Jetting questions
#2856160
12/06/20 05:51 PM
12/06/20 05:51 PM
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Joined: Jan 2007
Posts: 8,043 Mt Morris Michigan
mopar dave
OP
master
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OP
master
Joined: Jan 2007
Posts: 8,043
Mt Morris Michigan
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Here's something i would like to ask about 2 different combos requiring different jetting: Doms 470 requires more jet than my 511, why? Dom's 470 with RPM's ported, 12:1 compression, solid roller 274/280@50-.440/.427LL on 108- 61* overlap, M1 t ram, same 650 carbs as mine(1.325 venturi) 82 jet squared fenderwell header. My 511 with E MW ported, 12.5:1, SFT 270/276@50-.403/.410LL on 110-53* overlap, Indy T ram, same carbs as Dom 650(1.325 venturi) 78 jet squared , inframe headers. I would think the bigger cube higher compression motor would want more fuel, not the case. Can anyone explain why? Dom sees mid 12's on wideband in 66* weather and i see mid 13's in 50* weather WOT. My jetting should be close when the warm summer weather comes back here in Michigan and would expect 13 O range WOT.
Last edited by mopar dave; 12/06/20 06:01 PM.
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Re: Jetting questions
[Re: mopar dave]
#2856176
12/06/20 06:42 PM
12/06/20 06:42 PM
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Joined: Nov 2011
Posts: 289 PA
Harry's Taxi 2
enthusiast
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enthusiast
Joined: Nov 2011
Posts: 289
PA
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Maybe your larger engine has a stronger pull on the fuel through the boosters.
'86 Maple Grove KOS Mopar low qualifier......true street legal with no power adders.
NOS-used when losing since 1940.
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Re: Jetting questions
[Re: mopar dave]
#2856540
12/07/20 01:40 PM
12/07/20 01:40 PM
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Joined: Jul 2004
Posts: 19,318 State of confusion
Thumperdart
I Live Here
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I Live Here
Joined: Jul 2004
Posts: 19,318
State of confusion
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And like we spoke the other day, your manifold is a v-bath all sharing the same open area and my M-1 is a flat base manifold with minimal cross plenum up high for comparison almost making mine like the old IR manifolds acting more like 2 separate carbs requiring a damn near single carb tune x2. My tune now is actually more like two individual 750's as far as ifr's and jetting are concerned as opposed to dropping those down significantly like yours are tuned now however, I'm all ears here and would love other opinions cos the learning game never stops till you close the door......Remember too, I'm at 3500+ feet and run VP-101 Oxy fuel needing a richer mixture than as well and you are damn near sea lever so you would THINK i would need even less jet but not the case and why we always hear, "No two motors are the same even if built with similar components and compression...
Last edited by Thumperdart; 12/07/20 01:43 PM.
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
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Re: Jetting questions
[Re: Thumperdart]
#2856557
12/07/20 01:58 PM
12/07/20 01:58 PM
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Joined: Jan 2003
Posts: 19,384 Las Vegas
Al_Alguire
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 19,384
Las Vegas
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Many things affect the tune a carb needs, dom touched on a few. One he mentioned that I think often gets overlooked or is misunderstood is elevation, and as far as a carb is concerned it can be a BIG one. The higher up you go in elevation the lower the barometric pressure/air density becomes. For instance Vegas a great barometer is 28.00,(actual readings not the corrected ones used by your local weather man) in the midwest 29.5 is a typical good day. The lower barometer reading will require less jetting to achieve the same AFR's or tune. Not to mention the myriad of internal engine varibale that can effect the engines actual pull on the booster itself, the harder it pulls on the booster the less jet it will need in theory and vice versa.
"I am not ashamed to confess I am ignorant of what I do not know."
"It's never wrong to do the right thing"
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Re: Jetting questions
[Re: mopar dave]
#2856628
12/07/20 03:43 PM
12/07/20 03:43 PM
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Joined: Dec 2014
Posts: 304 Florida
Mark Whitener
enthusiast
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enthusiast
Joined: Dec 2014
Posts: 304
Florida
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Distribution and runner velocity are a big part of it. An engine that does both better will atomize, vaporize, and distribute better requiring less overall fuel. Then you add fuel variations, weather variation s in DA, it can be significant. Even a cam change can make a significant difference in jetting needs.
Mark Whitener [url=www.racingfuelsystems.com[/url]
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