Performance camshafts

by **chris** » Sun Apr 17, 2005 12:57 pm

Does any body know where I can obtain some race proven camshafts for my atmo GTA . It is fuel injected with six throttle bodies & carbon fibre ram tubes . I will post some pics soon .

by **David Gentleman** » Sun Apr 17, 2005 2:31 pm

Simon Auto Germany do the 296 duration high lift cams for the atmo odd fire engine. Only problem you may get running efi with such high profiles is reversion and hard to map low loads if your running a map sensor based system.

by **stephendell** » Mon Apr 18, 2005 12:40 am

I will post some pics soon

Please. For the visitors section.

by **chris** » Sun Apr 24, 2005 4:36 pm

David Gentleman wrote:Simon Auto Germany do the 296 duration high lift cams for the atmo odd fire engine. Only problem you may get running efi with such high profiles is reversion and hard to map low loads if your running a map sensor based system.

Thank you for your reply . Do you possibly have any more information on these cams ie , where to get them ,cost, lift & theoretical timing . Has any body tried the Rallye or Terre cams for sale from Ferry Development. How do the two compare , reversion and mapping are not a problem , my pistons have valve relief and I have installed the Porsche style tappet/lash adjusters . I can utillize up to 7.5 mm of lift.

Atmo GTA R 12/45 50/6
L 10/47 52/5

Simon 296 ?

Holbay 5.94 lift in 22/58 ex 58/22

Ferry terre 6.65 lift 40/78 73/45
Ferry rallye 6.90 lift 50/78 48/78
^ ^
all of these numbers above are confusing to me
they do not seem to relate between manufacturers
to where they are measured at .

Thankfull for any of these questions answered.

by **David Gentleman** » Sun Apr 24, 2005 9:57 pm

When you say 7.5mm of lift, I assume you mean at the cam, as with the Porsche adjusters you can run up to around 10-11mm lift at the valve, you just have to be weary of hitting the pistons..

The Holbay and Ferry items are measured at lift at the cam, and the rocker ratio on the GTA is 1.3, so the Ferrys for instance run 8.97mm valve lift on the hotter profile. The only problem I was talking about on reversion is just that map sensor efi systems normally dont like those wild a profile...MAF systems handle it better...it would idle pretty badly on carbs, let alone with an electronic map sensor trying to sort out the signals.

The problem with all the figures, is as you mention, there is no indication at what point of lift the timing figures are measured at. I would go for the Ferry road profile as a good all round profile, as they have the most experience in the matter.

..for reference though, the Simon cams are on www.simon-auto.de

David

by **Alan Moore** » Mon Apr 25, 2005 6:49 am

If using a Motec or equivalent computer, the MAP sensor is not primarily used on cammy engines. Using the potentiometer on the throttle is much more accurate, because as David has said, the vacuum it reads at low revs is all over the place.

Sounds like you are building something fairly hot. Maybe the rallye cam? Maybe some info on the useful RPM of the cam would make up your mind? The cam manufacturer should be able to give you this.

Duration at a lift of 50 thou gives a much better picture of what the cam is like, as large durations in the manner as they are shown above does not account for very long, slow ramps on the cams, making them out to be bigger than they are.

Add the two figures 40 / 78 together + 180 and you will have in this case the supposed duration of the cam of 298 Degees.

David, does the Turbo have the same rocker ratio as the atmo.