Good news! Got the car running no trouble, bled the cooling system, and took it out for a test run. Midrange torque seems improved I must say, at least by the butt dyno. Throttle response seems crisper too, not that it was bad before. Had the car to 6500 rpm a few times and thankfully did not bend any valves. That's my self-imposed redline, so hopefully I'll be safe for the time being at 3 degrees advanced. Once I get the Miller WAR chip and intake, it will be time dyno time and then we'll see what kind of power I can get out of this motor.
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'89 BMW 325is Zinnoberrot / '88 VW Jetta GLI 16v Tornado Red / '89 VW Jetta GLI 16v Tornado Red / '89 VW GTI 16v Bright Blue Metallic / '91 BMW 325i Black / '91 BMW 325i Sport Black / '92 VW GTI 16v Black / '92 VW GTI 16v Montana Green / '01 Audi A4 Avant TQM Silver Metallic / '01 VW Jetta GLX VR6 Black -
the only "special tool" you really need to measure piston/valve clearance is a flathead screwdriver (to compress the spring, stick it in the fork of the rocker) and a $10 harbor freight dial indicator..
anyway, aside from going off the cam card, the best way to set the timing IMO is on a dyno. it's not a bad idea to get a baseline of how far you can safely adjust it of course, but without dyno feedback you're just guessing (even if you go by the card).Comment
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also - I wouldn't be so afraid of the rockers. although, your cam is more agressive than what I have, and I've no idea about your spring rates - I don't have any special rockers, and my M20 will rev to 7500 all day long. 6500 is lazy for your motor, even the stock motor can go higher than that.
if you want to be conservative set the redline to 7200. I mostly set mine higher to avoid tagging it (or bouncing on longer autox courses), but with a different intake it still pulls nicely and makes an awesome sound from 7000-7500. aside from the rockers, M20s don't really have major weaknesses that keep them from reving (take an M52 or M54 to 7500 and see how long it holds together).
My bottom end is just an eta crank that I pulled from a low miles motor, and dropped in stock/untouched, and some used (but good) S52 rods, and stock M20 bearings actually the only thing that isn't a stock BMW part inside my engine are the pistons and the cam...
if you wanted to be safer, upgrade to IE HD rockers and appropriate valve spring rates. valve float is your enemy..Comment
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Very interesting nando. Besides the cam, my valve springs and rockers are both OEM BMW parts with possibly 175k miles on them. Head was cleaned up and rebuilt with new guides and seals by the last owner (and I went through it again with new seals when building the bottom end 5500 miles ago) but there is a good chance the valves/rockers are original.
And valve float is definitely my enemy! I can't imagine there's more than a millimeter or two between my valves and pistons at full lift when there's no valve float occurring.
Do you think I'd be safe to take it to 7000 RPM with the stock springs? Or will the valves start to float at that point?'89 BMW 325is Zinnoberrot / '88 VW Jetta GLI 16v Tornado Red / '89 VW Jetta GLI 16v Tornado Red / '89 VW GTI 16v Bright Blue Metallic / '91 BMW 325i Black / '91 BMW 325i Sport Black / '92 VW GTI 16v Black / '92 VW GTI 16v Montana Green / '01 Audi A4 Avant TQM Silver Metallic / '01 VW Jetta GLX VR6 BlackComment
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well, I'd be careful then. it's not a good idea to use old rockers with a new cam. since they're aluminum, they're subject to fatigue cycles. Aluminum parts will have a limit, some X number of cycles, before they will break (like wings on an airplane).
with 175,000 miles, many of those cycles are already used up. It's not a matter of if they will break, but when, and RPM isn't neccesarily going to cause it, except you use up the cycles faster (and if you float the valves, obviously bad things happen quickly).
springs don't neccesarily wear but they should be checked before re-use to make sure they're up to spec.
anyway, if there's any way to verify if they're original 175k mile parts or not - you won't want to push it very hard. Heck, I'd consider upgrading the springs and getting IE HD rockers regardless.Last edited by nando; 12-27-2011, 08:57 AM.Comment
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Yes, HD springs and rockers are definitely on my list. Looks like a rebuilt and ported/polished head is not as far in the future as I thought. I'll have to do some shopping around.
