If i was closer i definately would. Somebody help us out here! You never know, you could get comped a new set of headers!

 

So what ever happened to the PPE Headers? Were they ever developed?

 

There are 2 threads out there on headers for the GS4's, the other one is LONG TUBE HEADER - I contacted PPE not even knowing they were already in process of making the the headers and he sent me this picture yesterday. Still not sure when they will be released but at least they are on their way soon

 

The above is a quote from PPE. I wonder how they will fit the catalysts and Y pipe if their design is longer than stock. I guess we shall see. Not sure how well a 4-1 design is going to work and not sure what pipe size they are using. If I had to guess I would say 1.625.

 

wow finaly i can soon buy some headers any price estimate?

 

Those look shorter that my S&S I got from them. I bet those are direct fit. Damn They look good. They also kinda look like the studs might be easier to access too.

 

so since the old design was a 2+2-1 design (i guess thats how you say it) what are the changes good or bad in making this a 4-1 system?

also wouldn't 1.625 be fairly small for our applications?

 

I want one too.

 

Great question. It is also a very complicated question to answer.

Most people think of the pipes coming off each exhaust port as a water pipe with all pipes flowing at the same time in a consistent flow manner. If this were true the larger the better and as one or more pipes joined the total capacity must not be reduced. This is NOT how an engine flows exhaust.

Each port flows only during its valve opening and that is only 1/8th of the time. Also most of the pressure of combustion flows out at the end of the power stroke when the exhaust valve opens before bottom dead center (BDC). This is called blowdown. For the rest of the cycle it is the volume of the cylinder that flows out as the piston goes from BDC to top dead center (TDC) I call this pumpout as the piston pumps out the inert exhaust gas.

The higher the power an engine produces the larger the amount of blowdown occurs. The pumpout is different and is dependent on engine size and RPM. The high pressure of blowdown overcomes most restrictions. The relatively low pressure of pumpout is more susceptible to restriction. The larger the engine size and the higher the RPM requires larger pipe size. Our engines are small and we are limited to a relatively low 6200rpm. IMO a GOOD flowing 1.5" OD tube is plenty for our engines size and RPM range. Larger pipe lowers velocity and more easily allows the reversal of flow between exhaust cycles.

The difference of a 4-1 vs Tri-y on a shorty header is collector volume PER cylinder. This has a big effect on the cylinder to cylinder exhaust flow interaction. Tri-Y designs are usually considered "torque" headers. The larger the collector volume the lower the velocity and the more easily the flow can reverse. This is mostly at low to mid RPM but can also affect this at higher RPM. Collector design is VERY important and a Tri-Y usually has the advantage here... but a good 4-1 collector design can beat a poor Tri-Y collector design. IMO the Rush header which is a Tri-Y has mediocre collectors while 2 of the 3 collectors on each S&S use the much better "merge" design. Many of the PPE headers they list use merge collectors but I cannot be sure what design their Lexus part will use. From the outside it does not look like a merge but it is the inside which is not shown that makes ALL the difference.

I specified Tri-Y and 1.5" primaries for the S&S design for the above reasons. I also specified the "step" at the flange outlet where the S&S are flared to 1.625" as an anti-reversion feature. There are MANY compromises on the S&S design and it would be nice to improve some areas but we MUST remember ANY design is a compromise and the goal of stock fitment with stock catalysts was a driving force. The end result was an excellent working part that experienced unexpected cracking that was fixed with an increase in tube wall thickness and welding technique.

I look forward to seeing the PPE design go into production. Like the S&S it is a compromise but a MUCH better part than the stock 430 manifolds for power production. It will be interesting to see what happens to the lower RPM torque curve. The 4-1 collector and the 1.625" primary size (if this is what the size used is) are not terrible it is just not what I chose for the reasons I gave. I expect peak power to be similar between the two designs with the lower RPM torque curve to be in favor of the S&S. It is important to understand that a dyno chart will NOT show this difference or more likely little of this difference as most runs are made from 4000rpm and up due to the way the tranny shifts at WOT.