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  #1051  
Old November 28th 2011, 04:19
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still good numbers. got any plans over the winter for car?
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  #1052  
Old November 28th 2011, 07:38
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Originally Posted by judgie View Post
still good numbers. got any plans over the winter for car?
@ Rob: Plans, yes, I would like change the camshaft for a better breathing one. The current heads could really use more cam I realise now after my understanding of a turbo engine has changed quite somewhat over the past few years
@ Francelle: There is really little reason to open up the engine otherwise for inspection as the first part of the power curve is exactly the same as the one from early this year.

However, I am building a project T1 1200cc EFI turbo, so that will probably eat up all of the time and I might even miss a few events next year because of this.
OTOH, opening the engine for just a cam could mean I would want to replace more parts; you know how that goes and could mean downtime for a longer period.

Decision, decisions...

The engine will come out over X-mas holidays anyways and I can inspect the dual Black Magic disks and flywheel. Curious how that looks...
I also have one damaged Jenvey TB from the backfire that broke two rockers and bend the butterfly valves on one side. I straightenend them but it caused severe play on the TB/butterfly shaft I noticed and resulted in the linkage arms on the TB shaft to be blown off on boost... Fixed that by a locktited screw in the TB shaft but I also loose some spool probably over the shaft since, so may have to get one new TB as well anyways (ouch).

Thats about it
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  #1053  
Old November 29th 2011, 04:11
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so is the cam thats needed more duration or more lift? i would guess you want a faster ramp to open them and less overlap but not more lift? faster ramp would mean better springs to control the lift/close speeds. from what i understand big lift is not needed on turbo motors, just the time the valve is open, the turbo is pushing the mix so you dont need the lift, but you want the valves open for as long as possable with the least amount of overlap.
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  #1054  
Old November 29th 2011, 05:20
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so is the cam thats needed more duration or more lift? i would guess you want a faster ramp to open them and less overlap but not more lift? faster ramp would mean better springs to control the lift/close speeds
Yes, I would say you'd always want to have a ramp as fast and agressive as your lifter foot would support IF...and a big if...if the additional wear and extra needed spring wouldn't be an issue. However, it IS an issue and that means its always a compromise with what your particular valve train will support.
The other downfall of more duration is less torque down low.
If you can lessen both downsides of more duration, you optimize the engine's efficiency.
The first issue of spring control is 'easy' to manage by better parts. Lighter yet stronger is the goal.
The second issue is more difficult to control. A lot can be done here too though with cam timing: Most view duration as a "1-dimensional" property of a given single number of degrees duration. However, the duration is made up from both the opening AND closing of the valve. And that for both intake and exhaust valve which doesn't need to be the same either.
For example, you can have the same duration for intake and exhaust, yet still have different opening and closing timing for either. Most all cam makers have symmetrical opening and closing timing, its convenient, but that doesn't need to be.
Long story short, I have a (Pauter) cam here that has 20 degrees more duration, but its intake valve closes (that determines dynamic compression) at the same time as my current Webcam. That of course means it gets its extra duration from earlier opening resulting in more overlap. My take is that overlap can be managed by a better exhaust system, i.e. equal length exh. manifolds and even better: twin scroll design.
Guess what's on my car and for what reason?

Quote:
. from what i understand big lift is not needed on turbo motors, just the time the valve is open, the turbo is pushing the mix so you dont need the lift, but you want the valves open for as long as possable with the least amount of overlap.
So, overlap is manageble as shown above and the myth that turbo engines don't need the (extra) lift is pretty much busted by my first turbo engine (stock 914 2.0) when I just (only change) put a set of Pauter ratio rockers on and made 40-50 more hp (222->270hp) at the same boost!

A fast ramp of course is also favourable as it gives you the lift as soon and long as possible. If lift wasn't much of a concern, a fast ramp wouldn't be necessary either, which contradicts your saying that lift isn't much of a concern with turbo even more.

