need cam setup advice
 

First off, this is an almost stock 95 DE and I plan on staying NA for a while (nobody`s responded to my applications yet...) and just doing suspension until iCan afford a 300ish hp taabo setup.

mods atm are injen cai (the filters in the wheelwell and iNever have problems in the rain, just gets it really dirty.) NGK wires, and Bosch +4s (work better than what it had but i`m going NGK soon)

on to the question: given these mods (and a planned n1 dual or brm 2.5" and emissions removal) what combination of stock cams would make for the most usable power? I`ve got three sets (232/232, 248/248, and 240/248) in the shop being cleaned up and my head`s being rebuilt and shimmed. What iKnow so far is that the 232/232 setup isn`t the way to power, the 240/248 helps out some, and the 248/248 gives best top end. However i`ve seen a dyno sheet of the 248s that showed it as being lower than either stock or s13 cams (iForget...) up until it finally made a whopping single digit hp increase up above 5000 or something. Also, i`ve heard that running the 248 cam on the intake side with a 232 on the exhaust would be a good balanced setup. whether or not it`d be better than s13 cams iDunno, and if it is, i`d think running the s13 cams backwards with the 248 on the intake and 240 on the exhaust might be the best setup you can run of the stock cams. obviously iDont quite know enough about all this lift and duration other than that these things control when and how long the valves stay open and iWant them open for a long time with a second or so of scavenging where int and exh valves are open so the exhaust leaving pulls in more intake air.

also, i`m thinkin about running slightly higher compression (later sohc pistons and/or headwork) and running less boost when that time comes, so if increasing comp is relevant here, then please consider that too.

sorry about such a long post guys, but any word from the experienced big brains on this situation?

also, i`ll probably be selling whatever cams iDon`t use so if anybody needs some cams... like iSaid before i`ve got one set of s13, one of s14, and one of 248/248 all being cleaned up by a reputable shop right now.

Are those the only cams you have to work with? Best thing to do is probably match up your cams with your IM runner lengths. There is a simple way, and a harder way, which is used by probably big budget race teams:

the IM article has a couple of equations to determine at what rpm the runner length will make peak torque. I believe one of them is missing a coefficient.

You have to look at some cam specs and their dynos to see where the peak torque comes in typically with these cams and try to come in the same ballpark as the runner length's.

That's the simple way of doing it.

There's no valve lift/duration/overlap simulation equation to the best of my knowledge that links them to runner length.

There are cam ramp and valve lift coefficient equations for poppet valve lift curves to determine how fast you accelerate the valve open , valve flow curtain area calculations to determine the best valveface diameter, equations for trapping efficiency and scavenging efficiency but no direct cam spec - runner length relationship equations.

There are however, IM runner length equations that you test to determine your ramming factor or what we call the "delivery ratio" (amount delivered divided by 100% volumetric efficiency) and "pressure ratio" at the peak torque rpm.:

You have to first know the distance from the valveface surface on the combustion chamber side to the head intake port opening along the floor of the intake port (i.e along the short turn radius).

The total intake length (Ltot) in this equation is the sum of the IM runner length (Lrunner) and the head intake port length along the short turn radius (Lport).

Ramming Factor (RF) = rpm x Ltot / ao

where ao = the local reference speed of sound (in SI units) in the intake port.

optimum Ltot = ao x RF/ rpm

This is where the engineers begin to get ballpark lengths that best fit their engine packages using computer simulation software.

They then take these ballpark lengths and manufacture the runners at these lengths.

Then it's a matter of cut and try...empiricism to find the sweet spot.

That's the process if you are on a big budget team.

For us plebs, the best way is to use the simpleton method I described above that gets you "close enough" so that the parts aren't fighting one another making peak torque at different rpms.

I can't emphasize this enough: you have to play with the cam gears to zone in on the sweet spot. Valve timing is huge when it comes to getting the highest delivery ratio (ramming effect) at the right rpm (for your gearing).

Hope that helps...thanks to my buddy MD on that, btw.

wow the hard way went flying over my head. Thanks for all the tech advice though.

by the way, i`ve personally decided to run 248 (exhaust cam from any 91-93 s13) on the intake side and 232 (stock) on the exhaust side.
search fresh alloy under all posts and all forums for "cam setup" and you`ll find everything you need to know to see what convinced me.

Gotcha! Good luck with your setup, man!! Let us know how it runs when you're finished!

After reading this and searching other forums, I think I am going to try the 248/232 on my 95 KA. My buddy has a 92 ka that he is not using, so I am going to try and get that to work.

do some dynos after the swap please.

if iCan afford it... one of these days somebody`s gotta hire me, right?

plus i`m doing the head install on my own (for the first time) and everything`s a mess. chain, pistons, you name it is out of place, so i`m gonna take everything, set it all to TDC and put it together like a rebuild. i`m giving myself about 2 months to put it together starting at the point where iGet the head back.