Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

90 jett LX full pipe stinger diameter

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Old 10-24-2017, 01:22 PM
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SACKRC
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Default 90 jett LX full pipe stinger diameter

Running a 90 jett lx full pipe ,(no muffler) My stinger dia. is .320. comparing a dubb muffler with stinger .315 to .350 because of hex shape.
On 15 nitro I get 15,000 to 15,500., plug ware is good. using a MC 59..
Orignal max pipe was close to .400. Also pipe lenth is 14 inchs form plug to first band at flat spot. Had go small on stinger
to get better fuel feed from pressure. Looking for feed back if any , for more performance ?? 90 is in an cermack alley cat. Prop is apc 11/8


thanks rich b.
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Old 10-25-2017, 07:58 PM
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I run my own carbon fiber tuned pipes on all my engines, including 5 Dub Jetts. That being said I have never run a 90LX.. I know who has though... Why don't you shoot Dub an email and ask him. Not only is he a great guy, he built the thing so he knows how to tune it. He will be able to give you starting pipe length and outlet diameter.

Scott
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Old 10-26-2017, 05:27 AM
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Thanks , will do Rich B.
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Old 12-11-2017, 04:22 PM
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I have a used 90 RE. I need to send it in for an inspection someday.
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Old 12-13-2017, 07:41 PM
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Dubs large engines just never performed that well. A OS 95 AX with the same pipe does just as well if not better. The transfers are to high and the sleeve cant be lowered enough to get in a sweet spot. His best sport engines are the 35 LX and the 56/60LX.
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Old 12-13-2017, 08:54 PM
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Checked my notes , intakes 130 , exhaust 170 ? Whats your take on the number 120 / 170. I run rc boats also , 50 nitro 135 / 185.
So your looking for 50 on the blow down.??
Appreciate your interest found it difficult to get a response. Rich b.
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Old 12-14-2017, 03:37 AM
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I just couldn’t ever compare a ringed OS to an AAC Jett. Regardless of what makes more power, piston seal is paramount. AAC trumps ringed any day in my book.

FWIW - I run boats and trucks too. I run my truck engines at 34/60 crank timing and bored crank, 120 transfers,
122-127 Boost, and 170-182 exhaust.

Most of the engines I’ve measured (surface, air, and marine) have had at minimum 118 for the transfers - many in the 125-130 range. Boost is no different. Where I see most influence is in th crank timing, crank bore, and exhaust timing. If the transfers get too much higher than 130, you’ll likely get some blowback through the transfers.

I just checked my notes on my ringed ST S90K; Exhaust 150, Transfers 124, Boost 120, crank 32/50 (198 by my sleep deprived brain)

Last edited by 1QwkSport2.5r; 12-14-2017 at 03:52 AM.
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Old 12-14-2017, 10:14 AM
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The 135/185 is a MAC motor by CMB, also the new cmb s are using the same timing with good results. I run a AA parabolic pipe (or the old andy brown parabolic which is the same thing. The drum timing is 35 /62.
My 90 dub jett will do 16,000 on a cool day 15 nitro 11/8 apc prop.. I opened the carb to .475 and opened the case tracts a bit matched the ports.
I also believe the higher intake on the transfers helps low end for boats getting off the shore line with that
big speed prop. Planes it makes for a easy needle setting. As the blow down gets wider you may get the top end but low end suffers.

Rich B.

Last edited by SACKRC; 12-14-2017 at 07:12 PM.
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Old 12-14-2017, 11:24 PM
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Qwk is correct the Jett is made better and will last much longer than the OS. What is the crank hole dia? Usually you can open carb up to that Dia.
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Old 12-15-2017, 03:18 AM
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On engines that need a little help breathing, opening up the crank channel a bit helps. Just can’t get too thin around the inlet port. I’ll take a 9.5mm channel out to 10.2mm and be using a 9mm carb as an example. I think you need at least 1.5-2mm wall thickness if not a little thicker to be safe. This combined with the right inlet timing/dwell will have a more poignant influence on power. The timing of the liner ports influences where the powerband is at in the rpm range.
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Old 12-18-2017, 06:22 AM
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Whats the good numbers on the dubb 90 Crank port timing??? Rich B.
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Old 12-18-2017, 08:17 AM
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I run my high rpm buggy and truck engines around 34/60 for the induction port. Not all that radical IMO. I haven’t had the time to do an airplane engine yet. I will this winter or upcoming spring though.
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Old 12-18-2017, 08:32 PM
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Appreciate the numbers , didnt take a note on stock timing , just the sleeve a while back. On my boats ( riggers) are 35 / 65 is the number
but thats using 50% nitro. Thank for input. Rich B.
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Old 12-22-2017, 08:42 PM
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You all are so out of my league.
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Old 12-22-2017, 10:15 PM
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When looking at your engines an quick judgement with out measuring is to look at the visible light through the crank port (through the carb) by turning the crank. If your engine has four bolts to hold the back cover on you will see light around the bottom left screw hole and then close around the top right hole. Compare this to good engines you have messed with and then can quickly see if a new engine is good or bad on the crank.
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Old 12-31-2017, 09:06 AM
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I checked the crank timing on my 56LX. From BDC using a dial indicator to get absolute BDC, I got 36/66.

Just FWIW..
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