Low HP L71
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
There is something WAY off.
First...an L-88 cam is not going to idle at 750 RPM or lower...at least not happily. The L-88 cams REALLY like headers and OPEN exhaust. Mufflers of any sort take a lot away from it. A 427 with an L-88 cam and rectangular port heads isn't going to be a low end rocket....but with 4.11's it should still be pretty darn strong...especially from 3500-4000 on up. That cam is going to want to make power at 6500+ RPM if things are right.
12* initial is way too low. Need to ck total timing without vacuum. With decent gas in it I would expect it to be best with no less than 36* total....and most likely 38*-42* with the old heads. The more initial you can put in it and limit the total the better. Idling with 20*+ will help response a lot.
Any idea if they took compression out of it when they rebuilt it? Sure sounds like it.
Time to do a compression test. Maybe the cam is installed a tooth off?
I'd get timing handled first....then verify carbs are opening and go from there. The L-88 cam isn't a complete deal breaker...but it's not a super nice street cam.
JIM
First...an L-88 cam is not going to idle at 750 RPM or lower...at least not happily. The L-88 cams REALLY like headers and OPEN exhaust. Mufflers of any sort take a lot away from it. A 427 with an L-88 cam and rectangular port heads isn't going to be a low end rocket....but with 4.11's it should still be pretty darn strong...especially from 3500-4000 on up. That cam is going to want to make power at 6500+ RPM if things are right.
12* initial is way too low. Need to ck total timing without vacuum. With decent gas in it I would expect it to be best with no less than 36* total....and most likely 38*-42* with the old heads. The more initial you can put in it and limit the total the better. Idling with 20*+ will help response a lot.
Any idea if they took compression out of it when they rebuilt it? Sure sounds like it.
Time to do a compression test. Maybe the cam is installed a tooth off?
I'd get timing handled first....then verify carbs are opening and go from there. The L-88 cam isn't a complete deal breaker...but it's not a super nice street cam.
JIM
I can tell you that my 427/400 made a LOT of fan noise and an ancient Car and Driver confirms it......
When I changed out the pathetic 2" exhaust that all 69' Vettes came with to a 2 1/2" chambered system and set timing to 38 degrees total....this car TOOK OFF......night and day.....
Jebby
Burning Brakes
Joined: Dec 2003
Posts: 1,150
Likes: 154
The first thing I would check is to see if you are getting a full pedal.When I installed my tri power I only got about a half pedal and had to modify my brkt that connects to the last carb.I called a person who restored vettes and he said they had the same problem on tri powers.Just have someone push the pedal to the floor and check to see if the carb linkage will go further.
Burning Brakes
Joined: Jul 2016
Posts: 767
Likes: 74
From: Blaine MN
The first thing I would check is to see if you are getting a full pedal.When I installed my tri power I only got about a half pedal and had to modify my brkt that connects to the last carb.I called a person who restored vettes and he said they had the same problem on tri powers.Just have someone push the pedal to the floor and check to see if the carb linkage will go further.
Melting Slicks
Joined: Mar 2008
Posts: 2,666
Likes: 289
From: Spring Park MN
You always seem to think a lot like I do......
I can tell you that my 427/400 made a LOT of fan noise and an ancient Car and Driver confirms it......
When I changed out the pathetic 2" exhaust that all 69' Vettes came with to a 2 1/2" chambered system and set timing to 38 degrees total....this car TOOK OFF......night and day.....
Jebby
I can tell you that my 427/400 made a LOT of fan noise and an ancient Car and Driver confirms it......
When I changed out the pathetic 2" exhaust that all 69' Vettes came with to a 2 1/2" chambered system and set timing to 38 degrees total....this car TOOK OFF......night and day.....
Jebby
Last edited by v2racing; Jul 22, 2016 at 10:34 PM.
Thread Starter
Intermediate
Joined: Jul 2016
Posts: 31
Likes: 0
Great Response
Hey - great response in a couple of days...at least I'm not imagining the performance I should be getting!
To answer a couple of the questions in case it sheds any more light .....
I am in the UK.
The engine was rebuilt by Gellner Ohio, from what I can see the head cc was measured and recorded as 112 before milling, and compression measured after at 10.6:1 although its only recorded once.
The camshaft is Crane #968561 = 3925535 grind (L88 replacement) with
MA992 solid lifters
Triple carbs rebuilt by Holley Perf IL (although I had to fit a critical missing vac. o ring)
At 3500rpm full throttle ( I have reset middle carb butterfly opening travel to full) there is a normal progressive acceleration up to 4500 rpm or so (I don't want / shouldn't need on the street, to rev any higher) albeit relaxed - no wheelspin, no kick.
Yes its does idle at 750rpm, lumpy / rolling but will sit there, no attempt to stall.
There is a bit of hesitation in pulling away around town speeds and the car prefers more throttle at low speed than is normal....
