maximum lift

does any body know the maximum cam lift i can get on my gta turbo thinking of getting some made thanks in advance

Search through the forum and you will find cam debates. If youre talking about re-grinds of existing cams then dont go mad or you'll kill your duration and end up with a nasty dose of turbo lag. I sent mine to Kent cams and they did a mild re-grind for £100....added a few degrees of lift without harming the duration. They (and DavidG) advised against going for anything like a 270-290 as it would totally f*ck up the power band. Turbo cars (and in particular the GTA) dont respond to big lift as well as an atmo car.

Well they respond to increased lift, but you can't increase lift without increasing duration on a regrind, only with an original casting or adding material to the cam.

I have a pair of used, good condition late Z7W cams which will fit, and are 255 degree duration, with nearly 9mm lift, 2mm up on the originals. Same cam profile as A610. £150 for the pair.

thanks for the reply peter what i was thinking about was getting some cams made from new keeping around 260 duration but running around 9mm lift what i was wondering was is there enough room between valve and piston top

thanks for the reply peter what i was thinking about was getting some cams made from new keeping around 260 duration but running around 9mm lift what i was wondering was is there enough room between valve and piston top

Be very carefull of anybody trying to make PRV cams from scratch. Its a black art, as you have two completely different looking cams physically in your hands, but when installed they do exactly the same process.

Theres enough room between valve and piston top, if you don't run too much duration.

thanks for the advice david my plan is to stick to around 260 degrees duration for good road manners but be able to lift the valve fast off the seat and have as much lift as reliably possible is 10mm possible

Well they respond to increased lift, but you can't increase lift without increasing duration on a regrind, only with an original casting or adding material to the cam.

.

Please explain - as long as you take material away evenly around the entire radius of the "heel" (ie the circular part) than you will not be increasing duration, but you increase lift.

I have a pair of used, good condition late Z7W cams

David

Will these fit as a straight swop with no other mods required ? and what kind of noticeable benefits will they bring ?

http://www.softintegration.com/chhtml/t ... trans.html

But I can't be arsed
Better to send it off to someone who really knows what they are doing

Well they respond to increased lift, but you can't increase lift without increasing duration on a regrind, only with an original casting or adding material to the cam.

.

Please explain - as long as you take material away evenly around the entire radius of the "heel" (ie the circular part) than you will not be increasing duration, but you increase lift.

I dont actually understand how it works, but Kent cams who advised and re-ground mine said exaclty the same.....which is why I only went for a small inrease in lift.
But I guess you probably know better than them as well!

Well they respond to increased lift, but you can't increase lift without increasing duration on a regrind, only with an original casting or adding material to the cam.

.

Please explain - as long as you take material away evenly around the entire radius of the "heel" (ie the circular part) than you will not be increasing duration, but you increase lift.

I dont actually understand how it works, but Kent cams who advised and re-ground mine said exaclty the same.....which is why I only went for a small inrease in lift.
But I guess you probably know better than them as well!

It's the shape of the cam isn't it rather than the size ???? I dunno either but if you think about it , the rocker arm can be adjusted so a smaller diameter on the heel doesn't matter but the ' angle ' to the lobe can be machined with a diff shape and rate of attack ...............................So you can't just reduce the main diameter without having to blend it back in to the run up to the lobe .

Ok, I'm not trying to be a smart asp here, cam stuff -is- something I leave to "those who know" so I'm looking at this purely from a simple mechanical perspective

That calculator things is really cool BTW!

If you think about it, and that little animation shows really nicely the cam is basically circular for the most part - the lift is generated by riding up the lobe, so the amount of lift is govourned by

distance from the tip of the lobe to the centre of the shaft MINUS the radius of the heel (the circular bit).

If you take material off the base of the circular bit (the heel) then you reduce the radius and by the calc above, you get increased lift (when you adjust the tappets you wind them out a lot further to take up the slack, as it were.

To make the valve open and close at the same time as it used to (ie keep the duration the same) after a regrind, surely you just have to make sure the heel is ground all the way around its circular diameter.... don't you?

I'm not sure I'm making sense here...!

Z7W - is that the n/a 2.9 V6 cams (25 and GTA atmo)?

Don't confuse the even and odd fire engines. The Atmo is an odd-fire and although in *theory* the cams should be interchangable between the two types of engines, I don't know anyone who has tried it!