March 23rd, 2016, 11:09 AM | #1 |
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What octane gas do big bore high compression guys run?
I am unaware of anybody running aftermarket pistons in their pregen, so I will ask you guys. What bore size and compression ratio do you run (if over stock) and what octane gas do you use?
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March 23rd, 2016, 03:00 PM | #2 |
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new gen 13:1 89 octane ran great no detonation
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March 23rd, 2016, 08:19 PM | #3 |
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Big bore high compression? My 685 KLR at 10.5:1 runs on 89 unless it's super hot out...
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March 24th, 2016, 04:54 AM | #4 |
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Nothing more than 110. More like 100. Above 110 and the engine will not even start. I have gone with 13 to 1 and found 110 was good. From a detonation point. But the power was not as good as the lower. That was all using Rocket brand fuel. Since switching to VP I have not done much testing and not done anything but nitrous and lots of ignition advance.
Using the Brt ignition I can pull timing below 7500. That is the area I had problems with. 44 deg or even 42 deg caused detonation during the lower gear acceleration. Still pull a little timin at 10000+ but don't know if it is detonating or not. I can't hear anything but wind and exhaust.
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March 24th, 2016, 05:35 AM | #5 |
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Its interesting that you can push these motors so much with such low octane. They must have great cooling and great valve cooling. I was scared that a 13.5:1 would need 110 or maybe 118 e85.
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March 24th, 2016, 06:12 AM | #6 |
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I would see no reason to run straight 110 in just about any modded sport bike, I would be mixing 110 with 93 to end up somewhere closer to 100 if I had a machine that needed the extra octane.
What about 100LL av fuel? I know it is popular in the dirtbike community but I don't know if it would be safe/good to run in a 4t sport bike?
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March 24th, 2016, 06:20 AM | #7 |
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I belive av fuel doesn't make as much power as pump gas, but it should be ethanol free and leaded, which is nice.
Idealy I would want to run pump gasoline, and If I required a higher octane, I would try a COP swap, ignition advance, and run e85. I would also consider running 93 with a leaded octane booster. (Or I could polish the combustion chamber and the piston tops to help prevent detonation, but this is irrelevant, because if you can run 13.1:1 on 89, I'm sure you can run 13.5:1 on 92/93.)
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March 24th, 2016, 07:34 AM | #8 |
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there are commercial bikes that run 13.5:1 and some higher, I assume they are rated for 93
doesn't exactly mean much but well there it is lol
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March 24th, 2016, 08:18 AM | #9 |
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Compression ratio alone really means nothing as far as gas octane, its a combination of so many variables to determine anything, but ninja 250s to ninja 250s is a fair comparison, ninja 250's to zx10r is apples to oranges.
As RacerX said before, just by playing with cam timing he got his engine to go from some crazy low compression to 300 psi.
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March 24th, 2016, 08:45 AM | #10 | |
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Quote:
In general, to make max power, you want the lowest octane fuel that just barely keeps detonation away, and will lose power with any octane over that point. Detonation tends to start at lower RPMs and high loads, so you may be able to hear or feel it when cruising at a lower RPMs/speeds and opening the throttle significantly (heavy load). |
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March 24th, 2016, 09:06 AM | #11 | |
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Quote:
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December 24th, 2022, 11:36 AM | #12 |
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I'm about to put 66mm 12.5cr wiseco pistons in my 300.
The ecu is re-flashed, but is still stock timing (From 10° BTDC at 1 300 r/min (rpm)31° BTDC at 7 000 r/min (rpm)) if we check in the manual. it has about 43 hp to the wheel at the moment with stock piston and the reflash. I would prefer to use pump gas (91 shell v-power) but can go with some race fuel and make my own mix (Sunoco 98). Also, can I put a +XX% on the power commander to start the dyno test (ex: 335/296 = 13%)? It's a track only bike. Any advice here from racers? Thanks |
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January 13th, 2023, 05:06 AM | #13 |
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in my years of Modifying bikes (mostly 2 strokes) i discovered most bikes gain very little benefit from increasing compression.... oddly enough as v-8 engines really do gain alot.... I believe that is due to mutable cylinders...
