RX7 timing/overheating

[Red Dawg Riddley]

is timing as critical to a rotary engine as it is to a typical overhead valve engine?
I'm overheating at speed, large radiator, blanking sleeve.
all help really appreciated.
thanx

[Prince Makaha]

Many rotaries have cavitation problems in the water pump.

[Speed Raycer]

Yeah... what kind of RPM are you running?

Anything over 7K for extended amounts of time will start to run a stock pump/pulley hot.

Have you checked the thermostadt? Mazda stadts seem to be the ticket.

Also, do you have the radiator sealed off? We were running the short radiator and pulled the fan and shroud off and started having real heat problems as all of the air was flowing under the rad. instead of through it.

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Scott
It's not what you build...
it's how you build it

[moto62]

Timing isn't that critical as far as heat is concerned but you may want to check your fuel mixture. Sounds like you're running lean at the higher rpm's. What 7 are we talking about here? 1g or 2g, carb or FI?
Ray

[Red Dawg Riddley]

Hi Ray,
first gen, nikki carb

[moto62]

Originally posted by Red Dawg Riddley:
Hi Ray,
first gen, nikki carb

Check your float level. If your fuel level is at or below the mid point in the sight glass at idle, try raising the level up to midway between the 1/2 and the top of the sight glass. The procedure for this is in the Maz fac manual. Also, you may want to check out http://www.yawpower.com/racecarb.html . Lots of good info on nikki carbs.
I personally have had up to a 10deg variance in engine temps by merely playing with fuel mixture.
Also, do you still have the heavy metal undertray that fits in from below the rad to the cross member. If no, put it back. If yes, cool.
Ray

[jake7140]

Try this link into Felix's rotary engine faqs:
http://members.ij.net/mrmazda/cfaqtext.html#TSTAT.
From past recollection I think the idea is to "gut" the moving thermo parts so they don't bind up, but leave the shell in for restriction and bypass capabilities. Have not had to play with it myself though. Fuel mix/float level is a great place to look too.


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Steve
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[ddewhurst]

Dawg, let's back up to a point in time where your temp was OK & follow any possible changes to the point where the temp started rising.

DETAILS are always interesting.

Have Fun
David

[bldn10]

Speaking of overheating, I've heard differing opinions lately on how hot a rotary can safely run. At what point do you think damage/deterioration begins in earnest? And don't say "when you start it up!" :-)

[Festus E. Simkins]

In a 12A engine my experience is anything over 220 F is very dangerous. I have talked to people who have run hotter but for me 220 is the absolute highest I would go. I would rather slow down and lose the race than burn up a motor. My oil and water temps tend to mirror each other. I usually run between 190 & 200 F. Before I put on the new stock 3 tube auto transmission rad I would get up to 218 F. I have run a whole race at that temp with no problems.

Drive well.

[Jim Susko]

Originally posted by Red Dawg Riddley:
is timing as critical to a rotary engine as it is to a typical overhead valve engine?
I'm overheating at speed, large radiator, blanking sleeve.
all help really appreciated.
thanx

[Jim Susko]

To add to all the other comments, check to see if your radiator is flowing air by looking at the front of it. Sometimes the fins can get bent over by numerous objects that fly into it while racing.

Also make sure your oil bypass is not routing the oil around the radiator. A sticking oil pressure relief valve or the use of high pressure pumps/bypass valves can lift the spring off its seat and lead to overheating.

But getting the right mixture is critical and is probably your problem. Try dynoing your car on a Dynojet chassis dyno that has oxygen sensing and recording. You should look for a 13:1 A/F ratio.

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