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Titan IOX-370 Decision

rapid_ascent

Well Known Member
Last weekend at OSH I spoke to Continental about an IOX-370. I'm leaning toward that engine selection. JB offered a nice show discount as enticement. I want dual PMAGS and they are offering the Superior cold air sump so that is all perfect. My delima is which compression ratio should I pick. There is 8.3 with 187hp quoted or 9.6 which some have said is over 200hp. The cost delta isn't very much at a few hundred dollars. So the high compression option is a pretty good bang for the buck. When I was looking at an IO-360 I had set my compression ratio limit at 9:1, but that configuration isn't offered in the IO-370.

I'd like everyone's comments on any concerns I should have with such a high compression ratio. This does include the counterbalanced crankshaft. I'm feeling like I should be more conservative and go with the 8.3 but on the other hand...
 
My personal choice would be to stay at or below 8.5:1 compression ratio. Anything above 8.5:1 mandates use of 100LL. Given that we don't yet have our future fuel situation firmed up, having some flexibility in fuel requirements would seem a prudent influence in selecting compression ratio in a new engine purchase.
 
I recently installed a new 370 w/9.6 CR and Bendix mags, and couldn't be happier with the performance (my brother did the same and is also very happy).
I would caution you about using Pmags on a HC engine with their aggressive timing.
Not worried about 100LL going away anytime soon and I won't use mogas anyway.
I have a good friend that opted for the 370/8.3, he can't keep up.
 
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I’m fine with using 100LL and I’m not worried about it going away either.

I had planned on PMAGs but I get your point Walt. I also got a quote with the CMI mags by mistake so that route would save a little bit of money.

I’m not very knowledgeable in this area so I’ll have to rely on the VAF brain trust for advice.
 
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If you are concerned about too much advanced use P-mags with fixed timing. Or even time them to 2 or 3 degrees after TDC to retard the timing further. Just don't fit magnetos!
Pete
 
Well I think this falls into the category of I don?t know what I don?t know.

I think the concern would be too much advance. I think that is what Dan is trying to show with the related link.

This is an area where I don?t feel comfortable experimenting.
 
Well I think this falls into the category of I don’t know what I don’t know.

I think the concern would be too much advance. I think that is what Dan is trying to show with the related link.

This is an area where I don’t feel comfortable experimenting.

I'm not trying to argue for any particular view with the link. Nigel's data is the best available to the public, with excellent balance in presentation of the pros, cons, and alternatives.

Please note that the optimum values Nigel found for each flight condition would apply to a parallel valve engine, not an angle valve. All the incoming data says the angle valve wants far less advance.

Returning to the OP's question, increased CR does diminish detonation margin. High CHT, high oil temperature, combustion chamber oil contamination, high induction air temperature, decreased octane rating, and yes, additional timing advance are also factors reducing the margin. If you select high CR, you simply need to be aware of the other factors.

Ok, so now let's switch from education to opinion.

RV builders tend toward optionitis. The disease extends to engine choices. Your RV will fly great with a perfectly stock engine, and it will probably last longer and be easier to cool.

My own IO-390 is stock.
 
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What prop?

In choosing an engine it is helpful to keep in mind the prop you are considering, Hartzell for instance has restrictions on some engines, and many it has not tested for harmonics.
 
You can purchase the "stock" certified version of the 370/9.6 if you want a "certified" engine.
http://www.continentalmotors.aero/Prime/Continental_Prime_Certified_370_Engines.aspx

As for props, I talked to Les at Hartzell about this, he saw no reason for concern using the current Hartzell BA that Van's sells with no restrictions for the 370 engine with CB crank and mags. I'm pretty sure this is the same prop that has been STC'd with the 370.
 
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I?m now thinking I should go with Walt?s configuration which is a little more conservative and given my knowledge of engine timing and etc. The other option that is on par at least from my level of risk view would be the 8.3 w/ PMAGs. I think I?d like the extra performance though.

