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58 Posts
Whatever you do. Don't throw money at it. That's guaranteed to make things way worse. Unless you're like me and hoping for an excuse to spend 3 or 4 grand on an aftermarket big block block. In that case. Yes. Throw the money.
SBC lacking power
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If you’re going to a 383 in the future I say your just stuck till that happens.
When you say it’s a stock and apparently will used bottom end I’d hazard to guess that the botton end is tired. Obviously a 66 C10 predates a 350 being the original engine, so it’s something from somewhere else. 350’s from the factory cam in variations from 170ish horsepower to 375, there is a lot of difference in the Potomac ends of these engines. The thing most affecting power of these engines is the combination of cam and compression.
So without knowing exactly what version of 350 is installed in this truck nor its condition relative to ring sealing, blowby, oil consumption and how the details of your top end rebuild in terms of exact head used more specifically chamber volume, the thickness of the head gasket used and you must have seen the pistons so can deliver some insite as to what is the crown shape of the pistons. Basically the average 350 will be low compression, not every 350 is a Corvette as the popular press would lead you to believe, so there will be a round dished piston with 4 valve reliefs. A flat top with 2 or 4 valve reliefs perhaps even a small pop up dome would be a high compression piston.
In normal factory builds even with the more typical 64cc chamber iron head these would use a fairly thin shim gasket. If you installed aluminum heads with the recommended thick composite gasket you lost compression ratio. Added to that aluminum pull heat out of the burn faster than iron. Heat and pressure walk together through the Gas Laws. So here you get a double whammy of lower compression generating less heat therefore pressure thus less force on the piston.
Changing to aluminum heads and adding cam is not a guaranty of adding power. The Devil is in the damn details of how good the original bottom end is at holding compression and combustion pressure, ie are the rings and cylinder walls any good. What compression did you start with therefore we need to know the original head, they have a casting number between valve spring sets. The original head gasket and what the piston crown looks like from this we can determine pretty closely the original compression ratio. This then extends into the heads you put on and their chamber size and what thickness head gasket you used so we can calculate the new compression ratio.
This is not to say the carb or the ignition is not yet tuned adaquatly nor even if the cam is timed correctly. I’m trying to understand the physical constraints of the build to get an idea as to whether proper tune could ebven make a difference if there are oddities about the basic build which are not all that uncommon an event.
Bogie
When you say it’s a stock and apparently will used bottom end I’d hazard to guess that the botton end is tired. Obviously a 66 C10 predates a 350 being the original engine, so it’s something from somewhere else. 350’s from the factory cam in variations from 170ish horsepower to 375, there is a lot of difference in the Potomac ends of these engines. The thing most affecting power of these engines is the combination of cam and compression.
So without knowing exactly what version of 350 is installed in this truck nor its condition relative to ring sealing, blowby, oil consumption and how the details of your top end rebuild in terms of exact head used more specifically chamber volume, the thickness of the head gasket used and you must have seen the pistons so can deliver some insite as to what is the crown shape of the pistons. Basically the average 350 will be low compression, not every 350 is a Corvette as the popular press would lead you to believe, so there will be a round dished piston with 4 valve reliefs. A flat top with 2 or 4 valve reliefs perhaps even a small pop up dome would be a high compression piston.
In normal factory builds even with the more typical 64cc chamber iron head these would use a fairly thin shim gasket. If you installed aluminum heads with the recommended thick composite gasket you lost compression ratio. Added to that aluminum pull heat out of the burn faster than iron. Heat and pressure walk together through the Gas Laws. So here you get a double whammy of lower compression generating less heat therefore pressure thus less force on the piston.
Changing to aluminum heads and adding cam is not a guaranty of adding power. The Devil is in the damn details of how good the original bottom end is at holding compression and combustion pressure, ie are the rings and cylinder walls any good. What compression did you start with therefore we need to know the original head, they have a casting number between valve spring sets. The original head gasket and what the piston crown looks like from this we can determine pretty closely the original compression ratio. This then extends into the heads you put on and their chamber size and what thickness head gasket you used so we can calculate the new compression ratio.
This is not to say the carb or the ignition is not yet tuned adaquatly nor even if the cam is timed correctly. I’m trying to understand the physical constraints of the build to get an idea as to whether proper tune could ebven make a difference if there are oddities about the basic build which are not all that uncommon an event.