Off topic, but does anyone have suggestions for a source for upgraded M20 heads? I know MR 325 has them from Myster-e, and I know VAC (local to me) has them available? Other good options?'89 BMW 325is Zinnoberrot / '88 VW Jetta GLI 16v Tornado Red / '89 VW Jetta GLI 16v Tornado Red / '89 VW GTI 16v Bright Blue Metallic / '91 BMW 325i Black / '91 BMW 325i Sport Black / '92 VW GTI 16v Black / '92 VW GTI 16v Montana Green / '01 Audi A4 Avant TQM Silver Metallic / '01 VW Jetta GLX VR6 BlackComment
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there are a few - also metric mechanic. they do CNC'd intake ports but don't really touch the exhaust. They like to compromise for emissions/idle rather than towards max performance.
whoever does it make sure they really know what they are doing, 885 intake ports are actually pretty good as-is and a monkey with a die grinder is more likely to make them worse than better.
if you do a bunch of headwork, you'll of course want to do something about the stock intake manifold, airbox, and throttlebody. and of course exhaust. Modified BMW engines are a vicious circle, since everything was designed for 2.5l/168hp, you can't really upgrade one part without doing everything. whatever part you leave stock is going to be the weakest link..Comment
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Yes, I'm very familiar with the downsides of headwork if a person is not familiar with a particular head. I have a lot of experience with VW's 16v head and many shops that port them end up with a head that flows better over 5k RPM and worse below. Not a good trade off.
In my case, the bottom end is set and the exhaust is set. Currently have the Miller MAF and will upgrade to the WAR Chip and intake.
What do you recommend for the intake manifold and TB? I'm using ITBs on my 16v so for now I want to stay more reasonable and retain a single TB on the BMW. Do people extrude hone the M20 manifolds? Or does someone port them? Haven't run across that anywhere.'89 BMW 325is Zinnoberrot / '88 VW Jetta GLI 16v Tornado Red / '89 VW Jetta GLI 16v Tornado Red / '89 VW GTI 16v Bright Blue Metallic / '91 BMW 325i Black / '91 BMW 325i Sport Black / '92 VW GTI 16v Black / '92 VW GTI 16v Montana Green / '01 Audi A4 Avant TQM Silver Metallic / '01 VW Jetta GLX VR6 BlackComment
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you can get an EX manifold from IE for about $700. Expensive, but maybe the best option other than $2500 for ITB's. You can port them sort of, but it doesn't really do much since you can't reach very far inside the manifold. In stock form, the B25 manifold flows about 10-20cfm less than the stock head.. maybe it was designed that way for a reason, but if you've modified the head those reasons go out the window. :)
you can bore out an M20 TB to 65mm using an M30 throttle plate (or adapt the entire M30 throttle). the airbox you'll want to ditch, but whatever you replace it with MUST be shielded from hot engine bay air.
for the heads - on the 885, it's really more about optimizing flow around the valve seat at high lift, than increasing static CFM #s. agressive cams use more lift, but the 885 gets really turbulent above about 10.5mm of valve lift, so flow tends to flatline, but this can be fixed. Other than the short side radius, valve guide, and bowl, it's mostly cleanup work. definitely don't let anyone hog out the intake ports. People seem to get 195-210cfm per port if they know what they're doing. stock is around 180cfm.Comment
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Do you have a link to this? I searched but didn't find it. Maybe I missed something obvious. Thanks.Originally posted by nando View Post'89 BMW 325is Zinnoberrot / '88 VW Jetta GLI 16v Tornado Red / '89 VW Jetta GLI 16v Tornado Red / '89 VW GTI 16v Bright Blue Metallic / '91 BMW 325i Black / '91 BMW 325i Sport Black / '92 VW GTI 16v Black / '92 VW GTI 16v Montana Green / '01 Audi A4 Avant TQM Silver Metallic / '01 VW Jetta GLX VR6 BlackComment
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Is there anyone who makes the adapter for the M30 TB? just did a search and all i found was a thread about a prototype.
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