Dyno Test

[richardtys]

It's basically a garage queen with 7.7k miles.
632 rwhp, 548 lb-ft.
Dyno graph and video shown below, not sure if it makes good Air/fuel ratio.



IMG_1353.jpg

[sharmut]

Any power mods? CAM/heads/header.

[serpent]

Is this Viper Exchange H&C or Calvo's?

[richardtys]

ViperExchange stage II pack. C&H, ARH headers, Venom 2 RCM

[richardtys]

Is this Viper Exchange H&C or Calvo's?

ViperExchange stage II, advertised at around 733bhp I remember

[Stealth78]

Doesn't 632 seem kind of low for a H/C car on a Dynojet Dyno (speculating as I saw that banner on the wall)?

[Nth Moto]

Doesn't 632 seem kind of low for a H/C car on a Dynojet Dyno (speculating as I saw that banner on the wall)?

No, not necessarily.

[LmeaViper]

Looks like around 13 for the AFR, one of the tuners can chime in better, however I would think that is on the upper end for an NA Viper???? Can you advise what octane you are running too.

[Jack B]

Looks like around 13 for the AFR, one of the tuners can chime in better, however I would think that is on the upper end for an NA Viper???? Can you advise what octane you are running too.

The AF is actually leaning out above 5000. it looks to be above 13:1. There is some hp to be gained. It is hard to tell why HC cars start to lean out, it looks like either the injectors or pump are at the edge.

I pulled my pump recently and did not like the way the pump filter looked. I cannot say for sure, but, it looked as though it was could be restricting the flow. At the end of last year there were times the car would run a solid 12.2-12.4, then, I would see 13.1, this never made any sense to me.

[Scot@Prefix]

Here is a quote from a recent tech article:

the stoichiometric air-fuel ratio (14.7:1) that is the ideal ratio for lowest emissions, but this isn’t the best ratio for power. It used to be that 12.5:1 was considered the best power ratio, but with improved combustion chambers and hotter ignition systems, the ideal now is around 12.8:1 to 13.2:1. This is roughly 13 parts of air to one part fuel. It’s what combustion engineers call an excess fuel ratio and is intended to ensure that all the air is used to support the combustion process. This is because air is the oxidizer in combustion. Too many enthusiasts think that adding additional fuel beyond the ideal to create a richer mixture will make more power.

[richardtys]

Looks like around 13 for the AFR, one of the tuners can chime in better, however I would think that is on the upper end for an NA Viper???? Can you advise what octane you are running too.

I was using 92 octane(there are no 93s in Seattle area) mixed with 100 racing fuel. I think I mixed too little 100 octane in it then, it was like 12 gallons of 92 and 1 gallon of 100 octane.
The car has Arrow Venom II RCM, so it has a 93 octane tune.

[Whitey]

No, not necessarily.

Right.....

[Nth Moto]

The AF is actually leaning out above 5000. it looks to be above 13:1. There is some hp to be gained. It is hard to tell why HC cars start to lean out, it looks like either the injectors or pump are at the edge.

I pulled my pump recently and did not like the way the pump filter looked. I cannot say for sure, but, it looked as though it was could be restricting the flow. At the end of last year there were times the car would run a solid 12.2-12.4, then, I would see 13.1, this never made any sense to me.

We have to change the injectors on our head/cam cars. The factory fuel pressure control is just this side of atrocious to be honest, which doesn't help matters when trying to use 10/10's of available flow capability.

[Jack B]

We have to change the injectors on our head/cam cars. The factory fuel pressure control is just this side of atrocious to be honest, which doesn't help matters when trying to use 10/10's of available flow capability.

Aaron/Scott:

Can you answer the following riddle:

1. When the car was pre HC (with a tune), I thought the AF was predictable. At the track and WOT the AF would be approx 12.8-13.0. I would go to the dyno and it would be 11.9-12.1. The assumption was the ram air was leaning the car out. These numbers were at the same air temps and approx 600 rwhp.

