I'm pretty sure I've gone too wild with a Kent RL21 for my pinto and so I'm looking to go for something a bit milder.

I have my rolling road session booked on 03 May but I'm thinking I may change the cam so I'm not wasting my money.

Just wondering are there any Camshaft rules of thumb.

Thinking logically can you say

High valve lift=More power
Long duration=Top end power
Late exhaust valve=High torque

I guess it's probably not as simple as this but I just wondered if there were any rules that might help me select a replacement cam.

The following diagram shows my RL21 against a Piper 285 and A8. I think I not going to get the benefit of this cam as a mostly road based car.



rl 21

i put in piper 270 cam
no other mods
made big difference on kick and pulling power also runs to a higher redline
this was in 1800 ohc (vauxhall)
cheers
richard

Try advancing the cam that you have before swapping out and see how it feels, around 7 degrees advance should see a 10% gain in bottom end with 5% loss at the other end, thats assuming its timed dead centre now.

Regards Mark

RL 21 is ceratainly a lumpy cam and the power band is 3000 to 7750, pushing the standard rods and piston ring lands to the limit, however some friends have a complete Lightning Rod engine in there car and whilst it takes some starting once moving it is very tractable in the lower revs and just takes off once you hit the rev band.
I have a 285 cam and feel that it could do with a bit more cam as i get peak power at 5900.
Try the cam you have got you may be pleasently surprised.

Know where you are coming from i had rl21 and comp clutch in my escort, could not pull of without wheel spinning, good fun though

The 285 was always my fave cam in my pinto days, better power all the way through with just a hint of lumpy tick over.

One thing that did make a big difference to was fitting "roller" followers, the std pinto ones are about as agricultural as it gets, the roller ones release a fair bit of power simply by removing loads of friction, cam wear is eliminated to along with the spray bar if you go for a x drilled cam.

Another vote for the 285 in a Pinto. Made a big difference without any other mods, yet still very driveable.

I have a piper 285 but Bogg brothers say a piper A8 is good with bike carbs and big valves
Jacko

I found the FR33 was very good

Whilst replies are much welcome I was really only asking if there are any rules of thumb on which to base a judgement.

Like in "long duration is only important in the higher rev range" or "go for a later opening exhaust valve for more low down torque"

Maybe no such rules exist I was just curious.

It's not so much the fact it's lumpy, it idles surprisingly well but it is blowing back through the carbs and I'm not sure I'm really going to be able to drive everywhere at 4000-5000 rpm.

Having said that I will probably try what Mark says and set the cam timing later or go with Mookie's FR33.

[Edited on 20/4/08 by pajsh]

quote:

---

Originally posted by pajsh
Whilst replies are much welcome I was really only asking if there are any rules of thumb on which to base a judgement.

Like in "long duration is only important in the higher rev range" or "go for a later opening exhaust valve for more low down torque"

Maybe no such rules exist I was just curious.

---

Ive used FR32 - feel it is too mild.

Boggs and Dave Walker both suggested Piper A8 so might be worth comparing yours to that.

Mookys car went well on the FR33.

Ah ah ! 2 rules of thumb. LOL

1) long durations increase mid-peak power.

2) shorter durations but higher lifts combined with faster opening and closing ramps give better idle quality, emissions and bottom end power.

Only kidding!!

Am thinking of A8 or FR33. Diagrams posted earlier show A8 is actually similar to mine but slightly later opening and earlier closing but with higher lift.

FR33 from earlier research is very similar to A8 but more valve lift.

A8 - 12.8/304/47-77/71-41
FR33 - 11.76/300/45-75/74-43
RL21 - 11.92/314/52-82/92-42

It's the exhaust valve opening less than half way down the stroke (92 BBDC) that bothers me. I'm thinking I'm not going to get any decent power less the "rev the nuts off".

Have you read books by the likes of Des Hammil and David Vizard? I recall Des had some clear viws on what cams work best in Pinto's and that popular cams are oppposite to what is best. He was also critical of the valve train geometry.

Wasnt there an online guide by Puma race engines??

Yep read all that and got the "T" shirt.

Alot of it I find woolly and sometimes contradictory.

Des Hamill says Pinto's are not sensitive to long duration cams but I think Puma racing notes say you want high lift shorter duration.

It was the following Des Hamill's statement that got me thinking:

"it is a proven fact that road going engines should not have a camshaft fitted that opens the exhaust valve before 70 BBDC while the wildest racing camshafts should not open earlier than 85 BBDC"

A8 - 71 degrees
FR33 - 74 degrees
RL21 - 92 degrees

I think the best advice comes from the sort of practical experience on here.

[Edited on 22/4/08 by pajsh]