Hands On Experience With Doug Thorley Headers

[Tungsten]

I dumped about $4000 into my truck over the time that I have owned it and after going through some head aches I hope the following post will make someones life easier.

 

 

After using Doug Thorley headers for about a half a year I would like to post my experience and suggestions on what to do when installing them.

 

First of all, if you are planning to install these, make sure you are happy with what they do to your power band. The regular exhaust manifolds seemed to have a slightly different power band but not that much different from the headers. So you might want to check with someone that already owns these to see if you want to put these on your truck.

 

Are your studs broken?

The factory exhaust manifold studs are small, only 8mm in diameter so if you have the original studs, they are prone to cracking or breaking. If your current studs are broken, get the 300ZX turbo studs. They are initially golden in appearance but turn white as they will get hot. If your studs aren't broken, they are probably the revised grade 8 studs, which are probably the same as the 300ZX turbo studs. I suggest using studs over bolts as they are much easier to work with and are designed to work properly with the expansion/contraction rates. Go to your nearest Nissan dealer and buy all the proper fasteners. It will be around $120 but it is worth the expense.

 

Now what is that all about extending the EGR tube?

There are two different sets of headers made by DT. One is the short tube variant other is the long tube variant. The short tube ones are for the VG30E application and have the EGR port in a different location than the VG30i. The EGR tube on the VG30E engine does not need to be modified, it will fit right in. However, if you want to use the short tube headers on the VG30i engine then you need to extend the EGR tube to match. I don't know where the fitting goes on the long tubes and if its made for VG30E or VG30i.

 

Long tubes vs Short tubes?

I would say go with short, they are easy to install and have pretty much identical flow of the long tube. I don't think the long tubes are in production anymore.

 

Nickel Chrome vs Ceramic?

If you don't care about the looks, go with the chrome coated ones. They are cheaper and are just as tough as the counterpart. What will happen is the primary tubes will turn dark blue but because there is a stream of air by the crossover pipe, that part will stay shiny for a while. The ceramic coating will give you a few extra HP and will have a more even color tone over time but for a premium.

 

What about the Oil Filter Relocation Kit?

You do not need to install it, the oil filter can be changed easily without it. However, if you really do hate the filter in that location then you can get a kit and mount it happily next to the transmission somewhere. WARNING! Any damage to the hose or oil filter will leave you disabled and without an engine.

 

How do I connect the stupid slip fitting to make it leak proof?

So if you put these things together without anything, you will have an exhaust leak at the slip fitting. What you need to do is put some high temp silicone (preferably copper based) into the slip fitting before you slide the two pieces together. If you haven't done that then you can still wedge the silicone in on around the side. Then you put a 2.00" lap joint band clamp on the slip fitting. If you have a MIG welder and want more stability then put a small tack weld where it will be easy to cut it off in the future should you choose to take the system apart (disconnect the battery if you are welding). You can remove the black sealer from the band clamp as you won't need it. Torque that band clamp to specification which is around 50 to 60 ft lbs. Do not use a regular exhaust clamp as it just will not work (it will break). You can weld the slip joint around but then you will have to take the torsion bars out to remove the crossover pipe.

 

Why does the DT install manual says to use high temp silicone on the gaskets?

I was told by a professional mechanic (on the job for 15 years) that putting silicone on new gaskets is stupid so you don't have to do it.

You should check the torque on all the nuts after an initial drive because they sometimes tend to back off.

 

What the hell is that rattle?

When you put your headers together, you may hear a clunking sound from the front end. That is the exhaust pipe hitting the frame, but not where you might think. Yes the headers do run close to the frame but they will not touch. The part that actually does touch is that U-shaped bend thing around the left side of the transmission crossmember. Take a grinder and grind off about a half inch off the crossmember and the rattle will be gone. You should get rid of that rattle because it will trigger your knock sensor.

 

If you don't hear a knock but your truck still hesitates, it is most likely that the O2 sensor has failed from your modding. Go get a new one ($140 from dealer) and swap it in then reset the ECU by pulling out the negative battery terminal for a few minutes.

 

What to do next?

The Doug Thorley headers are designed to exit into a 2.5" pipe (or 2.25" for the long tube version). If you want to go smaller then use a reducer.

 

What to do for Muffler/Cat?

Anything. Make sure your muffler isn't too loud because you will hate the highway drone. The Flowmaster 50 seems to be perfect for me. While you are there, be sure to check on your catalytic converter and make sure it isn't plugged.

 

When installing the muffler, make sure it fits or make it fit. If you are re-using the old midpipe and notice the crimp that was made from the old exhaust clamp and muffler, don't worry about it, it will work as a flow enhancer. If you are installing a tough metal performance muffler like a Flowmaster, do not use the regular clamp. In fact, when doing a performance exhaust system, forget about regular clamps. You can use a band clamp and silicone combo identical to the header crossover pipe slip fitting or you can weld or both.

