86 Coupe GT

Slightly more lift and duration, if you must go with a stock cam. Check audifans.com, though, and you'll find a 272 cam for 135$. Having a 270+, I'll tell you it does make a difference.

Carter

- GT Style -

Huw's site info IS from his 1st hand account, not an old QL post.

boxerfan

Did the overlap calcs. Overlap is when the intake is open before the exhaust closes. In a turbo motor this causes reversion and is highly undesirable.

In an NA motor I think the overlap is designed so that the exiting exhaust gasses help draw in the non-compressed air. I can't see a real turbo cam ever being a real NA performance option. It doesn't add up. Now... as for why the MC2 and the NG cam are the same I have no idea. It is obvious that the 272 and others are open much longer and likely have a touch more lift. It is also obvious that they have a fair amount of overlap and I can't see that being a good thing for a turbo. I think it is interesting that the JT and WU motors have the largest separation in overlap (negative value). Overlap is the difference between the intake valve opening and the exhaust valve closing so if the exhaust is closed before the intake opens there is negative overlap.

The way I see it is that if, using the Blau 272 as an example, the incoming compressed air is rushing into the piston chamber and immediately out the exhaust valve. When the valve does close the flow of air changes and this must cause the reversion pulse in the system. If the exhaust valve is already closed then the air is only filling the piston chamber. When in an NA car there is no pressure to push the new air charge into the engine so the mechanical sucking action of the piston must complete the task. If the exhaust valve is open just for a moment the exhaust gas expanding out the exhaust valve port will help suck in the new air charge and is hence desirable.

At least that is the sense I can make of it. So... will a turbo cam be a performance improvement on an NA motor? I doubt it.

However... an MC1 motor has a little more duration and less negative overlap. Seems like a pile of work for little difference. KX and KZ would be better I think.

HTH.

treehunter

Thanks guys, it was just a thought seeing as I had a couple MC1 cams lying about and a JT in bits.

boxerfan

Just copy and paste... you'll need to sort the spacing out.

Code Years built cc HP @RPM Torque BoreStroke CR Cam timing: F.I.
Int Opens Int Closes Ex Opens Ex Closes
WE 80 83 2144 100@5100 110@2500 79.5 86.4 8.2 6 BT 40 AB 47 BB 1 AT K

WU 83.08 86.07 2144 100@5500 112@2500 79.5 86.4 8.2 1.5 AT 38.7 AB 41.5 BB 1.3 BT K

JT 84-87 2226 115@5500 126@3000 81.0 86.4 8.5 1.5 BT 38.7 AB 41.5 BB 1.3 BT KE

KX 84 87 2226 110@5500 122@2500 81 86.4 8.5 2 BT 39 AB 42 BB 1 BT KE

KZ 84.08 86.09 2226 110@5500 122@2500 81 86.4 8.5 2 BT 39 AB 42 BB 1 BT KE

KH 83.08 86.07 2144 140@5500 149@25\00 79.5 86.4 8.3 1.5 AT 38.7 AB 41.5 BB 1.3 BT K

MC1 86.06 88.10 2226 162@5500 166@3000 81 86.4 7.8 0 BT 41 AB 40 BB 1 BT KE
MC2 88.11 90.11 2226 162@5500 177@3000 81 86.4 8.4 4 BT 41 AB 46 BB 5 BT KE

NF 86.08 90.11 2309 130@5600 140@4000 82.5 86.4 10. 0 BT 41 AB 40 BB 1 BT KE3

NG 87.10 89.04 2309 130@5600 140@4500 82.5 86.4 10. 0 BT 41 AB 40 BB 1 BT KE3
89.05 92? 2309 135@? 140@? 82.5 86.4 10. 4 BT 41 AB 46 BB 5 BT KE3


Aftermarket cams
Duration Lift Lobe Center Valve Timing
Int Opens Int Closes Ex Opens Ex Closes Overlap
Blau hydraulic 272° 12mm 112 27 BT 65 AB 71 BB 21 BT 6

Elgin 270 11.8mm 110 25 BT 65 AB 60 BB 20 BT 5

Eurospec hyd. 272° 12mm 112 27 BT 65 AB 71 BB 21 BT 6

Eurospec mech. 280° 10.82mm 110 33 BT 67 AB 73 BB 27 BT 6

Eurospec mech. 282° 13.2 110 31 BT 71 AB 71 BB 31 BT 0

Eurospec mech. 306° 14.5mm 106 47 BT 79 AB 79 BB 47 BT 0

WE 226° 107 6 BT 40 AB 47 BB 1 AT 7

WU 217.2° 110.1 1.5 AT 38.7 AB 41.5 BB 1.3 BT -2.8

JT 220.2° 108.6 1.5 BT 38.7 AB 41.5 BB 1.3 BT -2.8

KX 221° 108.5 2 BT 39 AB 42 BB 1 BT 1

KZ 221° 108.5 2 BT 39 AB 42 BB 1 BT 1

KH 217.2° 110.1 1.5 AT 38.7 AB 41.5 BB 1.3 BT -2.8

MC1 221° 11.15mm 110.5 0 BT 41 AB 40 BB 1 BT -1
MC2 225° 108.5 4 BT 41 AB 46 BB 5 BT -1

NF 221° 110.5 0 BT 41 AB 40 BB 1 BT -1

NG 221° 110.5 0 BT 41 AB 40 BB 1 BT -1
225° 108.5 4 BT 41 AB 46 BB 5 BT -1

- GT Style -

<ul><li><a href="http://webpages.charter.net/typ85/engine%20Code.doc">http://webpages.charter.net/typ85/engine%20Code.doc</a</li></ul>

boxerfan

FYI:

I measured the MC1 lift to be 11.15mm this AM. Might want to add that to the list.

Kudos to the original author for sure. It is nice when information is tightly contained for easy evaluation.

- GT Style -

<ul><li><a href="https://forums.audiworld.com/4000/msgs/125291.phtml">https://forums.audiworld.com/4000/msgs/125291.phtml</a</li></ul>

SteveAngry

There is a slight gain on the MC1 cam, better gains on the 272.



Steve
Michigan

treehunter

Apparently it does have a slightly higher lift and duration.