'62 250hp to 340hp conversion
02-23-2003, 10:25 AM
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'62 250hp to 340hp conversion
Since I've been shot down (see weihemuller postings) by most of you on my idea to do engine performance modifications to my original '62 327/250hp powerglide car, how about this idea: What about converting my 250hp engine to the 340hp version, which means 461 heads, 340 intake, 2-1/2" exhaust manifolds, carb, 340 cam, 2-1/2 off-road exhaust, etc.? I would keep everything else on my car original and stock, what's wrong with a 340hp powerglide car? It would just be "top end" engine parts (except the cam). Of course, I would keep all the original parts. Would this stock looking and date code matching conversion be so bad? Would the value of the car suffer? It would look like and date match like Chevrolet built a 340hp powerglide Vette in '62. By the way, it's a 3.36 posi in case anyone was wondering.
A lot of you ask why don't I sell the car and buy a non-matching or 4 speed car. I drove a '61 Vette with a 4 speed and I did not care for my knee always hitting the steering wheel when I shifted. Not to mention, where I live there's lots of car events/traffic, so shifting an old 4 speed simply is a drag. Sure it looks cool, and it's fun to tell people it's a 4 speed, but come on, try to drive one a lot and you'll quickly begin to appreciate a powerglide.
Anyway, thanks for all your input. This Corvette forum is great!
A lot of you ask why don't I sell the car and buy a non-matching or 4 speed car. I drove a '61 Vette with a 4 speed and I did not care for my knee always hitting the steering wheel when I shifted. Not to mention, where I live there's lots of car events/traffic, so shifting an old 4 speed simply is a drag. Sure it looks cool, and it's fun to tell people it's a 4 speed, but come on, try to drive one a lot and you'll quickly begin to appreciate a powerglide.
Anyway, thanks for all your input. This Corvette forum is great!
02-23-2003, 10:48 AM
#2
Melting Slicks
Re: '62 250hp to 340hp conversion (weihemuller)
I guess I'm one of those who have been ragging you pretty heavily. I really don't care what you do with your car, just want to be sure you are making an informed decision and have all the facts before you do irreversable damage to the car. It's only a "survivor" once; after that it's just another restored car.
As to a 340 hp pg, there was a reason GM didn't offer the option to begin with. Poor low end torque. If I had a 327/250, I'd want to do something about it too. From a driveability standpoint, the 327/300 is one of the alltime greats. It puts out real good low end torque, (which is what around town driving is all about) and has decent top end power as well. With some very simple top end changes you can clone a 300 and perhaps sneak in a SLIGHTLY more agressive cam without killing the low end. If you scrounge around and fiond the proper dated intake and a proper type AFB, it woukld LOOK completely stock. You need the double bump heads (1.94 intakes, please; the 2.02's don't help low end and that's what we need here), but you don't need to worry about the dates since they are under the valve covers. All that, and some 2.5" ram's horns and you are good to go. Your stock air cleaner will fit right on and that's what most folks see anyway. :steering:
As to a 340 hp pg, there was a reason GM didn't offer the option to begin with. Poor low end torque. If I had a 327/250, I'd want to do something about it too. From a driveability standpoint, the 327/300 is one of the alltime greats. It puts out real good low end torque, (which is what around town driving is all about) and has decent top end power as well. With some very simple top end changes you can clone a 300 and perhaps sneak in a SLIGHTLY more agressive cam without killing the low end. If you scrounge around and fiond the proper dated intake and a proper type AFB, it woukld LOOK completely stock. You need the double bump heads (1.94 intakes, please; the 2.02's don't help low end and that's what we need here), but you don't need to worry about the dates since they are under the valve covers. All that, and some 2.5" ram's horns and you are good to go. Your stock air cleaner will fit right on and that's what most folks see anyway. :steering:
02-23-2003, 11:56 AM
#3
Safety Car
Re: '62 250hp to 340hp conversion (weihemuller)
well, if it were mine i'd either:
1) sell it, and get a hi HP 4 speed car, or
2) install more cam, like a 327/350HP, 300HP intake/carb, make the compression ~ 9.5:1 true static, do some head work (and KEEP ALL THE ORIGINAL PARTS)
just my opinion
1) sell it, and get a hi HP 4 speed car, or
2) install more cam, like a 327/350HP, 300HP intake/carb, make the compression ~ 9.5:1 true static, do some head work (and KEEP ALL THE ORIGINAL PARTS)
just my opinion
02-23-2003, 12:20 PM
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Re: '62 250hp to 340hp conversion (62fuelie)
I'm a little confused about trying to get maximum torque with my powerglide. If the vehicle weight is only 2900-3000 pounds, and I have 205/70 tires (BF Goodrich Touring TA's) on a 5" rim, my 327/250 hp motor can almost break the tires (posi) loose from a standing start now. If I build the motor up (whether 340hp conversion or otherwise), why would torque be a main concern? I've noticed that if I keep my car in low from off idle, I hit 3000 rpm's fairly quickly (about 35-40 mph). Keep in mind my tires are either 26.1 or 26.3" tall with a 3.36 rear. I've read that light cars with skinny street tires don't have to worry about maximum torque or a high rpm torque converter -- because you'll just sit and spin anyway.