...I think there is more to be gained in a properly tuned carburetor than raising compression, or even changing the cams is better than compression simply because you put so much more stress on the parts when increasing compression for very little gain... Larger carburetors and better cams would be my suggestion for motor hop up on a ninja.... not increased compression... .... my 2 cents worth ! Bob.......
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January 13th, 2023, 05:14 AM | #14 |
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in my case, I'm going from 10.6 to 12.5 (ninja 300)
according to this picture, it would be like a 4.35% ish gains |
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January 13th, 2023, 10:22 AM | #15 |
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You need to ignore static compression ratios & work out the dynamic compression ratio based on the cams you are running. 95RON is good for 11-11.5/1 dynamic ratio. Most unleaded fuelled bikes run 10.5-11/1 dynamic ratios. If your dynamic ratio is higher then you will need higher octane fuel. There are calculators on the net for this. Wallace Racing do one.
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January 13th, 2023, 07:48 PM | #16 |
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But you are not looking at the stress factor you are adding when you increase the compression ratio .
if you want a reliable bike this is a major consideration... Typically when increasing compression ratios on big V-8's the mechanics usually change the connecting rods for stronger ones this is necessary to keep the engine from blowing up and destroying itself... for just a few percent change in compression ratio obviously this is not a concern but consider what it is also doing to the main bearings....so now instead of the main bearings being hit with a 1lb hammer every time the piston fires it is being hit with a 1.75lb hammer every time....a small change in compression ratio changes to a large change in the main bearings and connecting rods....... you obviously know this, but seem to be disregarding it as a non-issue... let me assure you it is not a non-issue! Bob....
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January 14th, 2023, 10:00 AM | #17 |
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I ran this up to compare loads for the 300 Ninja engines I'm big boring.
https://www.dropbox.com/s/xfm3qns1da...Loads.JPG?dl=0 Rev & weight increase the load much more than combustion. And most engine have 10-20% over engineering for failure free longevity. By this I mean they design/test it to find practical limits then add material &/or strength to components to ensure they don't fail at the prak expected loads. If you don't go too crazy you can use some of that spare capacity & still have a reliable engine. Note that I am disappointed i the weight of the Wiseco pistons & should have just gone with ZZR600 ones. Last futzed with by Mohawk; January 14th, 2023 at 11:43 AM. |
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January 14th, 2023, 10:28 AM | #18 |
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that is probably quite true. especially given the RPM these bikes turn at.
but their is a surprising amount of weight you can remove from a piston with a die grinder.... but on doing twins they have to be the exact same weight,... i mean down to the nat's ass ! you just have to be real careful not to weaken the piston in the process ! .... Bob.....
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April 16th, 2024, 08:29 PM | #19 | |
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Quote:
12.6 SCR (from all my measurements) (Stock 10.6; 08 zx-10 = 12.9) int cam closing at 56° (08 zx-10 = 77°) Rod Length of 3.770" 10.56 DCR (stock would be 8.912; 08 zx-10 would be 9.028) From: https://www.omnicalculator.com/every...pression-ratio could you please tell us where you got the 95RON information and where did you find that most unleaded fuelled bikes run 10.5-11/1 dynamic ratios? Thank you |
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April 17th, 2024, 02:05 AM | #20 |
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OK so just re-read this thread to get back up to speed, it's been a while.
