4age 20v piston to valve question

3cxjay
Posts: 4
Joined: Fri Jan 01, 2016 7:40 am

4age 20v piston to valve question

Postby 3cxjay » Fri Jan 01, 2016 7:48 am

Hi guys, I'm Jay from the east of England uk, I race Westfield kit car in a sprint championship and the car has a 4age 20v engine bolted in. I am currently building up a blacktop with the following spec- 12.1 Pistons with Mrp rods, cat cam 291 11mm cams, toda gears non vvt and a steel 0.8mm gasket. The question is can I run 11mm 291 cams I'm my engine without the Pistons hitting the valves? The head will not be skimmed and the block deck height is standard. Any answers would be appreciated, I have been trailing through Google for ages but decided to ask you guys on here!

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hachirokkos
Club4AG Regular
Posts: 44
Joined: Sun Oct 04, 2015 9:44 am

Re: 4age 20v piston to valve question

Postby hachirokkos » Fri Jan 01, 2016 1:05 pm

I relly dont know the answer, but
It deppents on : the stroke of the crankshaft, the length of the rod, and the piston
If i assume that the crank is OEM, and the rod are the same size ( different meterial) then check the pistons you wish to run, if they have valve pockets. You can test with your current things, in order to calculate what to order. Also some other things play some role, like the thickness of the gasket used is critical.

I also enclose one photo, hope it helps

Image

I am also thinking of rebuilding mine, for my AE86 race car

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3cxjay
Posts: 4
Joined: Fri Jan 01, 2016 7:40 am

Re: 4age 20v piston to valve question

Postby 3cxjay » Sat Jan 02, 2016 12:04 am

The crank is standard, the rods are the same height and so are the Pistons except being higher compression so the top domes out more but they have bigger cutouts to compensate.

allencr
Club4AG Expert
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Re: 4age 20v piston to valve question

Postby allencr » Sat Jan 02, 2016 2:08 am

ALL piston & cam changes should be mocked up!
Then again, if these new pistons are trying to keep it non-interference(NFG, horribly cut up IMO), the even the wildest cam won't come anywhere close in operation & only touch with a belt break or mis-assembled.

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yoshimitsuspeed
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Re: 4age 20v piston to valve question

Postby yoshimitsuspeed » Mon Jan 04, 2016 10:40 am

Since you are not running stock cams or pistons we really can't be of any help. As allencr said the proper way to do this is to mock it up and check. You can put clay or something similar on the piston in a thin layer, then assemble and spin the motor around. Since with those cams you will likely be running adjustable cam gears it would be good to run a few different timing combinations. I would start timed to the cam card and then adjust +10 and then -10. Then pull it back apart and make sure you have enough clearance everywhere. On the valves I'd probably want to see over 1mm clearance vertically and at least .5mm axially.

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