Real world dyno numbers for this 540 config.....

[RandyAB]

I'm sizing my prop and need to know what the real world horsepower is for my engine. I'd appreciate input from anybody with the following configuration who has had their engine on the dyno.......IO540D4A5, 9:1 pistons, Barrett cold air induction, SDS fuel injection with electronic ignition, ported and polished.

[F1Boss]

You ought to talk to Barrett - they have had plenty of engines of that type on their dyno. I can tell you that you would be close to 290HP at 2700 @ SL, but Rhonda could give you a more reliable number.

[rocketman1988]

That is almost what I have but with EFII instead of sds.

Mine did right at 290 on the dyno.

[RandyAB]

Thanks fellas. I did get a response from Rhonda, who is always very helpful, and she said 287-293 depending on the servo used. FM200 or RSAS (287-289) FM300 or RSA10 (up to 293). I believe it?s the FM300 with the SDS but I will have to double check.

It seems that the MT prop that I am considering is rated to 300hp. I know that some go with the next model up when near the borderline like that. I?m not an engineer so it seems to me so I wonder what the advantages are of spending more money on the next beefier prop when the standard one is within its rating.

[DanH]

Originally Posted by RandyAB

I believe it’s the FM300 with the SDS but I will have to double check.

Airflow Performance (FM150, 200, 300), Precision (RSA-5 and -10), and AvStar are fuel metering and throttle in one unit, for mechanical constant flow injection. Electronic injections have no metering at the throttle. An SDS or EFII system would use a throttle body with temperature sensing and sometimes throttle position. If I recall correctly, SDS has their own machined, and EFII was using an 80mm BBK.

[rocketman1988]

I think that is correct on the throttle body for the EFII...two IAT sensors and a TPS sensor.

As far as the prop goes, the Van's recommended MT prop, MTV12, is rated for 300 HP max. After quite a bit of conversation with the MT guys, I opted for the MTV9, which is a bit heavier but is rated for 450 HP max.

My thought, and that of the MT guys I talked to, was that pushing the MTV12 to near it's max all the time was...undesirable.

The MTV9 with handle 300 HP easily. It does weigh a bit more, though. Can't remember exactly but I think it was around 11 pounds more, at about 52.9 pounds...still lighter than some comparable at 55+ pounds.

[RandyAB]

Originally Posted by rocketman1988

...My thought, and that of the MT guys I talked to, was that pushing the MTV12 to near it's max all the time was...undesirable.....

I'm not disagreeing but are you truly pushing it to it's max "all the time" though? I think that the vast majority of the time, you are going to be operating at <70% power.

[RandyAB]

Originally Posted by DanH

Airflow Performance (FM150, 200, 300), Precision (RSA-5 and -10), and AvStar are fuel metering and throttle in one unit, for mechanical constant flow injection. Electronic injections have no metering at the throttle. An SDS or EFII system would use a throttle body with temperature sensing and sometimes throttle position. If I recall correctly, SDS has their own machined, and EFII was using an 80mm BBK.

Thanks for this explanation Dan. Could you give me an opinion on how I would integrate this with what Rhonda told me? Clearly I have some reading to do regarding fuel injection design and operation.

[DanH]

Originally Posted by RandyAB

Thanks for this explanation Dan. Could you give me an opinion on how I would integrate this with what Rhonda told me?

Any way you shake it, the peak HP numbers will be similar enough to make no difference picking a prop.

[rocketman1988]

"...I'm not disagreeing but are you truly pushing it to it's max "all the time" though? I think that the vast majority of the time, you are going to be operating at <70% power..."

That is exactly what I said to the MT guys...and they still recommended the MTV9.

I am speculating but maybe it has to do with the margin, ie the prop was really meant for a 260 HP application which gives a healthy margin, whereas running it at 290+ HP greatly reduces the margin.

Nothing more than speculation, though...