2. The car now is HC/9L. As previously stated, most recently (end of 2017):

A. On the dyno it is +13.0.

B. At the track the AF is a flat line in the low 12's. These were also at similar temps. These numbers are not a one time event, the above stated numbers are very repeatable.

Any insight?

[Nth Moto]

Aaron/Scott:

Can you answer the following riddle:

1. When the car was pre HC (with a tune), I thought the AF was predictable. At the track and WOT the AF would be approx 12.8-13.0. I would go to the dyno and it would be 11.9-12.1. The assumption was the ram air was leaning the car out. These numbers were at the same air temps and approx 600 rwhp.

2. The car now is HC/9L. As previously stated, most recently (end of 2017):

A. On the dyno it is +13.0.

B. At the track the AF is a flat line in the low 12's. These were also at similar temps. These numbers are not a one time event, the above stated numbers are very repeatable.

Any insight?

Jack,

Your idea about the car in stock configuration (reference point 1) is valid and confirmed on our end. As far as reference point 2, that's hard to say given that will likely vary depending on calibration strategies being utilized. I wouldn't expect it to be different on your current tune unless that's a function of MAF range being seen in dynamic operation as opposed to static on the dyno. Typically that wouldn't make sense to me still seeing as that's usually fairly linear, but perhaps Scott can give you some insight on that better than I can.

[KB Viper]

Right.....

with your extreme 9.0 are you on stock injectors? hard to believe Arrow would leave HP on the table to avoid a injector swap that they would be paid to do...

[Jack B]

Jack,

Your idea about the car in stock configuration (reference point 1) is valid and confirmed on our end. As far as reference point 2, that's hard to say given that will likely vary depending on calibration strategies being utilized. I wouldn't expect it to be different on your current tune unless that's a function of MAF range being seen in dynamic operation as opposed to static on the dyno. Typically that wouldn't make sense to me still seeing as that's usually fairly linear, but perhaps Scott can give you some insight on that better than I can.

Aaron

The rpm's are logged in a different range.

Dyno: 3k to 6K

Track: 5K to 6K

The acceleration rate would be way different.

[Steve M]

Does the car have cats or no? Was it a tail pipe sniffer for the wideband on the dyno?

That AFR on the dyno would make me a little nervous - it's going lean up top, and I'd want to know if it was doing the same on the street. I'm aware of some heads/cam cars that have needed a bigger fuel pump due to the stock one not keeping up with the demand, and if it were my car, that AFR would make me wonder if mine did too.

[richardtys]

Does the car have cats or no? Was it a tail pipe sniffer for the wideband on the dyno?

That AFR on the dyno would make me a little nervous - it's going lean up top, and I'd want to know if it was doing the same on the street. I'm aware of some heads/cam cars that have needed a bigger fuel pump due to the stock one not keeping up with the demand, and if it were my car, that AFR would make me wonder if mine did too.

Hi steve,
No cats, ViperExchange titanium catback. All included in stage II package.
It has a Arrow Venom stage II tune up to 93 octane. I think I mixed too little higher octane with Seattle's 92 prior to those runs, will prob. mix more 100 octane and see if the AFR changes.

[kriskyk]

Pretty sure that higher octane fuel of the same or similar fuel density will not have a significant change to AFR?

[Whitey]

with your extreme 9.0 are you on stock injectors? hard to believe Arrow would leave HP on the table to avoid a injector swap that they would be paid to do...

Stock injectors - 810bhp.

Aaron,
Have you run a H/C car on the dyno and swapped out the injectors (stock vs performance injectors)? Have you seen any performance gains or losses?

[Jack B]

Pretty sure that higher octane fuel of the same or similar fuel density will not have a significant change to AFR?

It can change the stoic point, but, that volume is not a factor

[kriskyk]

Not challenging that, but can you clarify so I can better understand?

[Jack B]

Take a look at the stoic number for various types of race gas, it is not 14.7. If the software that interprets the WB is not adjusted, the AF does not display correctly, therefore, the tune is off.

[kriskyk]

Ahh interesting I just assumed that stoic was the same or very similar for most gas and didn't change until you got into ethanol or some other exotic fuels....