Rule Nerds Question

#1

How about an adjustable cam pulley so the timing can be returned to stock after head resurfacing? Rule bool does not address this, but anyone who has built a motor has had this problem. CB

#2

I was just talking about this with someone. Crazy, huh?

I didn’t get into the calculations, but within factory tolerances you would be changing the cam timing so little that it would barely be measurable, if you could measure it. Of which, I don’t think you can on the vehicle.

Fun stuff…

#3

It’s measurable.

#4

It’s a good question. In a perfect world we’d be allowed to adjust cam timing in a decked head back to OEM spec. The problem is creating a rule that keeps the whole issue constrained so that folks don’t get imaginative.

Maybe if we knew for sure that more than OEM cam advance was bad, then we could assert that the rule is self enforcing. I don’t know enough about cam timing to make that arguement.

As soon as someone suggests that there’s performance advantage in advancing beyond OEM cam timing, adjustable cam gears are doomed.

#5

The cam timing changes the compression a little and the charged air pulse. Its pretty dam small amounts especially at 150 HP. Basically your shifting the power band around. Advanced = torque a little earlier, retarded = a little higher reving. Were talking small amounts. I would like to be able to adjust it. I swear, these cars are kindof boring when it comes to tweaking and setup. My car sits in the trailer right up to 3 days before the event, then a oil change and valve adjust, oh and a car wash.

#6

That’s the kind of talk that ensures a rule change request will not fly.

#7

[quote=“Foglght” post=66788]I was just talking about this with someone. Crazy, huh?

I didn’t get into the calculations, but within factory tolerances you would be changing the cam timing so little that it would barely be measurable, if you could measure it. Of which, I don’t think you can on the vehicle. [/quote]
I get a change in timing of 2.3deg for every 0.010 off the head. There is a noticeable difference in the torque curve if you fully deck the head (to gain a touch of compression) and don’t correct the cam timing.

I think an adjustable cam sprocket open’s a Pandora’s box. But an offset bushing to bring the cam back into time is reasonable.

#8

[quote=“jlevie” post=66798][quote=“Foglght” post=66788]I get a change in timing of 2.3deg for every 0.010 off the head. There is a noticeable difference in the torque curve if you fully deck the head (to gain a touch of compression) and don’t correct the cam timing.

I think an adjustable cam sprocket open’s a Pandora’s box. But an offset bushing to bring the cam back into time is reasonable.[/quote]
How about this… We create a rule that says “There is on authorized method of returning the engine to OEM cam timing. Ccntact Chuck Baader and tell him your the height of your head. He will make you the appropriate offset bushing and provide a documentation card for your logbook”. Or something like that.

I agree that getting the engine back to OEM cam timing is a good idea. “Adjustable” cam timing isn’t in the spirit of the series tho, so the trick is to come up with a way to allow the cam timing to be fixed that’s reasonably controlled. If we can get a hold of a smart person and identify that OEM cam timing is optimal and deviation from it is a bad idea, then the idea is self enforcing.

If the idea did need to be enforced, inspecting your Baader bushing would be a helova lot easier than weighing flywheels looking for mystery metal.

#9

Rules discussion should be elsewhere. Do not add complexity to them.

Regardless, how in the heck are you going to enforce this level of engine build detail?

Bring out the dyno and your car had best not exceed _% over the numbers posted by your competitors on the same given day at the same given dyno.

If you exceed, don’t know what you did, don’t care. We’ve been doing this for quite some time and we know what to expect as the “norm”.

If you exceed, congratulations on spending too much money/time in preperation. Here is some penalty weight. Drive around with it until your engine mysteriously becomes weaker.

RP

Ps, I don’t make the rules.

#10

Yes, it changes the timing. Yes it hurts power. Yes, a $30 ebay adjustable pulley would be the easy button. Yes, it is easily teched.

Now, after spending 4 hours on the dyno with 2,4,6, & 8 degree plus and minus offset bushings I discovered that BMW got it right the first time. You WILL hurt your power by retarding the cam. You WILL hurt your power by advancing your cam. A simple means to return to factory timing would be nice. CB

#11

[quote=“cwbaader” post=66808]Yes, it changes the timing. Yes it hurts power. Yes, a $30 ebay adjustable pulley would be the easy button. Yes, it is easily teched.

