Hey all,
Although I'm building an H motor, I decided to try an experiment on my present F22A6. I took an extra butterfly unit, the 1" thick (brick) assembly between the plenum and lower intake manifold, removed the butterflies and vacuum assembly, and placed it between the lower intake and the original unit. Removal of the intake studs and use of longer bolts all around was needed (110 mm,) and the results are well worth it. Power from idle to redline is improved, but especially noticeable from idle to 4000. I'm definatately going to incorporate this on my H motor. I'm able to spin 225/45s on 17x8s even with 192,000 miles and an automatic tranny (no LSD, but I wasn't able to spin a tire before doing this mod.) All of the hoses and cables had enough slack in them to accomodate the added height, so it was a very starightforward installation.

Why it works:
The increased runner length increases port velocity thereby aiding cylinder filling at lower RPMs, improving power and throttle response, and I've noticed no sacrifice in high RPM power. Long runners can be a great thing (ever seen the cross-ram 426 Hemis?) This can be especially helpful to those of you with ported heads, long duration cams who have given up some low-mid range power in exchange from high RPM flow.


1992 Honda Accord EX, Green with Tan interior
Eibach Pro-kit, KYB AGXs, S/T rear sway bar, urethane bushings on front bar, strut tower braces, 5-Lug conversion with custom finished '05 TL wheels (17x8, +45 mm) and 225-45/17 Kumho 712s. Stainless brake lines, ceramic pads, 11" front rotors (vs 10" stock,) CAI, 2.25" mandrel cat-back, RV transmission cooler and Hurst Hot Shift fluid.

Coming soon: Destroked H23A1 using F20A parts (88 mm down from 95 mm) with H22 Type S pistons, ported head, 11.5:1 compression, 1.65:1 rod ratio, OBX header, UR crank pulley, AEM cam gears and fuel rail, ARP bolts and studs, crank scraper, etc.

 

I recently added a larger plenum to this setup, specifically, an H23A1 plenum that has beed reworked inside a bit (sharpening the port splitters, smoothing the transition around the throttle body) with accompaning throttle body. Using it allowed me to also eliminate the FICV and Cold Start Valve, and I performed a throttle body coolant bypass, and at last, no more hunting/surging idle. Compared to the stock plenum I might have lost a tad bit of idle torque with the H23A1 unit, but gained from about 2600 up. The lowend and throttle response is still better than the stock setup, only now I have a mugh stronger mid-high range. Peak gains are between 3000 and 4800, with no loss anywhere when compared to the stock intake manifold setup. I used my F22 TPS and have the idle srew turned out 1.5 turns. After driving for three weeks, I have noticed a 1.5-2 MPG increase on interstate, with slightly less gain in the city, as it turns out now I just pull out faster than before instead of being easier on the pedal!