So I wanted to check the overall health of the mystery 350 SBC motor in my Chevelle, and checked the cranking compression of each cylinder when the engine was cold. After reading more on how to do the cranking check, I realized I was supposed to have taken all of the spark plugs out then install the gauge in each cylinder one at a time. I left the plugs in other than the cylinder I was checking, so probably need to go back and do it again. I also didn't prop the choke wide open, so that may have affected the readings too.
Anyway, with the other plugs still in and the choke not propped open, here are the readings:
Cyl 1-120 psi
Cyl 2-110
Cyl 3-115
Cyl 4-120
Cyl 5-110
Cyl 6-120
Cyl 7-119
Cyl 8-120
The readings seem a little low, but they are within 10% of each other, which is what I understand is more important than the reading itself. Since I didn't remove all the plugs and prop the choke open, I'm guessing that could be why they are low as well.
What have you guys seen in an avg. SBC, and any reason to be concerned from these readings?
67ss said
Nov 6, 2016
Those numbers seem low to me. Stock engines usually make 125 or more. I know vortec truck motors run 150-175 psi.
Could be a poor combination of static compression and camshaft selection.
Does the engine seem really lazy?
SShink said
Nov 6, 2016
67ss wrote:
Those numbers seem low to me. Stock engines usually make 125 or more. I know vortec truck motors run 150-175 psi.
Could be a poor combination of static compression and camshaft selection.
Does the engine seem really lazy?
Thanks Chris.
It doesn't have much torque on the low end, at least compared to the one you built for me, but once it gets up in the rpm's it really wakes up and almost breaks the tire free (it's a 1 wheel wonder) from a 15 mph rolling start.
It doesn't sound like a big cam at idle, as it's pretty smooth, but sounds like it might be over cammed?
Lost in the 60s said
Nov 6, 2016
120 on a tired smog motor wouldn't be unusual. Better put your order in with Chris for another engine...
67ss said
Nov 6, 2016
Yea it sounds like to much cam if it is coming to life in the upper rpm range. Which again could count for the low cranking compression. Sound like you may have a cam swap in your future.
SShink said
Nov 6, 2016
67ss wrote:
Yea it sounds like to much cam if it is coming to life in the upper rpm range. Which again could count for the low cranking compression. Sound like you may have a cam swap in your future.
How did the 60103 cam sound and what was the throttle response like on the run stand in the 355 you built?
Would you recommend that with the camel hump heads I have now versus the Vortec heads?
dashboard said
Nov 7, 2016
Stan, if you have time, redo the test with the engine warm and all eight plugs out. Be interesting to see if the numbers change at the same rate.
You might also try a leak down test. If you'd like to try that let me know. I could send you the tool.
Or you might drive it and enjoy the ride. Small blocks are pretty durable and if put together will last just shy of forever.
SShink said
Nov 7, 2016
dashboard wrote:
Stan, if you have time, redo the test with the engine warm and all eight plugs out. Be interesting to see if the numbers change at the same rate. You might also try a leak down test. If you'd like to try that let me know. I could send you the tool. Or you might drive it and enjoy the ride. Small blocks are pretty durable and if put together will last just shy of forever.
I'd redo the cranking test but guess what's in the way and a pain to work around on the number 5 and 6 spark plugs... yep the d**n headers! So, I think I'll just drive it and not worry about it. Nothing's broken, and it runs fine, so I'll just enjoy it.
Lost in the 60s said
Nov 7, 2016
Sounds like the thing to do for now. If anything a converter change might help. In your other thread, you said it bogs down from a stop. If the converter is engaging at 1500 rpm with the throttle matted from a stop, it's not a 3,000 stall, or the engine doesn't have enough torque to override the stall. A 3,000 stall converter should let the engine rev up close to that before transferring power to the clutches and that should light your one tire up like napalm.
Something just doesn't sound right here with the combination of a smooth idle and low torque/bog from idle up. It could be over cammed but to me, that doesn't fit with the smooth idle. Your other thread shows flat tappet lifters and a hot grind is more evident at idle than with roller lifters.
