After x pipe....

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Mopar Tim

Mopar Tim

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So have a question, why does engine idle faster after x pipe install, BUT drop more RPM when put in gear?? Nothing else changed. B4 x pipe, it would idle at about 1200 RPM in gear, real nice running here. NOW it idles 1000 in gear and the more I turn up curb idle, the harder it engages into gear. BUT still stays at 1000 rpm?
408 stroker, 727 with 2500 stall converter, per engine builder. 750 Dolley DP.
 
SGBARRACUDA said:
I would think it has more to do with a change in Back Pressure.
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Agree, but engine needs to Idle at 1100-1200 to be "smooth". its not smooth but drive able without seeming it wants to stall. cant seem to get it there. might have to start from scratch on my tune. dang
 
The exhaust is more efficient with an X and leaning out the carb a tad I think.
 
I am adding a adjustable PCV valve, and see if I can tune it around that . No PCV valve now.
 
If you have a Holley make sure you have the appropriate power valve for the car when idleing in gear (number of valve should be about 1.5 numbers lower than the in gear idle vacuum generated). After that check if you are turning the idle up too high and exposing the transition slot under the throttle blades your carb may need more air and/ or fuel so you do not need to crank it up so high. Jetting would be a first step. You may also need to play with the idle air bleeds if it needs more air into the carb metering circuit.
 
What size cam, and what idle timing, and what idle vacuum now at 1000?

I wonder if you aren't way too far up on the transfer slots.

I lost a good chunk of idle torque when I took the H-pipe out. But I don't recall and idle rpm change. My engine is only a 367. And I think I was running a 276/286/110 cam at the time. Mine is a stick tho.
 
It ran perfect before the Xpipe. Was tuned by the engine builder on the Dyno. Cam is a custom grind, let me find the post

20170116_125443.jpg

I did have to do some re tuning when I got it home, at sea level, was 1200 ft above sea level at dyno. But got it running perfect.
 
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I think timing is set at 20 degrees BTDC. But not certain, I cant remember and engine is not running right now, putting in PCV valve and waiting on part.
There was no vacuum port to test vacuum, I am installing one now and tune better with new valve.
 
What carburetor are you running? I suspect it needs a little more jet. See post 14. What is your vacuum in gear and if a Holley what power valve do you have in there?
 
That seems like a lot of idle speed. I'm thinking you need to work your carb more. How much does your vacuum change when you put it in gear? Are you sure your mechanical advance isn't coming in and out of play at those speeds?
 
A 408 with that cam should not have to idle above 900. It should be happy around 800 with that carb to be honest. I think you need to re-think the base tuning. It's not right.
 
moper said:
A 408 with that cam should not have to idle above 900. It should be happy around 800 with that carb to be honest. I think you need to re-think the base tuning. It's not right.
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Well I do appreciate your comments, BUT how did the x pipe throw off the tune that was tuned on a dyno by the engine builder?
 
And it has ran perfect for months, and ran Good. Starts right up, no kickback, no overheating, no problems at all. Just added X pipe got the issue. Not a huge problem.
 
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