I'm building a new 13B standard bridgeport with superlight 89-91 NA rotors from RB. It will be fully balanced with an rx8 E-shaft and carbon apex seals.

1. Is it easy to destroy the carbon apex seals if I go to far with timing on a nonturbo setup?

2. I know the power to be gained on this setup will be with proper tuning. I'm hoping to get close to 225-230whp with around 20 degrees timing. I've heard 240whp is possible but I'd have to probably run closer to 23-24 degrees of timing but am scared of detonation and blowing an expensive new motor. Is this timing Ok? and what octane do I need if I run a more advanced timing.

 

1. i'm building a PP with carbon seals, and everyone else has been pretty paranoid about detonation/pre ignition. so i think that would be a yes.

2. the timing you end up with depends on the bridge (size, shape) and intake and exhaust. i'm hesitant just to spit out numbers, but ive seen anywhere from 22-27L. just be careful

 

That sounds about right. I'm pretty sure we ran about 20 with the last motor. Maybe we can step it up to 22 and still be conservative. Last motor jumped up 10 whp when I increased the timing to 24. I was to scared to run that timing for long periods of time on the track though. So we backed it off to 20

 

My only experience with the carbon seals has been with stock, 6-port engines in an ITS configuration. In those engines we've tested timing all the way to 30* BTDC leading on 87 octane and not had any issues. We just tuned one of our engines a few weeks ago and saw 184 whp. Timing at 27* BTDC on 87 octane. The seals have proven themselves to be reliable IMO.

That said the higher chamber filling of the bridge port should allow you to pull timing back a little. And if you run the car on 93 octane I would see no reason you couldn't run it at MBT and I would guess that would be somewhere around 24*. One of the keys is to keep the chambers cool. Doing the water jacket mod around the plugs would be a great idea. Also, keep the oil temps in check.

Are you running a programmable ignition or dizzy? Would help performance if you could add a few degrees of timing past the torque peak. Would help extend the top end and peak power while not having too much advance at peak torque. If you're running the locked dizzy like a lot of racers you'll have to compromise on timing.

 

We are running a MOTEC M4 FI. So I should leave the timing alone until past the peak torque, then increase slowly to 24 at about 8500rpm? I'm not sure where the timing is at when our torque peaks.

I will have to look into the water jacket mod. They may have it done allready, but I don't know. I will ask them about it. I haven't had to many problems with cooling since we installed the alluminum radiator, but I realize the chambers are warmer around the plugs.

Thanks for your help in the matter

 

Coolant jacket mod is pretty simple if it hasn't been done already.

I used (am using right now...) a large dremel engraver bit on the drill presss. I set the depth, move the housing around, lower the depth...repeat until done

First housing took about 1.5hours, second is moving along quicker.

 

Thing to do is settle on your fuel. If you think 93 will offer enough detonation resistance (I do but what's that worth? ) use that and stay with it. If you feel you need more maybe find some 100 octane race fuel or mix race fuel with the 93. I would think, but have no experience with your combination, 93 octane will be plenty to find MBT. Remember that in the 80's the pro racers were running wild port combinations and running low octane fuels.

At any rate settle on a fuel and stick with it. The required timing will be dependent on the fuel. Meaning if you decide you need 100 octane you might need a couple degrees more advance than you would with 93. If you tune it on 100 and then drop 93 in you're asking for problems.

I'd start out with about 20-22* across the board. Then add a degree at a time while making pulls on the dyno. Power should pick up quite a bit with each increment until you get close to MBT where there will be diminishing returns. Over MBT power will hold steady before beginning to fall again assuming you don't experience detonation. Once you have timing figured out around the torque peak I'd look at where torque begins to fall off and add timing in one degree increments past that RPM, probably somewhere around 6000-6500 rpm is where you'll start adding some advance. What happens at high RPM is that there is simply less time to complete the burn and you need to start the flame propagation sooner to achieve a proper burn. Past peak torque the VE has dropped off and cylinder filling is less making the engine less prone to detonation.

Also, work out your fuel first and keep an eye on EGT to see what effect your timing changes are having. To be effective your EGT probe NEEDS to have a fast response time. Shrouded probes are junk for tuning. They react far too slowly and provide measurements that are not accurate. I use these probes with excellent results. http://tscsensors.com/egtep0720001ssnexhau.html There is also a pretty good thread on this board somewhere about probe response time.

Lastly, there are some great tuners in your general area with experience with this type of engine. In the end it might be worth the expense to bring the engine or car to someone like Paul Yaw, Dave Lemmon, etc to make the car fast and reliable.

 

Ludwig - not to get too far off track on this thread, but whats been your experience with lifespan on those open element EGT probes?

 

Tripoint has been doing the tuning on the car. I'm not questioning their expertise, but they said they didn't want to run over 20 timing and be resposible for destroying my motor while tuning. I'm not sure how many nonturbo race motors they've built and tuned over the last 5 years. The last bridgeport they built made 217whp @ 8100rpm. That motor is toast, due to an 3rd gen oil pump shaft failure. I believe the motor they built would have lasted a long time if it hadn't been for that.