Where did you set the timing after the intake swap ? Initial timing has a lot to do with off idle performance. Did you check total advance at 3,000 rpm to see if it's enough, or too much ? Mechanical advance, vacuum advance plumbed in ?
SShink said
Nov 7, 2016
Lost in the 60s wrote:
Where did you set the timing after the intake swap ? Initial timing has a lot to do with off idle performance. Did you check total advance at 3,000 rpm to see if it's enough, or too much ? Mechanical advance, vacuum advance plumbed in ?
Initial timing at idle of 750 rpm is at 14 degrees, without any pinging, so I'm guessing it's not a stock cam as it seems happy there and starts immediately as well. I can't check it at 3K rpm as I just have a simple timing light without the control to adjust for a damper without timing tape that goes that high. The vacuum timing advance is connected to manifold vacuum I think? Or, it could be ported vacuum... I need to check again.
SShink said
Nov 11, 2016
I drove the Chevelle to work today, so of course had to take the long way home to enjoy the drive... and found myself on some remote two lane blacktop. So, I tried another burnout and discovered something interesting.
I power braked it and it still bogged down, but just as soon as I released the brake pedal with the throttle pegged, it broke the tire free and spun like crazy, so it's not like the engine isn't making enough power. And, as I mentioned before when I floor it from a roll at 5-10 mph, it will break the tire free, so it seems to have enough torque.
So, I'm guessing it could be the rear brakes are grabbing too hard to break the tire free when I'm power braking (there is probably 9" of tread on the ground since they are on 15 x 8 rims with 60 series tires). Or, it almost acts like there's a trans brake on it until I release the brake pedal. Could that be possible? Is there such a thing as a torque convertor that locks up when the brake is released and is tied into the brake system like a line lock?
I have no idea what's in the trans from a convertor or governor perspective other than I think it's a TH350.
Lost in the 60s said
Nov 12, 2016
A transmission brake works in the same way you describe, but they are usually driver activated with a switch/button. Could yours have one tied into the brake lights ?? Who knows. I take it you didn't buy the car from the person who had the engine/trans built ? Any way to get back to them for information ?
SShink said
Nov 12, 2016
Thanks Mitch. That seems to be how it's acting to me as well. I need to fix the howling blower fan motor on it today, so will look around the trans to see if I find any kind of electrical connections. I did find a switch under the dash with nothing connected to it, but I thought it was for fog lights as I also found a relay in the engine bay along with holes in the front bumper that had been covered up with bumper bolts where I thought the fog lights were mounted at one time.
I can contact the previous owner, but he's kind of an A#s... I figured out he lied about a few things on the car after I got it home, so I wouldn't trust him anyway. It does appear somebody did play with it (hot rodded) based on the camel hump heads and how I believe it was set up before the previous owner changed some things.
I'll see if I can find anything on the trans that looks like a trans brake connection.
SShink said
Nov 12, 2016
Found a canister on the trans hooked up to the vacuum line that is different than anything I've seen before on a TH350. Anyone have any ideas?
Yes, I know it's grimy and oily under there and the trans mount is toast. That will get replaced soon.
That's an adjustable vacuum module for controlling the shift points...perfectly normal.
SShink said
Nov 12, 2016
Lost in the 60s wrote:
That's an adjustable vacuum module for controlling the shift points...perfectly normal.
Thanks Mitch. I probably need to try to adjust it as it shifts the 1-2 shift in the first 10-15 ft. and the 2-3 isn't much longer after that, so shifting too soon IMO.
Lost in the 60s said
Nov 12, 2016
SShink wrote:
Lost in the 60s wrote:
That's an adjustable vacuum module for controlling the shift points...perfectly normal.
Thanks Mitch. I probably need to try to adjust it as it shifts the 1-2 shift in the first 10-15 ft. and the 2-3 isn't much longer after that, so shifting too soon IMO.
It may have a ruptured diagram and is non-functional, which can cause the short shift condition. AND that may be part of your poor off line performance, if it is shifting right away. Follow it up to the engine and make certain it is actually hooked up to a vacuum source too.
By the appearance, the rubber hose that connects the metal line to the canister may be off or ruptured right at the can too which, obviously, won't supply vacuum for it to function.