It has factory cast headers and a very subdued / quiet exhaust system, its 2 1/2" with a single tailbox each side.
Haven't measured dynamic advance but the dizi weights & springs are in situ and free.
From what I can tell in photos the vac pick up for the f/r carbs is high up on the centre carb and not the pick up point under the float bowl that is currently connected to the air pump and choke vac - tell me if this is wrong, maybe the carbs aren't seeing the correct vacuum. I did check the diaphragms for splits, they look OK, the springs seemed to be marked in orange.
Thats about all!
PS did anyone successfully fit a 'quiet' fan (electric or otherwise) as I'd rather be hearing the engine / induction noise than a very noisy but works superbly viscous fan!!
To answer a couple of the questions in case it sheds any more light .....
I am in the UK.
The engine was rebuilt by Gellner Ohio, from what I can see the head cc was measured and recorded as 112 before milling, and compression measured after at 10.6:1 although its only recorded once.
The camshaft is Crane #968561 = 3925535 grind (L88 replacement) with
MA992 solid lifters
Triple carbs rebuilt by Holley Perf IL (although I had to fit a critical missing vac. o ring)
At 3500rpm full throttle ( I have reset middle carb butterfly opening travel to full) there is a normal progressive acceleration up to 4500 rpm or so (I don't want / shouldn't need on the street, to rev any higher) albeit relaxed - no wheelspin, no kick.
Yes its does idle at 750rpm, lumpy / rolling but will sit there, no attempt to stall.
There is a bit of hesitation in pulling away around town speeds and the car prefers more throttle at low speed than is normal....
It has factory cast headers and a very subdued / quiet exhaust system, its 2 1/2" with a single tailbox each side.
Haven't measured dynamic advance but the dizi weights & springs are in situ and free.
From what I can tell in photos the vac pick up for the f/r carbs is high up on the centre carb and not the pick up point under the float bowl that is currently connected to the air pump and choke vac - tell me if this is wrong, maybe the carbs aren't seeing the correct vacuum. I did check the diaphragms for splits, they look OK, the springs seemed to be marked in orange.
Thats about all!
PS did anyone successfully fit a 'quiet' fan (electric or otherwise) as I'd rather be hearing the engine / induction noise than a very noisy but works superbly viscous fan!!
Thread Starter
Intermediate
Joined: Jul 2016
Posts: 31
Likes: 0
More info about behavior of this car!
1 last bit of information - i have been through the whole vacuum system and am pretty sure its airtight, and yet on startup invariably the headlamps lift so does the wiper door - obviously vacuum is low, after maybe 10s they close. Maybe this is a leak, maybe its low vac?
Thanks!
Thanks!
Race Director
Joined: Dec 1999
Posts: 11,096
Likes: 990
From: Sierra Foothills CA
Hey - great response in a couple of days...at least I'm not imagining the performance I should be getting!
To answer a couple of the questions in case it sheds any more light .....
I am in the UK.
The engine was rebuilt by Gellner Ohio, from what I can see the head cc was measured and recorded as 112 before milling, and compression measured after at 10.6:1 although its only recorded once.
The camshaft is Crane #968561 = 3925535 grind (L88 replacement) with
MA992 solid lifters
Triple carbs rebuilt by Holley Perf IL (although I had to fit a critical missing vac. o ring)
At 3500rpm full throttle ( I have reset middle carb butterfly opening travel to full) there is a normal progressive acceleration up to 4500 rpm or so (I don't want / shouldn't need on the street, to rev any higher) albeit relaxed - no wheelspin, no kick.
Yes its does idle at 750rpm, lumpy / rolling but will sit there, no attempt to stall.
There is a bit of hesitation in pulling away around town speeds and the car prefers more throttle at low speed than is normal....
It has factory cast headers and a very subdued / quiet exhaust system, its 2 1/2" with a single tailbox each side.
Haven't measured dynamic advance but the dizi weights & springs are in situ and free.
From what I can tell in photos the vac pick up for the f/r carbs is high up on the centre carb and not the pick up point under the float bowl that is currently connected to the air pump and choke vac - tell me if this is wrong, maybe the carbs aren't seeing the correct vacuum. I did check the diaphragms for splits, they look OK, the springs seemed to be marked in orange.
Thats about all!
PS did anyone successfully fit a 'quiet' fan (electric or otherwise) as I'd rather be hearing the engine / induction noise than a very noisy but works superbly viscous fan!!
To answer a couple of the questions in case it sheds any more light .....
I am in the UK.
The engine was rebuilt by Gellner Ohio, from what I can see the head cc was measured and recorded as 112 before milling, and compression measured after at 10.6:1 although its only recorded once.