Bogie
Ask him to give you the engine serial number
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21 Posts
Yeah, if that won't spin the tires on a pickup, something is way off. I am surprised it starts and runs well if timing is very far off. But that is where, I would begin. I might try to stop the secondaries from opening as well. To test if the carb is just going stupid lean, but then it might also spit back through the carb. I would be curious to run a compression check as well, it could offer up a clue.
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637 Posts
Getting an AFR gauge would be VERY helpful. They're not cheap, but they are well worth it. I have a dual, but even a single is much better than nothing.
The best that you can really do without tearing apart the engine and changing things, is to make sure your carb is tuned properly, your valves are adjusted properly, and make sure your timing is good.
Any other issues you'll just have to live with, until you're ready to build a bottom end.
If you don't know the specs of the bottom end, you can't even form expectations.
Ensure that carb, valves, and timing are adjusted properly, and if you aren't satisfied, start planning a proper bottom end build.
The best that you can really do without tearing apart the engine and changing things, is to make sure your carb is tuned properly, your valves are adjusted properly, and make sure your timing is good.
Any other issues you'll just have to live with, until you're ready to build a bottom end.
If you don't know the specs of the bottom end, you can't even form expectations.
Ensure that carb, valves, and timing are adjusted properly, and if you aren't satisfied, start planning a proper bottom end build.
Thanks for the reply gents.
I will get the block number, I have looked it up before and it’s out either a 62 truck or 80 truck. Both were turds looking at the power numbers. However, the pistons are not the 4 valve relief dish ones. They have a slight dish with no valve relief like the magnum 360 ones. Heads are 64cc and head gasket is 0.38 compressed thickness. NOT great compression but still shouldn’t kill it that bad.
I have ordered an air/fuel ratio gauge to check the carb and tuning. But I think Curtis may have nailed it. That is the sound I can hear at WOT! It’s a pretty distinctive sound that I have never heard. I bit like a turbo blow off valve. I will see if I can get a video. I guess I would drive, go wide open and then check the plugs and they would darken in the time that I went WOT the back to the garage so was thinking all was in the ball park. That’s why you need an Air/fuel gauge.
I will get the block number, I have looked it up before and it’s out either a 62 truck or 80 truck. Both were turds looking at the power numbers. However, the pistons are not the 4 valve relief dish ones. They have a slight dish with no valve relief like the magnum 360 ones. Heads are 64cc and head gasket is 0.38 compressed thickness. NOT great compression but still shouldn’t kill it that bad.
I have ordered an air/fuel ratio gauge to check the carb and tuning. But I think Curtis may have nailed it. That is the sound I can hear at WOT! It’s a pretty distinctive sound that I have never heard. I bit like a turbo blow off valve. I will see if I can get a video. I guess I would drive, go wide open and then check the plugs and they would darken in the time that I went WOT the back to the garage so was thinking all was in the ball park. That’s why you need an Air/fuel gauge.
1970 Nova 350 bored 60 over 4 bolt mains, 700R4, C-4 Corvette IRS 4 wheel power Disc Brakes, tubed
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2 Posts
My set up is close to what you have and my 1970 Nova runs 13 in the Quarter mile. Check your Air/Fuel and timing. If that's not it you have trans Issues. I had the same problem with another car changed out the trans and it was a night and day Difference. It then layed down some nice rubber on the road.
my set up is 350, Bored 60 over, 650 Edelbrock carb and performer intake XE272H comp cam, 1.55 Roller Rockers, flat top pistons Chevy power pack heads 64cc chambers, 700R4, 343 posi rear gears, 28 in tires.
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58 Posts
You don't need an AFR gauge, although it is helpful. You don't need a different engine. It will make the power just fine if you tune it right. It doesn't even have to be "right" as long as its working
Bogie nailed it as usual.
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10,482 Posts
I had a customer bring his 1971 C-10 into my shop in the 1990s.. Complaint was "low power".. He had this truck built. It had been in a couple big name shops in metro Phx AZ area. Simple answer was no body had checked for W O T while sitting in the truck.
I built a new throttle cable mount at the carb so W O T happened. The truck owner came by, test drove the truck. All you heard was engine & tire noise on his test drive around the area.
I built a new throttle cable mount at the carb so W O T happened. The truck owner came by, test drove the truck. All you heard was engine & tire noise on his test drive around the area.
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1,066 Posts
x already mentioned
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Not sure what that means.
The man knows of which he speaks
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mike many members here are good contributors.
Bogie is good at long winded explanations for less experienced people. He is good.
Bogie is good at long winded explanations for less experienced people. He is good.
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