Time to pull the motor..... the saga continues....

[Pat Bush #35083]

Hi guys.... The story continues from last week....

After doing a compression check, I found 4 cylinders to have 165, 3 others that leaked down to 130 and of course my favorite cylinder #5 which had a whopping 90. So I said, OK Pat, time for a second opinion at which point off it went to my local Corvette mechanic who confirmed the same readings I had. At this stage of the game, I have to believe it is the rings in the other 3 cylinders and a bent valve in #5 or possibly a cracked/collapsed piston. So I am pulling the motor and transmission and replacing the whole kit and caboodle with an authentic 76 Corvette motor that I have had (should have done that in the first place)in my shop. Just a couple of quick questions on optimal parts for this new motor.... But first some info on what I have here:

Heads are 882 style and I assume stock L-48 (1.94 intakes/1.5 exhausts). All numbers are correct on both the block and heads. Am magnafluxing, putting 16 guides, new intake/exhaust valves, PC seals, new springs, and rockers and having a light cut taken off the heads just to true them up (they are not warped). I am assuming these are 76cc smog heads.

Block is standard 2 bolt main 010 bored .040 with less than .004 taper in all cylinders and no ridge to speak of. I just glaze busted the cylinders and they look very good with no apparent scoring. Deck has no warpage. Crank is ground .010/.010 and is within tolerance. Will replace the rod bolts but the rods themselves are in great shape so I don't think I will recondition them. So I am thinking a good hot tanking, new pistons, rings, berings, oil pump and that should do on the lower half. I was planning on using Clevite berings, Duke's favorite L-82 GM cam 3896962, and a good set of sealed power chrome moly rings.

Question is --

I want a bit more compression than the stock dished 8.5-1 pistons. Like 9.0-9.5-1. With these 76cc heads, what would you guys recommend? Flat top w/valve recess or domed?

I know the stock L-48 (and even the L-82) in 76 was a real poor hp performer clocking in at a whopping 190 BHP. I want to basically build the motor to a 71-72 spec stock L-48/L-82 Corvette -- somewhere in the 250/270hp area. I don't want anything radical and I want to run on pump premium unleaded with a stock manifold and quadrajet.

Also, while I have this out, I am replacing the clutch, pressure plate, surfacing the flywheel, and re-sealing the tranny. Planning on a Center Force Dual Friction set-up. Any other recommendations while all of this is out?

Thanks in advance for your help.

Pat

[Jack layton #896]

Re: Time to pull the motor..... the saga continues

Recondition the rods. They do get egg shaped. The cost is minimal and if they fail a spun rod bearing will cause a lot of heart ache. Question: If the motor is not the original then why not consider a Chevy crate motor? All new parts and pieces, price is probably half close to a full rebuild. The horsepower upgrade is included. IMHO

[Jack layton #896]

Re: Time to pull the motor..... the saga continues

Recondition the rods. They do get egg shaped. The cost is minimal and if they fail a spun rod bearing will cause a lot of heart ache. Question: If the motor is not the original then why not consider a Chevy crate motor? All new parts and pieces, price is probably half close to a full rebuild. The horsepower upgrade is included. IMHO

[Patrick H.]

Re: Time to pull the motor..... the saga continues

Pat,

First of all, the 1971 motor was rated in GROSS horsepower. The exact same motor was used in 1972 and rated at 200 NET horsepower. So, there is really little difference between my 71 and your 76 as far as power is concerned when in stock configuration.

However, if I were in your position, I'd swap to a non-dished flat top piston (I did). Mine are hypereutectic with only two valve reliefs. It raised my compression by 0.8. I can find the numbers for you if you want. I would also consider advancing the cam 4 degrees as per Dale's favorite recommendations for more bottom end torque. For some Q-jet tricks, I can send you some info on jet/rod/spring swaps that might help. Otherwise, I think you're doing fine. My 350, with the aforementioned pistons and a slightly less radical cam does very well. If I were doing it again, I'd swap to the cam you mention and advance it as above.

By the way, are you saving your original motor for later?

