that is my experience yes. first we had mfr spec exh port, open at lest say 74 deg, engine did not respond to anything and flatined at 270 hp (13B). afterwards I increased port size and timing to turbo spec opening and got same hp, then I added slight amount of timing and picked up 15hp or so. ended up at 30hp more by just changing exh port size and also gained more midrange. this would be 45hp 20B equivalent.

also if you look at a renesis engine with the crappy exh port, it also doesnt react on timing at all.

 

So this may be unrelated......but, how far in advanced timing would you theoretically go before actually firing in the chamber before? Or how far advanced could you go before the leading would fire on the apex seal? Just curious.

 

So......how much does anyone out there think that the last 10% of throttle will be worth?
I'm an idiot. I only had 90% throttle opening.

 

So I measured the intake with where it ended up fitting under the bonnet. Centreline of the intake is 480mm / 18.9inch, to the face of the engine.
The headers measure roughly 2200mm / 86.6 inch.
So from what I've read so far the intake is too long for peak power. Thing is, the intake has to be where it is to fit in the car.
Now I cannot go longer with the headers but I can go shorter, in fact that would be much better to fit under here if they were.

 

Also, I will be setting up the primary ports on separate runners to open as well. So I'm not sure how to work this into the equation.

 

Im running 343mm header length in out 13B PP 48mm ID, can't recall throat diameter of the collector but from there it expands in 4' volume, much like a 2 stroke expansion chamber.

intake length is 430mm on our car, if you look in the topic 13B PP ign breakup you will see dyno on last page.

I think if the engine does not respond to timing there has to be a serious airflow restriction going on. the mixture you report seems slightly rich for max power, but every sensor reads slightly different. Im seeing max power/torque at around 13.5/1. I ditched now the wideband and just tune based on EGT. runnign around 25 deg leading with 3-5 deg split I try to keep EGT's below 1000°C on long striaghts.

I think for peak power these ports will not make too much difference as the PP you have are already healthy sized, and the Primary ports close way too soon to be of much help at high rpm. What is the port closing timing on the PP ports?

 

Best power delivery for a 2 rotor PP seems to be an exhaust length of about 90in. A decent size exhaust port, and a decent amount of overlap. Intake length does not seem to matter so much. The last 10% throttle will make next to no difference. I agree, you appear to have a restriction somewhere. - a decent 3 rotor PP can make over 500whp.

 

What if my timing was actually only 12deg adv not 22deg? I am running a FFE FD trigger wheel and I am thinking I have made an error setting TDC and am actually 10deg out.
I need to dig up my standard pulley to confirm this, but from all photos out there, this seems to be the case.

 

They are based around MFR timing. They are also round on the housing face, no square cut offs. I'm really hoping that run was done at 12deg advance, and that is my issue.

343mm header length, is that correct? So do they merge almost immediately out of the housings? My 90deg bend out of the port is 200mm alone.

 

thats correct yes, they merge just after the bell housing to engien flange.

 

Ok so good news. I used the oil-in-the-chamber method to find TDC. It turns out that by using an FD 13B-REW timing marks on a 20B pulley hub, the TDC marking was 15deg out!
So I was actually running about 7deg advance. This would probably explain why I didn't see any hp gain increasing timing.
Hopefully with the throttle at 100% and timing now set somewhere normal, I will see some nice increase.

 

that's a good bit of troubleshooting you did there to figure out the timing was so much off. good luck in round 2.

 

Hmm actually I would expect the gain in torque/deg timing would be higher the further you are away from optimal timing. the curve is like a quadratic, torque=f(ax^2+bx+c) (is this right word in english) parabol. around peak torque its almost flat an the further you go away from peak the gradiient gets steeper.

 

Well I'm not sure on the theory, but the thing drives like it should now. It felt a as if it was towing something before! To give an example, when I left the dyno it was wet, on a back road I clutched 2nd gear and it just bogged, wouldn't even turn 235 tires in the wet!

 

This is the exhaust template I used too.

 

For anyone that hasn't seen the thread about my timing issue, here it is. VALUABLE information for anyone wanting to run FD front cover / pulley on the 20B.
https://www.rx7club.com/20b-forum-95...quest-1091664/

 

Any updates on power after your pulley/timing issue?

 

its been a year, any updates?