Jeep SRT8 Dynos 355 rwhp [Archive] - Cherokee SRT8 Forum

: Jeep SRT8 Dynos 355 rwhp


John Hennessey
03-06-2006, 04:11 PM
I will post the dyno sheet tomorrow. It looks like the Jeep SRT8 makes about 10 rw hp less than the 300/Magnum/Charger.

Let the mods begin.......

BigHemi
03-06-2006, 05:22 PM
I will post the dyno sheet tomorrow. It looks like the Jeep SRT8 makes about 10 rw hp less than the 300/Magnum/Charger.

Let the mods begin.......

That was on an AWD dyno right? Did you take into account that 5-10% of the power is directed to the front wheels? Just asking...

Masta Z
03-06-2006, 06:46 PM
Lets see how these baby react to mods

John Hennessey
03-06-2006, 07:38 PM
That was on an AWD dyno right? Did you take into account that 5-10% of the power is directed to the front wheels? Just asking...

WE DISCONNECTED THE FRONT DRIVESHAFT AND DYNO'D IN RWD ON OUR DYNOJET.

tangled up in BLUE
03-06-2006, 08:58 PM
DC claims the reduced HP on the Jeep is due to the exhaust.....

John Hennessey
03-07-2006, 06:45 AM
DC claims the reduced HP on the Jeep is due to the exhaust.....

i would agree with them.

BahnBlastR
03-07-2006, 10:42 AM
So who do you guys think will be the first company will be to produce an after-market exhaust? I have contacted Borla and Zoomers to inquire where they are at with systems for the GC SRT8 and haven't gotten a response yet. Anyone have experience with either of these two products on DC vehicles?

MegaSRT-8
03-07-2006, 11:52 AM
So who do you guys think will be the first company will be to produce an after-market exhaust? I have contacted Borla and Zoomers to inquire where they are at with systems for the GC SRT8 and haven't gotten a response yet. Anyone have experience with either of these two products on DC vehicles?
I'll have dyno numbers (and video) on a system I'm getting done at a custom exhaust shop here in South Florida in two weeks. It will be a fraction of the cost with high quality materials. He'll also use any muffler/resonator system you want.

This guy currently packages SRT-4 systems for shipment all over the US, and has very reasonable prices. Don't jump on anything yet till I at least get #'s before and after his work and a final price.

Masta Z
03-07-2006, 12:29 PM
im sure magnaflow, borla will be making exhausts real soon

John Hennessey
03-07-2006, 03:07 PM
we deleted the rear mufflers and did a cold air kit and picked up 16 rw hp and 20 rw tq (371 rw hp and 375 rw tq). ported heads and torque converter go on next.

BigHemi
03-07-2006, 03:10 PM
we deleted the rear mufflers and did a cold air kit and picked up 16 rw hp and 20 rw tq (371 rw hp and 375 rw tq). ported heads and torque converter go on next.

Is this the company car you are working on?

John Hennessey
03-08-2006, 09:37 AM
Is this the company car you are working on?

this unit belongs to a dealer from the Detroit area.

bevsjeepsrt8
03-08-2006, 09:51 AM
a guy at a local shop told me that a Dynojet machine doesnt show the true RWHP the numbers are higheer than they should be. he uses a Dyno Dynamics one and people that have it done on his machine after having been on a Dynojet usually arent happy with the Hp decrease, but that is the true number.any one familiar with Dyno Dynamics

What do you guys think?

Hows2nd
03-08-2006, 09:54 AM
So who do you guys think will be the first company will be to produce an after-market exhaust? I have contacted Borla and Zoomers to inquire where they are at with systems for the GC SRT8 and haven't gotten a response yet. Anyone have experience with either of these two products on DC vehicles?

Zoomers is going to be starting on there system March 27. The system should be ready a short time later. Check out the group buy thread I just started. http://www.***********/forums/showthread.php?t=536 Check out the last few pages....

Inferno SRT8
03-09-2006, 10:36 PM
DC claims the reduced HP on the Jeep is due to the exhaust.....

