88' GTU with a 13b semi pp, efr 9280 running on a microtech LT10c. After breaking a side seal in half pushing it on straight 93oct w/o egt probes, after a rebuild and break in we switched to x85 and is making a healthy 520whp@6700rpm/450ftlbs@5500rpm (620hp/540tq at the crank) @ 25psi reving to only 7100rpm with egts just touching 1650f. Video is linked at the end.




RPM Signal to logger was dropping out towards the end, Blue dotted line is 10.0afr and Red dotted line is 11.0afr

This however did not come without a some trial..before strapping the car down we swapped in a new set of denso iridium racing 10.5 plugs 5720 (had been using a set for break in), made 3-4 power pulls with the last 2 starting to get choppy up top but nothing super alarming but decided to pull the plugs to be sure and boy im glad we did.


Front Rotor L

Front Rotor L

Rear Rotor L looks absolutly hammered even on the face

Rear Rotor L the ceramic was hammering its way out

​​​​​​As you can see the Center section of ceramic had broke right in half and was a few thousandths from falling right into the housing, talk about dodging a bullet. This was on both L and T for the Rear, fronts seemingly uneffected. After being sure all pieces were accounted for we put in some NGK Racing 11.5 heat range plugs gapped to .021 and did a chop without any tuning change


NGK Racing Plug has fully supported ceramic


From left to right, T1,L1,T2,L2

Clearly the rear was running lean relative to the front, even with the O2 sensor on rotor 2 reading 10.9-11.4afr so i'm sure those denso plugs "saw some s***". Im not saying they are bad plugs by any means as the conditions they saw were extreme but the sizing and placement of the center ceramics on the denso vs ngk are night and day. I will only run these from here on out.
Added fuel until the plugs looked happy (disregarding the o2 sensors value at this point) and kept turning up the boost.

Im attributing this hiccup to our unequal length undivided exhaust manifold, home brew LIM, semi p overlap and injection timing that causes the fuel that should be going into the chamber/combusted is getting pulled right out of the exhaust port giving a false o2 reading, I have read a few post on here touching on the idea so i know i'm not breaking any new ground just sharing my experience and thought process hoping others may have some input


Our current exhaust manifold

All in all, it's an absolute missile of a car even at this power level, next will be adding more WG spring as were at 100% duty and installing our Turblown Cast upper and lower intake manifold with more injectors when it shows up

 

In the name of science, I would be willing to give you a discout on one of our FC T4 EWG manifolds. I've personally seen some large back to back gains over improper units. I'm not one to talk about competitors units, but that just isn't going to cut it for your setup.
Obviously it will be a pain in the butt as you will have to refab items since turbo position will change.

 

I will be in touch about the manifold, I'm okay with ditching the dual o2 sensors for what looks like the addition of pressure sensors. Were currently running a 3" downpipe off the turbo, straight thru resonator then into dual 2.5 with magna flow mufflers. Our current shaft speed with addition to pressure sensors would really answer it, but should I be looking at a downpipe upsize on our list as well?

 

For a semi pport yes its on the small side. It is easy to dyno test, just unhook the midpipe and do another pull