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PostPosted: Tue Mar 20, 2012 7:39 am 
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Location: Hays, Kansas
I wonder if that big engine needs more plenum?

The vacuum pump made no difference either?

I'm wondering if that 2.50in² is killing this engine?

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PostPosted: Tue Mar 20, 2012 10:01 am 
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Location: Illinois
Gotta love injections throttle response. :)

Looks like there is some power to be had in correcting the fuel ratio after 6500. Smaller nozzle jets or a highspeed might be in order. I'd also think it would like less timing... something closer to 35*.

Did you try a bigger header? 1.875"?

You can call me to discuss

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PostPosted: Tue Mar 20, 2012 2:16 pm 
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Location: Back in the Mid West!!!
Now you can see the power and tq curve drop off.

Now would be the time to look at Headers, and pulling some timing out of it to broaden the usable tq curve to the higher rpm side.

Our 23* set up ran with timing in the 30* range.

Get yourself an EGT and get your idle at about 500* and your peak up to around 1100*.

Looks like a great place to start tuning from when it is in the car!

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PostPosted: Tue Mar 20, 2012 3:44 pm 
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Location: melbourne australia
Thanks Guys

I will be testing a set of 1 7/8step 2.0 3.5collector before i am done

And set up a high speed if needed to help fuel curve....

This engine on petrol or alcohol likes 38-40deg,,,anything under 36deg it kills a bit of power

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PostPosted: Thu Mar 22, 2012 6:11 am 
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Location: Townsville Nth Queensland Australia
If you can move that 575 ft lbs of torque curve another 1000 rpm higher where a cam of that Dur. should be peaking. and you have over 700hp at 7000 rpm. Maybe this better flowing/ speed head needs even wider lobe sep.
Also how big is the dome on the piston? 38 to 40 degrees timing sounds like old school chambers and large domes?
I'm still impressed with the output though at those rpms.
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PostPosted: Thu Mar 22, 2012 10:24 am 
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James, any progress?

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PostPosted: Fri Mar 23, 2012 8:48 pm 
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Here is the best pull after changing to a set of 1 7/8 step 2.0 pipes and a bit more fine tuning of the fuel curve.....pretty stout engine for the size of the head

Also correction factor for the day was 1.019 so around 900'

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PostPosted: Fri Mar 23, 2012 8:53 pm 
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Location: melbourne australia
Here is an overlay graph of test19(1 3/4pipes) and test26(1 7/8step pipe)

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PostPosted: Fri Mar 23, 2012 9:49 pm 
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There is still some more there!! Notice that the torque curve is flattening out and the peak is moving up...

Great Job!!!

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95 Spizter, 421" SB2.2, 1.041 60', 4.76 @ 142.85


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PostPosted: Sun Mar 25, 2012 2:37 pm 
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Location: Illinois
VERY NICE! The 1 3/4 headers were really holding it back.

What did you tweak in the fuel curve? What is the current tune-up? It is still going fat after 6400. Have you tried a bigger pill? If so, what does it do to the power upstairs? May need a high speed or smaller set of nozzle jets to extract that last 10 or so hp out of it. Depends on your answer to trying a larger pill.

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PostPosted: Sun Mar 25, 2012 3:35 pm 
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Location: Princeton WV
The head is the cork now. I am impressed with what you got out of it for that cross section. Good job.

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PostPosted: Sun Mar 25, 2012 4:07 pm 
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Best power was with a .080 jet,,,,,a .076 or a .082 hurt pk TQ,,,so i put a high speed can on main line with a .050 jet that cracks off at 65PSI...this droped 10psi fuel pressure at 7500,,,,

The high speed didnt make any more pk HP but made about 4-5more avg HP ,,,it is still going rich on lambda up top but im not sure if its safe to start going bigger than .050jet in the high speed

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PostPosted: Sun Mar 25, 2012 5:16 pm 
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Location: Illinois
You can bring it in a little earlier (lower pressure). This will make it start bypassing fuel not only a little sooner but also make sure the poppet is not restricting the flow. Right now you probably see the pressure get to and then just lay at 65psi until about 7200 or so rpms? A bigger pill won't help much right now as the poppet is the restriction until that point. We are starting to split hairs here but if you and the customer are willing to keep putting more dyno pulls on it then I think you should try to hunt down a smaller set of nozzle jets to try. Wish you were in the states... It would be easy to send you a set to try.

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PostPosted: Mon Mar 26, 2012 1:00 am 
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Using the data you provided on the motor, PIPEMAX calls for recommended CSA's of 2.63 to 2.74 so the head is likely a bit small for a 421 pulling 7k+ rpm. 2.4 is recommended smallest port CSA so 2.5" isnt bad, just not as optimal as it should be according to that program.


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PostPosted: Wed Apr 04, 2012 1:44 pm 
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Good deal on the headers..... I'm hacking up a set of Sprint Car headers right now for a DIRT Modified just for the same reasons you found, it REALLY changes the power band between the right and wrong headers.


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