Disappointing dyno results

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ch1ll said:
Your still not telling me if you cc’ed the cylinder with the piston at top dead center. This is going to make a difference in CR. I doubt your going to make stock hp with less than stock compression. Compression is a huge part of the equation.

If he didn’t have jets, he should not have even loaded it on the dyno till he did.

Did you have the advance curve checked?

If anything, your avs is too small. Using a dual plane intake, 4 cylinders are only getting 275-300 cfm. The other 4 are getting the other half of the carb. Think about that.


Did he have jets,air bleeds,power valves to tune the holley he used?
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I did cc'ed the cylinder (65.6 cc). Piston even with deck. CR calc at 9.687. Compression check was 160-170.

He is having a different carb delivered today. 600 cfm Holley.

He does not have carb parts that I know of just different carbs and no parts for my AVS. He put a 750 Holley on it but with similar results.
 
Killer6 said:
You don't need a different carb. It's an AVS, the secondary air doors/flaps may need adjusted, may be sticking/not opening correctly, it is capable of way more power than that.....and can never be too "big" if the tension on those secondary flaps is set correctly.
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We made sure secondary was open fully. That was a concern.
 
Jim Kueneman said:
You talking about my curve? That model was run with the parasitics that a later engine would have been tested to like waterpump, etc so it is a hybrid curve... early specs but running the test more like they had to in the later years (along with the lower performance specs of the early 70's). It is 10.5:1, 2.02 valves with measured flow data.
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Ok, I misunderstood. You are running through software? a Dyno model that projects end results? What I was saying is the later 340 style internals would produce less HP than the early engine with 2.02s high compression pistons X heads etc. Nicks garage on YT dynoed an early 340 that was basically stock internally save for carb and headers, I believe had had a 345 HP pull on his dyno with tuning.
 
I ain't much help, but you're not alone, whether its engine, suspension, electrical, these old gals can be mentally draining. Lots of good advice here, good luck!
jawbone said:
You then understand the long road as I. Glad to see your completed the task. I'm willing to bet you have a sweet running engine. Cats out of the bag with me so need to find the mental energy to correct the problem. Will be performing another pull today with smaller carb today but don't expect and different results. Thanks for the comments. I don't feel so alone.
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Man I'm sure you'll figure it out. A good dyno tuner should be able to latch on to the problem.
 
4spdragtop said:
I ain't much help, but you're not alone, whether its engine, suspension, electrical, these old gals can be mentally draining. Lots of good advice here, good luck!
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Thanks 4spdragtop. Will need a little push throughout this entire project.
 
jawbone said:
Big valve "O" heads, flat top JE pistons with 2 valve reliefs. Calculated 9.687:1 compression, dynamic at 11.103. cc"d at 65.6 Compression check at 150 after 5 revs.
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jawbone said:
Compression check was 160-170.
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Which one is it? 150, or 160-170? Did it change overnight?

And how is the dynamic compression higher than the static?
 
The "cylinder" measured 65.6 ccs? (Maybe the combustion chamber in the head? And where do the pistons sit at TDC?)

The cam was "degreed" but then installed dot to dot? (Maybe it was profiled to check lift and duration, but the OP has never explained what he meant by "degreed" or how degreeing it showed the first cam to be the wrong one.)

The "secondaries" were checked to see if they opened all the way? How? (We talking about the secondary butterflies in the carb base, which operate mechanically, or the air valve up top, with the engine running at full throttle?)

Sorry, don't mean to be a butt, but WTF?
 
jawbone said:
Those were my exact thoughts on doing it but based on results engine needs to come back apart. Cam selection and install was my doing.
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I think that you mentioned pulling the heads off to change the cam in a previous post. If in fact you change the cam you don’t need to pull the heads. I apologize in advance if I misunderstood that part of your pos.
 
mopowers said:
Which one is it? 150, or 160-170? Did it change overnight?

And how is the dynamic compression higher than the static?
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I am repeating what the builder observed. Initially 150 (5 turns). Run a second time he said 160-170. May be on second run he hit the starter over 5 turns.

Static and dynamic compression was done with online calculator. Static compression was 11.556/ dynamic was 11.103.
 
The way your carb is running rich would only give a 3% horsepower loss. I’m thinking that the secondaries air door needs adjustment. The vacuum pot needs to be adjusted to open easier and quicker. Since your dyno guy has no jets and rods, he may not have experience with carter carbs. In high performance applications, mostly after market, a holley is used as much as all other brands combined together.

But I’m still at compression is not high enough.
 
65 Cuda 340 said:
The "cylinder" measured 65.6 ccs? (Maybe the combustion chamber in the head? And where do the pistons sit at TDC?)

The cam was "degreed" but then installed dot to dot? (Maybe it was profiled to check lift and duration, but the OP has never explained what he meant by "degreed" or how degreeing it showed the first cam to be the wrong one.)

The "secondaries" were checked to see if they opened all the way? How? (We talking about the secondary butterflies in the carb base, which operate mechanically, or the air valve up top, with the engine running at full throttle?)

