Competition truck pull tech inspection question

[PetesonM]

What does this mean more specifically the 3/8" bolts part.





"Exhaust:

All vehicles must be equipped to direct exhaust upward or downward. Two 3/8 inch diameter bolts must be placed in the exhaust pipe in a cross pattern within one inch of each other as close to the final turbo as is practical. "





Also how many driveshaft loops do we really need? The rear-rear is a given. Do we need a mid shaft loop? The front-rear I do not believe is necessary. They go on to say any other visible joint. What angle is this site line based on? I mean if I get on my back under the truck I can clearly see everything. If I stand next to it none of them are visible. So which front guards do I need? I am trying to get into one of these and just want to make sure I pass tech.

 

[JDKammin]

Your exhaust rules are similar to the rules with the pulling tractors. The direct exhaust means a short, curved exhaust pipe going up or down. The tractors point up to get the smoke up and out of the way. The 3/8" bolts need to be installed through the center of the pipe so that the bolts cross each other at a right angle. One will be above the other. This is to help keep broken turbo wheels in the exhaust or slow them down so nobody will get hurt.



As far as the driveshaft loops go, I would install a loop every place you see a u-joint on the front and rear axles, especially the front of each shaft. If you lose a front u-joint on a shaft, you and the truck are going to be catapulted into the sky.

 

[Big MAK]

Personally; I hate the 3/8 bolt thing. Other orgs say it only has to be somewhere before the end of the exhaust so shrapnel can't come out the exhaust -- in which case I'd put it in the later part of my exhaust not close to the turbo. That's 3/4 inch of restriction (3/8 + 3/8) in the part of my exhaust where the gasses need to get out fast. OUCH. It doesn't make sense to need it that close; if shrapnel cuts thru my downpipe it still has to clear the fenders and wheel wells before it's a problem for spectators. And if it cuts thru the pipe it's momentum is greatly reduced by that point... then the fenders... it would be just as good to need the "X" bolts somewhere before the exhaust exit. I could make the arguement you want them later in the exhaust so the shrapnel collects in the exhaust instead of causing the downpipe to get blown to bits for the rest of the debris to get a free exit out of the pipe.



The only trucks that need those "X" bolts close to the turbo are the ones exiting their exhaust out the hood. And near as I know hood stacks aren't allowed in street. So this rule doesn't make sense.



But for now; my 3/8 bolts are in a cross pattern immediately after the elbow in my downpipe where it exits the turbo -- in accordance with the rules that I hope get changed!

 

[Amish Elegance]

Exhaust rules are there primarily to keep spectators safe from, as Jwilliams put it best, "2000 degree ninja stars. "



Mak... Say you have a straight pipe exhaust, 5" as many do. No bolts, it would be very easy for a hot wheel to take a trip down to the end and get there with a good deal of velocity. Cross bolts at the end would ensure the wheel fragmented nicely and spread the shrapnel among spectators evenly.

Thats why most rules have the bolts closer to the turbo. If the bolts dont catch it all, its got a whole lotta pipe to go before it sees daylight. When it does, if its pointed at the ground no biggie. Pointed up, catch em on your tongue for good luck. :-laf

 

[csevers]

Exhaust wheels have come out the tail pipe. If memory serves me right it was in muncie 3 or 4 years ago that a turbo pooped and the ex wheel went all the way down the exhaust pipe and out on the ground, the guy scooped it up with his hat and tossed it in the bed.



Another good reason for the bolts as close to the turbo as possible is if the wheel does go it can bounce between the bolts and the turbo housing witch is much thicker than exhaust pipe.



Craig

 

[seriousdiesel]

I remember the wheel coming out the guys exhaust at muncie, it ended up pretty close to spectators too. The 3/4 of an inch of restriction is minor compared to the troubles you'd have if you implanted a 2000 deg ninga star in someones leg.

 

[Big MAK]

Exhaust rules are there primarily to keep spectators safe from, as Jwilliams put it best, "2000 degree ninja stars. "



Mak... Say you have a straight pipe exhaust, 5" as many do. No bolts, it would be very easy for a hot wheel to take a trip down to the end and get there with a good deal of velocity. Cross bolts at the end would ensure the wheel fragmented nicely and spread the shrapnel among spectators evenly.

Thats why most rules have the bolts closer to the turbo. If the bolts dont catch it all, its got a whole lotta pipe to go before it sees daylight. When it does, if its pointed at the ground no biggie. Pointed up, catch em on your tongue for good luck. :-laf

I didn't say no cross bolts. I don't think they should be near the exit either -- just later then next to the turbo. Several feet from the exit would be good. Maybe even a rule that said an elbow has to follow the cross bolts before the exit. That close to the turbo is a lot of restriction at a high flow point. I think it just insures more engine damage. Along with the no water rule. Two rules to guarantee heat damage.



Specifically; I'd like to put cross bolts in the left and right sides of my "Y" pipe below the stacks (before the pipe elbows up).



And before someone says it. . yeah; yeah; I know. You can only tech just so much. I just want less damage from heat.

 

[TJarecke]

I must have missed the rule on driveshaft loops? I read the rules a couple times and didn't see where that was said. Just wondering?

 

[fest3er]

I didn't say no cross bolts. I don't think they should be near the exit either -- just later then next to the turbo. Several feet from the exit would be good. Maybe even a rule that said an elbow has to follow the cross bolts before the exit. That close to the turbo is a lot of restriction at a high flow point. I think it just insures more engine damage. Along with the no water rule. Two rules to guarantee heat damage.



Specifically; I'd like to put cross bolts in the left and right sides of my "Y" pipe below the stacks (before the pipe elbows up).



And before someone says it. . yeah; yeah; I know. You can only tech just so much. I just want less damage from heat.

Two important parts of the rule: "in the exhaust pipe" and "as is practical. " Is it impractical to put the bolts right at the turbo/elbow outlet? It is more practical to put the cross bolts 6-12 inches down the downpipe? As I recall, we wrote the rule that way to ensure the bolts are placed in the exhaust pipe close to the turbo end of the pipe, rather than in the middle or outlet end of the pipe.



Perhaps one could argue that "as is practical" means "as is practical, considering the engine and exhaust as a system", rather than "as is physically possible, regardless of the effect on the engine and exhaust as a system. " Also, one might consider that it doesn't make much sense to make and enforce a rule that makes trucks that 'must be street driveable' undriveable on the street by unduly restricting exhaust flow: the bolts block about 30% of the cross section in a 3" pipe, about 23% in a 4" pipe, and about 18% in a 5" pipe.



So much for the history of the rule. DHRA Tech Services (tech@dhraonline.com, +1-269-377-5952) are responsible for any official interpretation of the rule.



N

 

[PetesonM]

From the sound of this it seams like with even a full exhaust I still need the bolts if I am going to get by a picky inspector. I really don't feel like drilling holes and throwing bolts in my new downpipe. This fact may keep me out of anything but the small local pulls. My question is why doesn't NHRA or IHRA have rules like this for turbo motors? They may not generate the boost (My Gran National runs in the high 20's) but the wheel speed is about the same.



Is there any conclusion on the driveshaft loops. I have no problem putting one on the rear-rear joint and am concerned with others safety but it is mainly a tow vehicle and I really don't want a jungle gym under my truck.