 

If you hear banging by the gas tank, the tailpipe is probably not bent correctly. In my case, my Magnaflow catalytic converter expanded so much that it forced my tailpipe against the gas tank. After bending the tail pipe a little bit, that problem went away.

 

For a finishing touch:

Install a tip on the exhaust with an outlet diameter between 2.50" and 3.00". Not only does it look nice, it sounds good too. Get a stainless steel one because the chrome ones look like crap after a few weeks. Clamped or welded is up to you but I prefer a clamp one because they are easy to swap and clean.

 

So there you have it, I hope this helps someone with their sport exhaust system.

 

 

FYI:

If you do not wish to install headers, fix your exhaust manifold studs and throw out those heat shields, they are useless. Also, if you don't see any black spots on the engine from the exhaust manifolds, they are fine but dump those heat shields anyway as they might hurt the studs and cause an annoying rattle when they rust. Instructions on how to change studs can be found throughout the forum and here: http://www.nissanpathfinders.net/forum/index.php?showtopic=16196

 

Another FYI:

If you do mod the exhaust system, it is a good idea to install a transmission cooler as it will keep the transmission happy with your mods. Look elsewhere on this forum for instructions on that.

 

Any ECU problems?

The ECU does not have to be modified to run the headers however if you have a higher flowing set up, your truck will hesitate for the first few minutes when started from a cold state. This happens due to the timing being retarded for a quicker warm up. If you can hack the ECU, you can set the proper timing during warm up to prevent this from happening. I don't know if the California model ECU units respond in the same way. It is only a small problem and will go away as soon as the O2 sensor kicks in. Any other issues may be either MAF or O2 sensor related.

Edited January 9, 2012 by Tungsten

[PATHRIDER]

you forgot to mention what bolts to use..I went with grade 8 bolts 8X25X1.25..The set on my 93 has been on there for 3 years..I didnt bother using those thick washers so I opted with the 25MM lenght bolts..If you wish to use the thick washers get a 30MM bolts.

[Precise1]

you forgot to mention what bolts to use..I went with grade 8 bolts 8X25X1.25..The set on my 93 has been on there for 3 years..I didnt bother using those thick washers so I opted with the 25MM lenght bolts..If you wish to use the thick washers get a 30MM bolts.

I'm guessing that you used grade 8.8 bolts (metric values). I used grade 10.9 and so far so good. M8x1.25x25mm is the correct thread size/pitch/length designation. I used 30mm long bolts without the thick washers and there was sufficient thread in the hole so they didn't bottom out. No way in hell was I going to pay up to $100 for a factory set of studs/nuts. That's just insane!!

 

B

[Tungsten]

Maybe so but I highly recommend getting factory mounting hardware as opposed to bolts. The factory studs have correct expansion/contraction coefficients ever since the revised studs came out so they are guaranteed not to break in the most PITA location ever.

 

Initial post updated!

[MY1PATH]

LS1 headder bolts from a stock z28 camaro work too.

Yes, I tried it. I used to work on my buddies muscle cars allot.

[jj big shoe]

What about the Oil Filter Relocation Kit?

You do not need to install it, the oil filter can be changed easily without it. However, if you really do hate the filter in that location then you can get a kit and mount it happily next to the transmission somewhere. WARNING! Any damage to the hose or oil filter will leave you disabled and without an engine.

That's why I carry a stock filter in the truck. I can screw the adapter off and slap the stocker on the block if something happens to the lines.

[SurleyOne]

I dumped about $4000 into my truck over the time that I have owned it and after going through some head aches I hope the following post will make someones life easier.

 

 

After using Doug Thorley headers for about a half a year I would like to post my experience and suggestions on what to do when installing them.

 

First of all, if you are planning to install these, make sure you are happy with what they do to your power band. The regular exhaust manifolds seemed to have a slightly different power band but not that much different from the headers. So you might want to check with someone that already owns these to see if you want to put these on your truck.

 

Are your studs broken?

The factory exhaust manifold studs are small, only 8mm in diameter so if you have the original studs, they are prone to cracking or breaking. If your current studs are broken, get the 300ZX turbo studs. They are initially golden in appearance but turn white as they will get hot. If your studs aren't broken, they are probably the revised grade 8 studs, which are probably the same as the 300ZX turbo studs. I suggest using studs over bolts as they are much easier to work with and are designed to work properly with the expansion/contraction rates. Go to your nearest Nissan dealer and buy all the proper fasteners. It will be around $120 but it is worth the expense.

 

Now what is that all about extending the EGR tube?

