questions about cams...

[zed x]

hi
have a few questions about cams. i have a silvertop 20v in my ae86 btw

#1 is genrally the rule of thumb the bigger the cam the more it needs to rev to make its power?

#2 how much do cams go for genrally and do they come up for sale 2nd hand that often?

#3 do all cams sacrafise power somewhere to make more power somewhere else in the rev range?

#4 is this the next mod i should be doing to make more hp considering i have a silvertop runing off a mircotech?
looking forward to see what u guys have to say.,..

[86adz]

#1 by bigger cams i take u mean longer duration more lift can be beneficial too but if it gets too excessive u can find urself having to use shim under buckets also replacing valve springs goes hand in hand with bigger cams. power will increase and generally as you say more up in the rev range but exactly where the power is and its range can vary a bit with ur timing. a few variables to play with

#2 cams are around 300-400 bucks each and yes you do occasionally see 2nd handies for sale

#3 depending on how much larger you go will change how "drivable" ur car is for example if its a daily, large cams can (but not always) be a pain in the neck at low revs (stop start driving) basically your bottom end power increase will be negligible

#4 aftermarket ecu will help in improving power but its gains are probably not worth it unless ur running huge cams like >290 degree, havent experimented with ecus a lot but I'm sure some other people on here have and will give u some good info.

[zed x]

ok so all aftermarket cams will need upgraded valve springs?

what are some cams people are running in there 20valves and whats it like...?

[Jonny Rochester]

If you have a 20valve, and you are certain you are not going to turbo it, and you want more power... then you need different camshafts. You allmost certainly will need:

-different camshafts
-programable computer
-adjustable cam gears

And most likely you will want:
-upgraded valve springs
-upgraded conrods or rod bolts

And if you have the money:
-high comp pistons
-metal head gasket
-porting
-full motor balance
-elaborate exhaust system

But will also spend money on:
-another 20valve after putting hole in block
-dyno tuning
-gaskets, timing belt, seats, bolts, silicon etc...

I havn't done this, just a guess.

[Jonny Rochester]

For the 20valve, camshafts are available off the shelf from Toda in Japan, or Kelford in NZ. There are a few grinds available, people try different combinations, so no one knows what is "best". If you use high lift cams, or want to rev it hard, you will need uprated valve spings to stop valve float. Toda and Kelford sell the springs also. Toda sell the nicest looking cam gears.

The number of settings are infinite. You choose duration on each cam, lift on each cam, and lobe center angle (adjusted with cam gears) on each cam. In addition, you also choose your ignition graph to make power. Racers sometimes keep all this secret. But I can easliy give you ballpark figures for a good setup.

Get cams about 288 or 300 or 305 degrees duration.

The 20valve already has shim under bucket. You may need some different shims to set it up.

You may need a race engine mechanic/tuner to put it together and tune.

[af300e]

Johnny, is there an issue with big lift cams and the 5th valve lobes fouling on the plug tubes?

[zed x]

<div class='quotetop'>QUOTE (Jonny Rochester @ Jul 30 2008, 10:19 PM) </div>
farrrrk... well ive already got the computer so thats 1 thing haha

um well basically i was wanting to get some cams and cam gears to put in without having to upgrade valve springs or conrods.. then take it to the dyno get it tuned and yeah...
I'm not after ridiculous cams. jsut something to booost the power up a bit...

[Jonny Rochester]

Cams with a normal or medium lift will be better for endurance racing. Cams with high lift will have more peak power, but may not last as long as the lobe could wear out, or they could drive the valve springs too hard or something... and break a valve spring? Not sure.

Cams with more duration will be better for high rpm, at the expense or low rpm torque and idle. But this can also be adjusted with overlap and lobe centre, adjusted with cam gears.

My rough setup and prediction:
intake 304 degrees
exhaust 290 degrees
intake 102 degrees lobe centre
exhaust 105 degrees lobe centre
aftermarket conrods
toda valve springs
rev to 9000rpm
200hp at motor

Just a hyperthetical... Feel free to comment.

[Jonny Rochester]

I havn't done all this yet so I can't answer more questions. I have got some parts.

In secret, I plan to just use a silvertop with some wild cams and uprated springs, Toda cam gears. Then tune that as is and see when it breaks. Please don't tell anyone.

[Jonny Rochester]

Just another point. Before it goes near a dyno, it will need alot of time with valve clearances being set, then time with the degree wheel and cam gears. There is not enough time to play with cam gears on the dyno, not generaly. (Unless you work out a few setups and mark the possitions). You will spend all your dyno time adjusting fuel anyhow, and then ignition.