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Model Forum / Radio Controlled / Land Models / October 2005Question on Trucks and engines
OK, I've read through all the archives and am more confused than when I started. I've been looking for a truck now for a few weeks and I thought I had narrowed it down to a T-Maxx or a Savage. First question: Any opinions out there for a first time Nitro user? Second questions. With regards to the engines, I see the T-Maxx is a .15, the Savage is a .25, but the T-maxx advertises a 2.5? What's the easiest way to explain all the numbers? Thanks, Josh Replies Inline........ > OK, I've read through all the archives and am more confused than when I > started. He he he he! > I've been looking for a truck now for a few weeks and I thought I had > narrowed it down to a T-Maxx or a Savage. First question: Any opinions out > there for a first time Nitro user? Savage is the only way to go IMO, but I'm biassed as I own one and love it. My buddy has a T-Maxx and we bash pretty much every weekend. He has broken far more parts than I, the Savage is faster, louder, jumps better, climbs hills better, the list goes on and on. This is due to the powerplant mostly, which I will explain below. > Second questions. With regards to the engines, I see the T-Maxx is a .15, > the Savage is a .25, but the T-maxx advertises a 2.5? What's the easiest > way to explain all the numbers? The most common way nitro engines are numbered is by cubic inches of displacement. Generally speaking, the bigger the number the bigger the motor and more power. .15 = .15 cubic inches of displacement. Traxxas advertises their new engine as the TRX 2.5. This is 2.5 cubic CENTIMETERS of displacement or .15 cubic inches. They did this to make it sound bigger than it really is. Smallblocks range from .12 to .18 cubic inches. Big blocks range from .21 to .32 cubic inches. There are some outliers like the Cen .46 and the Thunder Tiger .70, but these are just that, outliers. The T-Maxx is a 1.35 HP .15 smallblock; the Savage 25 is a 2.5 HP .25 big block. There is no replacement for displacement, and the bigger the motor the more HP and more importantly in a monster truck, torque it will have. Last weekend my bud and I went to an old sand and gravel pit and ran our trucks out there. There was this wicked jump we were hitting, and about 15 feet after the jump was a 20 foot cliff, so when you landed you had to hit the brakes and turn real hard. Buddy broke his Maxx's front bumper and bulkheads on a wimpy 4 foot high jump that he nosedived into the ground. I hit the jump hard and unintentionally went OVER the cliff! The Savage landed on it's wheels believe it or not, 20' below, and I drove it around to a 60* hill, drove straight up and kept hitting the jump like nothing happened. I also own a Sportwerks Mayhem ST which is every bit as good as the Savage and much faster, but not a true monster truck if that's what you're set on. HTH, Doc Hey! Thanks for the explanation! You said it better than the hobby shop owner that looked at me like I had two heads... I think I've settled on a used Savage, a few mods, and everything I need to hit the ground running. Roughly $300, seems like a good deal to me. Thanks again, I'm sure I'll be posting more questions once I start running it! Josh > Replies Inline........ > [quoted text clipped - 48 lines] > > Doc > Hey! Thanks for the explanation! You said it better than the hobby shop > owner that looked at me like I had two heads... > > I think I've settled on a used Savage, a few mods, and everything I need > to hit the ground running. Roughly $300, seems like a good deal to me. You might want to look into a Traxxas Revo as well instead of the Tmaxx, I've heard nothing but good things about it. A guy I run with races one and it is FAST he also says it's pretty durable and good for bashing as well. > Thanks again, I'm sure I'll be posting more questions once I start running > it! [quoted text clipped - 53 lines] >> >> Doc > Hey! Thanks for the explanation! You said it better than the hobby shop > owner that looked at me like I had two heads... [quoted text clipped - 6 lines] > > Josh Yeah, $300 for a slightly modded Savage in good running order is a good price. A few things to check right off the bat: 1. Transmission outdrive cups (especially rear) can get pretty grooved and create a bind in the driveline. 2. Differential outdrive cups (especially rear) can get pretty grooved and create a bind in the driveline. 3. Axleshaft carrier bearings (sides of differentials) get sloppy then explode without warning! 