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donwhis 05-06-2013 02:30 PM

Dyno run question
 
I just had my car on a dyno (rear wheel) and it showed lower numbers than I expected. Without going into the detail of the engine I bought it came with a dyno report that I assume was a computer model of the build.

The computer model, I don't have it in front of me right now, showed to to make over 500HP. The rear wheel dyno showed 317HP and 355 torque.

Should I expect that much loss through the drive train?

The dyno was performed by the Carol Shelby Automotive school at a local community college on a Dynojet Research machine. 2 runs were recorded and they were within 5 points of each other.

cmefly 05-06-2013 03:34 PM

Re: Dyno run question
 
Quote:

Originally Posted by donwhis (Post 1809442)
I just had my car on a dyno (rear wheel) and it showed lower numbers than I expected. Without going into the detail of the engine I bought it came with a dyno report that I assume was a computer model of the build.

The computer model, I don't have it in front of me right now, showed to to make over 500HP. The rear wheel dyno showed 317HP and 355 torque.

Should I expect that much loss through the drive train?

The dyno was performed by the Carol Shelby Automotive school at a local community college on a Dynojet Research machine. 2 runs were recorded and they were within 5 points of each other.

That would equal about 400 at the crank. I would not worry about the low numbers. rear wheel dynos are great for tuning. take it to the track with some sticky tires and then you will see how much power it makes. How about some specifics on the engine. Did you make any changes with the jets and timing?

donwhis 05-06-2013 05:57 PM

Re: Dyno run question
 
I will get back with you in a couple of days with the engine build specs, it is in another city right now.

donwhis 05-08-2013 09:12 AM

Re: Dyno run question
 
Here is the 460 engine build:

Stock block 30 over
Ported iron heads with stainless valves 2.19 int and 1.76 exh, pocket porting
Comp cams roller rockers with stud conversion, push rods
Torker II intake with heat cross over welded up
Stock Crank
Hypereutectic pistons
Stock Rods with ARP hardware
Lunati Bracket Master II #00097 with .554 lift on int and exh
Hydraulic flat tappet lifters
Engine was balanced
FPA shorty headers
Holly 80508S carb
Stock C6
3:50 mini spool Ford 9"

donwhis 05-08-2013 09:15 AM

Re: Dyno run question
 
Forget all of your question:

Did not change or mess with the Holley in any way, it is out of the box.

I did set the timing to 13 degrees, I forgot if it was advanaced or retarded (like Me).

PSIG 05-08-2013 10:43 AM

Re: Dyno run question
 
You have losses. Some in the driveline, and some in tuning. You already know this, but running on a chassis dyno is nearly useless without testing changes for relative effect. The Shelby guys should know this, and should know this is not how a chassis dyno is used. All you got was a sheet of paper that says you need to work on it. Can you get a block of dyno time to make the exercise worthwhile?

David

donwhis 05-08-2013 01:02 PM

Re: Dyno run question
 
PSIG, to be fair to the Shelby guys they were offering 2 pulls for $35 which all went to charity for the car show they were hosting. And - I didn't understand how a chassis dyno was used, like other novices I just heard people quote their HP and TQ from having their car tested on a dyno.

It makes all the sense in the world to use the numbers generated as a bench mark for changes made to see if things got better or worse. I got it!

I will ask about a block of hours, but since they are a full time teaching school I am not hopeful they will do it.

PSIG 05-08-2013 01:57 PM

Re: Dyno run question
 
I hear ya. But, they could use your car to teach basic adjustments and reading results on a classic old-school setup to the students. Basic real-world stuff. Maybe some emissions-tuning instruction as well.

If their students are going into the performance market for jobs, learning how to do this to your volunteered carb-and-distributor car would be a basic prerequisite to gainful employment. I assume they are not just turning-out graduates that only understand tuning with a laptop. Give it a shot - for the kids, ya know. ;)

David

teyerdhal 05-10-2013 01:17 AM

Re: Dyno run question
 
Did you check if carb butterflies were fully open during the dyno run?
It is a common mistake (bad linkage issue)...

Hottarod 05-11-2013 09:58 PM

Re: Dyno run question
 
80508S is a vacuum secondary Holley 750. Comes with 70 primary jets and equivalent secondary plate to a 75 jet. I am going to guess that you were a NUDGE lean with that.

Lunati cam, 292 advertised, 1800 to 6000. With your carb like that I don't think you could pull to 6000. It probably runs out at less than 5000. The rest looks ok to me.

Initial timing might help to be bumped to 16 or so but it depends on your compression ratio.

donwhis 05-12-2013 07:32 AM

Re: Dyno run question
 
The MSD started cutting out cylinders at around 5500 RPM on the dyno. I had the timing at 16 but it was pinging so I turned it back to 13, I think. I need to check it again. I don't know for sure what comp ratio it has, but the computer model I got with the engine used 10/1 ratio.

n2omike 05-12-2013 07:50 AM

Re: Dyno run question
 
What sort of exhaust is on the car? A big 460 like that needs 3" mandrel bent pipe, and mufflers you can see straight through. If you have small crush bent pipe and restrictive mufflers, it won't run anywhere near its potential.

PSIG 05-12-2013 11:35 AM

Re: Dyno run question
 
Quote:

Originally Posted by donwhis (Post 1815338)
The MSD started cutting out cylinders at around 5500 RPM on the dyno...

How do you know it was the MSD cutting-out cylinders?
http://i.imgur.com/GQaEv.gif
David

PS: Can you post scans of the dyno pulls?

donwhis 05-13-2013 11:51 AM

Re: Dyno run question
 
I have 2" exhaust pipe from the FPA headers back with Magnaflow mufflers.

When I heard the cylinders banging at the end of the pull I said something to the instructor about valves floating. He said no it was the MSD dropping cylinders to limit the RPM and I do remember putting in the RPM limiter plug when I installed the box, I think it was 5500 or 6000.

I will post the dyno chart later this week. It also has the air/fuel mixture shown.

Thanks for all the feedback.

n2omike 05-13-2013 01:31 PM

Re: Dyno run question
 
Quote:

Originally Posted by donwhis (Post 1816546)
I have 2" exhaust pipe from the FPA headers back with Magnaflow mufflers.

The tiny 2" exhaust is costing you BIG power behind a warmed up 460! You need no less that 2.5" with see through mufflers, and preferably 3".

Cross sectional area of different sized pipe:

2.0" = 3.14 sq in
2.5" = 4.91 sq in
3.0" = 7.07 sq in

With 2" pipe, you are WAY under sized!


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