Poorly L71...Help!
Race Director
Joined: Jan 2003
Posts: 18,341
Likes: 101
DON'T go Hooker side pipes unless you are willing to run 'em without baffles (loud is cool for about 5 minutes but gets pretty annoying after that).
The dyno numbers WITH baffles are a sure power killer of pretty extreme proportion. REAL POWER in an exhaust you can live with will see you running Hooker Super Competition or some other equal length tube header and a set of properly size pipes and chambered mufflers. This will be stupid LOUD when you get on it but reasonable at less aggressive use of the "go" pedal.
Side pipes have the LOOK........ but they don't perform as well. Throw baffles in 'em to tone them down to a reasonable volume and you are throwing HP away BIG TIME.
Last edited by Krystal; Mar 2, 2019 at 09:25 AM.
Burning Brakes
Joined: Jul 2016
Posts: 767
Likes: 74
From: Blaine MN
Looking for power?
DON'T go Hooker side pipes unless you are willing to run 'em without baffles (loud is cool for about 5 minutes but gets pretty annoying after that).
The dyno numbers WITH baffles are a sure power killer of pretty extreme proportion. REAL POWER in an exhaust you can live with will see you running Hooker Super Competition or some other equal length tube header and a set of properly size pipes and chambered mufflers. This will be stupid LOUD when you get on it but reasonable at less aggressive use of the "go" pedal.
Side pipes have the LOOK........ but they don't perform as well. Throw baffles in 'em to tone them down to a reasonable volume and you are throwing HP away BIG TIME.
DON'T go Hooker side pipes unless you are willing to run 'em without baffles (loud is cool for about 5 minutes but gets pretty annoying after that).
The dyno numbers WITH baffles are a sure power killer of pretty extreme proportion. REAL POWER in an exhaust you can live with will see you running Hooker Super Competition or some other equal length tube header and a set of properly size pipes and chambered mufflers. This will be stupid LOUD when you get on it but reasonable at less aggressive use of the "go" pedal.
Side pipes have the LOOK........ but they don't perform as well. Throw baffles in 'em to tone them down to a reasonable volume and you are throwing HP away BIG TIME.
Melting Slicks
Joined: Jan 2000
Posts: 3,326
Likes: 523
From: home
Actually if you really want to make power, go with Stahl/ACP or Bill Thomas side exits. There is a set of Bill Thomas side exits for currently for sale in the C3 parts section, but they are $4500 a set. The Stahl/ACP's are about a third the price but aren't stainless.
Burning Brakes
Joined: Jul 2016
Posts: 767
Likes: 74
From: Blaine MN
Didn't know about the Stahl items, my Vert came with the Pipes but I 'm thinking under car exhaust in the future. I'll see how the new Motor does in the 1/4 when old man winter takes off, that may help me decide sooner to ditch the Side Pipes.
Race Director
Joined: Jan 2003
Posts: 18,341
Likes: 101
All
I have a 69 L71, its very original, I've had it a good few years, but its unused as it runs like a pig. About 2 years ago I had in dynoed and as I suspected it was around 180-200hp.
The engine was professionally rebuilt in MD, tri carbs in MI, I bought the car internationally without driving it (its in the UK now) so assume it always had issues with the previous owner.
It drives fine if you like a 180HP 427! We took it down to Le Mans even, its cool but gutless. The viscous fan is louder than the engine!
After some lay up I've been back to it today, stubborn not to be defeated, but could do with some basic guidance on where to start. I desperately don't want to start taking the engine apart to check cam timing. I even bought a 4bbl set up but don't have the heart to fit it as that would be defeatist!!
I notice it has no vac advance on the distributor. I seem to recall checking manifold vacuum and it was very low indeed, then again I've read that the take off point may be 'ported' so not correct. The car has its correct air injection and cast manifolds with a working (moving freely) downpipe valve. I even tried converting the 3 carbs to fixed simultaneous operation, didn't help!
A basic guide as to logical steps to check in order would be really useful if anyone has time to drop me a note specific to this 3 carb set up on the 427.
Many thanks!
Paul
I have a 69 L71, its very original, I've had it a good few years, but its unused as it runs like a pig. About 2 years ago I had in dynoed and as I suspected it was around 180-200hp.
The engine was professionally rebuilt in MD, tri carbs in MI, I bought the car internationally without driving it (its in the UK now) so assume it always had issues with the previous owner.
It drives fine if you like a 180HP 427! We took it down to Le Mans even, its cool but gutless. The viscous fan is louder than the engine!