Change the muffler and delete the resonators and you will be shocked, I did and im still grinning.

bevsjeepsrt8
03-13-2006, 03:57 PM
a guy at a local shop told me that a Dynojet machine doesnt show the true RWHP the numbers are higheer than they should be. he uses a Dyno Dynamics one and people that have it done on his machine after having been on a Dynojet usually arent happy with the Hp decrease, but that is the true number.any one familiar with Dyno Dynamics

What do you guys think?


ANYONE?????

Rboosted717
03-13-2006, 05:38 PM
a guy at a local shop told me that a Dynojet machine doesnt show the true RWHP the numbers are higheer than they should be. he uses a Dyno Dynamics one and people that have it done on his machine after having been on a Dynojet usually arent happy with the Hp decrease, but that is the true number.any one familiar with Dyno Dynamics

What do you guys think?

Of course a dyno dynamics owner will tell you that! hahaha

Put it this way, a Dynojet is the only dyno that 99% of racing organizations will use and is known by the REAL automotive industry to be the standard or baseline for dyno readings. If you ever looked at a baseline run of a bone stock car, it will read exactly what the power should be after drivetrain loss. EX: A 3.0 '95 E36 BMW M3 makes 240hp (engine rated). On a Dynojet it will read 200-210whp (varies on the motors condition). The difference between wheel hp and engine hp is the exact amount of power loss from the cars drivetrain. On many dyno's (dyno dynamics, dynapak, mustang dyno, etc...) the power/trq readings will either be lower or higher then what the true drivetrain loss should be. Only the dynojet (using the appropriate dyno, environmental conditions, etc...) will yield this precise result.
Additionally, a dynojet is a lot harder to fudge the numbers since the dyno operator does not have to enter in car weight, gearing, etc... This is the case on Dynojet's using Winpep 6 or 7 dyno software. Older dynojet software allows the operator to adjust the variables, hence why Dynojet updated the newer software to not be user adjustable.

Also a dynojet will read abnormal is if your using a Dynojet with small rollers that are typically used for low horsepower setups. Additionally, a Dynojet can read abnormal if the correction factor is too high or too low. The correction fact on a Dynojet is calculated by altitude, barometric pressure, humidity and air temp.

Here's how the correction factor works:
On a dynojet if you have a .98 correction factor, that mean the dyno software will take off 2% from your horsepower reading. This is typically seen if you dyno is very cold conditions or conditions that are better then typical.
If your correction factor is 1.03, then the dyno software is giving you a 3% increase to your horsepower reading. This happens if you dyno at very high altitudes, hot conditions, high humidity or conditions that are worse then typical.
As for correction readings and dynoplot reading here's what I know:
The SAE factor is the industry standard and is more of a middle-road reading in terms of correction. If you look at the print out using the "conditions" view, you will see how much correction factor is being applied to your dyno run.

The STD factor is more of a high-road reading in terms of correction factors. Often the STD will always give a higher horsepower reading to your dyno run.

The Uncorrected factor is your dyno run without any correction calculations applied. Depending on your environment conditions, this factor can either read higher or lower then the SAE or STD factor.

Also remember that some shops can also trick dyno readings by blowing hot air from a hair dryer or heat gun on the dyno calibration equipment. Doing this will make the dyno software think the air temp is extremely hot.

Also some shops will also dyno in rooms that are air conditioned so that the engine takes in very cold air and will set the dyno to use an "Uncorrected" factor so that the dyno does not take away power due to the cold conditions.

Also sometimes the shops will let off the gas or will slam the clutch in a second before the gas to cause a "spike" or slight increase to the peak horsepower reading since 99% of the consumers read only the peak power.

Another trick is some shops when comparing before and after dyno's, they will use the worst before dynorun (typically the run with the most heat soak or poor tune) and will compare it against an "after" dynorun that will typically be the best (with the best engine conditions (colder and perfectly tuned). Doing this gives the customer the impression of HUGE power gains when it may only by a few horsepower or none at all (I see this 95% of the time in the aftermarket industry).

