65Z01

I have an article with pics on this mod that says/shows they went in 3 1/2" into the intake base runners. With only about 5" of runner in the intake base I think a 3/4" x 1 3/4" hole between adjasent base runners would work out better. This gives about the same area of opening as the runner diameter does.

Has anyone here done this mod and have test results?

Black 'n Blue

I've been thinking about trying this as well, and I was thinking along those same lines--why make the hole any bigger than the runner opening. It seems like a larger hole would just create a lot of turbulence in there, and it may be that the shape and position of the hole is more important than the size. Seems like you're closer to getting this done than me though. Good luck.

Linn

65Z01

I've scanned our archives for "siamese" and am running a thread on http://www.thirdgen.org in the Message Boards, TPI section with the call sign "Jim 86 IROC".

So far I've found contradictory information so am going a little shallower on this first cut. Though some guys have gone 3"-5" into the base, we'll see what the time slips show. Maybe at the strip in 2wks or so.

want2drivemy85

mine are about 3 1/2" deep, i still have good torque, but sorry I don't have any test info on it.

65Z01

In our archives on this topic, "89 Paul in cal" reported that he got reversion from going too deep on the 5/7 partition. This was the main issue that concerned me; so I decided to go easy (shallow) initially.

Did you notice it pull longer/harder up top as often reported by others? I suspect there may be a little low end torque loss but maybe not enough to be noticed. I'm planning on doing heads next so a little drop down there now will be picked up then. My goal is to extend the high end while retaining original low end torque levels.

Black 'n Blue

I think I'll be going 3/8" x 1 3/4" -more like a slot than a hole. Which force is more likely to move air through the opening at higher rpms--vacuum/low pressure or flow/momentum?


[Modified by Black 'n Blue, 9:47 PM 4/12/2002]

65Z01

FYI, Madmax on the Thirdgen Forum just posted up an old thread on this mod with lots of discussion and several dyno comparrisons: http://www.thirdgen.org/techbb2/sho...ghlight=siamese

Black 'n Blue

Thanks for the info! One of the things I'm wondering about is if it would be feasible to mount some kind of sensors inside the base runners and try to get some readings of what's going on in there at different engine speeds. Any thoughts on this?

65Z01

Hmm. In "Desktop Dynos" it's mentioned that pressure transducers were used to study pressure changes during filling/emptying.

This would take several transduceers within each of the two runners and a good data gathering/analyzing program for your PC to gather enough data points during the intake valve opening/closing for the two cylinders to track the pressure waves.

Black 'n Blue

It's probably just wishful thinking on my part, but I was really just trying to think of a way to measure the difference between 5 and 7 since that seems to be an area of concern. My thought was that it might be possible to replace the #5 injector with a MAP sensor and take real time readings at different engine speeds, then do the same with #7 and compare the results. But for all I know that might not provide any useful information anyway. :crazy:

65Z01

I would feel better about drilling into each runner and inserting the pressure probe. Later you could pull the base and plug the access holes.

If you collected data every 2deg or crank rotation, at 6,000rpm it would require a frequency response on the data collector of about 30usec. This is quite reasonable today and not too expensive to setup. You would need a small signal conditioning breadboard fed into a lap top parallel port. Then there's the C++ or VB program to gather and store the data... I don't know if there are any plug in cards at reasonable prices to do the h/w inteface.

I think the spark plugs will tell the tale, soon as I get my oily situation figured out and corrected.

I'm having the Vette looked at tomorrow to isolate the oil leak. I hope to start the mod installation later this week. I'll be sending the injectors (including the cold start) off to Rich at Cruzin Performance. He still reconditions a set for $10/injector plus $5 for any replaced during blue printing.

So I may be at the strip in about two weeks to run the first set of tests.

pablocruise

just came across this. Jim, how's the intake? Port it yet? Need some pics of my "victim" intake and how NOT to port it? :lol:
Also of interest: Ever see the siamesed runners from SLP? Notice that they also do not merge 5/7 runners down at the base area.
Thru my own dumb independent misguided handywork, I un-intentionally came up with the same conclusion/empirical evidence apparently.

65Z01

Paul, the porting/polishing is done but I got delayed attending to three other issues: oil leak (rear of intake), blowing smoke at 1,000' (maybe bad MAF) and most recently severe surging and dying at idle (bad MAF). The compression check showed about 165psi +/-10psi on 4 cranks, with no low pairs, so I don't think the "puff of smoke" is due rings or head gasket. Since the plugs were very sooty (not oily)) let me blame it on the MAF, for now anyway. Since I'll have time I'm going to pull the valve covers and check out the lower seals (only replaced O-rings when I did the RRs).

This AM I finally pulled the plenum and runners (before the rains). I'll port match the used runners to the plenum and try to get the stock base out tomorrow. The stock injectors (including the 9th) will go to Rich at Cruzin Performance for reconditioning/blueprinting and hopefully be back when the Wells MAF arrives late next week. I'd like to take it to a local strip next Sun for some T&T passes.

I can't recall but was that reversion detected by spark plug condition? You can send some pics to jgkov@msn.com or post the thread URL if such they're up. There is quite a thread going (that I started) on http://www.thirdgen.org/ http://www.thirdgen.org/techbb2/show...threadid=98960
One of the guys there has siamesed his base on both sends leaving only an inch or two of wall in the middle; he swears by the performance results. But I'm conservative and so only went about an inch or so into the runner end; since it's a spare base, I can cut more later if no gain is seen with this shallow cut.

65Z01

Black 'n Blue, one of the guys responding to this thread on http://www.thridgen.org came with an interesting way to check for power imbalance. He suggested putting a scope on the motor and having a balance check done to show any differences in power developed between the cylinders. I don't know if this can be done at high rpm or just at idle, as power is cut to each cylinder in turn and the resulting drop in RPM measured. Would the balancer handle the imbalance at higher power points well enough to prevent engine damage during the test?? But it's something to check into once I have the mod implemented.

Black 'n Blue

I just read Dave Emanuel's description of the Holley Z Series intake manifold, and it's interesting how it compares to this situation--

a balance tube "connecting the runners for cylinders 7 and 8 serves to add volume to runner 7, which is usually robbed by cylinder 5, which fires immediately before it."

So this problem has been around for a while. Maybe it's just time to change the firing order. I don't know about the scope test damaging the engine, but isn't the timing belt supposedly the weakest link? That might be scary.

h rocks

Timing belt? :crazy: :confused: