Autech Pulsar GTi

well my clearances are apparently supposed to be 0.17mm on the intake valves, +/- 0.05mm, and the exhaust around 0.39mm +/-0.05mm. My intake are ok i think, but some of my exhaust are a tad tight, i'd need to work out the sizes. See my shims range from like 2.65mm to 3mm, are they all supposed to be 3 with no wear then??

dont fully understand this shimmin lark
 
Yeah Joe, its pretty straight forward to do, you'd just have to grind the guides to the correct sizes (if needs be) since they are only available in 3mm. Obviously you have modify the rocker arm slightly to accomodate it into the guide, but you already know that bit.

The key part is having the tool to measure the heights (the difference in height between the two valves) required in the first place. I made my own which was based loosely around the Custom Steel one.

http://www.sr20forum.com/custom-ste...m-measuring-tool-serious-engine-builders.html

Heres a guide on shimming an SR20 head:

http://www.sr20forum.com/technical-...5625-how-measure-valve-shim-heights-pics.html
 
Pimpin' out the old skool IES prepped SR20 Head:

JWT C3 Cams
BC Valve Springs
GSpec Cam Gears
Sodium Filled Exhaust Valves
RR Lash Adjusters


PA210675.jpg

PA210672.jpg


The overlap of JWT C3's at TDC (cylinder 4, dowels @10 and 12)
PA210670.jpg


Comparison between Stock 53J chamber depth and IES prepped 53J Chamber. Some simple measurements indicate a 2mm head shave to get a 36cc combustion chamber!
PA210665.jpg

PA210669.jpg


Because of the large skim ive been concerned about piston to valve clearance.

I had already done the maths with different HG thickness'
(Assuming 86mm bore, 86mm Stroke, 87mm HG bore, 36cc chamber, 0.4mm deck clearance, 0cc flat top pistons)
1.1mm = 12.1:1CR
1.5mm= 11.5:1CR
1.8mm= 11.2:1 CR

Those measurements of the depth of the chambers help calculate what HG to use to get the piston to valve clearance so its the same as a regular DE head.

Stock DE 53J Head : 4mm combustion chamber depth + 1.1mm Head Gasket + 0.4mm Piston to deck clearance = 5.5mm

IES Prepped Head: 2mm combustion chamber depth + 1.8mm Head Gasket + 0.4mm piston to deck clearance + 1.3mm Piston valve reliefs = 5.5mm

You can see that using a 1.8mm gasket is going to get the P2V clearance back on par with a regular DE head and allow me to run the C3's safely whilst retaining a suitable CR .:smartass:

Okay, so its a bit of a compromise using a thick HG like this on an N/A engine due to the loss of quench effect (supposed to improve knock resistance) but lets see how it performs...
 
awsum dale, thats the key to getting good head :clown:

do agree with comment at the bottom though, i would have thought a thicker head gasket is always the last resort

Steve
 
I agree Steve, it is a compromise im going to make.

Im not willing to spend the cash on custom pistons, DE's love tight lobe seperation with a big header and cams, but as much as id like the extra piston to valve clearance.....im not made of money!

Mongo, the gears are just slipped onto the dowels in no particular position..its just a mock up at the moment. Obviously its all got to come off so i can install the head on the block. But yeah, its fully retarded in the pic.
 
i had 2mm skimmed of my CG head dale, and ended up with the same 2mm quench step (and flat-top pistons also) and found that the valve timing had far more effect that HG thickness, the inlet is currently set open 1.6mm @ tdc with ample clearance (exhaust 1.1mm open @ tdc)

frank
 
Cheers frank, i think the max i can safely run is +5/-5, id love to run a lot more...

You can just can see from my pic of TDC on cylinder 4 (intake cam dowel at 10 o'clock) that the inlet valve is well beyond the quech step, a shade over 2mm past, so thats approx 4mm lift at TDC on factory cam timing.:eek:nline2long: More intake advance will mean more than 4mm lift @TDC!

13.36mm lift cams! :whistling:
 
Dale said:
Cheers frank, i think the max i can safely run is +5/-5, id love to run a lot more...

You can just can see from my pic of TDC on cylinder 4 (intake cam dowel at 10 o'clock) that the inlet valve is well beyond the quech step, a shade over 2mm past, so thats approx 4mm lift at TDC on factory cam timing.:eek:nline2long: More intake advance will mean more than 4mm lift @TDC!

13.36mm lift cams! :whistling:
Click to expand...

wow dale 4mm @ tdc is a huge overlap surely ? (thats a 300+ deg duration spec i would have thought )
 
I dunno Frank, obviously the measurement isnt bang on for TDC, the intake cam is roughly in the right position to indicate TDC. In certainly in the right ball park though.

The agressive ramp rate to reach peak lift must play a large contributing factor too.

Just look at the CAT CAMs specs...a 290/290 12.45mm lift cam has 3.45mm lift @TDC, a 298 having 4mm lift. Both of these cams having less agressive ramps.

http://www.catcams.be/800x600/mainframe.htm?english
 
Im no expert, just going from what i can see in front of me on the assembled head.

What do you think about me using a thicker head gasket for a high comp N/A engine?
 
i think i would assemble the engine and check the clearance with a used stock H/G personally dale, i would drift the cam sprocket dowels out and see how much lift @ tdc it can achieve before any contact (any contact is gonna be not long after tdc eh), then decide which option to go for (thicker H/G or less overlap)
 
You must log in or register to reply here.
Back
Top Bottom