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  Jetting the 408w w/o power valves?

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Author Topic:   Jetting the 408w w/o power valves?
steve'66
Gearhead

Posts: 9533
From: Sonoma,CA,USA
Registered: Mar 2000

posted 06-27-2002 08:54 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
The 408w has been leaving the line inconsistantly based on how long it's on the two step. So, I pluged both power valves in the 850dp'r. The stock jets were 80's squared, so I put 83s in the front and 85s in the back. When it was stock w/pv's and 80s it had 2 1/2 threads of gray. So, do you all think this will be close? Or what you'd you suggest as a starting point for this motor? Thanks!

SteveW

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Dave_C
Gearhead

Posts: 1069
From: Gadsden, Al
Registered: Aug 99

posted 06-27-2002 09:23 PM     Click Here to See the Profile for Dave_C   Click Here to Email Dave_C     Edit/Delete Message   Reply w/Quote
That should be very close. I have my 950Hp jetted at 83/84 w/o pv's.

Going to get a EGT setup before the next race so I can verify and go up or down as needed.

Later,

David Cole

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steve'66
Gearhead

Posts: 9533
From: Sonoma,CA,USA
Registered: Mar 2000

posted 06-27-2002 10:45 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
Dave,

Thanks! I would have liked to pump a little more fuel into it, but that was the end of my jet assortment on the big end. We'll only have 3 shots at it Wednesday night and then we'll leave it alone for the 4th's bracket race. We never did make it out to a TnT at Sac Raceway where the track is much stickier.
Oh well, we'll get it dialed later this summer.
I picked up 50 pounds of ballast today too...

SteveW

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67Coupster
Gearhead

Posts: 189
From: Fortson, GA, USA
Registered: Oct 2001

posted 06-28-2002 08:47 AM     Click Here to See the Profile for 67Coupster   Click Here to Email 67Coupster     Edit/Delete Message   Reply w/Quote
Let us know how the jetting works out. Sounds like we have the same carb. My 850 was 80 squared also. I removed only the rear PV and installed jet extensions. Currently my jetting is 82/90. I'm thinking I have it a little on the fat side. Just wanted it safe while dialing in the suspension. Later!!

------------------
James
67 Coupe
393W, 4 Speed,
7.07 @ 98MPH 1/8
1.52 60'
'66 Fairlane 500XL
Daily Driver

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MDF99
Gearhead

Posts: 234
From: Hamilton, Ohio, USA
Registered: May 2001

posted 06-29-2002 08:12 AM     Click Here to See the Profile for MDF99   Click Here to Email MDF99     Edit/Delete Message   Reply w/Quote
Is it fairly standard procedure in drag car tuning to remove both power valves? I understand removing the 2ndary power valve and increasing jet size there to compensate because it'll only be open when your at full throttle. It seems like you'd want to keep the primary power valve in place, otherwise the motors gonna be running rich at partial throttle and possibly fouling plugs, like when youre just cruising after a run or staging?

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Dave_C
Gearhead

Posts: 1069
From: Gadsden, Al
Registered: Aug 99

posted 06-29-2002 10:03 AM     Click Here to See the Profile for Dave_C   Click Here to Email Dave_C     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by MDF99:
Is it fairly standard procedure in drag car tuning to remove both power valves?

It can be done either way. If you launch with a Two Step rev limiter it is best to remove both power valves. If you launch w/o one then leave the front PV in.

When you are on the two step you are sitting there with your foot to the floor, throttle blades wide open, but the revs won't go any higher than whatever the chip is. Say 4000 rpm. The throttle blades all the way open causes the vac to go to 0 and the PV's dump all that extra gas into the engine because of the false vac signal. Makes it run pig rich and tends to wash the cylinders, foul plugs, etc. So you just remove them. Runs rich at idle and around the pits, but better on the track.

A foot-brake only car can leave the front pv in because when you slam the throttle open on lauch the engine *can* use the extra gas then.

Later,

David Cole

[This message has been edited by Dave_C (edited 06-29-2002).]

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MDF99
Gearhead

Posts: 234
From: Hamilton, Ohio, USA
Registered: May 2001

posted 06-29-2002 11:44 AM     Click Here to See the Profile for MDF99   Click Here to Email MDF99     Edit/Delete Message   Reply w/Quote
Right on, that makes sense.

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steve'66
Gearhead

Posts: 9533
From: Sonoma,CA,USA
Registered: Mar 2000

posted 06-29-2002 10:22 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
Dave and James,

Thanks for the tips and for explaining it to Matt. I have a pair of 88's now if the need arrises next Wednesday. It won't be that dense of air on July 3rd. It'll probably be about 2000ft d/a out there. I got the 50#s of ballast installed behind the tank's filler neck, so that should help with the traction. It's our last shot at the $20 contest so..... (actually July 4th is but we won't be TnT'ing on the bracket race day)

SteveW

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kid vishus
Gearhead

Posts: 6590
From: middle of NC
Registered: Oct 2000

posted 06-29-2002 10:35 PM     Click Here to See the Profile for kid vishus   Click Here to Email kid vishus     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by steve'66:
It'll probably be about 2000ft d/a out there.

I wish our d/a was "that bad" in July.

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steve'66
Gearhead

Posts: 9533
From: Sonoma,CA,USA
Registered: Mar 2000

posted 06-29-2002 10:41 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by kid vishus:
I wish our d/a was "that bad" in July.

Rob,

I'm just guessing! LOL
It could be 3600 like it is now.

SteveW

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steve'66
Gearhead

Posts: 9533
From: Sonoma,CA,USA
Registered: Mar 2000

posted 07-04-2002 06:40 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
Well the 60'ers are more consistant now. Consistantly bad 1.66-1.78.
The jetting is about perfect with 83s in front and 88s in the back w/o power valves in 1000' d/a air. FWIW

SteveW

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