msupra1 Posted November 25, 2015 Share Posted November 25, 2015 When the Supra was getting tuned last year, the crank pulley cracked and that also the stock cast tensioner snapped into two pieces. So I replaced those with an ATI (TITAN) dampener and a new factory tensioner. Its been just fine making 600whp for the past year. Now with the new tune and setup I am expecting about 700whp which is 800 at the crank. Considering I just put in a new tensioner should it be fine to run for this kind of power? or would a billet tensioner be recommended? I just spent a lot over my anticipated budget with the last phase of mods so trying not to spend on things that not absolutely necessary! cheers Quote Link to comment Share on other sites More sharing options...
mwilkinson Posted November 25, 2015 Share Posted November 25, 2015 In short is it nessessary, probably not. However, given your previous experience coupled with the outlay on your power upgrades I would most definately consider it a component of modifying the car. I'm running around 600 bhp on mine and I have upgraded to a billet tensioner bracket. Small price to pay vs the consequences of it failing on a spirited drive. Quote Link to comment Share on other sites More sharing options...
Luxluc Posted November 25, 2015 Share Posted November 25, 2015 I would change it mate. 800 bhp is more than double the original power ; better go safe than sorry. Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted November 25, 2015 Share Posted November 25, 2015 There is no extra stress on the cam belt or tensioner from running more BHP, unless your running uprated/stronger valve springs and really lumpy cams, BHP has no bearing on the belt as the most stress the belt comes under is during idle. Quote Link to comment Share on other sites More sharing options...
Ian C Posted November 25, 2015 Share Posted November 25, 2015 the most stress the belt comes under is during idle. Ooh why's that? Intrigued. Quote Link to comment Share on other sites More sharing options...
Loonyboyo Posted November 25, 2015 Share Posted November 25, 2015 The valve train has much more force exerted on it during idle and low RPM, at higher RPM inertia takes over and the strain is lessened. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted November 25, 2015 Share Posted November 25, 2015 Correct, the harmonics from the cam lobes opening valves at slow RPM are passed into the belt drive, and can perhaps cause a bit of tensioner movement. I fail to see how BHP level has any effect on belt strain, or tensioner strain. At more than stock RPM levles there could be some harmonics generated in the belt, and on sudden gear changes. the gear change issue is why manual TT's have a damper on the auxiliary belt. I suffered harmonics on the long PAS belt of my RB26DETT engine and fitted an idler pulley running on the long none tension side of the belt. It cured the belt turning inside out and coming off immediately. A race engine would not use an auto belt tensioner on the cam belt in the first place, and would thus rule that playing silly devils out from the get go. I'd be more interested in why the tensioner arm was braking, and would first investigate if was RPM related. As an aside the addition of more radical profile cams on VVTi's often results in a rattling noise at idle. this is caused by the extra pulsation of the different cam profile exciting the VVTi mechanism. It disappears as soon as you put a few RPM on the engine and the cams turn fast enough for the pulsation frequency to change to a higher level. Anyway, belt driven cams are an abortion in the first place, they only came into vogue as they are cheap and quiet Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted November 25, 2015 Share Posted November 25, 2015 Yes at idle there is more cylinder pressure to overcome, as its having to deal with maximum contact load at peak lift, more rpm reduces the peak lift contact loadings , that's also one reason most belts snap on start up or cold idle, especially diesel's. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted November 25, 2015 Share Posted November 25, 2015 Belt driven cams are an abortion in the first place, but that aside I see no correlation between BHP and cam belt or tensioner load. RPM harmonics related, possibly. Sudden throttle closure issues, possibly. VVti mechanisms often rattle at idle when more radical profile cams are used, but it disappears once a few RPM are used. No proper race engine would use an auto tensioner in the first place, if I was doing a serious 2JZ I would replace the tensioner with a threaded rod and manually adjust it in a fixed and stable manner. In fact, thinking about it I may offer one. Tensioner cartridge issues are more likely the cause of tensioner ARM issues than the tensioner arm itself. Hmmm... Quote Link to comment Share on other sites More sharing options...
Ian C Posted November 25, 2015 Share Posted November 25, 2015 Nice one, thank you all Quote Link to comment Share on other sites More sharing options...
msupra1 Posted November 26, 2015 Author Share Posted November 26, 2015 Thanks for all the input, I'm most likely going to get the billet bracket. To be more exact here is the history with my crank pulley issue. When BPU, the crank pulley rubber seal broke into pieces when doing a slight drift around a turn. I replaced that with a used Aristo pulley that a friend had laying around. I was running 460whp on that pulley no problems. Then on the dyno session the timing belt was wobbling so they refused to continue tuning it. Took it back to the shop which is when we found the rubber seal in the crank pulley cracked, as well as the tensioner bracket completely snapped. Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted November 26, 2015 Share Posted November 26, 2015 The pulley failing is a common problem, however it doesn't have any bearing on the cam drive, just the auxiliary belts, and is not affected by power output, its best replaced with a good std item or decent aftermarket damped harmonic balanced pulley. Quote Link to comment Share on other sites More sharing options...
absz Posted December 2, 2015 Share Posted December 2, 2015 I snapped a cam idler bracket few years ago was running stiffer valves springs and aftermarket pistons/valves both the hydraulic tensioner and idler pulley were OEM and had only done approx 2k miles when it let go.I was at WOT 7200RPM Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted December 2, 2015 Share Posted December 2, 2015 Sounds like belt harmonics, and I would suspect the tensioner cartridge is allowing the arm to oscillate and the stock arm fails. I personally would look to the tensioner rather than uprating the arm, as something nasty is obviously occurring. Quote Link to comment Share on other sites More sharing options...
Paul Whiffin Posted December 3, 2015 Share Posted December 3, 2015 I had one snap on me whilst Time Attacking at Knockhill, bent all 24 valves in the head(11.4m lift cams)and never had the issue again after fitting one of our billet brackets. Very highly recommend them and we always fit them on any 2JZ with uprated valve springs. Quote Link to comment Share on other sites More sharing options...
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