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Lycoming IO-390 C series - cold air induction

KeithB

Well Known Member
I posted this under the ?Superior Buy Back? thread and got no responses - I?m hoping it just got buried.

Lycoming offers a 390 with cold air induction - C3B6 model rated at 215 HP (available on the Cirrus SR20 for example). Vans does not offer this (it must be A3B6) and I suspect this is because the Lycoming cold air induction sump (like the Superior XP-400 sump) is lower and would interfere with the crossover exhaust (4 in 1) designed for the RV14. However, for my Superior XP400, I substituted a Vetterman trombone system (2x 2-in-1) which does not cross under the sump. Has anyone installed or investigated the C3B6 IO-390 (Thunderbolt, non-certified) engine for an RV-14? I realize I would face changes in cables (throttle and maybe mixture) but I?m more concerned with intake and exhaust pipe spacing and clearing the sump itself.
 
Following this thread. Keith I met you at OSH 2 years ago. Buddy of mine was parked in front of you in a 9A that was still in silver at the time like yours.
 
Cold sump option TB IO390

I looked at this as a possibllity rather the warm air sump two years ago.

I found that would require unspecified modifications to control cables, possibly the exhaust pipes, and possibly others.

I was also informed that it is a considerable cost increase of (my memory says) around $6K.
 
Hi Jeff:

Similar info here so far - although I?m facing the same issues with the stock IO-390 - exhaust pipes and control cables. As for price, the biggest part of the difference is that the C3B6 is NOT on the Van?s price list so you face list price.
 
Hi Kieth,
Thought I?d check to see what you found out. I have a Thunderbolt IO390 that just arrived. I remember asking about cold air induction and was told that it wasn?t an option (from Lycoming). I?m researching a couple other options such as Superior or Sky Dynamics and planning to use Vetterman exhaust. I?m hoping it can be accomplished without too much modification to the lower cowl. Any advice anyone has would be appreciated.
 
IO-390 exhaust

We fabricated a custom 2-in-1 exhaust for each side, now a non-issue
All fits in my RV8-A with cold air induction and Air Flow performance induction
Looks and works fantastic
 
Hi Kieth,
Thought I?d check to see what you found out. I have a Thunderbolt IO390 that just arrived. I remember asking about cold air induction and was told that it wasn?t an option (from Lycoming). I?m researching a couple other options such as Superior or Sky Dynamics and planning to use Vetterman exhaust. I?m hoping it can be accomplished without too much modification to the lower cowl. Any advice anyone has would be appreciated.

I ended up going with a Thunderbolt IO390 purchased through Van?s, and swapped the Superior cold air induction sump from my XP400, allowing my exhaust and cables to all fit.
 
There is unlikely to be a significant difference in induction air temperature between the standard forward induction, and the "cold air" sump.

The standard plenum intake does not pass induction air up through the hot oil like the updraft carb sump. It only has one hot surface (the plenum ceiling), "hot" being the sump oil temperature, perhaps 200F average. Both inductions are submerged in hot lower cowling air (120 to 180F in flight), and both have intake pipes running parallel to the exhaust headers.

If the new intake plenum actually nets better numbers on the dyno, I'd guess it is because of smaller plenum volume, i.e. intake wave tuning, not significantly reduced density.

The IO390C parts catalog is free for download at lycoming.com. Page 38 for the new sump.
 
Ashley Miller brought to my attention that the new 390 C and D sub types use RSA-10 size servos rather than RSA-5 which is interesting.

We find our 80mm throttles bodies (RSA-10 bolt pattern) on 540 engines produce no more manifold pressure past about 2/3rds throttle. With 150 less cubes, I'm not sure how much a 390 would benefit from such a large servo.
 
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Ashley Miller brought to my attention that the new 390 C and D sub types use RSA-10 size servos rather than RSA-5 which is interesting.

Interesting indeed. I didn't catch that change.

We find our 80mm throttles bodies (RSA-10 bolt pattern) on 540 engines produce no more manifold pressure past about 2/3rds throttle. With 150 less cubes, I'm not sure how much a 390 would benefit from such a large servo.

The 80mm body bolts to an RSA-10 size flange?
 
Thanks! I think that?s exactly what I do. I heard back from Clint at Vetterman and he informed me that they?ve done several exhausts for the 390 with a Superior cold air sump.
 
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