Roy Johnson, Jr

What is considered to br a safe degree level. The car is daily driven and I have a T-78 with streetported engine.

Thanks.

Roy Johnson, Jr

Has no one ever looked to see where their timing was at and found out whether it was in line or not? Come on, guys, how about a little input??

pluto

It depends on your application and at what boost level. in normal curising, you should run in the 30+ range.
at 10psi, you can safely run 20-22
at 15psi+, I run 14-15

waynespeed

If your timing is more than 5 degrees over what Pluto stated, I would be concerned with 92 octane street gas.

risc

I an running a lot less timing than that at low loads, especially at low RPMs. My engine was not happy with that much advance. I think that porting plays a big role in proper timing.

Roy Johnson, Jr

I'm running 17 degrees at 15-16 psi. So, if I decide to run race gas one weekend and turn the boost up 2-3 psi, you think I should leave the timing where it is? I'm running 11.8:1 A/F.

waynespeed

With all those goodies you should'nt have a problem running 20 psi on race gas.

RICE RACING

Porting plays a MASSIVE role in the engines tolerance to ignition advance.

Some peoples "street port" is nothing but a cleaned up std port, this combined with moderate exhaust port rework means that with pump gas you can run near stock port timming (ie around 20deg) up to 1 Bar gauge pressure.

Ported engines, street ports and higher, when done to their limit will significantly increase the gas pressure and flow in the rpm ranges above 6500rpm...The gains made in the Volumetric side tend to (as expected) put a lot more strain on the a/f mix when it gets compressed, because even though you are running the same 1 BAR BOOST the "effective" or dynamic compression ratio is increased a great deal over the std ported engine. Hence, in every application you will find that you need to run a lot less advance than you did on the stock ported engine. The average timming I run on street ported engines is around 15deg, this is to cover EVERY situation, High ambient conditions, bad fuel batch etc.

There are factors that can influence what I have stated above, such as the fact that if you run a restrictive exhaust system (re: wastegate/turbine/header/dump pipe) this will negate the extra flow potential of the porting you have, as will other sub systems such as IC/AIR filter/piping etc, anything that reduces the increse of VE% that the porting gives you will reduce the increse in effective compression ratio, and hence you will be able to run more advance.

It's all about the "effective compression ratio you have" the general proven rules (for a rotary with 9:1 static compression) are that at 1BAR boost assuming constant ambient temp of 15DEG C and charge temp of 30Deg C and porting used is not restricted then I have found the below limits to be a good guide, for good quality (pump) fuel.

(STOCK PORT) 20-23 deg advance ...lowest effective "dynamic" compression at max power.

(STREET PORT) 15-17 deg advance...midrange effective "dynamic" compression at max power.

(PERIPHERAL PORT) 10-12 deg advance...highest effective "dynamic" compression at max power.

RICE RACING

Roy, I run 32.5 avance up to 100kpa then to 130kpa I use around 20 deg avance and from there up to 225kpa I run 15deg avance in revs above 3000rpm.

I use pump fuel with water injection at a rate of 300ml/min at 15psi boost or around 12% of my fuel flow rate.

My engine makes 520bhp@8200rpm@15psi boost pressure on a std temp/pressure day (this would be around 450+rwhp on one of your dyno's over there).

With the water injection I have run that boost at that advance (15deg) on a ambient temp of 40degC (104F) with a water temp in the high 95+degC range while racing around a circuit lap after lap, my charge temp was around 50degC (122F) at it's highest point just before braking at the end of the main straight. With the water injection I could run lap after lap no problem at 1 BAR, with out it, my ECU would cut the revs of the engine because of to high a charge temp and water temp exceeding my preset limits.

I would stick with the 15 deg advance, it has worked for me for a long time, and I know that in a real world, things never stay as you would wish them too, a bad fuel batch could be just around the corner...not to mention a stinking hot day....ALL ARE KILLERS to turbocharged engines ! REMEMBER SAFTEY FACTORS, In Mechanical Engineering we use them ALOT......

qwck10th

Great thread!

The thread on timing split is located:
https://www.rx7club.com/vforums/show...t=timing+split

All best,
Steve C.

waynespeed

Hey Roy, Have you checked you duty cycle at 20psi and your A/F ratio at 20 psi? Be sure not to use pump gas. If available it it best to test with VP C-16 (117 octane) especially when testing and tuning. Better safe than sorry. It wont hurt to lower the timing to 15 and work your way to 17. If you don't see any results when raising the timing lower it back. Remember the rotary golden rule: "three strikes and your out"

Boostn7

GMonsen:
Gary, if run into detonation it will most likely over the peak torque area, therefore raising the timing in the area is not recommended.
Once you're past that peak torque area you could add timing carefully since chamber pressures are falling off.

Since every engine is different, Pluto's numbers are good ones to start with... even dropping as low as 12 degrees at 25+ psi. Any lower you run into high EGT's.
I know many run 15 degrees from 15psi and up, but I feel that the engine will need different timing at different boost levels and on the dyno is the only place to learn where your engine is happy.
Then again, anyone running close to 20 psi or higher should be using race gas to keep things together.

As far as the split I tried going from 15 to 12 degress and lost horsepower, it did gain hp at lower boost levels but 15 and up it lost power. So I locked it at 15 degrees all around (Wof3D).

Roy, you should be ok, but like Waynespeed mentioned start at the bottom and add as the engine needs it carefully.

Later,
John D
10.80 @ 130mph
88 10th Ann Ed T-II

RX7SV

This thread has been very helpful with my understanding of ignition tuning.
I have heard this comment, or similar, several times. What are the signs that you need to look for which tell you that you are starting to get near the limit of the amount of timing that you can run?

RX-7 Pilot

Heh,
This is is for Roy so he can see his own post again. The timing split post is also very helpful.

Kelvin