I've been thinking about this pretty heavily for the past few days, and I'd like to hear others' opinions.

Here's the setup;
1989GTU

Bareblock
Standalone for fuel
12A Dizzy setup
2.5" single header-back exhaust
3.5" metal CAI from the fender
Ported/polished/blasted S5 intake manifold

Now, the engine is about to be pulled apart and rebuilt. I'd origionally planned to do an Aux-Bridge (w/ functioning 5/6th ports & VDI [retuned]); but this will be my daily driver, and I really don't want to take the chance of this NOT working (I can't afford all new irons + rebuild costs again).

I've only been able to talk to 1 person who has tried the aux-bridge (Mazdaspeed7), and according to him, with the flow characteristics of the aux, you'd actually get power-loss with the stock manifold vs. a large SP. I'd spacifically like to talk to Ito about his bridged engines, but he's almost impossible to get ahold of. If I could get confirmation that this WILL work, then I'll drill the bridge myself; but without, I'm begining to err the side of caution, and just go w/ a big SP.

I eventually plan to do a completely custom intake setup (individual runners, etc) but that's down the road, and the time to get the engine together is now.

My question is, should I stick with the aux (which I know most people want to see work), or go with a tried and true big-SP?

Please chime in with your $0.02 and help me decide to go one way or another.

 

Im building an aux bridge right now out of an S4, Im putting it together as soon as I score an 89-91 rotating assembly (hopefully in a week or two it will be together).

I know that Judge Ito made a full bridgeport motor out of an S4 motor and with all stock (I believe) intake/exhaust there is a video of this bridgeport drag racing a TII and it was winning most of the time. Unfortunately God did not want this much power out of a NA and someone crashed it.

This leads me to believe that at least the S4 is not choked too badly by the intake manifolds and so I am going to try a measly aux bridge. I will use a Megasquirt ecu to control fuel in get rid of the AFM but I will try and start the car on the stock ecu and see how it runs. My advice is to wait and see how my auxbridge turns out then make your decision how you port you irons.

-Dan

 

Are you planning to bridge both ports on the endplates? or just the Aux? If it's just the aux, that's a very viable solution.

 

Are you planning to bridge both ports on the endplates? or just the Aux? If it's just the aux, that's a very viable solution.

 

Just the aux will be bridged

 

First, I can't count how many times I've heard "porting will ruin the VDI effect". Does anyone have any proof of that? My casual knowledge of dynamic supercharging theory leads me to believe that extended intake duration will benefit from having an S5 manifold, since such an effect is dependent almost solely upon engine speed, wavefront propagation speed (constant) and runner length.

Next, if you're going to go standalone, there's no reason to use a distributor. The 12A dizzy can be curved to suit a 13B, but it's still suboptimal, IMO.

Brandon
BR7 Racing

 

1st, I'm all about going fast for cheap; hence, my standalone is the MegaSquirt. The MS doesn't provide spark, and you can't piggyback it on a S5 ECU (you have to keep a lot of crap, or you'll go ito limp mode). I know the M/T is better and whatnot, but I don't need it.

Also, I'm not just throwing the shoddy 12A setup on. I'm doing a direct-fire setup.

 

The dizzy should hold him until the MegaJolt is released.

 

I briefly considered an aux bridge but did a street port instead because I have heard that the bridge can be fragile and not last 100k miles. It would alwo open a lot earlier than the secondary port which shares the same intake runner, which would mess up any kind of pressure wave tuning effect in the manifold.

So I did a street port . . . and it is very streetable. Pretty good torque in the 3-4000 rpm range and it appears to want to take off after that, but it is too new to rev to redline so I don't know how much ultimate power it has . . . yet.

One thing to consider . . the S5 manifold might not be the best choice for any kind of porting. I have read many times that the S4 unit is better suited, while the S5 is tuned for stock (and only stock) ports.

 

I did a street port in a S4 with S5 rotors and S4 stock injection, Racing Beat header, and 2 1/2 inch center muffler. With used housing and only 150 mi. on the motor it dynoed 163 RWHP on a near 100 degree day. There were no actuators so not much under 6,500rpm. But when it came on it drove good. My 184k. S5 GTU with same exhaust and stock motor got 140 RWHP. ITS race car with S5 FI and motor, no six port actulators, and 3 inch straight exhaust got 150 RWHP. I have seen stock 6 port motors put down over 170RWHP but they are all with S4 manifold and SAFC. I was thinking to do a street port S5 with actulators and SAFC, but I drove a GTUs that had the same of what I was going to do, it was not all that impressive to me. I am just going to do a 4 port with S5 turbo housings and fed by Holley, I don't think 200RWHP is unreasonable. I think a street port with S4 FI is as far as a 6 port can go, a bridge will just be too much. 4 port just seems that much better to get power from. A bridge port big or small will lump at idle and it get old fast if you are stuck in bumper to bumper traffic. I had 4 port small bridge sec., small bridge all ports. Small bridge will give you the lumpy idle and reduced economy with out the top end flow which a bridge port is meant for. The difference of a sec. bridge on 4 port is really not that much off from a street port 4 port. It is when I went J-bridge the high end power increase was obvious.

