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#150
by
theman53
on 31 Mar, 2010 14:35
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On this cam is there no time when the intake and exhaust are open at the same time? I figure that would be best for a turbo app. Also, I knew it was a custom grind and I am going to be in need of a Mech one though...but like I said I just need to get it done.
Nope, there's no room to have any overlap - the piston is essentially flat against the head at TDC, so you can't possibly have the intake and exhaust valves open at the same time like you would on a gasser.
Not overlap in the piston and cam, but the intake and exhaust lobes. Burn has a cam spec table and it shows overlap with every cam he has done stock. For highest boost without loss you would want close to zero if I am recalling correctly.
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#151
by
Smokey Eddy
on 01 Apr, 2010 00:08
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Not overlap in the piston and cam, but the intake and exhaust lobes. Burn has a cam spec table and it shows overlap with every cam he has done stock. For highest boost without loss you would want close to zero if I am recalling correctly.
If you had valve overlap you would bleed boost on the exhaust stroke. You don't really have to recall anything. just think about it - 4-stroke engine.
intake, compression, power, exhaust...
on intake stroke if you had some exhaust valve over lap it might rid the cylinder a little better of the exhaust gases with that rush of air from the turbo - but there is a fine line here between wasting boost and getting lots of clean 02 into the cylinder...
on compression ... well that doesn't need ANY thought hahahahh
power, same as compression...
exhaust, having a marginal amount [how much i have NO idea] of valve over lap here would be slightly beneficial but again its the same issue as the intake stroke - lost/wasted boost pressure unless you had such a big turbo and were fueling it enough such that you could "afford" to spend boost on such things... after all it would just go through the turbine on the other side anyways.
I know you all were already thinking what i just said, i just like to illustrate it - i find it easier to visualize.
In my completely inexperienced opinion; a tiny tiny amount of valve over lap might be advantageous to ensure the exhaust is totally getting out of there - just like how having a couple degrees of over lap helps a big/small block make bigger power.
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#152
by
truckinwagen
on 01 Apr, 2010 00:12
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I have a hard time believing that the diesel cam has much(if any ) overlap.
the piston to valve relationship would make it really difficult, and most of the stock gasser cams have negative overlap(that is rotation where both valves are closed)
what I would love to see is a diesel cam with stock duration and timing, but more lift.
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#153
by
Smokey Eddy
on 01 Apr, 2010 00:17
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I too would love to see Maximum lift on a cam. To the point where the valves are chasing the piston as it goes down. Also add 2 more valves per cylinder...
I agree that a stock cam would have zero over lap.
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#154
by
theman53
on 01 Apr, 2010 06:16
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This is from tylers post and if I read this correctly there is the overlap of intake and exhaust being open at the same time. On small and big blocks that get turbos the usually get a custom grind cam that has the intake closed and right after then the exhaust opens. That way the intake charge doesn't leave out the exhaust. For naturally aspirated the cams are built opposite and you can run tuned headers to actually pull more into the combustion chamber.
Disclaimer: I am not a professional engine builder, but I have stayed at a motel 8. This is just the way my head machinist and I have talked about it and he even said under 20lbs boost it really doesn't matter.
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#155
by
burn_your_money
on 01 Apr, 2010 09:44
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Yes there certainly is overlap. For the record, those are cam degrees,not crank.
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#156
by
Darkness_is_spreading
on 26 Jun, 2010 22:14
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Hey when you installed this motor into the Cabrio, did you have to change the passenger side engine mount... (Ie removing the IP and replacing the brackets to to match up)?
To me it looks like this must be done in order to support the motor properly in the first gen frame....
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#157
by
burn_your_money
on 27 Jun, 2010 17:37
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Yes the pass motor mount needs to be replaced with the MK1 diesel version.
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#158
by
rabbitman
on 28 Jun, 2010 09:55
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I did a leakdown test on my rabbit and found that at TDC on the exhaust stroke it wouldn't hold any pressure, when I turned it a little either way it sealed up. Definitely overlap.
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#159
by
ktownboostn
on 21 Feb, 2011 05:34
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Damn ! This car has come along way since i saw it at Jitterbug 09 !
Really interested in the info on the cam. IS it still possible to have them re-ground ? has the guy left the country ? Anyone else know the details ?
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#160
by
stewardc
on 21 Feb, 2011 06:51
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Isn't Giles (erformance Diesel Injection) the dealer for them now ?
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#161
by
Giles@PerformanceDiesel
on 21 Feb, 2011 18:26
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yes Dr D. has passed on the duty to me now.
i have two freshed gound cams in stock if anyone wants one.
Giles
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#162
by
8v-of-fury
on 21 Feb, 2011 18:27
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Amazazazing.
this looks great, how is it now!!
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#163
by
Digital K
on 07 Mar, 2011 00:25
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great thread