W2 408 Dyno results today !

[mbaird]

It’s quite common on single plane single carb stuff. That’s why companies like Wilson Manifolds find so much power in professional level porting and modifying on intakes. Lots of guys stagger the jetting to compensate. @mbaird how did the plug look on number 7? That’ll tell you if it was a sensor issue.

I have not pulled the plugs yet . It was getting late and I was starting to fade...lol

I would think #5 would be effected as well if it was just a distribution issue .
But I am ignorent about interpretting dyno data. Just pure speculation . But if the plug or cable was starting to misfire at high rpm/loads it would explain the flatline. I would gave guessed a lean situation if it was distribution .

 

[PRH]

Misfires show as lean on O2 sensors.

The line is flat at just over 10:1, because that’s basically the limit of the sensor.
Lambda .70 is about where they bottom out, which is like 10.3 on the gas scale.
So, anything that was actually richer than 10.3.......would still show 10.3.

 

[Phreakish]

AFR, or Lambda alone won't tell the whole tale. Here's a good read that illustrates some concepts.
It's entirely possible the AFR is lying and that something else is going on. I've seen plugs with internal defects, impossible-to-see cracks in porcelain, or which just plain don't work under load cause a random misfire. I chased an issue like this on an engine once which would buck under high load in high gear, but nowhere else and once above 3k would be fine (and I'm sure the opposite is possible too).
Point being, like PRH is alluding too: don't lose the forest for the trees. If you can get some additional data from a gas analyzer, it might help, but I'd be swapping plugs and wires around to see if the issue follows them, or if new plugs/wires (or routing) addresses the issue. I'd even be looking at the pickup to ensure there isn't a mechanical cause for a misfire.

 

[mbaird]

Misfires show as lean on O2 sensors.

The line is flat at just over 10:1, because that’s basically the limit of the sensor.
Lambda .70 is about where they bottom out, which is like 10.3 on the gas scale.
So, anything that was actually richer than 10.3.......would still show 10.3.

Yes .. that is exactly what Frank told me . So that cylinder cojld be 6:1 for all we know .
We only encountered this flatline under full throttle. Part throttle runs appeared ok .

 

[mbaird]

AFR, or Lambda alone won't tell the whole tale. Here's a good read that illustrates some concepts.
It's entirely possible the AFR is lying and that something else is going on. I've seen plugs with internal defects, impossible-to-see cracks in porcelain, or which just plain don't work under load cause a random misfire. I chased an issue like this on an engine once which would buck under high load in high gear, but nowhere else and once above 3k would be fine (and I'm sure the opposite is possible too).
Point being, like PRH is alluding too: don't lose the forest for the trees. If you can get some additional data from a gas analyzer, it might help, but I'd be swapping plugs and wires around to see if the issue follows them, or if new plugs/wires (or routing) addresses the issue. I'd even be looking at the pickup to ensure there isn't a mechanical cause for a misfire.

That is great advice. It never occured to me during the run it could be ignition related .

The question remains... could that
cylinder be the cause of power falling off after 6200 ? There seems to be a corelation between the afr curve on #7 and the power curve . Seems to be....

 

[Phreakish]

That is great advice. It never occured to me during the run it could be ignition related .

The question remains... could that
cylinder be the cause of power falling off after 6200 ? There seems to be a corelation between the afr curve on #7 and the power curve . Seems to be....


View attachment 1715817320 View attachment 1715817321 View attachment 1715817322

EGT might shed some light, rich but running I would expect to show different than a misfire. The power and the strange AFR on #7 could be related - hard to say but finding out will take more time and some money. As with anything engine-related, there's always a lot of 'maybe' involved.

In any event, if it's possible to tinker with #7 without a ton of extra cost - it would be worth it IMO to ensure it's dialed in. Then again, if it doesn't show up part throttle it might not actually show up in the car either, even at WOT. I'm sure the dyno is able to load the engine far more than it will see otherwise. Is it worth the added expense in order to get a prettier graph? It might boil down to a value judgement.

 

[PRH]

Like I said, I would have tried jetting for power, and maybe the bsfc and power numbers could have been improved upon(but, maybe not).
After I had tuned for power ........ then you could see if it had any bearing on the reading from that one cylinder.

In other words....... how would you go about tuning the motor if you didn’t have 8 O2’s on the motor and that info to look at?

I would venture to say that “most” dyno services don’t have the capability of reading the O2 on every cylinder.
I guess for those without it....... you don’t miss what you don’t know.

It looked like there were EGT probes in use too?
How much different was the ex temp on #7 compared to the others?

 

[PRH]

I assume this is an overlay of two runs.

What was different between the two pulls that resulted in the wildly different curves for the pink lines(I assume #7)?

 

[mbaird]

At this point it is just a mental excersize and a learning experience.
I am satisfied with the power output and will not spend more money on dyno time to eeke the last 35 ponies out of it. I will however try a different plug /cap and cable on 7 just for kicks.

 

[flyfish]

I would have expected ~520 ish hp with that combo. Might just be a stingy dyno (if so, no biggie, its just a tool). Just take it to the track and see what it actually does. Those heads look like they would support 600hp if you ever decide to built the engine with that as a goal.

The power peak hitting at about 6200 also sounds about right with the "small ish" cam. Strokers tend to eat duration a bit (i.e. they make their power at a lower RPM than a comparable stock stroke engine). If you put in a cam that is about 260° duration @0.05 you would push that HP curve up a fair bit (like 6800rpm)....but you would also probably need more compression to make it work well...so...yeah....Probably not worth it for a mostly street car.

Everything is tweakable, it just takes some time to iron out the kinks. Good luck

 

[mbaird]

I assume this is an overlay of two runs.

What was difference between the two pulls that resulted in the wildly different curves for the pink lines(I assume #7)?

View attachment 1715817328

We switched from an 1" open spacer to a 4 hole HMH 1" Super Sucker.

 

[PRH]

Interesting.
It doesn’t seem to have had much affect, a/f ratio wise, on the other cylinders.

What did it do to the power curve?

 

[mbaird]

I will get all the printouts when I pick up the engine on Wednesday .

Its amazing how much you learn while analyzing the data ! Assumptions I have made over the years and stuff I thought I understood go out the window . Like the fact that air and fuel can seprate when forced to abruptly change directions ... or outer runners being longer the inners even minutely can effect port flow....

 

[mbaird]

Interesting.
It doesn’t seem to have had much affect, a/f ratio wise, on the other cylinders.

What did it do to the power curve?

If you look at my power curve it increases about 4 hp per thousand starting around 4k and has a slowing trend from there. The other guys motors tend to climb at a rate of around 10-12 and taper off much slower past peak . The slowing rate of
Increase seems to mirror the afr of #7.

 

[PRH]

I have had my share of;
“Well........ that didn’t work” moments through the years.

For sure, it would have been nice to try swapping out the plug/wire/etc on the #7 cyl while it was on the dyno.

 

[PRH]

Honestly, aside from the numbers being a little shy of what I would have expected....... the only thing that stands out to me as “odd” on this sheet is how bad the bsfc numbers are.
The curve itself doesn’t seem off that much to me in light of the short cam timing.

 

[mbaird]

Honestly, aside from the numbers being a little shy of what I would have expected....... the only thing that stands out to me as “odd” on this sheet is how bad the bsfc numbers are.
The curve itself doesn’t seem off that much to me in light of the short cam timing.

View attachment 1715817336

Wouldnt the flatlining of #7 explain the poor bsfc #s ? I mean if the excess fuel ( or unburned fuel) of #7 just drag the whole curve down ?

 

[12many]

I am satisfied with the power output and will not spend more money on dyno time to eeke the last 35 ponies out of it.

That’s what test-n-tunes at the strip are for!

 

[mbaird]

That’s what test-n-tunes at the strip are for!

I have a local shop with a chassis dyno that will only charge me $100 for a session . Might be per hour but that is cheaper than going to our local track and only getting 3 runs...lol

 

[PRH]

Wouldnt the flatlining of #7 explain the poor bsfc #s ? I mean if the excess fuel ( or unburned fuel) of #7 just drag the whole curve down ?

