What did you do different for this test?
Disappointing dyno results
- Thread starter jawbone
- Start date
-
Due to inconsistencies in these results I'm having doubts about the worthiness of the dyno.
Nothing different. Warmed the engine up, did a pull. Made sure throttle plate fully opened.
Hopefully in reverse order!
OK. So. lets just go through this.
On all of the runs posted, AVS carb with no change in jets or rods, no change in timing, in fact no mechanical change in anything.
presumbaly you could see the choke was fully open before each pull. Throttle adjustment provided full throttle.
Am I missing anything?
Nope. You got it. Choke is wired open.
Well. Only suggestion I have is to compare to look for differences.
No way it should be that different run to run.
1. Possibly running on 7 cylinders
2. Discovered Running without 1 spark plug. new test on all 8. 600 rpm/sec
3. Next day, no changes known. Air consumption way down, VE way down at the upper end.
No way it should be that different run to run.
1. Possibly running on 7 cylinders
2. Discovered Running without 1 spark plug. new test on all 8. 600 rpm/sec
3. Next day, no changes known. Air consumption way down, VE way down at the upper end.
I am in agreement. Too many differences between runs (on 8 cyl) I don't know anything other than put it in the car else scrap it and build another.
VE is Volumetric Efficiency.
its the amount of air consumed (or trapped) in the cylinders compared to the cylinder volume.
At low rpm the valve overlap and slower airflow results in lower amount of air mass in the cylinder than theoretical.
Peak VE is where the engine combination is most efficient.
A decent engine ought to hit close to 95% at some rpm. A desktop dyno can point to specific VE one ought to expect from an engine combination.
A really good build can hit or exceeed 100% in a limited rpm range, usually high rpm, when the induction and exhuast can support the design. This is race engine territory.
its the amount of air consumed (or trapped) in the cylinders compared to the cylinder volume.
At low rpm the valve overlap and slower airflow results in lower amount of air mass in the cylinder than theoretical.
Peak VE is where the engine combination is most efficient.
A decent engine ought to hit close to 95% at some rpm. A desktop dyno can point to specific VE one ought to expect from an engine combination.
A really good build can hit or exceeed 100% in a limited rpm range, usually high rpm, when the induction and exhuast can support the design. This is race engine territory.
Is this were scavenging comes into play.
MILO
Well-Known Member
Do what you want if you want leaner work the carb if you want more horsepower change the cam its all that simple as others suggested
I understand.
So replace cam even though stock hardware would not support anything much bigger? How big of cam is possible running stock iron heads, HP exhaust manifolds and stock intake? Flow numbers on stock heads not that great.
junkyardhero
Well-Known Member
What to thank everyone that participated in helping me with the issue. I feel like it's been beat to death though and out of yours and my control at this point. I can accept constructive criticism very well but think were at the point that's not the case. Cannot do anything about the dyno nor the operator. What I can do is ask about cams but when I do am slammed. May be I did not word the question correctly. Again, many thanks to all that participated. Have learned much over the period of this build and will be much more to come. Jeff
Did you check if the Dyno throttle lever was opening it from the console, it can be opened all the way from the carb and the lever won't pull it completely open.
ir3333
Well-Known Member
did you ever give us the timing curve...maybe i missed it. But i know when my engine detonating i can tell
even before it's audible because the car is noticably held back. But surely the dyno operator would have picked up on it. My car runs terrible unless i use 94 octane!
even before it's audible because the car is noticably held back. But surely the dyno operator would have picked up on it. My car runs terrible unless i use 94 octane!
Did I read the last pull correctly? You A/F was 9.8 ? That cant help.
I dont think the cam is killing you . It may not be optimal but it should run decent . looks like your torque peaked before the pull started even being too rich .
150 lbs of cranking pressure does seem low for a mild cam . Since your engine is not installed yet you might want to find a knowledgeable shop that is familiar with degreeing cams and have them double check it .
should only take an hour to verify it .
Its a learning process. All the know it alls on here were there at one point . Some of the members ( Mattox, A/J etc..) give good constructive advice in an easy to follow manner . Search their posts on tuning etc .
I dont think the cam is killing you . It may not be optimal but it should run decent . looks like your torque peaked before the pull started even being too rich .
150 lbs of cranking pressure does seem low for a mild cam . Since your engine is not installed yet you might want to find a knowledgeable shop that is familiar with degreeing cams and have them double check it .
should only take an hour to verify it .
Its a learning process. All the know it alls on here were there at one point . Some of the members ( Mattox, A/J etc..) give good constructive advice in an easy to follow manner . Search their posts on tuning etc .
Yes but the Timing curve won‘t matter on the dyno because the pull starts at 3000 and its all in by then .
Phreakish
Well-Known Member
Assuming it's not well under 30, or worse, all-in. Do we even know? I haven't seen a timing figure posted.
Similarly I haven't seen any work done to verify the cam is anywhere close to designed icl. The compression reading suggests it might be off, and it's so easy to check that it should be ruled out even if another dyno pull isn't in the cards.
There's no way in hell I'd just throw that engine in and send it...
autoxcuda
Well-Known Member
- Joined
- Apr 6, 2007
- Messages
- 9,061
- Reaction score
- 4,173
AVS strip kits are long discontinued and I doubt many shops have those parts laying around since most people don't build performance engine with those OE carbs. The jets from an AFB do interchange though. But the 3-step rods and springs are unique to AVS’s.
BTW, 1968 AVS's have the idle adjustment screws blocked off and have center adjustment. They're sorta PITA. He said this might be the carb he’s using.
Was the Holley 600 ran after the plug wire issue corrected? If so, was that carb evaluated if it needed jet changes?
Comment about VE.
Although it is called volumetric efficiency, it is actually mass [ not volume being measured ].It is a misnomer that has become folk lore....
The volume of air inducted into a cyl at a particular rpm never changes; what changes is the density & hence the mass of air inducted.
Although it is called volumetric efficiency, it is actually mass [ not volume being measured ].It is a misnomer that has become folk lore....
The volume of air inducted into a cyl at a particular rpm never changes; what changes is the density & hence the mass of air inducted.
65TerrorCuda
Well-Known Member
At 3000 rpm your afr is 9, see below: That is really rich
And your bsfc (fuel consumption) is off the charts at .74, if we believe the dyno #'s.
And your bsfc (fuel consumption) is off the charts at .74, if we believe the dyno #'s.
The 2nd set of run sheets showed a bit too lean on a full power pull, in the mid 13's at some points, then the last sheet shows extra rich in the 9's with no jetting changes....sumting wong fuel control/pressure wise...or secondary air door flaps are hanging-up. Are You sure in wiring the choke open there's no interference with any of the linkage/rods???
He did supply the curve .
all in by 2800.
Worth checking the carb for changes to be sure, as well as the spark plug wires and spark plugs.
If the carb hasn't been touched then all its doing is responding to what the engine is calling for.
My guess will be one or more cylinders is not performing again. Not sparking, valve not sealing, ring ?
Again look at the plugs and wires, compare with plugs from the day before. If no clues there, then leakdown test.
If the carb hasn't been touched then all its doing is responding to what the engine is calling for.
My guess will be one or more cylinders is not performing again. Not sparking, valve not sealing, ring ?
Again look at the plugs and wires, compare with plugs from the day before. If no clues there, then leakdown test.
-