Have you tried a dead stop launch with the trans shifted manually into 1st gear so it can't shift ?
SShink said
Nov 12, 2016
Lost in the 60s wrote:
It may have a ruptured diagram and is non-functional, which can cause the short shift condition. AND that may be part of your poor off line performance, if it is shifting right away. Follow it up to the engine and make certain it is actually hooked up to a vacuum source too.
By the appearance, the rubber hose that connects the metal line to the canister may be off or ruptured right at the can too which, obviously, won't supply vacuum for it to function.
Have you tried a dead stop launch with the trans shifted manually into 1st gear so it can't shift ?
The vacuum line is connected at the manifold when I swapped intakes. Having said that, the line is probably dry rotted and should be replaced anyway since they all were before I replaced them during the intake swap.
Yep, I held it in 1st gear when trying to launch from a dead stop.
Lost in the 60s said
Nov 12, 2016
There is another hose at the can end and as oily as all that is, the hose could be swollen/split and not tight on the nipple or rotted right off. You can get a better look when you replace the trans mount..
That hose will most likely be a 90° formed hose too. Don't remember if it's 3/16ths or 1/4" but bending a fuel or vacuum hose doesn't work. If it's bad, get the right hose.
SShink said
Mar 24, 2017
Well, had a few hours off this afternoon to get ready for another week in Taiwan, so took the opportunity to re-do the compression check with the engine warmed up and the plugs removed this time.
Basically about 15-25 psi higher on each cylinder, which still seems low to me and the fastest engine builder in the club (23 min. at CC a few years ago if I remember right Chris P.?) thinks it's a bit low as well:
Cyl 1-120 psi After = 139
Cyl 2-110 After = 129
Cyl 3-115 After = 135
Cyl 4-120 After = 139
Cyl 5-110 After = 135
Cyl 6-120 After = 140
Cyl 7-119 After = 131
Cyl 8-120 After = 140
The readings are still within 8% of each other which is good, but overall the readings are lower than a fresh 350 at 150-170 psi, so I'm guessing it's a little tired. Although, it's pulling 19 inches of vacuum at 750 rpm idle, so it actually runs pretty good.
I also found the plugs to be really carbon fouled, so looks like I need to do some more work on the carb too.
So, the big decision is whether to sell the engine setup while it's running pretty good and go for new, or swap in the 2004R I had rebuilt with this engine, and drive it for awhile and see how it runs and spend the money on changing the front drum brakes to disc's, and maybe some new rims and tires.
Lost in the 60s said
Mar 24, 2017
As long as it's running good, I would leave it and do the other things you have listed.
SShink said
Mar 25, 2017
Lost in the 60s wrote:
As long as it's running good, I would leave it and do the other things you have listed.
Larry Lucast said
Mar 25, 2017
If you don't know the origin of the engine, those numbers could be OK for what the engine is. I have always felt that a top priority should be to makes the brakes as effective and dependable as possible, then go on to other things.
dashboard said
Mar 25, 2017
I like Larry's stop first philosophy. If the engines not smoking has reasonable performance and the AC works, drive it. Small blocks will just run forever.
Enganeer said
Mar 25, 2017
Look at trying one range hotter on the plugs if they keep getting fouled up.
OscarZ said
Mar 26, 2017
As someone who made the switch from front drums to discs last year I vote brakes first.
This year I'm switching to a 200R4 as well. Our 71's sound to be getting similar updates. :)
-- Edited by OscarZ on Sunday 26th of March 2017 02:10:32 PM
John D said
Mar 29, 2017
Those #'s are just fine... compression #'s, vacuum #'s, all tell of a healthy engine.
Yeah, it may be a little tired... but so what? Let the next guy rebuild it.
Do the trans & brakes and make the car economical and safe.
Lost in the 60s said
Mar 30, 2017
John D wrote:
Those #'s are just fine... compression #'s, vacuum #'s, all tell of a healthy engine. Yeah, it may be a little tired... but so what? Let the next guy rebuild it.
Do the trans & brakes and make the car economical and safe.
What are you trying to say here, John...
