JBrady

Thanks!

That looks like a LOUD system! No resonators.

Also, the Y pipe is very strange with nearly straight sections from the cats to the Y... doesn't seem like it would fit correctly. Shape should look like the other Y pipes pictured in this thread.

JBrady

At my local Lexus dealer there is an LS400 (nearly identical to mine) that crashed into water and HYDRO LOCKED the engine. This caused a broken rod. I may aquire the shortblock BUT this situation gave me the opportunity to further examine our engine (1UZ-FE VVTi is the same on 98-00 LS400, GS400, SC400).

The biggest surprise was the exhaust manifolds. I had assumed that they were the same as the 90-97 units but the are DRAMATICALLY different. Better, but still far from optimum.

The 90-97 cars used a 4-into-1 log style stainless steel tube manifold. This manifold has all the cylinders feeding one small tube that then flares to the catalyst opening. Here is a picture:





Also, the o2 sensor was placed in the small diameter section further reducing flow:

JBrady

The manifolds on my 99 are very well covered by heat shields so I was VERY surprised to find Tri-Y style shorty headers.

Here is the drivers side:

JBrady

Here is the passenger side. Note on both units there are 2 tubes each fed by 2 exhaust ports. They then join into a collector at the flange and the o2 sensor is inside the collector area and is not a restriction like the earlier manifolds.

JBrady

I did mention room for improvement. Both headers have ports entering at 90 degrees to the main tube with very short runners. I would like to see some runner length for each port and better transitions... certainly NOT 90 degrees. Here is a shot of the passenger header with a VERY strange pairing of the back 2 exhaust ports. Notice the main tube extends past the port and is "capped". Each port is VERY short and 90 degrees to the tube... this needs help. The 3rd port from the back has a little runner length but still runs 90 degrees into the tube. The front port looks great, nice bend, long runner to the collector... the only good port on the passenger side.

JBrady

The front 2 ports on the drivers side both have nice runners and shape.

JBrady

Both back ports on the drivers side join with SHORT runners at 90 degrees... again, not ideal.

healerhand

Hi John,

I am glad you are specializing in Lexus Exhaust. I have an extra engine at home too. Its a 95 SC400. The headers are very clean. I dont have a picture right now, but its nice to see you doing some much work for our 1UZ engine.

As for my twin turbo. I will post some new pictures. Its totally different now. The intake is from the front to back. Idle nice and run strong.

I am saving some money to get it tune and put in a FMU.

GR8TSCOT

iTrader: (1)

John, if you build 'em (and they're reasopnably priced), I'll buy 'em.

Have you done a straw vote to see if the market is big enough to justify developing headers? Or is this simply a labour of love, so numbers don't count?

JBrady

Howard, No test pole done and based on the small level of interest in even the air filter box mod... I am guess the market to be limited. One of the biggest obstacles is the removal of the factory manifolds. I was told by SRT that it requires the engine be removed At first I doubted this but after looking closely they may be right (or possibly the subframe could be removed from the bottom granting access). The earlier style manifolds were considerably more compact and a number of SC400 owners had installed the longtubes from Australia.

Anyway, I needed to at least have a set off a car to make measurements. Actually, I would need a car on a lift for several weeks to design these parts properly and I just don't currently have the resources to do this. So, bottom line is as much as I would like a set myself... these are on hold The rest of the exhaust is proceeding and "hopefully" I will be able to show parts within a month or so. Right now business has been very demanding so this is dependent on other influences.

JBrady

To do a TRUE cat back exhaust upgrade, the following parts need to be addressed. The following pictures will help everyone understand what I am talking about. Starting with a picture of a cat from a 1998-2000 LS400/GS400 and continuing with each segment I will discuss the consequences and considerations regarding any upgrades.

JBrady

Cat to Y pipe intersection showing after cat O2 sensor location. This qualifies as one of the STRANGEST stock exhaust parts I have seen. For some reason Toyota/Lexus decided to weld a straight section of 60mm pipe to the cat outlet flange, angle cut it, weld a 50mm pipe pipe that has its last couple of inches expanded to 60mm and match angle cut. This intersection SCREAMS turbulance. Very odd. Also note the O2 placement is in the 50mm sections of the Y pipe where the sensor tip takes up a good portion of the available flow area

JBrady

Y pipe

JBrady

Close up showing the reduction from 60mm (2.36") to 55mm (2.2") going from the juction of the stock LS400 Y pipe to the center resonator... VERY SMALL FOR APX 300hp

JBrady

Pipe from center resonator expands from 55mm back to 60mm