how are we supposed to tune timing on a rotary?

Old 08-16-15, 11:03 PM
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how are we supposed to tune timing on a rotary?

I have a single turbo 20b. Got a great base map from Howard Coleman, and the car runs great. I backed off timing ~5 degrees in all rpm especially in boost from the provided base map to be on the safe side.

I know my timing is too retarded. I'm waiting on a pulley to get here so I can set TDC. Once that's done, how do I safely advance the timing? what parameter do the rotary tuners use to advance timing? is it strictly experience? MBT? EGT? when "x" extra ft-lb is made with a degree advance? Thank you for any advice in advance.

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Old 08-17-15, 10:13 AM
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well the basic concept is no different than a piston engine, you're looking for either a knock limit or MBT, which ever comes first. the rotary though is less tolerant of knock, and its harder to detect. the MBT curve is also a different shape than the piston engine, its more flat.

EGT is nice to have, use it as a limit. with the stock seals stay under 1100c.

you also should be looking for knock in the areas around 0 psi. the average "safe" turbo map found on the internet is usually more aggressive than what the NA guys run. timing should be different between the two, but the turbo guys are always running way more timing at 0 psi, than the NA guys run at 0psi/full throttle.

the correction maps are important too, on a cold day, the air is denser, and its going to make more power, so you have to make sure you have a safety margin for that.
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Old 08-17-15, 02:28 PM
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great thank you.

what's the typical torque gain near MBT for 13b or 20b?

just one more follow-up question. why would high EGT damage seals? I thought you get high EGT with retarded timing and richer AFR which are both "good" for the engines. my EGT is probably in ~1500 *F range just cruising around judging by the amount the downpipe is glowing...

thanks for your advice. I will make another trip to dyno soon.
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Old 08-17-15, 08:14 PM
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the tq gain near MBT totally depends on the turbo (or not), port, boost, etc. its going to be different for everyone.

the OEM seals are neat because we know what the limits of them are, 1100c, is one. assume the seal fails much above that. note its in c and not F.
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Old 08-18-15, 10:57 AM
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Never messed with advancing the timing here, but as a reference here's what I've seen:

Both the prev single turbo 13b map and the 20b have/do run around 28-30* @ 0psi area near peak torque. Increasing up to 15* around 10psi, then -1 degree for each psi above that. Seems that split I've seen has always been around -10-12*, with sometimes zero split or inverse at idle.

Both engines run water injection over 15psi, so likely without that, timing should be pulled even more
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Old 08-18-15, 01:36 PM
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re the timing around 0 psi. detonation is a killer of engines. i remember when i was putting my P port engine together, that every time i mentioned the engine, people were warning me about detonation. i thought that was weird, but lo and behold i can get it to ping around 1800-2200rpm, i haven't tried to get it to ping anywhere else, but ~260hp in a 12A makes enough power that it certainly could.

there are a couple lightbulb moments, but this one time my friend had a 20B FC, and the turbo died, so he made a block off, sent the turbo out, and kept driving. it turned out to be that without the turbo, he could hear it pinging @0psi, so he ended up retuning that area...

detonation is insidious, and can happen in places other than full boost, i have a feeling that when people have "random" failures, where the engine was fine for a long time, and then one day just quits, that there was some part of the map that it either was detonating, or was on the edge.

for actual numbers, keep in mind that the turbo engine has a different VE and compression than the NA does, but Monsterbox is running 30BTDC and the average NA is only going to be 18-26BTDC. not to say that 30 is too much, but i wouldn't say that its conservative either...
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Old 08-18-15, 02:31 PM
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thanks both kindly for your inputs. It seems ironic that when inappropriate timing is what kills rotaries, there is very little talk about it. If we have good collection of EGT and MBT information on different 12a/13b/20b engines, we can probably come up with safe guidelines on tuning timing. I received some well-known tuners' maps and for our rotary, the timing curves look very distinct from one another. Some (most) jump up to 25-30 degrees advance by 2500 rpm. Some starts high, dips low around 2500 then goes back up. Some ramps up slowly across all rpm range. These are all single turbo rx7's.

I had an STI for a few years, and the tuned timing map is pretty much identical across nation, hell internationally even. Everyone seems to do their own thing with the rotaries.

Once I get some solid data during my dyno session in September, I will post my MBT with different timing I am trying. I don't have EGT gauge, and that's something I am debating whether it's going to be useful or not... that being said, I would love some ballpark MBT figure I need to watch out for 20b w/ GT4202.

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Old 08-19-15, 09:29 AM
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Originally Posted by j9fd3s View Post
re the timing around 0 psi. detonation is a killer of engines. i remember when i was putting my P port engine together, that every time i mentioned the engine, people were warning me about detonation. i thought that was weird, but lo and behold i can get it to ping around 1800-2200rpm, i haven't tried to get it to ping anywhere else, but ~260hp in a 12A makes enough power that it certainly could.

there are a couple lightbulb moments, but this one time my friend had a 20B FC, and the turbo died, so he made a block off, sent the turbo out, and kept driving. it turned out to be that without the turbo, he could hear it pinging @0psi, so he ended up retuning that area...

detonation is insidious, and can happen in places other than full boost, i have a feeling that when people have "random" failures, where the engine was fine for a long time, and then one day just quits, that there was some part of the map that it either was detonating, or was on the edge.

for actual numbers, keep in mind that the turbo engine has a different VE and compression than the NA does, but Monsterbox is running 30BTDC and the average NA is only going to be 18-26BTDC. not to say that 30 is too much, but i wouldn't say that its conservative either...
Good info!

Looked over the maps last night. The 13brew-67mm tuned by Ray Wilson was the map with 28-30* at 0.

The 20b map runs only around 17-20* across the 100kpa (0psi) pressure point.
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Old 08-19-15, 09:32 AM
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Originally Posted by stickmantijuana View Post
thanks both kindly for your inputs. It seems ironic that when inappropriate timing is what kills rotaries, there is very little talk about it. If we have good collection of EGT and MBT information on different 12a/13b/20b engines, we can probably come up with safe guidelines on tuning timing. I received some well-known tuners' maps and for our rotary, the timing curves look very distinct from one another. Some (most) jump up to 25-30 degrees advance by 2500 rpm. Some starts high, dips low around 2500 then goes back up. Some ramps up slowly across all rpm range. These are all single turbo rx7's.

I had an STI for a few years, and the tuned timing map is pretty much identical across nation, hell internationally even. Everyone seems to do their own thing with the rotaries.

Once I get some solid data during my dyno session in September, I will post my MBT with different timing I am trying. I don't have EGT gauge, and that's something I am debating whether it's going to be useful or not... that being said, I would love some ballpark MBT figure I need to watch out for 20b w/ GT4202.
if you can afford it would be great to see 3 #'s egt's on each runner, wish I had those funds
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Old 08-19-15, 10:16 AM
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Originally Posted by stickmantijuana View Post
thanks both kindly for your inputs. It seems ironic that when inappropriate timing is what kills rotaries
well keep in mind its not fact, its more of an educated guess. there is something that causes some tuners to have good reliability and some tuners to have engines that do fine for a while and then "randomly" fail.

i've actually seen people do this with piston engines too. my friend just blew up his turbo miata again, rod bearing this time, last time it cracked the block...
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Old 08-19-15, 01:47 PM
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I have always tuned my vacume maps to match oem 38* advance at the lowest vacume max rpm then ramp down to meet my timing at wot keeping the map as smooth as possible. It also depends on how big of a map your building.
12x12 is going to be different from a 16x16 or 24x24.
On a 16x16 0kpa max rpm im around 26-30 off the top of my head
I have yet to see any issues
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