Also on various dyno brands, older dynojets or old dyno software, some shops will “tweak” the preset and user adjustable settings to increase or decrease the dyno readings (EX: alter dyno drum weight, car gearing, car weight, etc...)

I have operated almost every type of dyno and I can tell you first hand that no matter the dyno, a shop can always "tweak" the horsepower numbers. Also it is very hard to compare two different dynoruns from different dynoshops with different or the same dyno. Even comparing dynoruns from different days on the same dyno can be hard. THE KEY RULE is to ONLY look at the power curve and trq curve, rather then just the peak number. I see consumers doing this 99% of the time and it is the stupidest thing one can do. The peak number means NOTHING!!! The curve of the reading is what really matters.
IMO the best dyno and dyno software to use is a Dynojet 248H, 248X or the AWD Dynojet 424X. As for dyno software I like the Dynojet Winpep 6 or 7. Anything older then Winpep 6 which gives dynoshops too many variables to adjust (causing inconsistent readings).

I hope that helps and clears up some of the confusion with Dyno's and Dyno readings. Remember the only thing that really matters is the shape of the curve and the back to back results on the same dyno, same conditions, with everything being equal minus the changed or desired modification.

cheukinjapan
03-13-2006, 05:46 PM
ANYONE?????

Dynojets are inertial only dynos. That is, the car accelerates a standard weight... the drum that the wheels are resting on. In most cases, it is around 2800-3000 lbs. Of course, the 4WD Dynojets have two drums... front and back... The total inertial weight accerated is anywhere from 4500-6000 lbs.(Depending on the model number of the front unit) Also, the load is not variable... that is the weight of the drums remain the same. So you can only perform acceleration runs.

Dyno dynamics and many other dynos are variable load dynos. Most use a variable load motor / water brake +/- a standard smaller inertial load.
The advantages are you can vary the load so that you can make slower or non acceleration runs... useful for easier tuning of specific points on an ECU. Also the Load can be adjusted to the exact weight of the vehicle... so that the wheels will be accelerating against a load equal to the car/truck that engine is in.

Now what does all that mean. It means that if the car/truck is heavier than 3000 lbs, the numbers on a dynojet will probably read high. But if the load on a dyno dynamics unit is not adjusted it may also read high or low. Also the computation required to determine hp on a system using both an inertial and a variable load motor is a bit more complicated and has more "fudge" factors.. so there is some additional errors there. Dynojet also has a optional variable load add on that most shops do not purchase.

The big thing to remember is to run the car on the same dyno using the same load. Power gain is the goal... not a specific number. It is very easy to adjust a couple of parameters on a dyno to get huge numbers to graph out.

Cheuk in Japan
GC SRT8 (on order)
E46 M3 Cab
R171 SLK 350 (wife's car)
R1 Single Turbo RX-7 (443 RWHP in storage)

Rboosted717
03-13-2006, 05:53 PM
Dynojets are inertial only dynos. That is, the car accelerates a standard weight... the drum that the wheels are resting on. In most cases, it is around 2800-3000 lbs. Of course, the 4WD Dynojets have two drums... front and back... The total inertial weight accerated is anywhere from 4500-6000 lbs.(Depending on the model number of the front unit) Also, the load is not variable... that is the weight of the drums remain the same. So you can only perform acceleration runs.

Dyno dynamics and many other dynos are variable load dynos. Most use a variable load motor / water brake +/- a standard smaller inertial load.
The advantages are you can vary the load so that you can make slower or non acceleration runs... useful for easier tuning of specific points on an ECU. Also the Load can be adjusted to the exact weight of the vehicle... so that the wheels will be accelerating against a load equal to the car/truck that engine is in.

Now what does all that mean. It means that if the car/truck is heavier than 3000 lbs, the numbers on a dynojet will probably read high. But if the load on a dyno dynamics unit is not adjusted it may also read high or low. Also the computation required to determine hp on a system using both an inertial and a variable load motor is a bit more complicated and has more "fudge" factors.. so there is some additional errors there. Dynojet also has a optional variable load add on that most shops do not purchase.

