Gti6 Cams

[Paul_13 212 1 Cars]

I was wondering if you can change just the inlet cam (on a GTI6 engine) and get a decent power/torque increase.

 

I'm after more torque than anything, but will this be unlocked by an exhuast cam aswell?

 

Also will the head need machining depending on the high lift cams?

 

 

I've done a search and scrolled through 8 pages of results but didn't come up with anything.

[Cameron 16]

Where are you after more torque, low or high revs?

[Paul_13 212 1 Cars]

Rather the torque was down low, but with a reasonable top end.

 

Is that possible?

[Anthony 1,003]

You can do the inlet cam only like on Mi16's, and Petert certainly does some inlet cam regrinds - have a look on his website.

 

You're pretty limited as to what cams you can run on a standard GTi-6 engine by the piston clearance at TDC and by the standard valve springs - certainly I'm pretty sure the later is a limitation before you need to start grinding the head.

 

It might be worth having a play with the cam timing first of all though (remembering the lack of clearance at TDC!) as advancing the inlet cam will increase mid-range at the expense of a little top end, which I'm assuming is what you mean when you say "torque"

[welshpug 1,662]

altering cam timing will get you more torque without changing them

 

also with this engine, you'll need different pistons way before you need to machine the head for larger cams.

 

PeterT has done a few cams for the RS engine which seemed to give very good results, details are on his website of the cams themselves, and here's a build by Magic using one - http://www.aussiefrogs.com/forum/showthread.php?t=54941

[kyepan 291]

Look at petert's site if you have not already. Iirc the standard 6 inlet cam is a fairly mild profile. And fiddling with the cam timing a little can help maximise the benifits of a longer duration cam. Not sure how the head flows when you add more lift, but would imagine it would help more at high rpm.

[welshpug 1,662]

link to PeterT's website http://www.taylor-eng.com/xu10j4rs/306_camgrinds.htm

[Paul_13 212 1 Cars]

It might be worth having a play with the cam timing first of all though (remembering the lack of clearance at TDC!) as advancing the inlet cam will increase mid-range at the expense of a little top end, which I'm assuming is what you mean when you say "torque"

 

Ok cheers for the information guys. That what I was getting at Anthony

 

What do I have to do to in order to change the cam timing?

 

Loosen the cam belt (and replace!) and move the inlet/exhaust pulleys?

1-2 teeth maybe.

 

I am also clueless which way I would have to move the inlet pulley to advance it.

 

 

 

Thanks for the link welshpug was trying to find his website

Edited December 16, 2009 by paul_xiii

[welshpug 1,662]

loosen the 3 bolts/1 bolt, hold cam in place and rotate crank back, or hold crank in place and rotate cam forwards.

 

Probably half a tooth at the most, ideally you would need to use a dial gauge and check how much lift you have at TDC and what angle your peak lift is.

 

A friend of mine has a 306 Rallye which has had the timing adjusted by Andy Gwynne of Gwynnespeed and it works very well, more torque than most standard J4RS engines I've come across but without sacrificing power.

 

I'm quite tempted to send a J4R cam to PeterT for his stage 1 RS grind, (or even an XU7JP4 one if they have enough meat)

[Anthony 1,003]

loosen the 3 bolts/1 bolt, hold cam in place and rotate crank back, or hold crank in place and rotate cam forwards.

 

Probably half a tooth at the most, ideally you would need to use a dial gauge and check how much lift you have at TDC and what angle your peak lift is.

No question, you NEED a dial gauge to do it properly - clearance at TDC is so tight on GTi-6 engines that swinging the timing around blindly is a receipe for dinked valves and a tapping head. Standard timing is around 0.5mm @ TDC, and about 1.2mm @ TDC is the limit before you're running dangerously short on clearance (especially if the head has been skimmed etc)

 

Sandy's recommended figures were 1.2mm @ TDC inlet, and 1.0mm @ TDC exhaust. I've used them on a couple of engines now and they seem to work well with a good spread of power.

 

I'm quite tempted to send a J4R cam to PeterT for his stage 1 RS grind, (or even an XU7JP4 one if they have enough meat)

I've got both J4R and XU7JP4 cams in the garage, so I can have a quick look/measure and see - from memory though, the XU7 cams looked very mild!

[Paul_13 212 1 Cars]

loosen the 3 bolts/1 bolt, hold cam in place and rotate crank back, or hold crank in place and rotate cam forwards.

 

Probably half a tooth at the most, ideally you would need to use a dial gauge and check how much lift you have at TDC and what angle your peak lift is.

 

A friend of mine has a 306 Rallye which has had the timing adjusted by Andy Gwynne of Gwynnespeed and it works very well, more torque than most standard J4RS engines I've come across but without sacrificing power.

 

I'm quite tempted to send a J4R cam to PeterT for his stage 1 RS grind, (or even an XU7JP4 one if they have enough meat)

 

When you say rotate cam forwards, I take it you mean towards you. (if stood in front of engine, inlet side)

 

 

Don't worry Anthony i'm not going to be swinging the cams around and not giving a f*ck about it lol

 

My last 6' head that I smashed into a million pieces, was tapping really badly due to me letting the cam pulley slip when timing it

I think it might of been fate that the head bolts were loose/rounded or the valve head could of snapped off and voila! BIG headache and a hole fiercly burning in my pocket.

 

The bloke still hasn't bothered to reply/cough up money, since I got hold of him despite regular texts.

Edited December 16, 2009 by paul_xiii

[welshpug 1,662]

forwards as in advancing the camshafts position as it rotates clockwise looking end on at the pulley meaning the valve opens sooner

 

I'm just looking for some figures on the standard cams, I can't remember how much lift @ TDC they have, but you don't want too much more than 1mm.

[kyepan 291]

i thought i had this all sorted in my head.

 

I thought that you had to retard the inlet cam slightly, if the duration was increased, because extending the duration moved the point at which most lift was produced, you needed to control where you got the most lift.

 

And now i can't remember if it's that,

 

or if it's that on longer duration you need maximum lift to happen earlier to help control the increased overlap between the inlet and the exhaust valves, to try and prevent the inlet charge going straight out of the exhaust valve.

 

or earlier to make sure it's not started the compression stroke with the inlet valve open.

 

or if it just needs adjusting and retesting a number of times until the optimum position is found.

 

confused.com.

 

also reading Vizards book last night again, it would seem that valve lift adheres to the law of diminishing returns... it gets to a point where the valve is so far off the seat, that another point in the inlet tract / port / seat is causing the restriction, and not the back of the valve..

[petert 591]

Changing the exhaust cam will decrease torque and increase top end hp. This is because the force pushing the piston down is there for less time before the exhaust valve opens. The GTi6 head has heaps of exhaust flow, so it's not a restriction. In fact, it's better to have slightly more inlet timing to keep the gas flow ratios at their optimum. Unlike old Chev V8's for example, which need more exhaust timing to make up for poor flowing exhaust ports.

 

Since many people have been munching valves into pistons on GTi6 engines, I've re-assessed my GTi6 cam range. The Stage I profile is now very similar to an Mi16 standard inlet (with more lift). Thus 215 deg. rather than 205 deg. That extra 10 degrees at 0.050" is still quite a big jump but keeps the valve-piston clearance tame.