I thought I would show this and then if you guys/gals thought it was good Maybe it could go in the FAQ...


"Naturally, porting and polishing excessively won't yield good results -- it will only upset the balance between displacement and peak rpm's. Some basic physics explained... In any cylindrical enclosure/piping, the closer air is to the metal wall, it will flow slower, and the closer it is to the center of the cylinder, it will flow faster. As rpm's increase, slight variations in the enclosure will cause for serious air flow disturbances. Logically speaking, a straight, cylindrical port would prevent any problems of air-flow disturbance, but with street cars and their limited engine bay space, the port has to be bent. The stock port is built to within such precision that it can already withstand rpm's of up to 7,000 rpm without creating any unwanted air-flow disturbances, but once it reaches 8,500 rpm, the engine struggles to keep the air flowing smoothly. To augment this problem, two of the best mechanics at Honda were selected and assigned to manually port and polish the engine components. Though this limits production to 25 engines a day, this allows for the engine to reach 8,500 rpm, and respectively, 200 horsepower. For those of us who want to port and polish our GS-R engine parts, unfortunately, Honda would not disclose to us the details of this procedure.
Next, the valves and the valve springs needed to be upgraded in order to be able to withstand the high rpm's and the increased fuel injection. In order to increase air flow efficiency, the angle of the valve seat opening was tightened from 60 to 45 degrees. Also, bigger and lighter valves help to deliver more fuel. Instead of making the valve bigger, Honda engineers made the cone bigger and reduced the stem radius even further. In specific, the underside of the valve cone was shaved to its limit, and the valve shaft width was decreased from 5.5mm to 4.6mm -- making the valve 12% lighter than stock. Amazingly, the valves are made so precisely that their static balance differential is basically 0.0. We jokingly asked Mr. Suga what he would do if Honda's parts manufacturers sent over valves that had weight differences. His reply was quick and simple. "We would toss them out." Hm... very strict. Past 8,000 rpm, other valve-related problems occur. Such problems include surging, jumping, bouncing, etc... In order to prevent such problems, the valve springs are made by dual-bound springs. Furthermore, Honda used non-cylindrical, "flat" springs in order to keep the spring height near-stock, and still increase rebounding power.
The camshaft lift amount was changed for both intake and exhaust valves. The intake lift was increased from 10.6mm to 11.5mm, and the exhaust lift was increased from 9.4mm to 10.5mm. To compensate, the intake opening timing was increased from 10 to 15 degrees before piston apex, and closing timing was increased from 40 to 45 degrees after the piston reaching base. Likewise, the exhaust opening timing was increased from 40 to 45 degrees before the piston reaching base, and the closing timing was increased from 7 to 10 degrees after piston apex. By doing so, the valves remain open longer -- allowing for more air to enter the combustion chamber.

Two of the best mechanics at Honda port and polish the manifolds by hand in order to create a high-rpm engine. Due to the manual process, only 25 engines a day can be created.

The intake port was simplified from a dual-port to a single-port -- in hopes of making high-speed air flow better. The stock exhaust piping that varied in width from 48.6mm~50.8mm was upgraded to a full piping with 57.2mm width all the way. Furthermore, the fully stainless-steel header a-pipe employs a 4-2-1 design, but with no sharp edges in the A-pipe when going from 2 to 1. This is a feature that is said to be impossible to do in mass-production."


I know its all old info but there is a lot of new ITR owners and thought they migh want to read

 

very good info. That belongs on the FAQ page. It's pretty amazing how good Honda's Engineers are.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bbasso &raquo;</TD></TR><TR><TD CLASS="quote">Two of the best mechanics at Honda port and polish the manifolds by hand in order to create a high-rpm engine. Due to the manual process, only 25 engines a day can be created.</TD></TR></TABLE>

On '98-Spec ITR's (and USDM, CDM, etc.), the process was done by machine. The results were claimed to be better/more consistent, and production volume was most likely able to be increased.

 

I'm pretty sure that was for the 96/97 ITRs through mid 98 or so.

After that they (the ITR heads) were ported by CNC machine, and it seemed they were doing the head work a little deeper into the ports ... Ed

Oops ... what Padawan said.

 

to clarify, and make my self sound dumber.
That the the difference between a GSR and a ITR head. Correct?

Are there any other differences such as material of head and or oil lines etc?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Renegade &raquo;</TD></TR><TR><TD CLASS="quote">That's the the difference between a GSR and a ITR head. Correct?</TD></TR></TABLE>

There's a difference in the combustion chamber shape of the GSR vs. ITR head (ITR head has a different "squish" area and is about 5cc more in volume), also the ITR head has inner and outer (double) springs which the GSR doesn't.
Also the intake port configuration/angle might be different because of the GSR IM.

 

actually the gsr head handles more volume, there is an old thread here done by Mike K, and the GSR head handles more volume. The combustion chamber is smaller on the GSR head than the ITR. I could be wrong but the intake ports on GSR might be slightly larger, I could be wrong so don't flame me.

 

If I wanted to build up a head for the ITR, make believe I don't already have an ITR head, which one would be best, the ITR or GSR head?

Any benefits to using the GSR?

Since the GSR has more volume, if I mill the head and throw in a thinner head gasket ( to raise Compresion), that may yield more torque, right?

Unless I read and understood wrong form previous threads I have read, I am under the impression that more volume equals more torque, and I know this may not apply here, hence the reason I ask. Looking for any benefits if any to using a GSR head.

 

From MY experience the GSR head makes more power. This is of course all other things being equal. The .2 extra compression also helps.

 

Sorry to bring up an old thread, but after reading it a couple of important questions popped into my head (pun)

I just built a head for my LS (with a gsr swap). I used ferrea valves, 1mm over intake and .5mm on exhaust. Ferrea dual (flat) springs and hardware. 70mm throttle body, skunk2 intake manifold.

Since my upgrades weren't engineered by honda and hand ported and polished at the factory, how do you think my head will stack up as far as efficency? I'm not concerned nor am I asking how much power it will make, or if it is better or worse than the ITR head. but I am asking if you think using high-end after market components on a GSR head will be as efficent as an ITR head?


EDIT: BTW this is a forced induction application