Did a few pulls last night at about 16psi front rotor is about 1620F and rear rotor is about 1680F should I try to lower these egt's? If so what is the best method to do so? My afrs are about 11.2 : 1 and ignition lead timing is 9* at 16psi. Would you sugest bumping up the lead timing a few degrees at that boost level to lower the egt's?

 

the temp i've been told to shoot for, is 1650F, so you're really close, given that its going to depend on the weather, where the probe is and such.

so since you're really close, i would maybe richen it up and see what that does. if its at 11.2:1 then try 11:1. depending on what that does i'd then add a degree of timing, and then maybe another.

i think if it was mine id be ok with 1620-1680, but if i could be in the 1600-1650 range i'd be happier

 

It could definitely use more leading timing but what is your split?

thewird

 

split is 10*. Houw much more lead timing do you think I could use?

 

Forget about some numbers. EGTs doesn´t vary only based on boost, AFR, timing. It has direct correlation with IATs, exhaust backpressure and of course, with the point where you are measuring and with what kind of probe. And never forget main factor - actual load applied on engine.

Don´t forget that EGTs work inversely with internal temperatures so only concern regarding actual EGT number should be if the turbine wheel can live in it. Once you reach minimum best timing, there isn´t further EGT decrease with more advancing.

 

rotary EGT readings need to be read quite differently than non-rotary.

just about perfect piston EGT is around 1320F

turbo'd rotary is 1650 and non-turbo rotary is 1750.

anything more than 1650-1700 and you will start warping apex seals.

as to your situation... you aren't providing much info. are you running AI? what setup and what injectant?

generally EGTs rise w output. do you plan to run more than 16? what turbo?

do you have an EGT log you could post? do your EGTs rise linearly?

there of course is a point where timing has so little advance that you end up firing a good bit out the exhaust port and consequently show higher EGT than what is going on inside the engine.

knock readings, power readings as well as EGT call the shots... AFR, not so much.

let's see your log.

howard

 

My set up:

13B Rew w/large street port
Garrett gt 4094R
Pre turbo water injection
Dual EGT -not logged (reading taken at end of a pull and appear to rise linearly)

Plan to take it to just a little over 20psi. What egt should I aim for at that point.

 

Try 13 degrees leading with 14 split @ 6,000 RPM climbing to 14 leading with a 12 split @ 7,000 RPM and then climbing to 15-16 leading with a 12 split @ 8,000 RPM. This is for 16 PSi boost. Below 6,000 RPM obviously less timing is needed, you can leave it with 14 split.

I consider this safe with 93/94 fuel however this is only a suggestion and I hold no responsibility for its use. Timing is only one part of the equation when tuning and all available data should be considered.

thewird

 

Short answer: advancing timing is risky because there is a direct link between timing advance and engine knock. The link between EGT and engine knock is murky; proper apex seal lubrication can help protect it from warping.

Long answer:

If you have a divided turbo manifold, the biggest concern with high EGT is accelerated wear on the turbo. Of course you stress the exhaust piping, and you will burn out a cat pretty quickly--but I doubt you have one installed in this case. A divided turbo manifold, especially with twin scroll, reduces the exhaust backpressure and potential exhaust blowback effects into the engine.

There are two other temperature concerns: apex seal temperature and rotor wall temperature, both of which Mazda engineers have discussed in the literature. AI may be helping to reduce both of these.

So on the subject of warping apex seals: Under WOT the apex seal tends to get hottest right in the top middle portion of the seal. The temperature is directly related to the engine load (BMEP=Brake Mean Effective Pressure, a way of measuring engine load):



Here's a test Mazda did where they held an engine WOT at 5000rpm for 45 seconds:



Increasing the amount of lubrication to the apex seal helps keep the apex seal temperatures down, up to a limit.

 

The other temperature concern is the rotor wall temperature. Knock is most likely to occur in the trailing portion of the combustion chamber due to squish flows. A squish flow is a concentrated pocket of air/fuel mixture--both piston and rotary engines have them. On the rotary engine, the trochoidal motion tends to create a squish flow in the trailing portion of the chamber. This squish flow causes fuel economy issues and is also correlated with engine knock.



As the rotor wall temperature heats up, especially in this trailing portion of the combustion chamber, knock will occur. The rotor wall temperature--and in turn, the tendency to knock--is directly related to the ignition timing advance.



It is for these reasons that I feel the ignition timing is vital for controlling knock. If the timing is advanced too much, the rotor wall gets too hot and knocking occurs. AI has the potential to reduce this temperature, and obviously using E85 or racing fuel drastically reduces the risk of knock due to the stability of the fuel.

Since Rx-7's usually have no effective knock system, you have to be really careful with the timing and leave a wide safety margin.

This is a solid starting point for US 93 octane equivalent fuel.

 

more good info on tuning

 

 

jetlude, you are OK at 1650 F.

This is what my EGT's look like. This is C deg so it would be about 2000F deg.

EGTs climb just like the HP curve. The turbine housing burns up first.

Lots of good contributions guys (especially Raymond, WOW!).
Barry

 

Not to get off track, and I understand the disclaimer/risks involved, but how far off would your recommendation be if the best you can get is 91 fuel?