The camshaft is Crane #968561 = 3925535 grind (L88 replacement) with
MA992 solid lifters
Triple carbs rebuilt by Holley Perf IL (although I had to fit a critical missing vac. o ring)
At 3500rpm full throttle ( I have reset middle carb butterfly opening travel to full) there is a normal progressive acceleration up to 4500 rpm or so (I don't want / shouldn't need on the street, to rev any higher) albeit relaxed - no wheelspin, no kick.
Yes its does idle at 750rpm, lumpy / rolling but will sit there, no attempt to stall.
There is a bit of hesitation in pulling away around town speeds and the car prefers more throttle at low speed than is normal....
It has factory cast headers and a very subdued / quiet exhaust system, its 2 1/2" with a single tailbox each side.
Haven't measured dynamic advance but the dizi weights & springs are in situ and free.
From what I can tell in photos the vac pick up for the f/r carbs is high up on the centre carb and not the pick up point under the float bowl that is currently connected to the air pump and choke vac - tell me if this is wrong, maybe the carbs aren't seeing the correct vacuum. I did check the diaphragms for splits, they look OK, the springs seemed to be marked in orange.
Thats about all!
PS did anyone successfully fit a 'quiet' fan (electric or otherwise) as I'd rather be hearing the engine / induction noise than a very noisy but works superbly viscous fan!!
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Burning Brakes
Joined: Jul 2016
Posts: 767
Likes: 74
From: Blaine MN
Hey - great response in a couple of days...at least I'm not imagining the performance I should be getting!
To answer a couple of the questions in case it sheds any more light .....
I am in the UK.
The engine was rebuilt by Gellner Ohio, from what I can see the head cc was measured and recorded as 112 before milling, and compression measured after at 10.6:1 although its only recorded once.
The camshaft is Crane #968561 = 3925535 grind (L88 replacement) with
MA992 solid lifters
Triple carbs rebuilt by Holley Perf IL (although I had to fit a critical missing vac. o ring)
At 3500rpm full throttle ( I have reset middle carb butterfly opening travel to full) there is a normal progressive acceleration up to 4500 rpm or so (I don't want / shouldn't need on the street, to rev any higher) albeit relaxed - no wheelspin, no kick.
Yes its does idle at 750rpm, lumpy / rolling but will sit there, no attempt to stall.
There is a bit of hesitation in pulling away around town speeds and the car prefers more throttle at low speed than is normal....
It has factory cast headers and a very subdued / quiet exhaust system, its 2 1/2" with a single tailbox each side.
Haven't measured dynamic advance but the dizi weights & springs are in situ and free.
From what I can tell in photos the vac pick up for the f/r carbs is high up on the centre carb and not the pick up point under the float bowl that is currently connected to the air pump and choke vac - tell me if this is wrong, maybe the carbs aren't seeing the correct vacuum. I did check the diaphragms for splits, they look OK, the springs seemed to be marked in orange.
Thats about all!
PS did anyone successfully fit a 'quiet' fan (electric or otherwise) as I'd rather be hearing the engine / induction noise than a very noisy but works superbly viscous fan!!
To answer a couple of the questions in case it sheds any more light .....
I am in the UK.
The engine was rebuilt by Gellner Ohio, from what I can see the head cc was measured and recorded as 112 before milling, and compression measured after at 10.6:1 although its only recorded once.
The camshaft is Crane #968561 = 3925535 grind (L88 replacement) with
MA992 solid lifters
Triple carbs rebuilt by Holley Perf IL (although I had to fit a critical missing vac. o ring)
At 3500rpm full throttle ( I have reset middle carb butterfly opening travel to full) there is a normal progressive acceleration up to 4500 rpm or so (I don't want / shouldn't need on the street, to rev any higher) albeit relaxed - no wheelspin, no kick.
Yes its does idle at 750rpm, lumpy / rolling but will sit there, no attempt to stall.
There is a bit of hesitation in pulling away around town speeds and the car prefers more throttle at low speed than is normal....
It has factory cast headers and a very subdued / quiet exhaust system, its 2 1/2" with a single tailbox each side.
Haven't measured dynamic advance but the dizi weights & springs are in situ and free.
From what I can tell in photos the vac pick up for the f/r carbs is high up on the centre carb and not the pick up point under the float bowl that is currently connected to the air pump and choke vac - tell me if this is wrong, maybe the carbs aren't seeing the correct vacuum. I did check the diaphragms for splits, they look OK, the springs seemed to be marked in orange.
Thats about all!
PS did anyone successfully fit a 'quiet' fan (electric or otherwise) as I'd rather be hearing the engine / induction noise than a very noisy but works superbly viscous fan!!
Burning Brakes
Joined: Jul 2016
Posts: 767
Likes: 74
From: Blaine MN
Aside from the troubleshooting you're doing, based upon your statement in bold above, you should really consider changing to a cam that better matches your intended usage. Your current cam is just starting to come on hard at 4500 RPMs and you'll never enjoy what the engine was built to do if you don't intend to go past 4500 RPMs.
