Doug Thorley Headers - Air Injection Question (1 Viewer)

[youngbill87]

Hi Everyone,

First time poster here, and I really appreciate any input you can give.

I bought my 2008 GX470 last December, and have been loving it. I have the typical leaky exhaust manifolds, and finally purchased a set of headers from Doug Thorley last week. The headers are currently out of stock, but since I put the order in ahead of time, they gave me a deal on the price. They are supposed to ship out to me on October 5th.

I have been planning to delete the Secondary Air Injection system, so I purchased the headers for the 03-04 version of the truck (without the air injection rails), assuming they would bolt on without issue. I also read that the installation would be easier without having the rails in the way, and as a bonus they are about $150 cheaper.

After looking through the limited pictures, and scouring the Internet for hours, i'm starting to worry that the non-SAI headers may not fit on an SAI equipped engine. It kind of looks like the air injection rails have a separate port into the engine, but it's really hard to tell from the information out there. I do know (now) that I'll need to order a set of manifold gaskets, as the 03-04 trucks used different, more durable gaskets, than the 05-09 trucks. I had just assumed that the only difference between the actual manifolds would be the addition of the air injection rails...

So my question is - does anyone know for sure that the 03-04 version Doug Thorley headers will fit on a 2008 GX470?

Thanks again,
Dustin

 

[bravoleader]

I unfortunately cannot add any useful information. But I was wondering about this same idea whereas I would replace my 2006 exhaust manifold with the 2003-04 version to remove the unnecessary SAI system.

 

[JLee]

I have heard that they will not, though I'm not 100% sure of the reason why.

 

[Onefastrx7turbo]

the bolt patterns should be the same, but the air injection system and the fact that the later manifolds have the cats built in means they are not a bolt on. Why not just buy their air injection version? I think you will end up with some DTCs trying to use these.

 

[CebuGX]

I've looked into this as well. From what I can tell, using DT headers for an '03-'04 GX will leave the SAI holes exposed on the block of an '05+ GX. I would suspect some sort of modification either on the '05+ block needs to be done (some sort of plug) or modify the '03-'04 gasket to plug the SAI holes of the '05+.

 

[bravoleader]

I've looked into this as well. From what I can tell, using DT headers for an '03-'04 GX will leave the SAI holes exposed on the block of an '05+ GX. I would suspect some sort of modification either on the '05+ block needs to be done (some sort of plug) or modify the '03-'04 gasket to plug the SAI holes of the '05+.

I wonder is the block off plates for the SAIS bypass kits would fix this problem: ASV Block-Off Plates

 

[JLee]

I wonder is the block off plates for the SAIS bypass kits would fix this problem: ASV Block-Off Plates

The block off plates I installed with my Hewitt kit used the flange from the air injection tube assembly to lock them in place. I suppose it may work if you were to remove the pipes, cut off the flange, and bolt the flange back on over the plate? Unsure..

 

[youngbill87]

Thanks for the information, everyone. I ended up switching the order to the 05-09 style headers, and they were delivered to my house today! Next I'm going to order the URD cat-back exhaust for it. It's a little depressing to think how much money I'm dropping to correct a design flaw, but once this is done, the GX should be pretty much bullet-proof. And it should sound pretty good too!

 

[GXO]

If you have the pre2005 headers still...send me a PM

 

[JLee]

Thanks for the information, everyone. I ended up switching the order to the 05-09 style headers, and they were delivered to my house today! Next I'm going to order the URD cat-back exhaust for it. It's a little depressing to think how much money I'm dropping to correct a design flaw, but once this is done, the GX should be pretty much bullet-proof. And it should sound pretty good too!

If you have a nearby dyno, a before/after would be fun to see

 

[LaserNomad]

Thanks for the information, everyone. I ended up switching the order to the 05-09 style headers, and they were delivered to my house today! Next I'm going to order the URD cat-back exhaust for it. It's a little depressing to think how much money I'm dropping to correct a design flaw, but once this is done, the GX should be pretty much bullet-proof. And it should sound pretty good too!

Its not a design flaw, its government interference, I dont think Toyota would have added any of that if they were not legally obligated to sell it in California/ USA.

 

[ChaseTruck]

...

Last time I read a post about Doug Thorley headers was when I was still hanging out on the Chevy Blazer internet board.
Never thought I'd see those mentioned on the Land Cruiser board, let alone on the GX forum...

Don't know about the GX, but on a Blazer, the Doug Thorley sticker on the tail gate was already good for about 30hp

 

[DSRTRDR]

Its not a design flaw, its government interference, I dont think Toyota would have added any of that if they were not legally obligated to sell it in California/ USA.

Lexus was never obligated to sell in CA - they chose to do so

whoever wants to sell a product in the US has the choice of not doing so, just sayin' - and yes, whatever rules/laws exist were made by elected government bodies

[so go and vote]

 

[GXMac]

Its not a design flaw, its government interference, I dont think Toyota would have added any of that if they were not legally obligated to sell it in California/ USA.

I'm pretty sure the leaky/ cracking manifolds are a design flaw since I don't think it was Toyota's intent to have them fail like this. They fail regardless of whether the engine was equipped with SAI or not.