MP 472 crate motor performs poorly in my 70 Challenger

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.

I was going to suggest a carb problem but it looks like you looked into that.

Who's crate is it?What carb?Where is the timing set,is it vacume advanced or locked out?? I'll stop there for now

welcome aboard! Might start w the basics and a compresssion test (a leakdown if you have the gauges & shop air). What is your initial/total (and at what rpm). Might check for vac leaks. If some of the basics are good it'll get you started. Holler back anytime

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.

The first thing is pretty obvious but it sounds like the firing order might be off. Since I assume you checked that and it's correct, it really, really sounds like the cam is installed incorrectly.

I would tear down the front of the engine and degree the cam. Then check absolutely everything else twice as you put it back together.

Good Luck.

Have had AED 850 double pumper, Demon 850 double pumper on it, and has out of the box Quick fuel vacuum 850 on it now. The best the car ever ran as to not having a bog was when I first bought the car. It had the AED, MP electronic ditributor with chrome box and was set at 22 degrees total timimg. It ran 12.80 @ 111 mph with drag radials. Once I put timimg to 33 degrees the problem started. With the bog it runs 8.50's in the 1/8th. Have not put timing back to 22 degrees as 2 wrongs do not make a right? This motor is unmodified and was installed new from Mopar when the car was built in March of '06. The motor came from Bill Luke Chrysler in AZ. Part # is P5249666-AC Crate Engine 55310000 at a cost of $18,600. It has original hemi style exhaust manifolds with TTI 2.5" exhaust. The current ignition is MSD6-AL with out of the box MSD billet mechanical advance distributor. On the street the motor runs fine. The problem starts when a heavy load is placed on the motor. The trasition from idle to full throttle is where the problem shows up. Springs are stock with pinion snubber and traction is not a problem with 10" slicks. Love your car!

The motor was purchased new and installed out of the box in 2006. I have heard there were issues with these motors (after I bought it and the problem showed up). I am thinking the cam may be advanced too much?

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*

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.

Sounds like cam is to far advanced. If it runs better at 22 then 33 thats a good indication. Peek cylinder presure is at 70 ATDC to get maximun power. To get that you need a total advance of around 34 degree's. I'd pull the cover and degree the cam as mentioned above. With lower comp i would keep total at 34 to 36 no higher.

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.

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.

Makes sense to verify where the cam is installed. If nothing else, it resolves that question. I do believe the problem is deeper having had both a Mopar electronic vacuum advance and a MSD billet mechanical advance distributor on the motor. Also, it is worse with a mechanical secondary vs. a vacuum secondary carb. I guess that makes sense if the cam were too far advanced in that shooting more gas at snap open WOT would produce a more severe stumble or bog. I researched hemi timimg and they seem to run better with lower timing than 440's. Mopar Action ran a 426 crate motor on the dyno @ 38* and then at lower settings. They found peak power at 33*. Several comments so far point to cam timing and sloppy crate motor quality control issues.

Thank you for your input. I will follow your and others advice and check the cam timing. Am still concerned the overall combination of cam, intake and compression of this motor from Mopar is not conducive to a good performing Hemi. If so, hoping to hear from someone who has experience with one of these crate motors and what if anything can be done to improve performance. Cam timing may be all it takes.

I have an earlier crate motor 528.
Issues were ring sealing, a lot of oil use.
And not enough oil in the heads. it purned up the rocker tips. oil in heads was fixed by cutting journal on #4 cam.
Still uses oil, but runs fine.

I have looked at the 528. Aside from being bigger, one other big difference is a higher compression ratio. I have considered buying a current gen 528 to replace this 472 due to lack of confidence that anything about it is right. Also, since Ray Barton has his name on it, I would hope it is the real deal. I have no oil consumption problems. I am glad to know you are happy with yours as to how it runs. Have you ever been to the strip with it? 610hp/650tq is impressive. Is yours a pump gas motor? Thx for the input.

yes, pump gas. runs 180 deg in florida summer. I think the difference other than compression is alum heads. I have been to track once, but have no traction/driving skill. With drag radials, spinning thru first and second, ran 8.18 with 2.1 60' in 1/8th. I think it was around 92 mph. Car has not really been tuned at all, and would need 9" slicks to get some good times.
Running HP 4150 950 cfm tti 2 1/8th with tti h pipe.

also mine was built by cummins. so the barton may be a whole bunch better.

8.18 with a 2.1 short time is excellent. 1.60-1.70's short times with slicks should be acheivable. 7.70's are within reach. 92 mph is a lot of mph. Your input has given me some good direction. Thanks!