Did the EGT show that as a dead cylinder?
It’s not like it’s EFI with an injector for each cylinder....... and one is on all the time.
The bsfc number is a reflection of the power being made and the fuel used to do it.
How is it that cylinder is getting a lions share of fuel, but the other cylinders aren’t being starved.
They’re all pulling from the same fuel source.
If it was really 10:1....... how much extra fuel would it take(lbs/hr) for that to happen on that one cylinder?
Is it enough to change the bsfc value by a full tenth(mid-5’s down to mid-4’s).

I know that had I seen those bsfc numbers, along with the overall richness of the fuel curve...... I’d have tried leaning it out to see how that might have affected the power/bsfc numbers.
Might have done something, might not have.

In order for the bsfc at peak hp to change from .534(from that screen shot) down to about .450, the fuel flow would have to drop by about 40lbs/hr(230’s down to 190’s).

 

[12many]

I have a local shop with a chassis dyno that will only charge me $100 for a session . Might be per hour but that is cheaper than going to our local track and only getting 3 runs...lol

I hear you, I’m spoiled as I’ve got three tracks about 45 minutes drive and they are $10 to run on tnt nights.

 

[PRH]

I hear you, I’m spoiled as I’ve got three tracks about 45 minutes drive and they are $10 to run on tnt nights.

Wow!!
Livin the dream!!

 

[PRH]

Here is a sheet for a 416 with a SFT cam, mild rpm heads, SV intake, 1-7/8” headers.
I considered these to be good numbers for this build, and didn’t feel like there was an issue with how the power fell off after peak.
Your motor lost about 10hp 500rpm after peak.
This one loses about 18hp 500rpm after peak.

You can see the VE numbers are dropping off hard at the top end.
It’s used up the available area of the heads, and the valvetrain has started to give up.
The cam was 265/270-106...... easy on parts lobes.

 

[rmchrgr]

Did the EGT show that as a dead cylinder?
It’s not like it’s EFI with an injector for each cylinder....... and one is on all the time.
The bsfc number is a reflection of the power being made and the fuel used to do it.
How is it that cylinder is getting a lions share of fuel, but the other cylinders aren’t being starved.
They’re all pulling from the same fuel source.
If it was really 10:1....... how much extra fuel would it take(lbs/hr) for that to happen on that one cylinder?
Is it enough to change the bsfc value by a full tenth(mid-5’s down to mid-4’s).

I know that had I seen those bsfc numbers, along with the overall richness of the fuel curve...... I’d have tried leaning it out to see how that might have affected the power/bsfc numbers.
Might have done something, might not have.

In order for the bsfc at peak hp to change from .534(from that screen shot) down to about .450, the fuel flow would have to drop by about 40lbs/hr(230’s down to 190’s).

Chasing questions from a disappointing dyno day and then trying to ascertain why you're seeing .5+ BSFC numbers after the fact over the internet.... BTDT!

It's a learning curve for sure. I've had similar, ongoing conversations with Mr. Porter here about my own bummer of a dyno session including the particular subject of not-so-great BSFC numbers. Thanks Dwayne for always being willing to lend all us rubes a hand, your insight on these subjects is appreciated.
Safe to say I know just enough to be dangerous now.

 

[Hysteric]

AFR, or Lambda alone won't tell the whole tale. Here's a good read that illustrates some concepts.
It's entirely possible the AFR is lying and that something else is going on. I've seen plugs with internal defects, impossible-to-see cracks in porcelain, or which just plain don't work under load cause a random misfire. I chased an issue like this on an engine once which would buck under high load in high gear, but nowhere else and once above 3k would be fine (and I'm sure the opposite is possible too).
Point being, like PRH is alluding too: don't lose the forest for the trees. If you can get some additional data from a gas analyzer, it might help, but I'd be swapping plugs and wires around to see if the issue follows them, or if new plugs/wires (or routing) addresses the issue. I'd even be looking at the pickup to ensure there isn't a mechanical cause for a misfire.

Very WISE words indeed. It took 3 trips to the parts store to get 8 good spark plugs that all tested correctly. I've seen half a volt drop from my alternator affect combustion enough to foul plugs and run "rich" according to the O2's.

You cant beat a gas bench for understanding what is really going on but an ignition scope will tell you plenty also.