 

Here's a Q for Adam.

If I were to do an aux-bridge, and it didn't turn out; couldn't I just replace the sleeves with some un-notched ones, and drive it as normal? In other words, forever closing the aux-bridge.

 

With the way the bridge is angled, the 6 port sleeve will only block abotu half of the bridge when its open. Ill take a pic later to show you.

The problem with the VDI manifold is twofold. First, the runners are very small in the upper part. Second, the VDI effect does NOT seem to work on ported motors. On my last 2 ported motors, my car had more power EVERYWHERE with the VDI wired to high. The VDI manifold is a waste on anything but a stock, or very mildly ported motor. Both of my engines were far from mild. I dont understand the intricacies of the tuning of the VDI manifold to try to explain why, but it simply does not work good on ported motors.

The simple fact that I pulled my perfectly running aux bridge out of my car at 15K miles, and put in a street port motor should be enough to convince you its not worth it. In all honesty, no matter how well I could have got that aux bridge to run, Im pretty sure my SP will make more power, and have a better powerband. My SP motor is surpassing all my expectations, and I only have 500 miles on it.

I believe most of your setup is wrong for any high hp n/a, especially an aux bridge. First, the exhaust will need to breathe. A single 2.5 will cost you power on the top end. Rotaries in general really like to breathe, especially on the exhaust side. Next, the S5 manifold will not cut it. I could NEVER get my car to run right with the 6 ports open. I drove for 15K miles with them wired shut, and I tried everything to make it run, all to no avail. With the VDI set to low, there was a spike in the torque from 4500-5000 rpm, with power falling off rapidly afterwards. With it wired to high, it was a dog to 8K rpm, where it started to pick up some, but nowhere near enough. My car was faster with the 6 ports wired closed.

I do not think an aux bridge will make enough power to justify ALL the work necessary to get the power from it.

 

One more thing. If anyone wants to read up on the runner issues, click here.

 

Still Adam.

w/ an unnotched 5/6th port sleeve, the ENTIRE bridge opening would just be sleeve-face.

If that were to happen, and the bridge were to be closed off, you'd have no more issues, correct? (other than possible water leakage, or much less likely the bridge breaking more than 100K into the engine's life)

 

I'd really like an answer to this...

 

I distinctly remember an unmodified sleeve only blocking half of the bridge when its open. But Ill get a pic tomorrow to settle your doubts.

I still think youre making a mistake doing that motor, unless you have something to prove. Its easier and cheaper to get the power out of a half bridge 4 port, or even a SP 6 port if you know what youre doing.

 

All I wanna know is, was "cermac coating for power" worth the two hundred bucks?

 

When did I ever say it was $200?

 

Heres an unmodified sleeve, fully seated in the runner, and fully open.

 

damn this forum blows.....it took me 10 tries to make that last post with the pic, and now th epic wont show up in the post, even with the proper tags.....

 

So it was more? Aircraft Spruce only had that listed when I searched for 'ceramic coating'.

Or maybe it was less . . oh well, you have your secrets and I won't ask any more. Dyno that beast of yours! I'm going to do mine sometime soon, a couple months maybe.

 

I paid WAY less than that.

 

That is one seriously rough bridging job. If that was what you installed I'm not suprised it didn't run well.

 

Thats not the plate in the motor. I didnt use it because the bridge eyebrow cut rarther into the bridge than I wanted. I purposely left the bridge thick so it wouldnt break. The ports in my motor look much better.

 

That's OK then. I was worried for a second.

Back on thread: I am intrigued by the trade off involved here, and whilst I am sure that a good SP will give better results on an OEM intake it would be interesting to see how it behaves on a more optimised inlet.

I do a lot of playing around with motorbike throttle bodies as they are cheap and plentiful and was seriously considering a 5 throttle setup on a 6-port one day. With one throttle per secondary runner this opens up some interesting possibilities.

I am also aware of someone building up a bridged aux port using a Euro spec lower manifold. The euro aux ports were vac rather than back pressure operated and had a butterfly in the LIM rather than a rotating sleeve. Oh and no cats as stock :-) It will be interesting to see how that pans out, even if the differences between dyno methods between USA and the rest of the world differ.