Patrick

[Patrick H.]

Re: Time to pull the motor..... the saga continues

Pat,

First of all, the 1971 motor was rated in GROSS horsepower. The exact same motor was used in 1972 and rated at 200 NET horsepower. So, there is really little difference between my 71 and your 76 as far as power is concerned when in stock configuration.

However, if I were in your position, I'd swap to a non-dished flat top piston (I did). Mine are hypereutectic with only two valve reliefs. It raised my compression by 0.8. I can find the numbers for you if you want. I would also consider advancing the cam 4 degrees as per Dale's favorite recommendations for more bottom end torque. For some Q-jet tricks, I can send you some info on jet/rod/spring swaps that might help. Otherwise, I think you're doing fine. My 350, with the aforementioned pistons and a slightly less radical cam does very well. If I were doing it again, I'd swap to the cam you mention and advance it as above.

By the way, are you saving your original motor for later?

Patrick

[Joe L.]

Re: Time to pull the motor..... the saga continues

Pat------

Your plan sounds like a good one for a good, streetable engine which is the main priority as far as I'm concerned. A few suggestions:

1) Use flat top with "4 eyebrow" pistons. This will give you about 9.0:1 with the heads you have (which are 76 cc, nominal). Using pistons with just 2 eyebrows (or a single slot) will give about 9.25:1. This assumes, of course, the use of stock-type head gaskets. I don't really like these type of gaskets, but the Fel-Pro 1003s will reduce your compression somewhat from your goal;

2) Don't use domed pistons; they'll increase your compression ratio out of the range you're after and will otherwise significantly increase the detonation tendency as a result of interference of "flame path";

3) For your application using stock bottom end components, I think that I'd use a modern, dual profile camshaft rather than the GM L-46/L-82 cam you mentioned. This will allow you to keep your rpm in the range that your bottom end was designed for. More important, it will produce much more power and torque in the rpm range that folks actually use on the street. My choice would be a Speed-Pro 1070R retrofit hydraulic roller. This is a high quality, reasonably priced set-up;

4) If you replace your rod bolts, which I highly recommend, you will need to, at least, re-size the big ends. I'd recommend using ARP "Professional Series" Wave-Lock rod bolts;

[Joe L.]

Re: Time to pull the motor..... the saga continues

Pat------

Your plan sounds like a good one for a good, streetable engine which is the main priority as far as I'm concerned. A few suggestions:

1) Use flat top with "4 eyebrow" pistons. This will give you about 9.0:1 with the heads you have (which are 76 cc, nominal). Using pistons with just 2 eyebrows (or a single slot) will give about 9.25:1. This assumes, of course, the use of stock-type head gaskets. I don't really like these type of gaskets, but the Fel-Pro 1003s will reduce your compression somewhat from your goal;

2) Don't use domed pistons; they'll increase your compression ratio out of the range you're after and will otherwise significantly increase the detonation tendency as a result of interference of "flame path";

3) For your application using stock bottom end components, I think that I'd use a modern, dual profile camshaft rather than the GM L-46/L-82 cam you mentioned. This will allow you to keep your rpm in the range that your bottom end was designed for. More important, it will produce much more power and torque in the rpm range that folks actually use on the street. My choice would be a Speed-Pro 1070R retrofit hydraulic roller. This is a high quality, reasonably priced set-up;

4) If you replace your rod bolts, which I highly recommend, you will need to, at least, re-size the big ends. I'd recommend using ARP "Professional Series" Wave-Lock rod bolts;

[John H.]

Re: Time to pull the motor..... the saga continues

Pat -

My charts show you'll get 9.0:1 with 4-relief flat-tops and composition gaskets with your 76cc heads - I wouldn't use the factory steel shim gaskets on a non-decked block; I've always used Fel-Pros, never had a problem.

I'm with Joe on the ARP Wave-Locs - most critical fastener in the whole engine; you WILL need to re-size the big ends any time you change the bolts.

I think the Centerforce "Dual-Friction" is a bit much for your intended use - that disc is tough on flywheel and pressure plate surfaces; I've used six or seven of the "Centerforce II" setups on past project cars, including several Cobras and my Grand Sport, and no problems with any of them - great grip, smooth engagement, low pedal pressure. I'd also recommend the GM needle roller pilot bearing instead of the bronze one - have used them for years; they don't wear, and last forever.

[John H.]

Re: Time to pull the motor..... the saga continues

Pat -

My charts show you'll get 9.0:1 with 4-relief flat-tops and composition gaskets with your 76cc heads - I wouldn't use the factory steel shim gaskets on a non-decked block; I've always used Fel-Pros, never had a problem.

I'm with Joe on the ARP Wave-Locs - most critical fastener in the whole engine; you WILL need to re-size the big ends any time you change the bolts.

I think the Centerforce "Dual-Friction" is a bit much for your intended use - that disc is tough on flywheel and pressure plate surfaces; I've used six or seven of the "Centerforce II" setups on past project cars, including several Cobras and my Grand Sport, and no problems with any of them - great grip, smooth engagement, low pedal pressure. I'd also recommend the GM needle roller pilot bearing instead of the bronze one - have used them for years; they don't wear, and last forever.

[Pat Bush #35083]

Re: Time to pull the motor..... the saga continues

Jack -

Had thought about a crate motor. I just happen to have this one in my shop and since I do all the machine work except for tanking and resurfacing, it is just the parts I need for the motor and a little time. That would be my second choice if things didn't go well on this motor.

Thanks -

Pat

[Pat Bush #35083]

Re: Time to pull the motor..... the saga continues

Jack -

Had thought about a crate motor. I just happen to have this one in my shop and since I do all the machine work except for tanking and resurfacing, it is just the parts I need for the motor and a little time. That would be my second choice if things didn't go well on this motor.

Thanks -

Pat

[Pat Bush #35083]

Re: Time to pull the motor..... the saga continues

Patrick -

Oh, I am not done with that motor..... I am just sick of futzing with it :-) It wasn't the original block and had a bunch of work done on the heads (hogged out for 2.02 and 1.6 valves), pinned studs etc... plus it was stroked so I would have to replace the rods and crank to put it back to where it used to be. So, given my current frame of mind, I figured it would be simpler to just put this one together and be done with it. At some point, I will tear the original one down and figure out exactly what gremlin is at work here. Was trying for a "turnkey" solution here so I can get that car back on the road.

Pat

[Pat Bush #35083]

Re: Time to pull the motor..... the saga continues

Patrick -

Oh, I am not done with that motor..... I am just sick of futzing with it :-) It wasn't the original block and had a bunch of work done on the heads (hogged out for 2.02 and 1.6 valves), pinned studs etc... plus it was stroked so I would have to replace the rods and crank to put it back to where it used to be. So, given my current frame of mind, I figured it would be simpler to just put this one together and be done with it. At some point, I will tear the original one down and figure out exactly what gremlin is at work here. Was trying for a "turnkey" solution here so I can get that car back on the road.

Pat

[Pat Bush #35083]

Re: Time to pull the motor..... the saga continues

John/Joe -

Awesome advice as usual! Thanks. Will go with the flat-tops w/4 valve reliefs and call it a day. I'll do the rod ends too as suggested. They won't take too long. I just finished the guides and seats in the heads today so I get the rods ready tomorrow.

I picked that Centerforce set-up based on the restoration shop's advice. That seems to be what they put in all the Vettes they restore. But I will take a peek at the Centerforce II unit you suggested.

Thanks as always for your help.

pat

[Pat Bush #35083]

Re: Time to pull the motor..... the saga continues

John/Joe -

Awesome advice as usual! Thanks. Will go with the flat-tops w/4 valve reliefs and call it a day. I'll do the rod ends too as suggested. They won't take too long. I just finished the guides and seats in the heads today so I get the rods ready tomorrow.

I picked that Centerforce set-up based on the restoration shop's advice. That seems to be what they put in all the Vettes they restore. But I will take a peek at the Centerforce II unit you suggested.

Thanks as always for your help.

pat