There are two different sets of headers made by DT. One is the short tube variant other is the long tube variant. The short tube ones are for the VG30E application and have the EGR port in a different location than the VG30i. The EGR tube on the VG30E engine does not need to be modified, it will fit right in. However, if you want to use the short tube headers on the VG30i engine then you need to extend the EGR tube to match. I don't know where the fitting goes on the long tubes and if its made for VG30E or VG30i.

 

Long tubes vs Short tubes?

I would say go with short, they are easy to install and have pretty much identical flow of the long tube. I don't think the long tubes are in production anymore.

 

Nickel Chrome vs Ceramic?

If you don't care about the looks, go with the chrome coated ones. They are cheaper and are just as tough as the counterpart. What will happen is the primary tubes will turn dark blue but because there is a stream of air by the crossover pipe, that part will stay shiny for a while.

 

What about the Oil Filter Relocation Kit?

You do not need to install it, the oil filter can be changed easily without it. However, if you really do hate the filter in that location then you can get a kit and mount it happily next to the transmission somewhere. WARNING! Any damage to the hose or oil filter will leave you disabled and without an engine.

 

How do I connect the stupid slip fitting to make it leak proof?

So if you put these things together without anything, you will have an exhaust leak at the slip fitting. What you need to do is put some high temp silicone (preferably copper based) into the slip fitting before you slide the two pieces together. If you haven't done that then you can still wedge the silicone in on around the side. Then you put a 2.00" lap joint band clamp on the slip fitting. If you have a MIG welder and want more stability then put a small tack weld where it will be easy to cut it off in the future should you choose to take the system apart (disconnect the battery if you are welding). You can remove the black sealer from the band clamp as you won't need it. Torque that band clamp to specification which is around 50 to 60 ft lbs. Do not use a regular exhaust clamp as it just will not work (it will break). I advise to not weld the slip joint around completely because you will have to drop the torsion bars to take the crossover pipe out.

 

Why does the DT install manual says to use high temp silicone on the gaskets?

I was told by a professional mechanic (on the job for 15 years) that putting silicone on new gaskets is stupid so you don't have to do it.

 

You should check the torque on all the nuts after an initial drive because they sometimes tend to back off.

 

What the hell is that rattle?

When you put your headers together, you may hear a clunking sound from the front end. That is the exhaust pipe hitting the frame, but not where you might think. Yes the headers do run close to the frame but they will not touch. The part that actually does touch is that U-shaped bend thing around the left side of the transmission crossmember. Take a grinder and grind off about a half inch off the crossmember and the rattle will be gone. You should get rid of that rattle because it will trigger your knock sensor.

 

If you don't hear a knock but your truck still hesitates, it is most likely that the O2 sensor has failed from your modding. Go get a new one ($140 from dealer) and swap it in then reset the ECU by pulling out the negative battery terminal for a few minutes.

 

What to do next?

Ideally you want 2.25" piping all the way from the collector (Y-pipe) to the tailpipe but if you choose to, you can re-use the auto store 2.00" piping. The stock is around 1.8750" so you will still gain a little diameter. Buy (or fab) new pipes if yours are completely rusty. My tailpipe was rusty so I replaced it with a NAPA one. My midpipe was ok so I reused it.

 

What to do for Muffler/Cat?

Anything. You can do a Magnaflow cat in either 2.25" or 2.00" and a Flowmaster 60 muffler. Make sure your muffler isn't too loud because you will hate the highway drone. The Flowmaster 60 seemed to make a perfect sound for me. Keep in mind that Flowmaster is not the best and I only got it because I know it works and don't know much about mufflers. While you are there, be sure to check on your catalytic converter and make sure it isn't plugged.

 

When installing the muffler, make sure it fits or make it fit. If you are re-using the old midpipe and notice the crimp that was made from the old exhaust clamp and muffler, don't worry about it, it will work as a flow enhancer. If you are installing a tough metal performance muffler like a Flowmaster, do not use the regular clamp. In fact, when doing a performance exhaust system, forget about regular clamps. You can use a band clamp and silicone combo identical to the header crossover pipe slip fitting or you can weld or both.

 

If you hear banging by the gas tank, the tailpipe is probably not bent correctly. In my case, my Magnaflow catalytic converter expanded so much that it forced my tailpipe against the gas tank. After bending the tail pipe a little bit, that problem went away.

 

For a finishing touch:

Install a tip on the exhaust with an outlet diameter between 2.25" and 3.00". Not only does it look nice, it sounds good too. Get a stainless steel one because the chrome ones look like crap after a few weeks. Clamped or welded is up to you but I prefer a clamp one because they are easy to swap and clean.

 

 

So there you have it, I hope this helps someone with their sport exhaust system.