The big thing to remember is to run the car on the same dyno using the same load. Power gain is the goal... not a specific number. It is very easy to adjust a couple of parameters on a dyno to get huge numbers to graph out.

Cheuk in Japan
GC SRT8 (on order)
E46 M3 Cab
R171 SLK 350 (wife's car)
R1 Single Turbo RX-7 (443 RWHP in storage)


I agree, the main aspect to remember is to never compare another persons dynorun to yours, never just look at peak power and by all means ask questions and ask for multiple print-outs of various correction factors (SAE, STD and Uncorrected). Also ask for a print out showing the dynorun conditions and dynorun setup/settings. Doing this will allow you or others to see if the shop is "tweaking" your results.

As for load dyno's or load tuning, I personally would rather test the car at the track or in the real conditions rather then trying to simulate all aspects of the conditions on a dyno. A dyno should only be used for testing the power/trq curve at full throttle and to allow the setup to be tuned accordingly to achieve the desired results. After that, road testing and real-world testing/logging should be carried out since load and conditions will change will every track, altitude, turn, traction, etc...

A good dyno tuner should obvisouly be able to tune the car correctly at wide-open throttle on the dyno. Additionally, a good tuner should also be able to get a close idea or exect idea of what the tune should be at other loads/conditions (don't forget most modern EMS's (engine management computer systems) will also adjust to various conditions. I personally race 850+whp drag cars, low & high powered road race cars on EMS's system ranging from stock setups to MoTec setups and have never had a tune go wrong as long as the tuner adjusted the program correctly for the applicable conditions.

John Hennessey
03-14-2006, 05:37 PM
its not really important what the actual measured dyno number is. what is important is that the test equipment is able to measure power in a repeatable and consistent way. dynojets have a strong reputation for being able to do this.

so if the dynojet says 355 rw hp stock and then you make some mods and get 385 rw hp - you know you gained 30 to the tires. dynojet is and will continue to be the benchmark of how power is measured amongst tuners and enthusiasts. mustang dynos are also getting more popular and do a great job too. as long as you are comparing dynojet vs dynojet numbers, etc. then the data compared can be very accurate.

whats important is the delta - the change in before and after.

bevsjeepsrt8
03-15-2006, 02:39 PM
thank's for all the input guy's...as soon as i get some miles on my ride I will get it dyno'd and post the results.

carazyguy
03-21-2006, 06:14 AM
So who do you guys think will be the first company will be to produce an after-market exhaust? I have contacted Borla and Zoomers to inquire where they are at with systems for the GC SRT8 and haven't gotten a response yet. Anyone have experience with either of these two products on DC vehicles?


I have an SRT-4 and have the full borla system on my car, you can't buy it from no where other than through your dealer. I have the mopar cat-delete and cat back which is a full exhaust and its made all by borla, it even has borla on the tips, however if you go to their site they don't list it because it is licensed by mopar.

Good product and sounds and flows better than the competitors, however most srt4 owners are cheap and won't pay a little extra for quality.

Red SRT-8
03-21-2006, 08:38 AM
its not really important what the actual measured dyno number is. what is important is that the test equipment is able to measure power in a repeatable and consistent way.

John is 100% right. Dynos are first and foremost diagnostic tools. Too many times we get in a peeing contest and try to get the highest number possible simply for bragging rights. Those numbers are only good for getting a rough idea of performance. You can't compare dyno results taken from different dynos in different locales on different days. There are too many variables. It's easy to even get different results on the same dyno on the same day by simply tightening or loosening the tie down straps. Some less than honest companies take advantage of this to inflate the power gains of their products. But, any decent dyno in the hands of a good operator/tuner like John H. is invaluable and an essential tuning tool to get the most out of a particular vehicle.