The Pre-gen 250 has always had 12.5:1 SCR. Running 10.6:1 DCR. The 300 because it was sold in South East Asia as well where fuel quality is generally lower they lengthened the stoke but kept the same bore & reduced the SCR to 10.5:1 so it will run on any fuel. The engine bottom end is the same as the pre/new gen 250 except for the longer stroke. The pre-gen with heavier pistons revved to 14K/rpm, the 300 to 13K/rpm due to the longer stroke but similar conrods. The 250 had 10gram heavier pistons & produced approx 8% more average inertia than the 300 with a peak 14% BDC inertia, so the 300 has some leeway to play with. If you add a bigbore, the piston weight will have the biggest impact. Check the table I added. If the DCR does not change much then apart from adjusting fuelling to match the increased air volume to keep the AFR in a good range then everything should be fine. The closer the new pistons are to the weight of the old ones the lower the additional stress level on the motor. YMMV. Stock 300 SCR @10.6:1 gives 8.93:1 DCR, my 64mm 12.5:1 SCR gives 10.5:1 DCR which is right on the money for 95RON fuel. Regarding the fuel, please note in Europe we use the RON measurement system, in US & US influenced areas they use the MON system. The numbers are NOT the same & the anti-knock levels are thus different. In Europe there are generally only two levels of unleaded fuel available 95RON is the basic unleaded & 97-98RON is the "Super" unleaded. There are a few sources of 99RON & or some street side higher octane rating fuel pumps, but these are generally only near race circuits, where the rules state many classes MUST run pump fuel, hence pumps near race circuits ! Plus you can buy octane booster to mix with Super for a higher octane rating again YMMV. As to the info on DCR, I have run the numbers through the DCR calculator for many bikes over the years & regardless what SCR the maker claims the DCR's have all come out between 10.5-11:1 based on the valve timings. You will notice that any bikes with greater than 12:1 SCR will all have fairly large valve overlaps & you can't compress a gas in a cylinder until the valves close & as engines are designed to run on standard unleaded, then they can't have a DCR higher than 11-11.5:1 max without knocking. Have fun running numbers �� |
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April 17th, 2024, 03:45 AM | #21 | |
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Quote:
FYI, I put Carrillo rods too (I'll post the engine build when i'n done), so i'm not too worried about the heavier pistons ( I would've been with the stock con rod though). As for the Fuel, I bought Fuel Factory 2WL race fuel which is RON: 103, MON: 85, AKI: 94 and will dyno tune the bike with this fuel. If you think I should use a fuel with more MON also, please say so. I have access to higher octane fuel also. Do not worry for the injectors / gas pump, those are upgraded too. Thanks again for the great reply. |
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April 17th, 2024, 10:03 AM | #22 |
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NP what DCR did you end up with ?
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April 17th, 2024, 10:21 AM | #23 |
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April 18th, 2024, 04:07 AM | #24 |
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So you should be able to run pump gas at that DCR & save a fortune on expensive high octane fuel
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April 18th, 2024, 06:07 AM | #25 | |
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Quote:
What was confusing for me was that all DCR information I could find was for big V8 and they were all talking about 9.5 being the max for pump gas. I guess bikes and bike muscle car are not an apple to apple comparaison. Thanks again. |
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May 8th, 2024, 06:18 AM | #26 |
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335cc setup Dyno tested
The numbers are in folks! just had my Dyno session yesterday. The fuel was great even though it smell like pure pepper mint cancer hahaha.
The mods (power related): 66mm Wiseco pistons 12.5:1 CR (Real SCR @ 12.6 + DCR @ 10.56) Bored out and Nickasil plated cylinders Carrillo Rods ZX-6r valve springs Ported head (cleaned and stepless from TB to valves) EAT-255 Suzuki injectors (225cc/min) flow-matched Opened up Air box + no flame arrester full Yosh exhaust Ninja 650 Fuel Pump Fuel Factory 2WL race fuel (VP MR12 equivalent) The Numbers: 52.13 whp @ 11 127 rpm, 27.5 lbs/ft @ 6000 rpm Pretty happy about that. I had 42.95 whp, 20.96 lbs/ft with the stock 296cc setup. About 21.37% gain for a 13.2% increase in displacement. I think that the runners are now the restriction 20240507_114849_2.jpg 2021 dyno run: _20210528_105725.jpg Overlay: 2 Dyno Runs.jpg Last futzed with by Fred659; May 9th, 2024 at 09:23 AM. |
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