After some lay up I've been back to it today, stubborn not to be defeated, but could do with some basic guidance on where to start. I desperately don't want to start taking the engine apart to check cam timing. I even bought a 4bbl set up but don't have the heart to fit it as that would be defeatist!!
I notice it has no vac advance on the distributor. I seem to recall checking manifold vacuum and it was very low indeed, then again I've read that the take off point may be 'ported' so not correct. The car has its correct air injection and cast manifolds with a working (moving freely) downpipe valve. I even tried converting the 3 carbs to fixed simultaneous operation, didn't help!
A basic guide as to logical steps to check in order would be really useful if anyone has time to drop me a note specific to this 3 carb set up on the 427.
Many thanks!
Paul
You don't have to go with fuel injection and the big changes that might require. The after market has lot's of good replacement crate engines to pick from that are "bolt in" and go. The old Corvette experience shouldn't include a zero to 60MPH sprint slower than a typical modern economy car.
Burning Brakes
Joined: Jul 2016
Posts: 767
Likes: 74
From: Blaine MN
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Race Director
Joined: Jan 2003
Posts: 18,341
Likes: 101
Yeah, I do understand that.
Thing is though he could replace the tired original Big Block with an updated modern Big Block painted the correct color and most folks looking wouldn't know they weren't looking at the original engine when the hood is lifted.
If there is originality to worry about......value tied up in a matching numbers block.......that newer Big Block solves another problem too. While the VALUABLE engine is sitting on a stand in the corner of a garage he's now free to beat on the car at the drag strip or just the silly stuff that makes these cars fun without worrying about hurting an important piece of the car's resale.
Tri power carb set ups look cool.......and he could stick with it if he really wants to for the "look".......though it's hardly a secret that he would be tossing away some horse power vs the use of a manifold that will use just one big *** Holley.
Thing is though he could replace the tired original Big Block with an updated modern Big Block painted the correct color and most folks looking wouldn't know they weren't looking at the original engine when the hood is lifted.
If there is originality to worry about......value tied up in a matching numbers block.......that newer Big Block solves another problem too. While the VALUABLE engine is sitting on a stand in the corner of a garage he's now free to beat on the car at the drag strip or just the silly stuff that makes these cars fun without worrying about hurting an important piece of the car's resale.
Tri power carb set ups look cool.......and he could stick with it if he really wants to for the "look".......though it's hardly a secret that he would be tossing away some horse power vs the use of a manifold that will use just one big *** Holley.
Last edited by Krystal; Mar 9, 2019 at 08:44 AM.
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
But it is a tripower car. And the consensus is his issue is carbs, ignition or a combo of the two. Even if his block and heads were tired and down to 75% compression, the right timing advance and fuel mixture would be a tire smoker easy.
Race Director
Joined: Jan 2003
Posts: 18,341
Likes: 101
Ignition or carb issue alone or in combination? I suppose that's certainly possible but I'd have expected him to say the car is also getting horrendously bad MPG and/or it's been stumbling if that were the case.
Sounds like a lot to expect from simple tweaks and adjustments when 180HP is your dyno peak power. I wonder if he's measured lift on his cam along with the compression you point to. "tired"......is the right description sometimes. We've all seen "that engine" the one that has really fallen on it's face over time......but it did so without a catastrophic and obvious failure than made it really obvious in the way the engine has been running. A healthy big block 427. It's just a guess on my part but I'd expect he should probably be making double what he's seeing for power, wouldn't he?
Last edited by Krystal; Mar 9, 2019 at 11:44 AM.
Race Director
Joined: Jan 2003
Posts: 18,341
Likes: 101
Here's the thing. You want to go drag racing?
The smart and easiest play is to just buy a new car or at least a late model car worth taking to the strip.
But imagine you want to be someone who isn't just one more guy or girl showing up in a late model Corvette, Camaro, Mustang or Challenger........you want to bring the old Corvette.
I'm not sure there are a lot of people willing to bet the value of their matching #s big block Corvette on the idea that they will get lucky....... every-time they go to the track.
Then there is those 50 years worth of tech improvement. The old 427 was a damned impressive motor in it's day but it isn't nearly as impressive by modern standards. You don't have to go all out with EFI and computers either modern Carburated Big and Small Block Chevy offerings will run far stronger than virtually anything from the late 60s and early 70s. But the best part is found in how your really valuable motor is sitting on a stand free of the abuse.
To me it's a have your cake and eat too thing.
Last edited by Krystal; Mar 9, 2019 at 11:42 AM.