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Sled Pulling From Street to Pro-Mod, get your Sled Pulling fix here!

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Old 03-16-2012, 11:03 AM   #1
Leadfoot
 
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Machining intake off head on a Cummins

I am no longer the tech official for our club, but people seem to come to me for advice. I know how I "feel" about the issue but wondered how most interpret the following rules.
Aftermarket intakes are allowed
Must use factory Head

A gentleman who is "building" a 2.5 truck asked if machining the intake off of his Cummin's would be acceptable. I told him I would discuss it, meet with our tech guys, and give him a ruling within the next week so he can proceed with his build. He did not want to spend time/money and then be told he can't pull.

He feels that it's still utilizing the factory head for airflow in/out as the valves are unaffected and that he is only changing the intake. Unfortunately on a Cummins (unlike the other brands), they head and intake were cast together as a single unit.

While most think of a diesel intake as pre-turbo, there are Duramax guys who are altering their "Y bridge" which is post I/C and where air enters the two sides of the motor. He feels if Duramax guys are allowed to change the "Y bridge" to a custom larger diameter unit, he should be able to do the same to his "intake".

He also states all 3 makes allow porting, polishing, large valves, different valve springs, cams, etc. so even the factory heads are being "massaged".

Thoughts?

I did a search and found guys who had done it, but nothing as to legality per rules (unless I missed it, and if I did, I apologize).
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Old 03-16-2012, 11:10 AM   #2
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I say it'd be acceptable. Like you mentioned, other makes allow for intake porting while the factory cummins head doesn't get the full effect without milling the intake plenum off. Obviously I have no grounds on my opinion as I'm not involved in pulling. Might be nice to have an unbiased opinion. Are people running ford and GM complaining about the plenum machining or are you just gathering thoughts?
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Old 03-16-2012, 11:56 AM   #3
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It's a turbo inducer limited class, leave it fly.
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Old 03-16-2012, 12:06 PM   #4
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X2. The chargers are only going to push so much air being limited via the inducer bore size. All the porting/polishing in the world isn't going to make much difference without a matched air supply. IMO Let them have it.
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Old 03-16-2012, 01:01 PM   #5
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Let the intake run. You can run them on the street so they should be accepted in any pulling class IMO. I also agree with ^^^
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Old 03-16-2012, 02:51 PM   #6
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I am all for the shelf style intake in the 2.5 class around here. But not for the big runner style. The 2.5 class was made so the average person can get in it, and still have a good chance at a win. If we don't keep a lid on it, it will be as bad as the 2.6 class is now. Basicly anything go's as long as it's 2.6 turbo. If you don't have a difference in the rules between the two, then why do we have a 2.5 class.
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Old 03-16-2012, 03:04 PM   #7
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Modifying the y bridge on a duramax to me is the same as changing the intake horn on a Cummins, not like cutting off the side of the head. You will have to let Duramax's run sheet metal intakes also then. I would allow y-bridge or air horn mods but nothing further in the 2.5 class.
 
Old 03-16-2012, 03:15 PM   #8
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Quote:
Originally Posted by White Duramax View Post
Modifying the y bridge on a duramax to me is the same as changing the intake horn on a Cummins, not like cutting off the side of the head. You will have to let Duramax's run sheet metal intakes also then. I would allow y-bridge or air horn mods but nothing further in the 2.5 class.

I would say they could run sheet metal intakes if they are the same shape/size as the OEM one. The cummins folks have to cut off the intake to get at the intake valves for porting.

I don't think a runner manifold should be allowed. It really shouldn't be allowed in the 2.6 though either lol.
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Old 03-16-2012, 03:20 PM   #9
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Need more specific rules. If the only limits are stock head/heads and a 2.5" turbo, then i dont see a problem with cutting off the cast intake.
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Old 03-16-2012, 03:37 PM   #10
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Gotta love rules interpretation. I take "factory" heads to mean that the casting needs to be supplied by the factory and open to modifications of any sort.

Then again, who's "factory" does it have to be..........

I take "stock" heads to mean they should look stock in every way on the outside.
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Old 03-16-2012, 06:33 PM   #11
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Quote:
Originally Posted by White Duramax View Post
Modifying the y bridge on a duramax to me is the same as changing the intake horn on a Cummins, not like cutting off the side of the head. You will have to let Duramax's run sheet metal intakes also then. I would allow y-bridge or air horn mods but nothing further in the 2.5 class.
Exactly, I feel the same way Raymond. The Y bridge is like putting a different intake horn on a cummins. IMHO i still think its not going to matter as like jake and others said, Its a turbo inducer limited class. I also see what Gavin is saying. It sucks the 2.5 class is coming down to something like this. Oh yea, you can cut off the intake on a cummins head do all the head work you want and still attach a stock appearing intake runner back on. Ive seen it
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Old 03-16-2012, 10:27 PM   #12
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Quote:
Originally Posted by Diehard Ram View Post
I am all for the shelf style intake in the 2.5 class around here. But not for the big runner style. The 2.5 class was made so the average person can get in it, and still have a good chance at a win. If we don't keep a lid on it, it will be as bad as the 2.6 class is now. Basicly anything go's as long as it's 2.6 turbo. If you don't have a difference in the rules between the two, then why do we have a 2.5 class.

That was my feeling on it.

I like to see more seperation than turbo and hanging weight. We are a club though and an organization (not dictatorship), so I thought I would get input on pro's/con's and weigh them out for the betterment of the class/sport.

Thanks to all those that responded (and yet to respond).
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The current state of pulling:

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Old 03-17-2012, 03:12 AM   #13
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I say allow it, being as he wont gain alot. ya itll spool better and flow better and less heat and blah blah blah. 2.6 workstocks do just fine with exhaust matching and a horn. IMO hes wasting money for the 2.5 class milling the intake is unnessisary for that power level. but it does look cool...
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Old 03-17-2012, 05:45 AM   #14
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for a 2.5 class i say let them cut off the intake for portwork only. state in the rules when plenum is reattached that it has to be a shelf or "stock style" log intake. individual runners should not be allowed in my personal opinion. the 2.6 class is pretty much legal to run anything so keep the 2.5 class conservative so people can tell the difference in classes. if you let it get out of control ex: hood stacks, IR, water air coolers, and extra weight, people wont be able to tell the difference in classes IMO and that takes away from the whole point of having another charger limited class. if you let them get away with runners ect. you may as well just run a 2.6 class. just my . i'm not a truck puller so my opinion isnt worth much but i am around it continuously and understand what these rules are made for.
 
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