The BMW UUC Digest Volume 2 : Issue 711 : "text" Format Messages in this Issue: Re: <E30> Stroker or bored (long semi technical read) Re: <E30> Stroker or bored Re: <E30> Stroker or bored Re: Need a SRS sensor mat connector
---------------------------------------------------------------------- Date: Thu, 23 Jun 2005 19:51:25 -0500 From: "Craig Robson" <[EMAIL PROTECTED]> To: "UUC Digest" <bmwuucdigest@uucdigest.com> Subject: Re: <E30> Stroker or bored (long semi technical read) Message-ID: <[EMAIL PROTECTED]> Well, two things are going here that cannot be ignored. With the increase in HP, usually there is an increase in torque, unless you turn 19,000 rpms.... So, with this increase in torque, there is more tangential force at the surface of the sprocket/gear/pulley/etc. This increase in tangential force is what creates all the problem. Yes, the belt simply spins a relatively light weight part of the engine, but it spins it nonetheless. So, to increase the speed of these parts is to impart force. The factory belt is designed for a particular force, and if the force is increased (the tangential force) then the belt must "work" harder to spin the valvetrain. Let me explain it this way... If the engine sat at one speed all day long and never decelerated/accelerated, then a string would likely be used as a lifetime timing belt (a little exaggerated, keep reading). But since you, me, and everyone else accel/deccels their engines, then the belt must deal with feeding that force to the valvetrain. Now, on to the exaggerated part... There is a small amount of force used to keep the valvetrain spinning since we live in the real world and experience friction. This small amount of friction requires force, so the string must hold up to that force. Secondly, there must be a certain amount of tension on the belt otherwise it would not move with the pulleys. So, you have tension necessary to spin the belt, and then you have force imparted to overcome the friction in the valvetrain. I think that is all right information, I fell asleep during the class where we discussed chain/sprocket belt/pulley design. So, the end result is yes, if you increase torque/power, your belt will not last as long. However, it is likely due to be a small amount. Craig Robson 01 M3 ------------------------------ Date: Thu, 23 Jun 2005 20:00:45 -0500 From: Jenny Morgan <[EMAIL PROTECTED]> To: UUC Digest <bmwuucdigest@uucdigest.com> Subject: Re: <E30> Stroker or bored Message-ID: <[EMAIL PROTECTED]> I think this is largely a non-issue, in the long term experience. Yuppers, ya build an engine with extra ponies and no doubt, your gonna use them. But what is the problem with the belt? Extra abuse? Scary deltas?? What does it all add up to? Answer: additional wear. So how do you deal with it? Answer: Change the belt more frequently. I have put fairly muscular 2.7s out there and what I do with the owners, is to encourage them to change the belt each school/race season. Every other at the most. Regardless of miles. If they are DIYers, it costs what? Forty bucks in parts? If they're not DIYers, well, too bad. That's the cost of wasting gas and drivin' fast... Money down the toi-toi. Flush it , Baby. The idea here is to protect the investment of the engine, and if a belt job does it, GREAT! I suppose there would be an upper limit to how much additional stress, drag, deltas, whatever you can put on these belts before the motor goes lunch-city, but I don't think any typical modifications most of us all will ever do approaches that. Look at the iX... how much more stress is on that belt on each accel/decel cycle? Ok, that's might not be a good comparison... I see LOTS of iX belts blowing before 50K. Which adds to my argument, more stress, change it earlier. I recommend 40K on an iX. And if that stock iX is a school junkie... 30K or less. Jenny Morgan On Jun 23, 2005, at 5:39 PM, Brian Ruiz wrote: > > > --- Marco Romani <[EMAIL PROTECTED]> wrote: > >> ok maybe I'm stupid. > > No, no, not stupid. ;) > > But why would there be >> significantly more stress on >> the belt? Doesn't the belt just turn the camshafts? > > Of course. > > >> I could see if you're putting in monster valve > springs or really heavy >> camshafts or spinning the >> motor to 17bazillion rpm but it's not like the belt >> is turning the crank - >> it's the other way around. > > That's all true, but I think the stronger springs (and > higher RPM too?) would just cause deltas in the > frictional coefficients necessary to maintain the belt > in contact with all the pulleys. > > I'm no physics major or engineer, but in my opinion > formed by my limited experience, I would say that even > though the belt is moving