4. Plastic steering servo bushings (if not modded already) get really sloppy really fast. Best fix is to replace with bearings instead of more plastic. 5. Replace wimpy stock clutch springs with Mugen 1.0mm springs. Hooks up way better off the line and reduces clutchbell heat. Those are the only parts I have found that wear pretty predictably. Everything else on mine is pretty much original after 5 gallons of fuel (aside from the parts I've replaced after some terrific crashes!). I keep extra driveshafts and drive cups handy, and change my axleshaft carrier bearings every 1-2 gallons as preventive maintenance. Doc ////////////////////////////////////////////////////////////////////////////////// >> Replies Inline........ >> [quoted text clipped - 48 lines] >> >> Doc > > Hey! Thanks for the explanation! You said it better than the hobby shop > > owner that looked at me like I had two heads... [quoted text clipped - 28 lines] > > Doc <snip> Hey Doc, can I ask why you changed your clutch springs to tighter ones? I assume that you did that so the clutch shoes dont rub when its idling?? Cheers Dre > <snip> > Hey Doc, can I ask why you changed your clutch springs to tighter ones? I > assume that you did that so the clutch shoes dont rub when its idling?? > > Cheers Dre I wanted the truck to hook up harder off the line from a dead stop, and the stiffer springs allow the engine to get the revs up before the clutch engages, so the engine is producing more power when the clutch engages and she takes off. A definite improvement in off-the-line punch, she kinda "leaps" off the line now. I can also set my idle much higher than before and get zero clutch rubbing, which is nice when she's first fired up and the engine is cold, as she likes a fast idle until she hits 200* or so. I had an intermittant bog off the line I couldn't tune out, and I think this was partially due to the softer springs (clutch engaging when engine was at low RPM and producing very little useable power) After changing to the 1.0mm springs, I haven't had a single bog off the line in six or so tanks. Wheelies are gone for some reason or another with the stiffer springs, which I don't really mind as I was really mashing my bodies up quickly and they were getting kind of annoying. I stuck with the original, stock shoes, which still look brand new after 5 gallons of fuel! I just sanded the glaze off em' and roughed up the clutchbell a bit before reassembley. I'm seriously considering grabbing a Sportwerks .26, 7-port motor for the Sav over the winter as I have one in my Mayhem ST and it is insanely powerful, VERY reliable, and holds a tune like you wouldn't believe. I also like the Sportwerks starting system much better than HPI's rotostart. As soon as Sportwerks comes out with a MT I'll be the first in line to buy one. They started with buggies, then ST's, the next logical step is a MT! Doc > > <snip> > > Hey Doc, can I ask why you changed your clutch springs to tighter ones? I [quoted text clipped - 29 lines] > > Doc Nice, thanks for the info, I'll look into it.. I find it weird though that you now cant wheelie considering you have more off line punch. You haven't changed your springs or shock oil to different types by any chance?? I haven't had a chance to do anything to my Savage for the last 3 weeks as I've been busy with other stuff and its been raining heaps on the w/e's. When I do get a chance I plan to do some more tuning, it isn't running as well as it could so keen to sort it... Cheers Dre > Nice, thanks for the info, I'll look into it. Well worth the $4.49 I paid! > I find it weird though that you now cant wheelie considering you have more > off line punch. You haven't changed your springs or shock oil to > different > types by any chance?? Nope, everything else is the same per way of setup. I agree, it is weird. It takes off just as fast as it used to, the front end just stays put, which is rather nice actually! Maybe she's starting to get tired after 5 gallons of fuel? Seems to run just as strong as it always has. > I haven't had a chance to do anything to my Savage for the last 3 weeks as > I've been busy with other stuff and its been raining heaps on the w/e's. > When I do get a chance I plan to do some more tuning, it isn't running as > well as it could so keen to sort it... You have the K-4.6 right? Is it as finnicky to tune as the S-25? I have been fighting with my S-25 since I bought it, and while it runs well, it has never run as well as it "should." Every now and then I'll get 2-3 minutes of insane performance, then it's back to where it usually runs with