SShink said
Mar 30, 2017
Lost in the 60s wrote:
John D wrote:
Those #'s are just fine... compression #'s, vacuum #'s, all tell of a healthy engine. Yeah, it may be a little tired... but so what? Let the next guy rebuild it.
Do the trans & brakes and make the car economical and safe.
What are you trying to say here, John...
Yeah, I read that between the lines too Mitch.
John D said
Apr 2, 2017
So, the big decision is whether to sell the engine setup while it's running pretty good...
Nothing between the lines, you said it yourself you may sell it.
HOWEVER
You are coming up on your historical "Chevelle Expiration Date"
So I wanted to check the overall health of the mystery 350 SBC motor in my Chevelle, and checked the cranking compression of each cylinder when the engine was cold. After reading more on how to do the cranking check, I realized I was supposed to have taken all of the spark plugs out then install the gauge in each cylinder one at a time. I left the plugs in other than the cylinder I was checking, so probably need to go back and do it again. I also didn't prop the choke wide open, so that may have affected the readings too.
Anyway, with the other plugs still in and the choke not propped open, here are the readings:
Cyl 1-120 psi
Cyl 2-110
Cyl 3-115
Cyl 4-120
Cyl 5-110
Cyl 6-120
Cyl 7-119
Cyl 8-120
The readings seem a little low, but they are within 10% of each other, which is what I understand is more important than the reading itself. Since I didn't remove all the plugs and prop the choke open, I'm guessing that could be why they are low as well.
What have you guys seen in an avg. SBC, and any reason to be concerned from these readings?
Those numbers seem low to me. Stock engines usually make 125 or more. I know vortec truck motors run 150-175 psi.
Could be a poor combination of static compression and camshaft selection.
Does the engine seem really lazy?
Thanks Chris.
It doesn't have much torque on the low end, at least compared to the one you built for me, but once it gets up in the rpm's it really wakes up and almost breaks the tire free (it's a 1 wheel wonder) from a 15 mph rolling start.
It doesn't sound like a big cam at idle, as it's pretty smooth, but sounds like it might be over cammed?
120 on a tired smog motor wouldn't be unusual.
Better put your order in with Chris for another engine...
Yea it sounds like to much cam if it is coming to life in the upper rpm range. Which again could count for the low cranking compression. Sound like you may have a cam swap in your future.
How did the 60103 cam sound and what was the throttle response like on the run stand in the 355 you built?
Would you recommend that with the camel hump heads I have now versus the Vortec heads?
I'd redo the cranking test but guess what's in the way and a pain to work around on the number 5 and 6 spark plugs... yep the d**n headers!
So, I think I'll just drive it and not worry about it. Nothing's broken, and it runs fine, so I'll just enjoy it.
Something just doesn't sound right here with the combination of a smooth idle and low torque/bog from idle up. It could be over cammed but to me, that doesn't fit with the smooth idle. Your other thread shows flat tappet lifters and a hot grind is more evident at idle than with roller lifters.
Where did you set the timing after the intake swap ? Initial timing has a lot to do with off idle performance. Did you check total advance at 3,000 rpm to see if it's enough, or too much ? Mechanical advance, vacuum advance plumbed in ?
Initial timing at idle of 750 rpm is at 14 degrees, without any pinging, so I'm guessing it's not a stock cam as it seems happy there and starts immediately as well. I can't check it at 3K rpm as I just have a simple timing light without the control to adjust for a damper without timing tape that goes that high. The vacuum timing advance is connected to manifold vacuum I think? Or, it could be ported vacuum... I need to check again.
I drove the Chevelle to work today, so of course had to take the long way home to enjoy the drive... and found myself on some remote two lane blacktop. So, I tried another burnout and discovered something interesting.
I power braked it and it still bogged down, but just as soon as I released the brake pedal with the throttle pegged, it broke the tire free and spun like crazy, so it's not like the engine isn't making enough power. And, as I mentioned before when I floor it from a roll at 5-10 mph, it will break the tire free, so it seems to have enough torque.
So, I'm guessing it could be the rear brakes are grabbing too hard to break the tire free when I'm power braking (there is probably 9" of tread on the ground since they are on 15 x 8 rims with 60 series tires). Or, it almost acts like there's a trans brake on it until I release the brake pedal. Could that be possible? Is there such a thing as a torque convertor that locks up when the brake is released and is tied into the brake system like a line lock?
