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Jett torque curves?

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Old 09-11-2011, 11:52 AM
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Jim Oliver
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Default Jett torque curves?

Hi Bob,

Are there any torque curves or tables available for the Jett .61/.65 or .90?

Thanks,
Jim
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Old 09-12-2011, 09:35 AM
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Default RE: Jett torque curves?

Hi Jim,

Thanks for writing.

Unfortunately no we do not have HP or Torque curves we can provide for the engines. There is a reason for this... too many variables involved to make the data meaningful.

The performance of an engine with a tuned exhaust, its torque peak and rpm, is a factor of the tuned system. The system includes the engine, exhaust system, prop, and to some extent the airframe. It is possible set up a long pipe and get lower rpm and a bit more torque. Or set up a short pipe for more rpm trading down for torque.

For example, The standard SJ-60L engine....
This with the standard jett-stream muffler turns a 10x6 prop around 16,500-17,000 rpm.
That same engine with a "torque" jett-stream muffler, longer, is just as happy turning an 11x6 around 14,000
Configured with a full size long pipe, the same engine has been set up to run as low as 11-12,000 with 13x4 and 14x4 props.
On the other end, we had the SJ-60LX configuration (short racing tuned jett-stream) which turned 9x8 prop at 18,500 rpm.

Same can be said for the SJ-90L, and the original big block SJ-61/65 engines.

A few of the heavy-lift academic teams have run their own test and dyno trials on the engines over the years. Rare that any two got the same results for the same type of setup.

Bob
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Old 09-12-2011, 01:45 PM
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Default RE: Jett torque curves?

Bob,

I understand about the different set-ups.

If I wanted to run a SJ 90 with a 12x10 or 12x12 APC, would I need the "T" muffler?

How about the big case SJ .60 or .65 with an 11x9 or 11x10 APC?

You have posted to prop all these engines for 13,500 to 14,000 as I recall, for the regular muff.

Thanks for your help.
Jim
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Old 09-13-2011, 08:15 AM
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Default RE: Jett torque curves?


ORIGINAL: Jim Oliver

Bob,

I understand about the different set-ups.

If I wanted to run a SJ 90 with a 12x10 or 12x12 APC, would I need the ''T'' muffler?

How about the big case SJ .60 or .65 with an 11x9 or 11x10 APC?

You have posted to prop all these engines for 13,500 to 14,000 as I recall, for the regular muff.

Thanks for your help.
Jim
With the 90T muffler you can run 12x8, 12x9 ... mayyyybe the 12x10. It will give you power down in the 11,000-12,000 ground peak rpm range. The 12x12 might be a bit too much, but worth trying.

The large block 61 and 65 are not commonly available. They were produced about 10-15 years ago. Jett builds the SJ-76 and SJ-90 as the big blocks now. But yes, they had that same 14,000 ground peak rpm target.

The current Jett SJ-60L and BSE-65 are "small block" .46 size engines. Great power, just smaller crankcase size.
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Old 09-13-2011, 10:04 AM
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Default RE: Jett torque curves?

Bob,

I have a big case SJ .65 and big case SJ .61 (.65 NIB, .61 nearly so); to run them at lower revs, with more than 6" pitch, which muff would be correct?

Thanks
Jim

Several weeks ago, I spent some time on the phone with Dub, attempting (without success) to get him to make up some Classic Pattern large case FIRE .61 packages, so I'm sorta stuck with the FISE engines (or getting lucky on "that site").

Thanks,
Jim
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Old 09-13-2011, 11:23 AM
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Default RE: Jett torque curves?

The standard Jett-stream 90 muffler is what you would want to use on the older .61 and .65 engines. 11x7 - 12x6 props work well. And...... since you have a SJ-61 - don't be affraid to try a full size pipe too. Header bolts match ST-61. 10cc pipe. If you can find a Hatori 725 pipe... you are golden.

The reason Dub stopped making the bigger-block .61 engines is that the smaller engines were capable of pretty much the same power output. A BSE FIRE-60L with a full size pipe runs as well as my old Rossi 61 ever did with an 10.75x7.5 or 11x7 prop. Tuned for around 13,500-14,000ish - lots of power on the top end. And it is lighter/smaller than the last generation of OSVF and YS61 engines, and more along the size of the original Webra Speed .61 and HP.61 engines. For those 700-750sq in designs, 7.5 lbs planes... pleanty there. Probably not a good choice for an EU-1A or anything over 800 sq that was designed to go slow starting in the late 80s-early 90s.

The only limitation on the FIRE-60L for pattern would be the rpm - it is not going to lug-down to 11000 rpm like the pumper engines did. You have to plan on it being old-school 1980 style pattern turning and burning. Prop it for over 13,000 ground rpm, tuned with the correct long pipe, and it will produce pleanty of power.

Read back in here a few threads on the post about the Phoenix 7 and SJ-50 power
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