Dan, thanks for the article. It does seem to show that you really aren?t gaining that much with ignition advance. Yes if I wanted every bit of performance it might matter but I don?t need that.

Walt, do you know what the HP ended up being on your engine?

Thanks everyone for their comments. I still have a lot to learn in this area.
 
I’m now thinking I should go with Walt’s configuration which is a little more conservative and given my knowledge of engine timing and etc. The other option that is on par at least from my level of risk view would be the 8.3 w/ PMAGs. I think I’d like the extra performance though.

Dan, thanks for the article. It does seem to show that you really aren’t gaining that much with ignition advance. Yes if I wanted every bit of performance it might matter but I don’t need that.

Walt, do you know what the HP ended up being on your engine?

The engine is rated at 195 on the data plate, CM is currently not providing dyno numbers for each engine, however, I was able to get a look at an assortment of dyno runs from other similarly configured engines, HP averaged about 205.

I can tell you the performance increase compared to my old stock 360 is noticeable.
 
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Dyno

Interesting, my Titan engine (370 and 9.6 CR) has 200HP on the data plate. I was there as an observer for the build and dyno run, which was 208 HP. I'm using Robert Paisley's EFII system, which was also used on the dyno run.
 
You can purchase the "stock" certified version of the 370/9.6 if you want a "certified" engine.
http://www.continentalmotors.aero/Prime/Continental_Prime_Certified_370_Engines.aspx

As for props, I talked to Les at Hartzell about this, he saw no reason for concern using the current Hartzell BA that Van's sells with no restrictions for the 370 engine with CB crank and mags. I'm pretty sure this is the same prop that has been STC'd with the 370.

That's a good point Walt. I assume certification would have required a detonation survey per the usual standards. If so (assuming the same timing), the higher CR isn't pushing the envelope.

That said, the specified timing for the IO-370-CLC1U8 / IO-370-CMC1U8 is 20 BTDC, per the latest manual. I assume the 20 degree spec is the source of your caution about p-mags.
 
John, thanks for that info. With my quick look it seems like about 5% for the 8.3 to 9.6 change. That seems match what people have reported.

I did some more reading on the PMAGs. After I got more of an understanding of their timing advance it made me wonder if Continental would ship the 9.6 CR version with the standard timing configuration from Emagair or modify it to what they consider acceptable values. It seems the max advance could be set if you knew what that value should be. Do they consider it the buyer?s problem to deal with or set it as needed?
 
Well I?ve decided to go with the PMAGs after all. After reading up more and realizing that I can limit the advance through the PMAG configuration I don?t see the down side. I talked to Continental and they set the PMAG to operate between about 20 and 29 ATDC by clocking the PMAG. If I want though I could decrease the max advance through the configuration. If fact I think you can adjust it down so that it really doesn?t advance at all and acts essentially like a standard mag.
 
I[n] fact I think you can adjust it down so that it really doesn?t advance at all and acts essentially like a standard mag.

Correct. You can also disconnect the MAP line and it will not advance. I recently configured the P-Mags for an RV-8 with 10.5:1 CR using the PC application (ver 4) provided by EMag and set Adv Shift to -7 or 19.6 and Max Adv to 29.4. No issues with CHTs.
 
Correct. You can also disconnect the MAP line and it will not advance.

Don't think it works that way. As you climb, the air density decreases, resulting in lower ambient pressures. The Pmag will see that as reduced MAP (it cares only about inches of mercury at it's port and doesn't care if that is ambient or MAP) and start advancing according to it's table.

Larry
 
CR does reduce detonation margins. Detonation is not detectable by pilot and can cause catastrophic failure (hole in piston). It is avoided by rich mixture and reduced power.

Engines in combinations of displacement and CR never certified are experimental.

High compression and more power can mean different power pulses and harmonics in crank and prop... See above... experimental.

I have a stock (except for EI) O-360A1A with 8:5:1 CR. I have no intent of running Mogas but I could. Higher CR forget it (please).
 
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