no explanation as to why! Doc > > Nice, thanks for the info, I'll look into it. > > Well worth the $4.49 I paid! Exactly, and I can allways use the old springs in another clutch :) You dont happen to have the part number by any chance? If not, I should be able to find it, me the lazy bum :) > > I find it weird though that you now cant wheelie considering you have more > > off line punch. You haven't changed your springs or shock oil to [quoted text clipped - 5 lines] > is rather nice actually! Maybe she's starting to get tired after 5 gallons > of fuel? Seems to run just as strong as it always has. Maybe its a bit upset at you crashing it the other week, LOL :) But serious, that is hell weird, you would have though that a tighter clutch would give opposite results! Keeping the fronts down can only give you better handling, agreed wheelies are fun, but there are times you wish it just stayed down and hooked up! > > I haven't had a chance to do anything to my Savage for the last 3 weeks as > > I've been busy with other stuff and its been raining heaps on the w/e's. [quoted text clipped - 8 lines] > > Doc Yep, I've got the K4.6 with bugger all tanks through it, so little in fact that I haven't nailed the tuning down yet. Intially as per the manual and other engines I've run in, I've simply leaned the main mixture screw in until performance drops and temps rise to around 120deg C. This engine didn't respond to that at all. It would be so rich bottom end (from factory) that there would be so much fuel in the crank case that when you floored it it would take off, but then not get above say 3/4 of the revs it should be able get to, ie, lean top end (even though there is plenty of smoke). Last time I ran it I leaned the top end to the point where is stalled out! so turned the main mixture back in and started screwing the low end in, but unfortunately it started to rain so had to call it a day. I also changed plugs after that cause I thought that might have something to do with it.. Actually now that I remember, what kind of plug are you running in your S-25? The K46 came with a HPI cold plug and recommends the same, with the cold plug I had craploads of low end power, but bugger all top end (and no revs). I'm running 20% nitro too. All this messing around would have nailed the 2 Picco's down perfect I have in the Inferno's... The only other HPI engine I've ever had apart from this one was an absolute bitch to get right, it was an old .12 in an RS4 nitro, when it packed it in I dropped an OS in there and never looked back. Maybe its a HPI thing (cant get the carbs right :) More tweaking required. Cheers Dre Inline............. > You dont happen to have the part number by any chance? If not, I should > be > able to find it, me the lazy bum :) http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXNJ81&P=7 > But serious, that is hell weird, you would have though that a tighter > clutch > would give opposite results! No kidding. I was just so happy to get rid of that annoying low-end bog I could care less if it never wheelies again! > Actually now that I remember, what kind of plug are you running in your > S-25? The K46 came with a HPI cold plug and recommends the same, with the > cold plug I had craploads of low end power, but bugger all top end (and no > revs). I'm running 20% nitro too. All this messing around would have > nailed the 2 Picco's down perfect I have in the Inferno's... I'm running OS A5 (medium-cold) plugs in my HPI S-25 and my Sportwerks .26 and both of them seem to agree with them pretty nicely. They last a helluva long time, and I've only actually killed one of them; the rest have been replaced just cause they'd been in there so damn long I figured they were due for a change anyhow. This is with O'Donnels 20% racing blend fuel. I use OS A3 plugs (HOT) for break-in as they keep her running while sloppy rich and also help to get the HSN and LSN close to where they need to be. I find with cold plugs during break-in, the tendency to overlean the HSN while compensating for a super-rich LSN is really easy. With a hot plug, no matter how rich the idle is, it tends to burn it all off when you hit the gas and allow for a more realistic HSN setting. > The only other HPI engine I've ever had apart from this one was an > absolute [quoted text clipped - 5 lines] > > More tweaking required. Aye, it's a constant with the Savage. The Sportwerks .26 was the easiest engine to tune I've ever run, but with the S-25 I'm constantly fighting with the damn thing! Doc > Inline............. > [quoted text clipped - 3 