Roadracing7

iTrader: (2)

I know this topic is VERY old, and I apologize for starting this one. Maybe we should have a Non-sequential forum set up so that when we don't feel like hearing everyone argue over which is better we don't have to...

Anyway, I recently went to the dyno after converting to non-sequential as just a precautionary measure to be sure I wasn't running lean in certain parts of the fuel map and that it was safe with the same maps. I don't have a wideband, so I have to go to the dyno to use their's. I wanted to be sure that the transition fuel correction that is put in maps for sequential operation wouldn't cause bad AFR when running under constant boost. I did a run and watched the AFR remain below 11, so I knew I was safe. I also recently reinitialized my PFC and put Tim Benton's maps in (in no way are the results any indication of the quality of Tim's maps as my car is just generally similarly modded to his.) I used the maps as a good starting point to tune my particular car. After three runs, I had more or less stabilized the AFR and was happy with the results, so I brought up an old graph that I had back in January and overlayed it on the new graph to compare sequential to non-sequential.

My original theory when converting to non-sequential was that the initial lag created by spooling two turbos at the same time would be outweighed by the fact that I would reach full boost before the normal "transition" point and the car would have a flatter power curve, however, at the same peak power. After converting to non-sequential, the car felt faster, at least according to the butt dyno and I was happy with the modificiation. See old posts on the subject... The next step was to make sure the engine was safe, then to tune the car for hp to see what was available in the non-sequential setup.

I realize that the two dyno graphs are not 100% telltale of sequential vs non due to the fact that the runs were over 5 months apart with ambient temperatures differing by some 30F+. I can say that the water temp and air temps were within 5F on the two pulls (I used ice) according to the PFC. Humidity was slightly higher on the non sequential pull, so I am keeping that in mind as well. The difference in the two sets of maps I believe could change the curves either higher or lower, but the basic shape should remain the same. Both pulls were taken with a peak boost reading of 0.85 bar. The main point I am making with these two graphs is the basic shape and characteristics of the curves because I beleive we all agree that peak power will not increase past the "transition point".

(Download pic now if you haven't already and follow along)

The blue run was the January run and resulted in 291.6rwhp. You can see the transition "surge" of power that I have noticed shows up often with the PFC on stock sequential twins. Late in the run, I had a bad electrical breakup and the run was aborted (I think the bag of ice melted and water got around the coils/wires, pretty stupid... )
The red run was the recent run with non sequential setup and resulted in 269.7rwhp. The rwhp differences don't bother me as I have a lot of variables affecting peak power, so that will change. (out of curiosity, what do you consider a reasonable goal for the mods listed at 12.5lbs?)
Notice the area between the blue and red curves from 50-75mph (sorry no RPM). This was to be expected for the most part, however the red curve was supposed to be above the blue curve before the 75mph mark for the mod to be beneficial. Then as the pulls progress, the red curve comes up to touch the blue curve proving the fact that after transition, the power is the same. What I found interesting after this intersection is the sine wave effect as the red curve touches the blue curve, bounces down, touches again, bounces down, then flattens from 102-125. The only logical explanation I can reach, is that the boost is fluctuating through this point and had I had a datalogit, this would be easy to find. This matches the problem lots of non-sequential people have described as reaching full boost and then having the boost slowly drop as it increases revs. Maybe the PFC is compensating for some kind of fluctuating input it is receiving (boost sensor/solenoid duty cycle?)If that's not the case, then, I could have a small leak in my piping (very possible since TB o-rings don't seat well in my car). The flat lining I believe is an issue associated with tuning the fuel and ignition maps to increase power.

My conclusion is that sequential turbos are the original design of the car, and should not be tampered with because though the theory that boost is reached earlier has merit, it does not hold up under testing (without moderate to heavy tuning with a Datalogit). I have switched my car back to sequential (took only 20 min which is nice) and plan to work with the new maps (w/ a datalogit hopefully) on the dyno to get optimal AFR and hp. Then, if my car still hasn't sold, switch back to non-sequential, tune again, and then run back to back with optimal maps on the same day under the same conditions on both setups. I would appreciate any feedback on what you would add to this "project" to fairly compare the two on the dyno. (no comments about "Dyno doesn't mean anything to me, I only car about ET and traps...")

Street King

Very insteresting. I still see too many variables that happened between non and seq runs. But good overall. Iam still going through with mine though.

RX-8

iTrader: (6)

great info!!

kwikrx7

Interesting info. I don't think that this debate will ever die. The car was made sequential for a reason - not to be like a 300ZX TT or VR4 running parallel - but having endless boost at any speed. If Mazda would have made the sequential system more reliable (like a Supra's) then not many would do this mod. It would really take somebody getting dynoed with sequential - doing the poorman's non-sequential and dyno again to really hash this out. Either way the peak power won't be any different. After transition, the both turbos run parallel anyway so there wouldn't be any difference up top. Exchanging low end for midrange is all it is. It does show by your info that the sequential car has more power most of the way through the powerband but with some tuning with datalogit that would change. Nice graphs though!