I own a dyno shop and use a Dynapack Dyno. It's somewhat newer technology out of New Zealand that eliminates most of the variables that limit accuracy in inertia dynos. My dyno doesn't use a roller of any kind as it couples directly to the wheel hubs. This kind of dyno has been popular with F1 racing, Rally, Touring Car, etc., etc. throughout Europe and the Southern Pacific for quite awhile and is now being used by several NASCAR teams including the Pettys. You can learn more about this kind of dyno at http://www.dynopak.com if any of you are interested.

BTW, if any of the forum members here are ever passing through or live in Utah, come on by for a free dyno pull.

ekool
03-24-2006, 04:29 PM
WE DISCONNECTED THE FRONT DRIVESHAFT AND DYNO'D IN RWD ON OUR DYNOJET.

John,

How long did it take you to disconnect the front driveshaft?

John Hennessey
03-26-2006, 10:53 AM
John,

How long did it take you to disconnect the front driveshaft?

maybe 30 minutes?

Red SRT-8
03-27-2006, 06:40 AM
I have an AWD dyno and will put my Jeep on there after it's good and broke in. We'll be able to see how much power goes to each wheel.

MegaSRT-8
03-27-2006, 11:03 AM
I have an AWD dyno and will put my Jeep on there after it's good and broke in. We'll be able to see how much power goes to each wheel.
Here's what I got last week on an AWD dynojet. I'm in South Florida, and the temps ranged from 93 - 99 degrees inside the ******, and the humidity was around 25%. So the numbers are a little low.

Dynojet Results w/ 981mi on the odometer - BONE STOCK

2nd Gear:
- Max total tq = 329.81@4850rpm
- Max total hp = 342.06@6000rpm

3rd Gear:
- Max total tq = 346.07@4800rpm
- Max total hp = 348.99@6000rpm

4th gear: Top speed = 138mph (IT WAS VERY LOUD AT THIS POINT!!!!)
- Max total tq = 340.64@4750rpm
- Max total hp = 337.75@5700rpm

He said the torque came 90% from the rear wheels. The horse power was almost split even - 178hp rear vs 170hp front.

MegaSRT-8
03-27-2006, 11:06 AM
Here's some phone pics of the truck on the dyno
http://www.cherokeesrt8.com/forums/attachment.php?attachmentid=16&d=1143042144
http://www.cherokeesrt8.com/forums/attachment.php?attachmentid=17&d=1143042158

and a video from phone (poor quality - and tiny)
http://media.putfile.com/GC-SRT8-on-the-dyno

goldsgym
04-02-2006, 05:04 PM
Is it too loud or just right?

Sgt Stanko
05-01-2006, 09:25 PM
we deleted the rear mufflers and did a cold air kit and picked up 16 rw hp and 20 rw tq (371 rw hp and 375 rw tq). ported heads and torque converter go on next.

I sure am glad it is now MAY 2006 and we are all alot smarter and experienced than to believe you picked up 16/20 with removing the resonators. I know for a fact this claim is impossible. The resonators are flow thru, the front muffler has two chambers one is flow thru the other has a block or diverter and prevents the driver side from being flow thru. It does however share the same chamber with the first tube and a 2nd tube that connects to the final exhaust pipe.

After dyno runs with the stock vs "other" exhausts some made less than stock and others at most made 5 hp................so what you are saying is the stock system is the best...............save your money!!!!!!!

ARH1956
05-02-2006, 05:26 AM
I sure am glad it is now MAY 2006 and we are all alot smarter and experienced than to believe you picked up 16/20 with removing the resonators. I know for a fact this claim is impossible. The resonators are flow thru, the front muffler has two chambers one is flow thru the other has a block or diverter and prevents the driver side from being flow thru. It does however share the same chamber with the first tube and a 2nd tube that connects to the final exhaust pipe.

After dyno runs with the stock vs "other" exhausts some made less than stock and others at most made 5 hp................so what you are saying is the stock system is the best...............save your money!!!!!!!How much HP did your Zoomer's cat-back make?