 

 

FYI:

If you do not wish to install headers, fix your exhaust manifold studs and throw out those heat shields, they are useless. Also, if you don't see any black spots on the engine from the exhaust manifolds, they are fine but dump those heat shields anyway as they might hurt the studs and cause an annoying rattle when they rust. Instructions on how to change studs can be found throughout the forum and here: http://www.nissanpathfinders.net/forum/index.php?showtopic=16196

 

Another FYI:

If you do mod the exhaust system, it is a good idea to install a transmission cooler as it will keep the transmission happy with your mods. Look elsewhere on this forum for instructions on that.

 

 

I'm too lazy and tired to format all this crap but please read it...

[SurleyOne]

Thanks a lot this is a big help for me. Surleyone

[beastpath]

LS1 headder bolts from a stock z28 camaro work too.

Yes, I tried it. I used to work on my buddies muscle cars allot.

 

 

x2

[Kingman]

Maybe so but I highly recommend getting factory mounting hardware as opposed to bolts. The factory studs have correct expansion/contraction coefficients ever since the revised studs came out so they are guaranteed not to break in the most PITA location ever.

 

Initial post updated!

 

I agree. Bolting stuff to an aluminum head is generally a bad idea, especially if accidentally over torqued and you strip the weaker threads. It's just much safer to fasten headers/manifolds to a stud inside the head rather than bolting them straight to it.

[Precise1]

Accidentally overtorque??

 

Look, if you 'overtorque' a stud, versus a bolt, where do you think the added stress goes?? Into the threads of the aluminum head. I can pull a stud out of the head just as easy as I can rip the threads out with a bolt. The real point is not to be a monkey and overtorque and either fastener will work fine.

 

I used 10.9 grade bolts since I had a box of them and I'm not about to pay 80-$100 for exhaust hardware. They are working fine so far.

 

B

[Kingman]

With the stud secured you're no longer twisting into the head threads directly with force, instead the nut is twisting onto the stud with the flange as a buffer, whereas a bolt you're still tightening and twisting into the threads while trying to secure the flange. I've seen quite a few people swap bolts for studs because they're too lazy to fix them and cause even more problems for themselves in the long run. I've mentioned swapping bolts for studs to a few mechanics and each one of them about came out of their pants because it was such a bad idea. After talking with a 30 year Nissan mechanic (M.B. Anderson & CO) about the VG motors he's seen come in that are insanely messed up because of bolted on manifolds and heads, I know I'll take the safe route and buy a set of upgraded studs when I put my headers on.

 

Because you're a machinist, I understand you're more aware of torquing and being extremely careful not to damage anything. Most people aren't though, and this is why things get destroyed... It's simply much safer to use upgraded studs in an aluminum head.

Edited August 20, 2010 by Kingman

[Tungsten]

Yes it is true that both bolts and studs work however the studs are much more "user friendly" to the average home mechanic.

 

Update: I added a bit regarding the ECU performance.

[Tungsten]

Updated and corrected the Y-pipe specification.

The Doug Thorley headers exit in 2.5" not 2.25".

[robertjame]

If your unaware of torque spec or how to pay attention to over tightening then you shouldn't be working on sensitive equipment. There are advantages to both studs and bolts, both points are valid but in my opinion using bolts is easier because of the close quarters on the vg30 to the wheel wall. Pulling the header over the studs is much much more difficult then simply lining it up and sliding the bolts in. Buy a torque wrench and learn.

[Tungsten]

Yes I agree either works but headers are more difficult to install on studs inside the bay because of how the studs stick out. The best part about studs is once you get the headers on then tightening them down evenly is great. Remember that you also have to put the gasket on the studs first. You can do the same with bolts but have fun with the gasket.

[heythurr]

Got Doug Thorley Hedders on my rig, LOVE em. Unfortunately, it's about that time (maybe way past that time) where I've got to do the Exhaust Manifold Gaskets.. Horrid ticking unless I'm idling or holding my foot at a steady 3000rpm. Hoping that I don't break any studs when I go to do this job..

[Precise1]

Try tightening them first. They might be loose, not the stud being broken...

 

B

[Tungsten]

I have been chasing down an annoying tick as well. It's not a crazy sounding tap that you hear from a broken manifold either so I don't know. No idea what it is but It may most likely be the joining flanges at the Y-pipe. I know for sure there are no leaks at my headers.

[tmoore4512]

I need to do mine. Will wait til I pull the motor and replace all the leaks first...

[Precise1]

Remember that you also have to put the gasket on the studs first. You can do the same with bolts but have fun with the gasket.

Remember that high temp silicone that you should never have to use? Well, it sticks the gasket to the head quite well so it's back to just slipping the bolts in...

 

No point in arguing about it, everyone will do what and how they see best or what they are comfortable with.

 

B