13 replies to this topic

[andyjmapex]

Right - a techy question for all those cam experts that understand the data sheets on camshafts.

 

I understand valve/lobe lift, overlap and clearances. but can someone please tell me how to read intake/exhaust timing and duration please?

 

Say the metty cam has the following:

 

intake timing: 16/56

exhaust timing: 59/29

duration: 268

 

Probably basic - i assumed this meant intake opens at 16 deg and shut at 56 deg and the same for the exhaust but that would mean that the exhaust is open for 330 degrees - which isn't right!!

 

I'm tyring to decide on a camshaft for my supercharged 998 build if anyone asks why i care!

 

Andy

[mini13]

Right....

 

digs back into the depths of memory.......

 

 

intake timing.... 16 deg BTDC (before top dead cantre and 56 deg ABDC (after bottom dead centre) sooo 16 + 180 +56 =252 deg.

 

exhaust......59 deb BBDC (befor bottom dead centre) and 29 deg ATDC (after tdp dead centre soooo  59 + 180 +29  = 268 deg.

 

I asume thats a Kent 266 your looking at.

 

also this chart might help yopu visulize it.

 

[ACDodd]

Good luck the duration figures they actually mean very little unless you know the checking height they are stated at. Far more important for cam characteristics, is the Overlap lift figure, total lobe lift and the lobe separation angle.

 

Basically you need a cam with relatively low overlap lift and reasonable duration coupled with high lobe lift and a wider than usual lobe separation angle. Cams that fall into this are are those which are sold as cams for forced induction engines.

 

AC

Edited by ACDodd, 28 May 2013 - 07:42 PM.

[Gr4h4m]

Andy supercharged cars like a wide lca, around 112 works well. Most of the information you will find relates to big american v8's. Graham Russell produces a re13t cam for supercharged engines, available from calver st.

I have run a 266 with good results, I have just swapped to an re13t and it was ground ban on to the key way. It's not o the rollers until the middle of next month to know the differance.
The Kent 274 looks good too.

[Gr4h4m]

Oh the supercharged suck through cars seem to like a bit more welly...

[andyjmapex]

Brilliant! I spent too long trying to work that out and would never have got that!

 

I'm looking at the 266 but if i'm honest the price of the minisport cams seem appealing. the closest one they seem to have is the st731 (the old BL one) which has a bit of overlap (not good on a S/C i know) and i've heard it's a dud cam in general.

 

I'm now thinking its either going to be a metro cam which provides good lift and no overlap - OR the 266. as far i can tell the metro cam (or minisport st948) is as good on paper as the kent 266.

 

someone correct me please? why would i pay £200 for the kent 266 as opposed to the £50 st948? will these provide enough 'welly' for my charged lump?

 

 

Thanks again

 

Andy

[Gr4h4m]

I doubt many will have experience with the old cam grinds and a supercharged engine... You get what you pay for. Try Keith calver for the re13t on a supercharged 112lca

[mini13]

i think the re13 might be a bit much for a 998, its wrth asking Keith if he can get the RE282 ground.

 

the RE cams ar good because they dont wear that much as the nose is very rounded so you dont get the same kind of stresses.

 

My re13t was about 110 quid from keith iirc

[andyjmapex]

thanks i will get in contact.

 

just comparing the kent 266 and metro next to each other - the metro has similar lift, duration and duration as the 266. any resons not to go ahead with a metro?

[andyjmapex]

so ignore that post above, in my (unproffesional) opinion this engine isn't going to be analy tuned, balanced etc so i think the gain difference bettween the two above cams will be neglagible. I'm looking at metro cams for price reasons, its going in a '88 998, what do i need to look out for? fuel pump drive? slot/spider drives?

 

will this fit?

 

http://www.ebay.co.u...#ht_2410wt_1018

 

 

sorry for the questions guys!

 

Andy

[Mighty made]

Hi Andy,
Not sure what engine you have, but the eBay cam is for a low spec K series.
I assume from the question that you have a 998 A series, so the short answer is no.

[andyjmapex]

DOH   I posted the wrong link....

 

http://www.ebay.co.u...d#ht_379wt_1141

 

I know that one will fit! is that a reasonable price to pick a metro cam up for?

 

will i have to change the bearings? the ones in there have only done 50k!

[andyjmapex]

is this a bottom of the range metro cam?? or one that's similar to the kent 266

 

http://www.ebay.co.u...3#ht_207wt_1327

[BritishRacingGreen]

No, that's the one similar to the 266/sw5, so long as the seller has listed it correctly. You're looking for a 1/4 inch groove machined inbetween lobes 1 & 2 (from timing chain end).

 

The one you want is the NA MG Metro cam, which that is.