Disappointing dyno results
- Thread starter jawbone
- Start date
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SO all you did was change carbs and gained 20 hp at 5000. I see the horsepower is still climbing at 5200 on the second pull. You haven't reached maximum horsepower yet. Slap that dyno operator upside the head for me will ya!
I have run both a 340 and 440 AVS on my 340 with good results. Both have to be jetted properly for the engine combination and altitude you are at. I am at 5800 feet so need to lean out the A/F mixture. But the engine ran better on the 440 AVS. My next carb will be the 800 CFM TQ. The 340 likes air flow.
I would run a cranking compression test and leakdown test on the engine to be sure you have good cylinder sealing and have the cam installed correctly. Sea level CCC should be in the 180 PSIG range and not much lower. And it should be within 5-10 PSI between all cylinders on a really good build. Leakdown should be less than 10% and 5% is better. This will tell you more about sealing than CCC. CCC is impacted by cam timing as well as duration and other factors such as craking speed.
I ran my 340 with a 318 cam and original AVS carb during the first Fuel Economy crisis. It ran 14.50 @ 98 at OCIR with 2.94 gears, so it was making good power even with that tiny cam. But it also got 22 to 24 MPG which at that time was highly important. I did run a desert cooler radiator and electric fan to cut paracitic load and jetted the carb on the lean side but still rich enough to maintain good power and avoid detonation. Timing was maxed at 34° distributor and 51° with vacuum advance.
All components must work on concert to optimize engine performance.
I would run a cranking compression test and leakdown test on the engine to be sure you have good cylinder sealing and have the cam installed correctly. Sea level CCC should be in the 180 PSIG range and not much lower. And it should be within 5-10 PSI between all cylinders on a really good build. Leakdown should be less than 10% and 5% is better. This will tell you more about sealing than CCC. CCC is impacted by cam timing as well as duration and other factors such as craking speed.
I ran my 340 with a 318 cam and original AVS carb during the first Fuel Economy crisis. It ran 14.50 @ 98 at OCIR with 2.94 gears, so it was making good power even with that tiny cam. But it also got 22 to 24 MPG which at that time was highly important. I did run a desert cooler radiator and electric fan to cut paracitic load and jetted the carb on the lean side but still rich enough to maintain good power and avoid detonation. Timing was maxed at 34° distributor and 51° with vacuum advance.
All components must work on concert to optimize engine performance.
True? I thought you were going to switch carbs this morning for today's pull.
There's a not joking thing I have with my boss right now and remains forever. If I see a 268 weak *** comp Chevy grind Mopar cam in the shop I'm snapping the junk over my knee.
To the OP.
Don't be to disappointed at least your engine still runs. I moved a few years ago and left my engine over there and paid the guy to assemble it for me.
It made some power but it didn't last long. The 1st time something went wrong was the 1st or 2nd pull on the Dyno.
Something went wrong every fuhreeekin pull seemingly. It would lose 10 HP a pull every day till it couldn't be tuned and killed the rings.
I had just about pissed off my good buddy but the engine got pissed first.
There were all kinds of craps wrong inside that engine....too much to list and to much to remember.
So nearly a year later I'll get back on the pony and ride. With better **** !
Long story short, don't just give up or just be okay with what it is... it's yours and you only live once
To the OP.
Don't be to disappointed at least your engine still runs. I moved a few years ago and left my engine over there and paid the guy to assemble it for me.
It made some power but it didn't last long. The 1st time something went wrong was the 1st or 2nd pull on the Dyno.
Something went wrong every fuhreeekin pull seemingly. It would lose 10 HP a pull every day till it couldn't be tuned and killed the rings.
I had just about pissed off my good buddy but the engine got pissed first.
There were all kinds of craps wrong inside that engine....too much to list and to much to remember.
So nearly a year later I'll get back on the pony and ride. With better **** !
Long story short, don't just give up or just be okay with what it is... it's yours and you only live once
Ran carb yesterday with 600 holley and avs. AVS on last two pulls. Holley (first two pulls of the day) had better A/F numbers but room was cooler. Was more interested in pull with my carb this morning in cooler environment.
Stock 1970 340 manifold.
Was your dyno sheet on page 1 here with the Holley? And the latest dyno sheet with the AVS? Just making sure.
All dyno sheets posted were with avs.
Off to run my last pull. Wish me luck.
ve % much better numbers intern better
still down 50 to 60 lb ft trq and 60 hp from what a proper fresh tight tuned 340 with headers should make ve% should be closer to 95% or better both of those carbs will put it down 20 hp from 650 700 750 dp
still down 50 to 60 lb ft trq and 60 hp from what a proper fresh tight tuned 340 with headers should make ve% should be closer to 95% or better both of those carbs will put it down 20 hp from 650 700 750 dp
AFR appears to be jumping around a bit until 4000 rpm, when it finally settles in.
it looks to be calculated from BSFC and Air consumption. If so thats about as real as it gets.
With your compression ratio, 160-170 is about right.
And the power numbers follow the AFR around 4,000. Jumping around quite a bit.
What is with the 5200 rpm? The hp is still going up. Rev the dam thing up and see what it is producing.
That's what I said earlier. You can't get to maximum horsepower until you get there and then it starts falling off. Heck, there may be another 500+ rpm to go before that happens.
Rev it to 6500 then see what you have. All you're doing now is tuning the motor for 5200 rpm. Is that going to be your cruising RPM or what?
Think about this, Ma Mopar rated the 340s at 5000 rpm. (low numbers for insurance purposes) They did the same thing with the Hemi's. 425 horse my azz! The op added a different cam at unknown cam timing (it could be retarded a few degrees) and the peak doesn't show up until 6,000 or so. Who knows! 
It's running out of breath.
Well could have gone better. Here are the latest results. Last pull.
What is ve%. Is that affected by A/F ratio?
Now you're just wasting everybody's time including the Dynamo wizard. Set the timing total where it's supposed to be make sure your throttle is opening all the way, fire it up and rev it until it stops making more power. Once the power drops off. shut it down. Stop wasting everybody's time and your money. That motor can safely rev to 7500 if they built the bottom end correctly.
And use fresh gas without ethanol in it.
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