02-23-2003, 12:38 PM
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Re: '62 250hp to 340hp conversion (66427-450)
Ed gives sage advice. The Duntov or other mechanical lifter cams kill too much low end torque to be compatible with the Powerglide. My recommendation would be to go with a slightly warmed up 300 HP conversion. This combination would still work best with the OEM cam, but if you insist, you could install a 151 cam. It will kill low end torque and reduce low speed driveability and idle quality - possibly to the point of being unacceptable. The '62 off road mufflers will definitely give the car more "character". I'm not sure if the SHP FI engines had bigger exhaust pipes. I always thought they all had 2" pipes, but the SHP/FI engines did have the 2.5" manifolds.
If you pocket port/port match the heads/manifold and do a multi-angle valve job you will see an improvement in top end power averaging seven percent without much impact on the low end and the engine should pull strongly to at least 5500. Like Ed says, keep the 1.94" inlet valves, but is some benefit to opening up the exhaust side to accept 1.6" valves.
Used 461 or 462 heads are reasonalbly common for about a hundred bucks a set. They are visually indistiguishable with "double humps" and no accessory bosses/holes on the front; 2.5" manifolds are reproduced, but they are visually distinguishable for the originals. The "correct" cast iron inlet manifold and AFB will probably be the toughest parts to locate, but depending on how original you want the engine to look, you could go with a modern aluminum aftermarket manifold and Edelbrock AFB clone.
Of couse, you can do this conversion without pulling the engine, so the scope of work will be much less.
Duke
P.S. If you convert to the 151 cam, be sure to install a NAPA/Echlin VC1810 vacuum can in place of the original.
[Modified by SWCDuke, 9:40 AM 2/23/2003]
If you pocket port/port match the heads/manifold and do a multi-angle valve job you will see an improvement in top end power averaging seven percent without much impact on the low end and the engine should pull strongly to at least 5500. Like Ed says, keep the 1.94" inlet valves, but is some benefit to opening up the exhaust side to accept 1.6" valves.
Used 461 or 462 heads are reasonalbly common for about a hundred bucks a set. They are visually indistiguishable with "double humps" and no accessory bosses/holes on the front; 2.5" manifolds are reproduced, but they are visually distinguishable for the originals. The "correct" cast iron inlet manifold and AFB will probably be the toughest parts to locate, but depending on how original you want the engine to look, you could go with a modern aluminum aftermarket manifold and Edelbrock AFB clone.
Of couse, you can do this conversion without pulling the engine, so the scope of work will be much less.
Duke
P.S. If you convert to the 151 cam, be sure to install a NAPA/Echlin VC1810 vacuum can in place of the original.
[Modified by SWCDuke, 9:40 AM 2/23/2003]
02-23-2003, 02:04 PM
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Re: '62 250hp to 340hp conversion (weihemuller)
I am not a matcching numbers freak/geek, but I DO have a VERY high regard for those cars which have been restored to or retain their true originality. It is nice to be able to see what a truly correct car looked like when it was brand new. If it were my car, and it was TOTALLY original/matching numbers and I wanted to increase the performance, then I would not hesitate to do it (I WOULD save the original 250hp parts).
Not only would I make the changes that you have considered, but I would also go one more step further-----------------and it works, because I have built 3 engines like the following. You can stroke the 327 by using a 350 crank. This is done by having your machine shop turn down the main journals of the 350 crank to the size of the 327 journals. Then you simply use the bigger 350 rods and 350 pistons. With a .030 bore, this would make a 355. Its TOOOOOOOOOOOOOOO easy! Also, I'd use the 350 timing cover with the 8in 350 balancer.
Regarding the PG with a performance engine. --------------------?????????????????----------------------I don't understand what these guys are telling you?????????????? For years, the PG has been, and still is, a commonly used auto tranny for high performance applications. By increasing the hp output of your 327, what little, if any, low end torque you may loose, will more than be compensated for by the increased output of the 327. I am a 100% diehard 4sp person (at the age of 60), thus I am not totally familiar with automatics. But, I do know for a fact that PG trannys have been used extensively behind performance engines for MANY years and worked very satisfactorily. If I wanted to retain the PG and modify the 327, I'd do it!