lines] > > http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXNJ81&P=7 Awesome, you legend! > > But serious, that is hell weird, you would have though that a tighter > > clutch > > would give opposite results! > > No kidding. I was just so happy to get rid of that annoying low-end bog I > could care less if it never wheelies again! > > Actually now that I remember, what kind of plug are you running in your > > S-25? The K46 came with a HPI cold plug and recommends the same, with the [quoted text clipped - 9 lines] > use OS A3 plugs (HOT) for break-in as they keep her running while sloppy > rich and also help to get the HSN and LSN close to where they need to be. This paragraph: " I find with cold plugs during break-in, the tendency to overlean the HSN while > compensating for a super-rich LSN is really easy. With a hot plug, no > matter how rich the idle is, it tends to burn it all off when you hit the > gas and allow for a more realistic HSN setting." is exactly what happened to me last time I ran it. Except I didn't put a hotter plug in there to find out. (plugs in there now, but I haven't tested it yet) You just nailed it right on the head :) I think I might take her out tonight and see what I can come up with. Funny, the plug I replaced the HPI cold one with was an OS A5! (great minds think alike eh :) > > The only other HPI engine I've ever had apart from this one was an > > absolute [quoted text clipped - 11 lines] > > Doc Hmmm, well I'm going to keep going with it for a while as I really haven't tuned it up yet so I dont know how well it'll hold its tune or how good it is over some more tanks... Thanks for the info! Cheers Dre > This paragraph: > [quoted text clipped - 15 lines] > minds > think alike eh :) Just make sure you leave her tuned a bit rich with the hot plug if you end up using an A3 for initial tuning as it'll reduce the tendency towards detonation. Once you switch from A3 (hot) to A5 (medium cold) you'll have to lean a bit further as well. My method for break-in and tuning pretty much any new nitro motor is thus: 1. Yank factory plug (throw in garbage!) and pop in an OS A3. 2. Run sloppy rich at factory settings for 1 tank at idle 3. Run sloppy rich at no more than 25% constant throttle with very brief 100% throttle blips for 2-4 more tanks, heat-cycling after each tank (making sure piston is at bottom of stroke when she flames out at empty tank and allow to cool this way) 4. Begin leaning HSN at tank 5 until "decent" top-end performance is reached, but NOT max RPM, you still want it smoking like a freight train at this point, not boggy, but really smoky 5. Begin leaning LSN after HSN is roughly set until take off is rich and smoky but not boggy 6. Yank OS A3 and pitch it, replace with OS A5 7. Dial in HSN for max RPM 8. Dial in LSN for max bottom-end punch (lean more) 9. Set idle. If you do it right, by the time you get to #7 and #8 you're only about 1/2 turn away from pure nitro bliss! I really like the A3's as they burn hotter than Hades and keep her lit during the super rich break-in and allow her to reach temps high-enough for a decent heat-cycle between tanks. Doc > > This paragraph: > > [quoted text clipped - 44 lines] > > Doc They are some really good points there, thanks heaps for writing them out! I follow a similar procedure but I have never considered using different plugs. My problem this time round was when I got to step 4, I kept leaning out for max rpm and couldn't get there. This has worked with all my other engines, but not this one. Not a problem, I'm keen as mustard to have a fiddle with it tonight, if I do get a chance (and I have enough charge in the reciever pack), I'll let you know how I go tomorrow... Now, to pretty much reset the carb screws and start again :) Cheers Dre "Doc" wrote: > Replies Inline........ > [quoted text clipped - 47 lines] > > Doc Just curious. I know Traxxas used to use the Pro .15 engine. Now they have the 2.5r enginge. Both are .15 cu inches, correct? They claim the 2.5r is up to 60% more powerful. How is that possible? > Just curious. I know Traxxas used to use the Pro .15 engine. Now they > have the 2.5r enginge. Both are .15 cu inches, correct? They claim the > 2.5r is up to 60% more powerful. How is that possible? It's a combination of higher compression, better porting and a better carb. If you know anything about 1:1 scale engines, take a Chevy 350 (5.7L) for example. They range in HP from 150-450 from the factory, the only differences being compression ratios, head porting and air/fuel induction systems. Doc |
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