If it all works out as I have thought it out, remains to be seen of course. Its difficult to do 'scientific' and therefore conclusive testing for a privateer (and even for a shop), but if I could do just a cam change and nothing else, that would be very interesting. Not sure if it comes to that in 2012 though...
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Last edited by Wally; November 29th 2011 at 06:04.
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  #1055  
Old November 29th 2011, 12:53
70Turbobug 70Turbobug is offline
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Quote:
The other downfall of more duration is less torque down low.
If you can lessen both downsides of more duration, you optimize the engine's efficiency.
Another way to compensate for that and have an aggressive ramp,prolonging valve open timing is to use a smaller base circle and a wider lobe center.If you can use a higher compression ratio also.Wally mentioned picking up 40hp just by changing rockers.One reason is not only the extra lift but with the higher ratio the valve opening rate in mm per second also rose dramatically.Basically the same effect as having a steeper ramp on the cam.
Wally is running a pretty big turbo with relatively small displacement.Most of the ricers that run these large turbos don't have much power below 4500rpm but therefore rev easily 8500rpm.What's the point? Wally's cam may be too mild and the lift too low to spool the turbo sooner, making the whole set up less responsive.Sounds like the opposite of what Wally said above, but it's not really.If you have a typical drag race cam an NA engine may be a little sluggish in the lower rpm range.That's due to lack of airflow actually airspeed causing a lower inefficient cylinder pressure.This is where the efficiency of the turbo and the rest of the system i.e twin scroll,static compression ratio,tuning etc. come into play.
True a turbo engine does not need a high lift high duration cam to make power,but if you want high boost and responsiveness that low lift low duration will become more of a restriction especially if you want a lot of power out of a small displacent engine.
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  #1056  
Old November 29th 2011, 13:01
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it wasn't as much the amount of lift i said the turbo responeds to but the amount of time its open. the valve needs to be open and flowing for as long as pratical but big lift numbers are not allways needed as long as the flow is there.
hence why i said a faster ramp to get to the max lift would poss work better than just more lift, but you need the valve train to support the faster ramp.
the amount of boost will also play a big part in this. at a guess you could almost stall the airflow in the port with high boost, this would cuase a lot of turbulance around the back of the valve and poss even fuel seperation.
i have no real data to back any of that up just info from what i have seen and been told.
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  #1057  
Old November 29th 2011, 13:47
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.. but big lift numbers are not allways needed as long as the flow is there.
Thats just the point Rob: more lift usually means more flow, especially in my case: I have 46mm intake valve and just 0.50" lift, which just isn't optimizing what the port can flow, at all.
A turbo engine really responds to that the same as n/a, maybe even more so.
YMMV of course
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  #1058  
Old November 29th 2011, 15:31
70Turbobug 70Turbobug is offline
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Quote:
Thats just the point Rob: more lift usually means more flow, especially in my case: I have 46mm intake valve and just 0.50" lift, which just isn't optimizing what the port can flow, at all.
That depends on the engine's off boost efficiency,also.The trick is to gain cfm and velocity.Portdesign and valve size and valve timing are important for that.
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  #1059  
Old November 30th 2011, 10:21
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more lift? well in the situation of Wally's stock 914 gaining significant HP with ratio rackers....
Even if the original peak lift exceeded the flow capacity of the port, adding ratio rackers increases the average lift during the cycle so has more flow for longer even if the peak flow might be unchanged.

more duration? perhaps not totally suited to turbo engines but a higher compression ratio means you can advance the exhaust openning point. That way you can get longer exhaust duration without increasing overlap. This is because with high compression ratios, the cylinder pressure falls faster as the piston moves away from the head on the detonation stoke.
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  #1060  
Old December 1st 2011, 15:30
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Steel front hood is 8.8kg, this Kerscher 'super leicht' 1303 hood (this light weight version is not on their web-site) weighs 4.9 kg, but needs some adhesive and hood handle, so more like a 3,5kg difference.
At least it won't rust anymore



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  #1061  
Old December 1st 2011, 15:49
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Niiiiiice!

If I wasn't going to rally my car, I'd be looking for composite panels. Too much heartbreak when you kiss a snowbank though...which happens more often then we'd like to admit!

-Dave
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  #1062  
Old December 2nd 2011, 05:57
70Turbobug 70Turbobug is offline
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I see you´re making progress on the 1200 also...
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  #1063  
Old December 2nd 2011, 09:06
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Good eye!
But, yes indeed 2,2 will go out somewhere in the coming weeks after the longblock is done to test-install and adapt the intake and exhaust routing of the 1200T.
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  #1064  
Old December 2nd 2011, 09:09
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Niiiiiice!

If I wasn't going to rally my car, I'd be looking for composite panels. Too much heartbreak when you kiss a snowbank though...which happens more often then we'd like to admit!

-Dave
Hi

I've found that fibre glass panels have a bit of flex before breaking where as the steel versions just bend.

Steve
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  #1065  
Old December 6th 2011, 11:30
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Niiiiiice!

If I wasn't going to rally my car, I'd be looking for composite panels. Too much heartbreak when you kiss a snowbank though...which happens more often then we'd like to admit!

-Dave
Dave, don't you use the snowbanks in good Scandinavian style? On the rare occasions we have decent snow with better than 1/2m high banks I just love kissing the banks to aid turn in!

( we are fortunate here because when the snow is that high the roads are really clear 'cos us Brits hate snow dontcha know)

Clive
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