constantly while the engine > is running, there is still static state torque applied > to the belt at any given moment. As the torque of the > engine increases (i.e. the crank spins "harder"), the > static torque applied at the instant the crank > experiences the greater torque would result in greater > tension being applied to the belt, causing it to > stretch a bit more than on a normal engine. Of course > at a certain point the belt might just slip on the > crank, but the friction of the belt on the crank and > cams is generally great enough that this doesn't occur > (and I don't know of any M20 powerful enough to do > that ;). > > > Brian > 95 M3 > > >> -----Original Message----- >> From: [EMAIL PROTECTED] >> [mailto:[EMAIL PROTECTED] Behalf >> Of [EMAIL PROTECTED] >> Sent: Thursday, June 23, 2005 1:32 PM >> To: bmwuucdigest@uucdigest.com >> Subject: [UUC] <E30> Stroker or bored >> >> >> On the issue of the M20 taken out to 2.7 or even 3.0 >> liters, here's the >> question. How much can the timing belt take? Anyone >> have experience or >> knowledge of guidelines? I would imagine that you >> would have to reduce the >> mileage intervals to account for the added stress >> put on the belt by the >> increase in HP. >> >> Thanks, >> -Kevin >> >> Search the >> > ARCHIVES:http://www.mail-archive.com/bmwuucdigest@uucdigest.com >> >> >> > _______________________________________________________________________ > ___ >> In memory of Michel Potheau - friend, enthusiast, >> founder of the BMW CCA. >> >> UUC Motorwerks - BMW Performance Fine-tuning and >> home of the Ultimate >> Short Shifter - accept no substitutes! >> 908-874-9092 . http://www.uucmotorwerks.com >> >> Search the >> > ARCHIVES:http://www.mail-archive.com/bmwuucdigest@uucdigest.com >> >> >> > _______________________________________________________________________ > ___ >> In memory of Michel Potheau - friend, enthusiast, >> founder of the BMW CCA. >> >> UUC Motorwerks - BMW Performance Fine-tuning and >> home of the Ultimate >> Short Shifter - accept no substitutes! >> 908-874-9092 . http://www.uucmotorwerks.com >> > > > > > __________________________________ > Yahoo! Mail > Stay connected, organized, and protected. Take the tour: > http://tour.mail.yahoo.com/mailtour.html > > Search the > ARCHIVES:http://www.mail-archive.com/bmwuucdigest@uucdigest.com > > > _______________________________________________________________________ > ___ > In memory of Michel Potheau - friend, enthusiast, founder of the BMW > CCA. > > UUC Motorwerks - BMW Performance Fine-tuning and home of the Ultimate > Short Shifter - accept no substitutes! > 908-874-9092 . http://www.uucmotorwerks.com > ------------------------------ Date: Thu, 23 Jun 2005 19:00:30 -0700 From: John Bolhuis <[EMAIL PROTECTED]> To: bmwuucdigest@uucdigest.com Subject: Re: <E30> Stroker or bored Message-ID: <[EMAIL PROTECTED]> > > On the issue of the M20 taken out to 2.7 or even 3.0 > > liters, here's the > > question. How much can the timing belt take? Anyone > > have experience or > > knowledge of guidelines? I would imagine that you > > would have to reduce the > > mileage intervals to account for the added stress > > put on the belt by the > > increase in HP. I can think of 2 factors: First, if the motor generates more power and has higher cylinder pressure, more force will be required to open the exhaust valves. This is especially true with forced induction, probably not so much with simple displacement increases. Second, if the motor can accelerate faster, more force will be applied to the belt just to bring the valve train up to speed, as others have pointed out. However, the highest rate of acceleration occurs under no load, such as when you miss a shift. (or just blipping the throttle because it sounds good) The time to hit redline under no load probably won't increase much after the modifications. I broke 2 timing belts in the life of an old Mitsu (non-inteference) engine, and both snapped during deceleration downshifting - I suspect the sudden RPM change was the last straw each time. -- "It is an honor to be Cookie Monster." -Sesame Street spokeswoman Audrey Shapiro ------------------------------ Date: Fri, 24 Jun 2005 13:40:22 -0400 From: [EMAIL PROTECTED] To: bmwuucdigest@uucdigest.com Subject: Re: Need a SRS sensor mat connector Message-ID: <[EMAIL PROTECTED]> Will shortly be installing racing shells/harnesses/rollcage in my M Coupe. Planning to build a circut to trick the SRS system to believe that the sensor mat is still installed and need a spare connector. If NE1 has one, please let me know. TIA. Neil Simon Wash, DC 99 M Coupe ------------------------------ End of [bmwuucdigest] digest(4 messages) **********