This new motor I'm taking a step further. We are doing the superlight 89-91 rotors with rx8 e-shaft with a full balanced assembly. The motor will probably make a little more hp just with that setup, but figured there is even more power in timing. I found out that my old motor did not have the water jacket mod. The old motor I was mixing 4gal/1gal 91octane/103octane. At nationals I put 93 in the car.

With more timing advance, can we get power to peak closer to 8500rpm rather than 8100? I spoke to racing beat and they told me a really good standard bridgeport, depending on intake/exhaust etc, should make peak power close to 8500rpm. I was generally shifting at or before 8500rpm with the old motor and had a rev limiter at 9000. There was no point in going higher since power started falling off and I have a close ration transmission anyway. It would be nice to make a little more power and have the motor pull strong to 9000

 

Quite good. Haven't killed one yet.

 

The bridgeport is going to be very sensitive to exhaust and intake tuning. Timing probably isn't going to shift the entire curve the way I think you're suggesting unless it's wayyyy off. It's more likely the exhaust and intake aren't jiving with where you want the power band. I've spent a good deal of time on the phone with Jim Mederer at RB. He's very informative and will tell you exactly what you need in the way of intake and exhaust to maximize the port scheme. He'd be a great person to get on the phone. He'd be able to tell you without a doubt what kind of timing you need as well.

If power is peaking at 8100 you probably don't want to shift at 8100. What you're trying to do is maximize average power. With the ITS engine power peaks at around 7400 but the shift point will be around 8200. Even with a close ratio box you'll probably need to rev a little past the power peak to maximize average power.

 

The only potentially restrictive part of the intake, not including the port itself, is the manifold/throttle body. I'm using a port matched 3rd gen lower & upper intake manifold with throttle body. After the throttle body, everything forward is custom. I make good power from 6000 - 8500. If I shift around 8200-8500, I end up around 6500-7000 rpm in the next gear. My range is good, I would just like a little more power overall. I'm also running a 4.875 final drive, in 5th gear at 8000rpm I'm going about 131-132mph. There are only a few tracks I get that fast, Willow Springs - 132, Fontana - 134, and Mid Ohio - 131. Roughly

Sounds like you have a fast ITS car. What region do you run with SCCA? Where are you based - Indiana? Over 180whp with a stock 6 port is really damn good!

 

I'm not talking about restriction in the intake or exhaust. I'm talking about tuning the length and volume of each to suit what the engine needs. With the high overlap of the bridgeport the tuning of the intake and exhaust runners becomes critical to power. If they're too long or short you'll kill the power.

I had a fast ITS car but have gotten out of racing myself. We were Cen-Div champs in 05 then I sold the car. We won 5 races in a row at Mid-Ohio that year until we lost our good engine to a failed rubber plug on the heater hose outlet on the rear iron. Don't use rubber plugs there! Guy I've built engines and done tuning for won the Mid-Div championship last year. Another guy in Cen-Div has the high HP car. He's one of the lucky few to have the SDJ header which helps. I put his engine together, installed the Haltech system, and tuned it. He's actually on this board.

Is this a j-bridge or standard bridge. I spoke with Jim at RB a couple years ago when I built a j-bridge engine for a guy. Jim gave me all the measurements for the intake and exhaust. If it's a standard bridge those measurements wouldn't exactly apply though. For the j-bridge the runner length should be 16" from the iron to the trumpet. A standard bridge would probably need something slightly longer I would guess.

 

The motor is a standard bridge port. I will measure the length of the intake sometime next week, I have a feeling that it's probably close to 24"

I only ran once at Mid-Ohio, it was just a couple of weeks ago for NASA nationals. That's when my oil pump failed on the first day. I had about 25min worth of driving time on the track. I was still getting use to the track but was able to run a 1:34.1.

 

+1...

um rotary god has a nice post about intakes. i think he mentions the stock intake lengths in the post, as well as how to calculate the "right" one.

the cool thing about sevenstock is you get to meet everyone, jim is a very nice guy.

 

I think this is the thread j9fd3s is referering to. An oldie buy goody.
https://www.rx7club.com/showthread.p...ghlight=tuning

 

yep, thats the one.

 

Thanks to both of you. How was sevenstock? My car was there with Tripoint, but I had to work on Saturday.

 

I think my proper intake length should be between 12.4-12.9" according to the calculation. That is tuning for peak HP between 8200-8500 rpm. Those figures may be off slightly since he didn't list the duration for a standard bridge port. I used the opening and closing for the old 4 port street port.

My car has a stock 3rd gen intake manifold tuned for 6500rpm, It is probably around 17-17.5" like the other stock intakes. It would be interesting to see the changes if I could take 4-5" of the length. HHHMMMMMM

Also, I'm looking into the exhaust tuning now. I may benefit from shorting the distance to the Y pipe. Currently just before the rear axle.