Sorry, don't mean to be a butt, but WTF?
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cyl vol = bore squared x stroke = 4.070 x 4.070 x 12.87 = 213.19026
213.19026 x 3.313 = 706.2993 cc

gasket vol advertised = 8.9 cc
valve relief advertised = 6.8 cc
piston relative to top of deck = 0.0
combustion chamber cc = 65.6
BDC vol = 706.2993 + 6.8 + 65.6 + 8.90 = 787.599
TDC vol = 8.90 + 65.6 + 6.8 = 81.3
CR = BDC vol \ TDC vol = 9.687:1

Cam was degreed and installed dot to dot.
Stood next to engine during pull to verify secondaries opened.
 
jawbone said:
I did cc'ed the cylinder (65.6 cc). Piston even with deck. CR calc at 9.687. Compression check was 160-170.

He is having a different carb delivered today. 600 cfm Holley.

He does not have carb parts that I know of just different carbs and no parts for my AVS. He put a 750 Holley on it but with similar results.
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If he doesn’t tune carbs to their engines, why is he running a dyno? Just to sell dyno sheets?
 
jawbone said:
I am repeating what the builder observed. Initially 150 (5 turns). Run a second time he said 160-170. May be on second run he hit the starter over 5 turns.

Static and dynamic compression was done with online calculator. Static compression was 11.556/ dynamic was 11.103.
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With that much compression I believe your compression test should be around 180-190 psi.
 
jawbone said:
cyl vol = bore squared x stroke = 4.070 x 4.070 x 12.87 = 213.19026
213.19026 x 3.313 = 706.2993 cc

gasket vol advertised = 8.9 cc
valve relief advertised = 6.8 cc
piston relative to top of deck = 0.0
combustion chamber cc = 65.6
BDC vol = 706.2993 + 6.8 + 65.6 + 8.90 = 787.599
TDC vol = 8.90 + 65.6 + 6.8 = 81.3
CR = BDC vol \ TDC vol = 9.687:1

Cam was degreed and installed dot to dot.
Stood next to engine during pull to verify secondaries opened.
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You forgot to add in the area for the valve relief eyebrows.

Did you check piston to deck height with a depth micrometer?

And on the subject of cylinder pressure, did you have a 5 angle valve job done and have the valves lapped in?


I know I’m throwing a lot of **** at you, but I want to see you get through this. Success at your first engine build is important for your future builds and rebuilds.

Also its important to smoke chevies and fords at all opportunities given.
 
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Bore scope each of the cylinders. We had a motor on our dyno and it was down on power from a like build. We scoped the cylinders and the piston was starting to stick. All I will say is custom CP Carillo pistons are not what they use to be….. yea, free rebuild on the house for that customer….
 
I figured your static compression ratio at 9.77:1 with the information you provided. I also figured your dynamic CR to be 8.14:1 with your cam specs.
 
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ch1ll said:
You forgot to add in the area for the valve relief eyebrows.

Did you check piston to deck height with a depth micrometer?

And on the subject of cylinder pressure, did you have a 5 angle valve job done and have the valves lapped in?


I know I’m throwing a lot of **** at you, but I want to see you get through this. Success at your first engine build is important for your future builds and rebuilds.

Also its important to smoke chevies and fords at all opportunities given.
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Valve relief was 6.8 cc as advertised and included in calc. That number came from manufacturer. Are not eyebrows part of relief or am I not understanding?

Piston to deck height was done with a straight edge. You can poke fun a me on this one for it was an estimate. Looked flush to me.

Valve job question for the builder. Will ask next time I see him.

I appreciate your involvement. Really would like to see this through to the end. I sit here trying to think what it could be but no ideas other than take engine apart to verify cam install for everyone. That's going be very difficult to convey. And if it's correct, which I think it is; I'm back where I started.
 
Jim Kueneman said:
The Performance Trends software has a validated 1968 stock 340 example engine so I ran that and compared it to your data.... It matches up nicely at 2500 then it makes no sense. Cam timing is not going to give you that sort of a curve... personally I would start by seriously questioning the dyno and test itself unless you can find something seriously wrong with the engine (like it has lost a lobe on the cam or something like that)....

View attachment 1716141949
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Thanks for the graph. Shows just how bad things are. I sit here staring at it trying to think what could be so wrong. The engine sounds good and strong during pulls. In fact I asked about the dyno possibly as the cause. That did not get me anywhere.
 
Ok, I re read your post, missed it the first time. Straight edge is acceptable, I would have used a feeler gauge with it. I was a tool and die maker during my working years, so measure,measure,measure. See my above post on compress.

I know you are frustrated, its a long road but your going to get through this.

I question your dyno guy. Don’t you want to run your avs after you get this straightened out.
 
I miss calculated, I have edited my post. Keep in mind that these are simple calculators and do not take into consideration of all variables.
 
If you were to pull cam to double chk/degree, you may as well install a better suited cam/lifters. Sell the current one, someone will buy it and put that $$ towards new set. You might be out $100-150 ??
Just a thought. I wouldnt be content with current cam if it turns out that's all it needs is a cam swap.
 
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