View Full Version : 86 or 89 intake runners (need quick reply )

01-13-2002, 01:42 AM
Sunday I'm doing the intake on my 2nd gen 89 rx, and was looking at an 86 set of intake runners at how straight they went, and thought (late in the game) these look better, faster,smoother,... so while I have a few hours to go I see if the ol' IT boys are up for the quick challenge. Thanks in advance for any pertinent info. Rick

01-13-2002, 01:51 AM
1. They are not supposed to be as good as the 89-91 setup. I haven't seen any empirical evidence one way or another.

2. You'll need the upper and lower intake manifolds, and possibly the 86-88 primary fuel rail.. I've heard that the 89 fuel rail will not fit on the older style manifold.



C. Ludwig
01-13-2002, 11:29 AM
The primary rails, while not identical, can be interchanged. The secondary rail have different mounting bosses so you'll need the correct rail.

Like Silkworm I haven't seen the data but my WAG guess would be that the 89+ intake has shorter runners when in the high RPM mode which might account for a bit more high RPM power. The later cars had a slightly higher redline and power peak which might be made possible by a shorter runner intake. ???


01-13-2002, 12:01 PM
Thank you so much for your quick responce, I do have the complete 86 set up, and I did note the different rail set up , I in fact tried to rob it for the 89 but to no avail. I gotta quit thinking, and just get the ol' girl up and running, Feb 16th is our season openner and we're still a long way off (kinda). Well thanks again, you both are so helpful, and extremely RX wise. Rick

Karl Bocchieri
01-13-2002, 12:17 PM
With the 86 motor and computer and 86 injection equipment in place, just changing the upper and lower intake showed 3 hp on my car. The problem is the 86 air flow meter and computer. To be 100% legal you have to change the entire setup from the air meter to the computer. Unfortunatly the wiring harness is not the same, a major headache to change, and very expensive. You still have the low compression rotors of the 86.
A full 89 system has the potental to make more power than an 86 system, but possibly not enough to go through the trouble of doing the swap.

01-14-2002, 02:14 PM
So the theory here is the longer runners make more low end and shorter runners make more top? It seems like there is not a huge dif. in runner length between the two.

C. Ludwig
01-14-2002, 10:09 PM
I looked at both mine today and the early intake actually looks shorter but the chamber on top looks to be more of a jumbled mess instead of smooth like the later intake. I really don't have a clue I'm just trying to make BALLZOUT feel better about the job at hand! http://Forums.ImprovedTouring.com/it/biggrin.gifJ/K


01-15-2002, 01:03 AM
The latter intake is alittle better across the whole rpm range if the rotary valve is working. Better low end torque, better top end breathing in the short runner position due to a ramcharging effect of intake pulses.
Brian B

01-15-2002, 02:29 PM
but if we are using the latter one with the valve wired in the short runner pos does it act the same? And if the old style manifold were cleaned up would it equal the new style?

01-16-2002, 12:32 AM
The early manifold is a compromise for low end, high end performance much like a header thats tuned for optimum performance at a high mid range rpm. The latter is less so due to the rotary valve that creates two intake runner lenghts,one for low to mid range,the other for mid to high rpms( valve opens at approx.4500 rpms). In the short runner position at higher rpms there is an additional benefit of intake pulses traveling in the manifold that create a ramcharging effect and can produce power to a higher rpm. The early manifold falls short of this.
A latter manifold with the runner wired in the short position, you lose some low end. Might not miss alittle low end in a track car. An autocrosser would,an operating rotary valve would be best.

01-17-2002, 01:27 AM
keep everything 89-91. better air flow memter, computer with no rev limit, better intake runners.

same setup on our cars and we have three track records here in the northeast.

mixing the components was thought of as the hot ticket but not now.

Karl Bocchieri
01-17-2002, 09:45 AM
After removing the 6 port actuators and polution controls I wired the rotary valve in the short runner position. How could you activate the rotary valve without putting back the rest of the polution garbage?

01-17-2002, 10:11 AM
Now I'm confussed (as usual) My car is an EP car but you guys are always a good sorse of info. I use a haltech injection system so that negates the advantage of the latter computer and AFM. The roto intake valves are long gone and the long / short runner flapper is wired in the short pos. I'm just wondering if I have effectivly negated all the advantages of the latter manifold and are these advantages even applical to what we are doing? I am planning on setting up an old manifold to test against the new style on the dyno. I'll let you know what happens.
PS who's in on this? I see Mark C. from PA and Brian B.from NH. Are you whom I think you are?...

01-17-2002, 07:35 PM
For Eprod and ITS, the latter intake with the rotary valve wired in the short position is probably the most reliable setup (no moving parts,controls)for a car operating above 5000rpms 95% of the time.
Is that John W. from South CT?
Brian B from WMass