggestions
Decreasing the LSA to 109 deg. from the OE 116 will kill 10-20 percent of the low end torque with no increase in power. In fact it may even make less top end power. You're listenig to the wrong people. The LT-1 cam is one best solid lifter road engine cams you will ever find out of the hundreds of available designs - about as long duration as is practical for a road engine, but less overlap than typical hot rod cams of similar duration.
Chances are the valve guides are worn, so start by removing the heads and having the guides rebuilt. If you want more top end power and revs massaged the heads.
Whoever changed the valve seats should have determined valve guide wear. It's as simple as dropping the valve slightly off the seat and wiggling it. They should have virtually no detectable wiggle.
With the heads off you can check bore wear and if more than .003" consider pulling the block for a rebuilt. Raise the CR to 10-10.5, which will require domes of about 12-14 cc with the 76 or so cc heads.
Measure the rods for proper dimensions, but do no resize them. The "pink" rods are okay to use as is, or just set them aside and buy a new set of Eagle SIR 5700s.
The oil pump is likely reuseable as is as long as the gears are not chewed up from debris ingestion. Just take it apart, inspect and inspect/adjust for 2-3 thou end play.
There are a lot of detailed discussions about rebuilding small blocks, so do some searching or contact me for more information.
The LT-1 was the last and best SHP smallblock. Chevrolet said it had more NET power than any previous, eventhough the last FI engines had 5 HP more gross rating. The best modification is massaging the heads if you want more power and revs and raising the CR on the '71-'72 versions, and if you have the budget, go with a stroker 3.75" crank that will handle 6500 revs, and you'll have an easy 300+ SAE corrected RWHP, with good low end torque and around town driving manners and none of the modifications will be visible.
Other than that it's just a matter of "blueprinting" if you want the best running and most reliable engine.
The quality of any engine restoration is a function of proper planning and most fall short, which ends up making for a lot of disasters. The archives are full of them.
DukeComment
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