Not only would I make the changes that you have considered, but I would also go one more step further-----------------and it works, because I have built 3 engines like the following. You can stroke the 327 by using a 350 crank. This is done by having your machine shop turn down the main journals of the 350 crank to the size of the 327 journals. Then you simply use the bigger 350 rods and 350 pistons. With a .030 bore, this would make a 355. Its TOOOOOOOOOOOOOOO easy! Also, I'd use the 350 timing cover with the 8in 350 balancer.
Regarding the PG with a performance engine. --------------------?????????????????----------------------I don't understand what these guys are telling you?????????????? For years, the PG has been, and still is, a commonly used auto tranny for high performance applications. By increasing the hp output of your 327, what little, if any, low end torque you may loose, will more than be compensated for by the increased output of the 327. I am a 100% diehard 4sp person (at the age of 60), thus I am not totally familiar with automatics. But, I do know for a fact that PG trannys have been used extensively behind performance engines for MANY years and worked very satisfactorily. If I wanted to retain the PG and modify the 327, I'd do it!
02-24-2003, 02:31 PM
#7
Melting Slicks
Re: '62 250hp to 340hp conversion (weihemuller)
If you want to make your 250 look like a 340, you have to change the following.
1. carburetor - $500
2. intake manifold - $400
3. heads - ?
4. cam and lifters - $200
5. valve covers - $200
6. exhaust manifolds - $250
7. front exhaust pipes with crossover - $200
8. harmonic balancer - $200
9. distributor - $200
10. generator - $450
I forgot some stuff, but this gives you an idea. The above are parts prices -on the low side. You supply the labor and do the running around to get the parts. Not sure about the timing chain cover, pulleys, and the gas line. There will be lots of little things, that'll add up - same as any other job.
This'll give you a low compression 340 looking engine. Lower end torque will be worse than what you have now. Not sure about upper rpm horsepower. Gas mileage will fall off because you'll need to keep your foot into it to keep the power up. Gas mileage, driveability, and overheating will become a problem because of the lack of vacuum advance. How's your radiator? Your maintenance increases because of the solid lifters.
Consider a GM crate engine for this kind of money. Or, build a 300 HP with a hotter hydraulic lifter cam. Then you can use your same heads, valve covers, distributor, generator, harmonic balancer and all the same pulleys.
BTW, the 300, 340, and 360 used 2 1/2' exhaust manifolds with a cross-over pipe. Your 250 used 2" manifolds w/o a crossover pipe. But both systems used the same exhaust pipes and mufflers. The higher HP engines did not have bigger pipes. 2 1/2" exhaust manifolds were only used by Chevy from 1962 through 1965. After that, all the hot rod small blocks used 2" exhaust manifolds. Makes ya wonder why they didn't bother offering the bigger exhaust manifolds for all those hot rod motors in the late '60s. Especially where they had them in inventory already.
1. carburetor - $500
2. intake manifold - $400
3. heads - ?
4. cam and lifters - $200
5. valve covers - $200
6. exhaust manifolds - $250
7. front exhaust pipes with crossover - $200
8. harmonic balancer - $200
9. distributor - $200
10. generator - $450
I forgot some stuff, but this gives you an idea. The above are parts prices -on the low side. You supply the labor and do the running around to get the parts. Not sure about the timing chain cover, pulleys, and the gas line. There will be lots of little things, that'll add up - same as any other job.
This'll give you a low compression 340 looking engine. Lower end torque will be worse than what you have now. Not sure about upper rpm horsepower. Gas mileage will fall off because you'll need to keep your foot into it to keep the power up. Gas mileage, driveability, and overheating will become a problem because of the lack of vacuum advance. How's your radiator? Your maintenance increases because of the solid lifters.
Consider a GM crate engine for this kind of money. Or, build a 300 HP with a hotter hydraulic lifter cam. Then you can use your same heads, valve covers, distributor, generator, harmonic balancer and all the same pulleys.
BTW, the 300, 340, and 360 used 2 1/2' exhaust manifolds with a cross-over pipe. Your 250 used 2" manifolds w/o a crossover pipe. But both systems used the same exhaust pipes and mufflers. The higher HP engines did not have bigger pipes. 2 1/2" exhaust manifolds were only used by Chevy from 1962 through 1965. After that, all the hot rod small blocks used 2" exhaust manifolds. Makes ya wonder why they didn't bother offering the bigger exhaust manifolds for all those hot rod motors in the late '60s. Especially where they had them in inventory already.
