MP 472 crate motor performs poorly in my 70 Challenger
#611895
02/12/10 09:46 PM
02/12/10 09:46 PM
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Joined: Feb 2010
Posts: 13 Jacksboro, TX
rodthedeerguy
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OP
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Jacksboro, TX
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I have a 70 4-spd 3.54 Dana Challenger. I can not get this car to leave at the strip without bogging, loading up and/or hesitating. I have changed timing, carbs, ignition, launch rpm, slipping the clutch...everything. When you "rap" the carb from off idle to full throttle you can see a noticeable spray of gas like a back fire out of the primaries of the carb. It is a stumble that I can not tune out. I am wondering if this may be the result of a bad combination of cam, intake, low compression and pump gas, etc. that is inherrant in this motor from Mopar. For 525hp/540tq, this motor runs like crap. Any ideas? I am an older guy new to forums. This is my first post ever! Take it easy on me.
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Re: MP 472 crate motor performs poorly in my 70 Challenger
[Re: rodthedeerguy]
#611896
02/12/10 10:02 PM
02/12/10 10:02 PM
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Joined: Dec 2007
Posts: 10,542 BROOK PARK, OH
WILD BILL
Senior Member of the Junior Dragster Club
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Senior Member of the Junior Dragster Club
Joined: Dec 2007
Posts: 10,542
BROOK PARK, OH
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I was going to suggest a carb problem but it looks like you looked into that.
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Re: MP 472 crate motor performs poorly in my 70 Challenger
[Re: WILD BILL]
#611899
02/12/10 10:10 PM
02/12/10 10:10 PM
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Joined: Sep 2005
Posts: 12,481 Chino Valley
RodStRace
I Live Here
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I Live Here
Joined: Sep 2005
Posts: 12,481
Chino Valley
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Welcome ol' dude! Sounds like it needs a serious tune-up. A few questions to start, so the really smart guys here can weigh in. Initial timing, and total timing (no vacuum advance)? Is the vacuum advance connected to manifold or ported vacuum? Brand and size of carbs, and jetting? any other particulars that were changed or added to the crate motor. When was the motor purchased, and built? There were some issues with crate Hemis before, so this may be important.
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Re: MP 472 crate motor performs poorly in my 70 Challenger
[Re: rodthedeerguy]
#611903
02/12/10 11:23 PM
02/12/10 11:23 PM
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Joined: Dec 2007
Posts: 10,542 BROOK PARK, OH
WILD BILL
Senior Member of the Junior Dragster Club
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Senior Member of the Junior Dragster Club
Joined: Dec 2007
Posts: 10,542
BROOK PARK, OH
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Thanks
Now, I'm no expert on hemis but even 33* timing sounds way low. Try bringing it up to 3000 rpm and then set the total at 38*
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Re: MP 472 crate motor performs poorly in my 70 Challenger
[Re: rodthedeerguy]
#611904
02/12/10 11:26 PM
02/12/10 11:26 PM
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Joined: Apr 2003
Posts: 1,054 Roswell, GA - near Atlanta
cloneguy
super street
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super street
Joined: Apr 2003
Posts: 1,054
Roswell, GA - near Atlanta
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I could be way off as I've never had a crate engine. We build our own.
But, I think the tell-tale sign is the gas spray you taked about in your initial posting.
I've only seen that in three cases -
Once when my partner the body man was helping me and I somehow got two spark plug wires crossed.
Another time when a customer brought in a car with a flat lobe on the cam.
And, finally when another engine came in with the cam out of time.
There are many horror stories about crate engines, although as I said, I've never had one. Lots of guys, and I'm guessing many at the factory just line up the dots on the timing gears and let her rip.
Your timing should be fine at 33 total. Once again, I assume you've verified that the timing is advancing properly.
I'm not willing to stake my life on it but my top three suspects are cam, Cam and CAM.
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Re: MP 472 crate motor performs poorly in my 70 Challenger
[Re: cloneguy]
#611906
02/12/10 11:35 PM
02/12/10 11:35 PM
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Joined: Feb 2010
Posts: 13 Jacksboro, TX
rodthedeerguy
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OP
member
Joined: Feb 2010
Posts: 13
Jacksboro, TX
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Sounds like good advice. Firing order is good-no missing. I am really wondering if this motor from Mopar (contract builders) has problems out of the box. If it does, it may be hard to straighten out the problems. Hopefully someone has installed one of these and has experience in getting them to run right.
I have a 3550 lb race weight 68 Valiant with an out of the box 402 crate motor, 750 Holley HP, TTI headers, 4.10's, ATI 8" 4,100 stall, 727 manual valve body, MSD Digital6, with Cal Tracs springs/shocks/bars, and 275/50/15 MT drag radials (pulls the wheels!) that runs 7.50's in the 1/8th on motor and 6.90's on Zex perimeter plate with a 150 shot. The Challenger is 400 or so pounds heavier and is 1 second slower. I would expect the hemi should be capable of at least 7.80's-7.90's. Thx for your input.
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Re: MP 472 crate motor performs poorly in my 70 Challenger
[Re: Dougsmopars]
#611907
02/12/10 11:38 PM
02/12/10 11:38 PM
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Joined: Feb 2003
Posts: 21,318 Manitoba, Canada
DaytonaTurbo
Too Many Posts
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Too Many Posts
Joined: Feb 2003
Posts: 21,318
Manitoba, Canada
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With your total timing set at 33, what does your initial timing come in at? I have had the situation like you describe where normal driving is fine but a snap to WOT and I have found that an improperly curved distributor can be the cause. If the distributor has too much mechanical advance, that can put your initial advance too low even though your total is fine. 33* timing sounds low, however my experience is with wedge engines, not hemis.
Also as suggested, checking your cam timing would be a good move at this point too. A pain I know, you gotta pull apart the front of the motor, but then you will have peace of mind knowing whether that is a problem or not.
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