Hey guys, I've been lurking for a while but haven't posted much. Just about everything I've needed can be found with a search, lots of good info here. I've had this car for 15+ years, but its been stored for several years waiting to be restored. I bought it back in college and never did much work on it till now.

I'm in the process of a body off restore/upgrade of my 1975 L48, auto, rear end is 2.73. I'm not looking to race, but I'm looking for a sporty weekend cruiser.

Like expected this project continues to blossom. I've got my suspension, steering and brake upgrades purchased or planned out. Frame is about ready for parts to go back on.

I have planned from the start to swap out for a manual transmission and after finally getting the rear end cleaned up and identified I was not thrilled with the 2.73. For now I'd rather spend the money on a transmission and upgrade the differential down the road if I choose. Looking at the first gear ratios a TKO 500 looks like its going to be my best bet to get at least a reasonable take off. Any thoughts or better ideas?

Engine wise I'm not quite as confident, I've looked at rebuilding the original myself, yearone's rebuilt 400hp crate, new ZZ5 crate or GM's 290hp new crate. There tons of old discussions here on each so no need to rehash all that. If anybody has any recent experiences they'd like to share that would be great. I'm thinking I might go with the 290hp crate and put the money towards some of the other upgrades I want to do. (Like new radiator/electric fans and adding A/C that my wife told me I WILL add, I always thought if I was hot I just wasn't driving fast enough) In a year or two once my savings account recovers I probably will come back and upgrade the top half of the engine and try to get in the 350+ range.

Last quick question for today. Looks like Willcox has wiring harnesses on sale and I need to replace my engine harness. Any reason not to just get the direct replacement harness? That would be the auto harness with seat belt interlocks (which is currently disconnected anyway). I guess I could get the manual harness but that would just create more work for somebody if they wanted to put the auto back in it.

Thanks...

 

I'll jump in -

I'd buy the 290 HP motor, that will save you enough money to buy diff gears too, not too sure what someone would charge to put them in but wouldn't think it'd be more than a couple of hundred to have the gears setup. Then like you said you can always do a top end kit on the motor later, heads and cam will get you your 350 HP pretty easy. I bought the 260 HP motor and just recently did a top end kit, I'm probably right there at the 350 HP mark or just below.

 

I'm a rookie at this---if your funds are fairly limited:

 

I'll look it up if nobody knows off the top of their head, but is the bottom end of the GM 350 260hp and 290hp crate motors the same? Might be a way to get a bit more savings now and not change my upgrade plans in the future.

I've thought about rebuilding the calipers and I might, but I need to do a little more research there. 2 of the calipers look to have rust damage on the female side, where the end of the mounting bolt looks to have broke through the caliper wall. Unless they were cast that way.

I'm hoping the first gear of the TKO will help that 2.73 rear end out. If I could I would go tell my college self to do a little more research before buying it. Now I have too much sentimental value in it, so I guess I'll just keep at it...

 

I've not really done any comparison of the 260hp vs the 290hp motors but I'd bet the are basically the same except probably cam and pistons to give the extra 30hp. My 260hp motor ran great but I was not happy at all with the power level so the top end kit went in, now it feels much better but still not a barn burner.

I have a 3.55 rear gear and am looking to get a tko 500 which would be about right with my gears, I would think with 2.73 your 1 - 4 gears would be way too high but then there will probably be someone who's a lot more familiar with gearing than I give you a better/different answer.

 

Your effective ratio on a TKO500 with the 3.37 1st gear will be 8.9. Optimal would be around 10, but a m21 with a 2.54 ration and standard 3.36 gears (1973) is 8.5. I think you will be fine until you are ready for a change.

 

Doing a little research it looks to me that the only difference between the 260hp and 290hp is the cam. I think the price difference is about $500, that being the case I probably will just get the 260hp since either way when I'm ready to upgrade the cam will get swapped out.

Found a nice SuperChevy article on upgrading that 260hp engine.

Thanks Petes, that was my thought as well. Just wanted to hear it from somebody else.

 

Don't forget that those HP numbers are gross and not net like your car's original engine.

260 gross HP is around 195ish net.