Now, after spending 4 hours on the dyno with 2,4,6, & 8 degree plus and minus offset bushings I discovered that BMW got it right the first time. You WILL hurt your power by retarding the cam. You WILL hurt your power by advancing your cam. A simple means to return to factory timing would be nice. CB[/quote]

Kinda agrees with, “we’ve been doing this for quite some time and know what the norm is”.

Yeah, yeah, I’m gonna shave the head till the valves kiss the pistons. Go ahead, knock yourself out, you’ll pay for it elsewhere cause you can’t index the cam back to where it was.

Yes, the BMW goober engineers were/are kinda smart.

RP

#12

You can, with the stock pulley, return the timing to stock. Done it many times. Chuck

#13

but not so simple means I suppose.

#14

Depends on the equipment you have. On the later mod pulleys, I use a lathe, and drill press. On the earlier I use a mill with a rotary table. Relatively easy either way. CB

#15

[quote=“jlevie” post=66798][quote=“Foglght” post=66788]I was just talking about this with someone. Crazy, huh?

I didn’t get into the calculations, but within factory tolerances you would be changing the cam timing so little that it would barely be measurable, if you could measure it. Of which, I don’t think you can on the vehicle. [/quote]
I get a change in timing of 2.3deg for every 0.010 off the head. There is a noticeable difference in the torque curve if you fully deck the head (to gain a touch of compression) and don’t correct the cam timing.

I think an adjustable cam sprocket open’s a Pandora’s box. But an offset bushing to bring the cam back into time is reasonable.[/quote]

So, lets assume the bores are round and not tapered and you can just re-ring it. I’m getting some mixed numbers when it comes to what the actual BMW factory compression tolerances are. If you deck the head and had a loosey goosey bottom end with blowby, maybe you don’t need a thicker gasket to compensate. In that case, I suppose if you go to max on everything, you would notice. Don’t know how much area is available on that head, but I can’t imagine its a lot.

About measuring it, the intent of my comment was about measuring it at a race event.

#16

[quote=“Foglght” post=66821][quote=“jlevie” post=66798][quote=“Foglght” post=66788]I was just talking about this with someone. Crazy, huh?

I didn’t get into the calculations, but within factory tolerances you would be changing the cam timing so little that it would barely be measurable, if you could measure it. Of which, I don’t think you can on the vehicle. [/quote]
I get a change in timing of 2.3deg for every 0.010 off the head. There is a noticeable difference in the torque curve if you fully deck the head (to gain a touch of compression) and don’t correct the cam timing.

I think an adjustable cam sprocket open’s a Pandora’s box. But an offset bushing to bring the cam back into time is reasonable.[/quote]

So, lets assume the bores are round and not tapered and you can just re-ring it. I’m getting some mixed numbers when it comes to what the actual BMW factory compression tolerances are. If you deck the head and had a loosey goosey bottom end with blowby, maybe you don’t need a thicker gasket to compensate. In that case, I suppose if you go to max on everything, you would notice. Don’t know how much area is available on that head, but I can’t imagine its a lot.
[/quote]
I didn’t understand that.

What does piston-cylinder wall gap and compression #'s have to do with a thicker HG or valves hitting pistons?

Area available on the head? Area?

#17

I accidentally ordered a +.003 VR HG if anyone’s interested.

#18

One too many 0’s I suspect…should read .030" oversize. CB

#19

likely.

#20

[quote=“Ranger” post=66823]
What does piston-cylinder wall gap and compression #'s have to do with a thicker HG or valves hitting pistons?

Area available on the head? Area?[/quote]

Part of the function of compression ratio is bore size. Increase the bore size and you increase compression. You’d only need to account for that if you had to bore for oversize pistons rather than hone and re-ring. If you increase compression due to overbore, you would want to think about a thicker head gasket.

However, I am interested in the actual BMW specs for compression tolerance, as well as chamber size.