Which Poncams To Use For A Particular Application

[joeyjoejoejuniorshabadoo]

now this is a lot more productive than the usual "cams are the bes thing ever" brigade...

[allthewaytotheskyline]

mmm you all have quite a valid point, well the point of the question more so was not wether to use cams or not but which cams would be a best choice for my particular application (which is to keep the lag minimal but fatten up the torque range in the middle of the rev's and not having to rev it off its chops to make that same power)

i must say the headporting is tempting but atm im wanting to keep the engine in one piece.

keep em coming...

[allthewaytotheskyline]

also..just got off the phone with my tuner, he explains that if i use the 260 9.15mm lift in/ex and use a cam gear on ex i can maximise air flow and bring the turbo on a bit earlier by working the cam gear obviously back or forth.

is this true?

[joeyjoejoejuniorshabadoo]

yes, this is what i did, but without cams....

to bring boost on earlier with a cam gear you will lose top end kw....

its worth it tho...

[discopotato03]

This is just the way I see it and I'm happy to be corrected .

Mild aftermarket cams seek to make for a bit better cylinder filling by opening and closing the valves earlier and later and adding a bit more valve lift within the reliable limits of the std valve train .

Significantly longer duration cams are really aimed at engines that don't spend any time at lowish (round town) revs or when choppy running is of no consequence - like a race engine . Real race cars usually have close ratio gearboxes so when taken up to dizzy revs they don't "fall off" the cams because the rev drop between gears is a lot less .

I think the main (mechanical) advantage R34 spec RB25DETs have is that nice "solid" bucket setup and can get away with a little more valve lift than the hydraulic R33 system . If you looked closely at the mild R34 Neo Poncams they have a little less duration than the R33 ones and a bit more lift .

This is a better way to fill the cylinders and make torque without needing big revs IMO .

Something else worth thinking about is the compression ratio and how its affects low down poke with aftermarket cams . In the NA world is very important to raise the CR with big cams because all else being equal thats the only way to not lose all the lower end squirt .

You mentioned that you don't want to go inside the head which is a pity because it leaves you with the std porting/valve sizes/compression ratio .

That's fine because not everyone wants go there but we need to remember that you can only go so far with external bolt ons before the state of tune gets a little cranky and then it's not a nice thing to cruise around in . IMO part time cars that don't drive nicely get driven less often .

Sorry this is going so far off the track but the engine spec I'm following lost boost pressure when the modified head went on but made more grunt everywhere .

Basically if it was a choice of head or cams I'd do the head every time , looks std with factory reliability and allows good power with less extreme bolt ons/state of tune .

In a std engine my vote goes to the milder 252/9.15 (?) cams , how it goes on the road is more important IMO than a dyno print out number .

Butt dyno is the hardest one to impress overall , cheers A .

[allthewaytotheskyline]

very valid point discopotato03, i like your thinking.

keeps me wondering..

[discopotato03]

Just a bit more food for thought , the milder cams could be a good first try and if they're not enough I don't think they would be hard to turn back into money . If however the higher spec cams were a bit over the top you can't easily tone them down plus if the word got out they may be harder to sell .

I know its money and inconvenience but you only have to do the head once and then suitable bolt ons keep making a better thing better . I believe its one of those hard to go backwards mods provided its done properly .

A .

[allthewaytotheskyline]

Just a bit more food for thought , the milder cams could be a good first try and if they're not enough I don't think they would be hard to turn back into money . If however the higher spec cams were a bit over the top you can't easily tone them down plus if the word got out they may be harder to sell .

I know its money and inconvenience but you only have to do the head once and then suitable bolt ons keep making a better thing better . I believe its one of those hard to go backwards mods provided its done properly .

A .

i agree with what your saying, im not really wanting to be doing any porting at this stage.

the mild approach i believe would be sufficient but i keep getting that but, or what if...thought niggling in my head.

really when it comes down to the math...the 252's should do exactly what i require.

all that said...what are the standard came lobes ground at in a rb25det neo??

[Kranker]

neo runs 236 8.4mm intake and 232 8.7mm exaust

if memory serves me correctly

if it was me id be looking at doing the other mods first (turbo, ecu what ever else you had planned, etc), getting it on the dyno, adjusting the cam gears, and seeing where it makes its power.

you never know, it may do everythign you want without the need for aftermarket cams

[allthewaytotheskyline]

so even 252's with 9.15mm lift would help it breathe alot more in comparison to standard.

see im doing my full 100k service so ill have the opportunity to put cams in during it, which will save me some $$$$

hence the reason why i might as well do it, as after if i dont do it n bolt turbo n supporting mods on it will cost me atleast $400 extra to install!

so it comes down to cost as well.

[SLAPS]

2835pros on an rb25 my vote goes with the 252 9mm cams.

A GT30 or larger with a .82 rear i'd look at the 260's.

[SS8_Gohan]

what $$'s are we talking roughly for the head work on a NEO?