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Discussion Starter · #1 ·
I asked similar questios before on Vage ,but lets not go into that.......
Anyway , with a 9a running between 175 and 200bhp , what's the best gearbox to use in a MK1? Top speed is irrelevant , once I'll pull about 115mph I'm happy , acceleration is king IMO.
Also , does the 9a head which I'm told is the same as a KR head respond well to porting and polishing? And is there scope or even need to fit larger valves?
 

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Any of the 020 box's are ok for nearly 200 bhp. I think the box in the 16V GTi has a longer gearing on the final drive. So stick to a box from a 1.6 or 1.8 8V. Over that power you should go for a box from a VR6 (02A), but this requires more work, clutch, starter, flywheel etc.

Not sure if the 9A and KR heads are the same, but if you have a 9A head you could compare it to one I have in the garage, (going on in the next 3 days).

Porting always produces more power if it's done properly, but do not polish. A 80 grit finish is as smooth as you should go for. There are many casting defects that can be removed on the heads, and then match the ports, inlet only, to the gasket and do the same to the inlet manifold. Leave the exhaust at least 1 mm larger on the manifold than the ports. clean up the ports and smooth the short side radius. Don't increase the size of the ports.

John
 

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I would just go for mk2 16v o2o box, most of the big power mk1's in ireland and the uk run these as they are relativly easy to fit, but i would have a diff put into iot as they tend to shear the diff rivits(see Geo's track car thread for pics of the resulting damage) and this will kill the box, but a rebuilt box with a diff should be fine for your car
 

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George, throught the gears the 16v box is closer ratios
The 8v box may have a longer final ratio, but that is for top speed and i am assuming the car is to have nice quick acceleration, so go with an 020 box with a limo diff and your gonna be fine for 200 bhp

as for road going n/a 8v's with 200bhp, i have nerver seen them, but the principle should be fine, lots of work, be b etter off to start with an 8v g60
 

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Discussion Starter · #11 ·
So the o2o is the standard Mk2 16v box , as found in golf's and Jtta 16v's? is it anything else? And there's no serious issues with clutch actuation , or gear selection , putting that box into a Mk1?

@Jonny , cheers , I understand the principles of porting and polishing , I've done a few heads in my time , I was juxst curious if the VW heads were responsive to it. Why would u leave the manifold bigger tho'? I normally dowel it to the head with short rollpins , and port match them together...
 

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Discussion Starter · #12 ·
Found these figures on Vortex , for a 2.ol with SuperTech oversized valves....

oem
intake
.050 26.40
.100 60.20
.105 90.60
.200 128.30
.250 149.00
.300 165.30
.350 170.10
.400 176.80
exhaust
.050 21.80
.100 55.10
.150 93.20
.200 113.80
.250 117.70
.300 123.50
.350 127.80
.400 130.10
big valve
intake
.050 41.80
.100 92.30
.150 128.30
.200 163.50
.250 196.10
.300 215.60
.350 229.50
.400 240.40
exhaust
.050 33.60
.100 72.40
.150 121.80
.200 146.00
.250 165.70
.300 180.10
.350 188.20
.400 191.30

Inches of valve lift and the corresponding cfm.....serious airflow , what? So what increase in valve size is practical?
 

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Only match the inlet manifold to the head. The exhaust manifold should be larger than the ports because this acts as an anti-reversion dam to discourage the exhaust gasses returning to the cylinder before the valve closes.
This oversize should be biased to the top of the port also.

It's based on sound wave theory. Sound wave theory also dictates that it assists cylinder scavanging. I understand porting very well but the sound wave theory is very complicated, for me anyway.


If there's someone on the forum that can enlighten us, please feel free, as I would like to get a handle on it.

Books are availible on the subject of porting and I find Dave Vizard to be one of the best.

John

 

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Discussion Starter · #14 ·
Cheers John , veruy interesting that.... Vizard is a genius alright.
 

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QUOTE (RedLexus @ Dec 28 2005, 04:49 PM) <{POST_SNAPBACK}>So the o2o is the standard Mk2 16v box , as found in golf's and Jtta 16v's? is it anything else? And there's no serious issues with clutch actuation , or gear selection , putting that box into a Mk1?

020 is also found in an 8v if I am not mistaken, its the box type so its the ratios you are after to decide. To be honest, when it comes to ratios of boxes to use with a 9a engine in a mk1 you would probably be better speaking to someone who has actually done it to see what their opinion is.
As Dave pointed out the box will cope with your power so the ratios is a matter of preference.
 
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