I have no idea what's in the trans from a convertor or governor perspective other than I think it's a TH350.
Thanks Mitch. That seems to be how it's acting to me as well. I need to fix the howling blower fan motor on it today, so will look around the trans to see if I find any kind of electrical connections. I did find a switch under the dash with nothing connected to it, but I thought it was for fog lights as I also found a relay in the engine bay along with holes in the front bumper that had been covered up with bumper bolts where I thought the fog lights were mounted at one time.
I can contact the previous owner, but he's kind of an A#s... I figured out he lied about a few things on the car after I got it home, so I wouldn't trust him anyway. It does appear somebody did play with it (hot rodded) based on the camel hump heads and how I believe it was set up before the previous owner changed some things.
I'll see if I can find anything on the trans that looks like a trans brake connection.
Found a canister on the trans hooked up to the vacuum line that is different than anything I've seen before on a TH350. Anyone have any ideas?
Yes, I know it's grimy and oily under there and the trans mount is toast. That will get replaced soon.
Thanks Mitch. I probably need to try to adjust it as it shifts the 1-2 shift in the first 10-15 ft. and the 2-3 isn't much longer after that, so shifting too soon IMO.
It may have a ruptured diagram and is non-functional, which can cause the short shift condition. AND that may be part of your poor off line performance, if it is shifting right away. Follow it up to the engine and make certain it is actually hooked up to a vacuum source too.
By the appearance, the rubber hose that connects the metal line to the canister may be off or ruptured right at the can too which, obviously, won't supply vacuum for it to function.
Have you tried a dead stop launch with the trans shifted manually into 1st gear so it can't shift ?
The vacuum line is connected at the manifold when I swapped intakes. Having said that, the line is probably dry rotted and should be replaced anyway since they all were before I replaced them during the intake swap.
Yep, I held it in 1st gear when trying to launch from a dead stop.
There is another hose at the can end and as oily as all that is, the hose could be swollen/split and not tight on the nipple or rotted right off. You can get a better look when you replace the trans mount..
That hose will most likely be a 90° formed hose too. Don't remember if it's 3/16ths or 1/4" but bending a fuel or vacuum hose doesn't work. If it's bad, get the right hose.
Well, had a few hours off this afternoon to get ready for another week in Taiwan, so took the opportunity to re-do the compression check with the engine warmed up and the plugs removed this time.
Basically about 15-25 psi higher on each cylinder, which still seems low to me and the fastest engine builder in the club (23 min. at CC a few years ago if I remember right Chris P.?) thinks it's a bit low as well:
Cyl 1-120 psi After = 139
Cyl 2-110 After = 129
Cyl 3-115 After = 135
Cyl 4-120 After = 139
Cyl 5-110 After = 135
Cyl 6-120 After = 140
Cyl 7-119 After = 131
Cyl 8-120 After = 140
The readings are still within 8% of each other which is good, but overall the readings are lower than a fresh 350 at 150-170 psi, so I'm guessing it's a little tired. Although, it's pulling 19 inches of vacuum at 750 rpm idle, so it actually runs pretty good.
I also found the plugs to be really carbon fouled, so looks like I need to do some more work on the carb too.
So, the big decision is whether to sell the engine setup while it's running pretty good and go for new, or swap in the 2004R I had rebuilt with this engine, and drive it for awhile and see how it runs and spend the money on changing the front drum brakes to disc's, and maybe some new rims and tires.
As someone who made the switch from front drums to discs last year I vote brakes first.
This year I'm switching to a 200R4 as well. Our 71's sound to be getting similar updates. :)
-- Edited by OscarZ on Sunday 26th of March 2017 02:10:32 PM
Yeah, it may be a little tired... but so what? Let the next guy rebuild it.
Do the trans & brakes and make the car economical and safe.
What are you trying to say here, John...
Yeah, I read that between the lines too Mitch.
Nothing between the lines, you said it yourself you may sell it.
HOWEVER
You are coming up on your historical "Chevelle Expiration Date"