NOT ANOTHER CAM THREAD...... But need facts plz

[s_ikari2015]

This does sound like a very good idea, in fact I'm looking at something very similar. I too want to only do each thing once, eventually as time, money and opportunity progresses ending with a well balanced FI CV8 Monaro. I'd not be after something as mild though, and have been looking into a Comp Cam 227/235 0.614 0.621 LSA113 with 1.7:1 ratio rockers etc. Possible extra head work too. The car currently has the 241 casting heads as standard, but I've been looking at either finding a complete rebuilt set of 243 castings or having my heads machined to match the 243 specs.

Basically I want to enjoy good returns from the NA modifications for a while, yet when the time comes being able to effectively "bolt-on" a top mount supercharger with very little extra work.

I will be following your progress and research with great interest. I too believe there must be a happy medium.

 

[ari666]

so... youre saying you need this to suit a stock torque converter, but that seems a bit silly, since youre going to want a BIG converter once you go boost, so what youre asking for is "is there a stick that i can use on a stock converter which will also be useful on a 5k stally?" which the answer is easily "NO" or are you just going to do a couple of small/easy breathing snails that dont pump too many atomspheres in?

me personally id be researching very low lift cams, with good duration (235-245 ish) and a minor overlap. then when youve got it running on a NA application stick some crazy rockers on to get the lift you need and make the overlap *sort of* a little bit longer. on a flat tappet, youd get a couple of anti-pumps to get rid of the squishyness of the lifters at low rpm so theyre taking up slack pretty much immidiatly.

there are kids on here running 1.9X rockers which to me would be entering the danger zone as far as ramp rates and sideloading of pushrods, but if it were just an interim feature, probably wouldnt do that much excess wear, unless youre planning power WOT runs all day everyday for the next few weeks. then it could get a bit rattly.


but yeah as far as "hey man is there a cam thats gonna give me RPM's on NA, then power on FI?" then no, that answer is no.

(IMO)

 

[ari666]

The part of concern is that ultimately one day this cam/kit needs to suit a big single turbo kit running around 10psi on E85, spinning to around 7200rpm max and AFR's and timing to match repeatability....

lol no chance.

 

[ari666]

I too believe there must be a happy medium.

there isnt. its really that simple.

its like asking "can i have a DC engine that will also run on AC when i dont have DC available?"

no. the aswer is no.

horsepower=torque X rpm/5252.

to get an NA to make power, we need to make it REV. to make it rev, we reduce almost every single restricting factor in the intake-compression-combustion-exhaust system that it has. since we cant restrict the compression or combustion (in fact we want to make compresion HARDER), we're stuck with intake and exhaust. intake just needs a good free flowing head design so it can freely suck a nice atomised breath of fresh O2 and a bit of fuel, as close to a 14.7:1 ratio as we can get it, so thats that out the way, now what can we do with the exhaust?

ok here is where it gets tricky

so the piston is coming down off its BAM on the combustion stroke, and then when it gets sorta to the bottom, it starts running out of puff, holywhatthefkshitballs its actually creating a vaccum as it comes down to the bottom of the stroke, what we need now is some way to stop it creating a vacuum, cos' thats actually stopping it from going down.

ok cool, easy, we'll open the exhaust valve. the valve cracks and although were trying to suck in an expended gas from the exhaust system, we're not actually sucking it in, we're just scavanging it from the other valve thats on the top of its exhaust stoke atm and we have "extractors" so thats a good thing, the top of the valve gets a bit of **** gas, but thats just gonna get pushed out anyway.

so easy, we've free'd up a but of HP by not restricting the downward stroke of the piston, ok now we're going up. and going up is hard cos' gravity is a bitch and life is hard. everything is cool. as we go up the gas is pushed out the exhaust valve cos' we have a nice free flowing exhaust and the when we get to the top, we have another piston is nice enough to suck out some gas for us like we did for it, so karma bitch, something to look forward to. so we can keep going up to the intake stroke.

but WAIT! whats that?? if we go to the top of the intake stroke with nothing but exhaust gas, that means the 80cc's or so of our cylinder head chambers are filled with extrememly hot and expelled exhaust gas! not only that our exhaust valve needs to be open fully when the piston is at TDC which means we cant get any lift out of it or itll hit the piston crown! hmmmm how can we fix this? hmmm ok, lets try somethign weird, lets open the intake valve only a few degrees before the exhaust valve closes, this MAY allow us to a) have a restriction free interchange betwen exhaust and intake on TDC, but not only that, because cylinder #3 is actually sucking a bit of gas out, its helping draw in cooler intake air into the exhaust b)a less saturated combustion chamber at the start of the intake stroke c) have a much cooler beginning to the intake cycle.

ok so that worked. and we've now descovered that our once lowly restrictive cycle, is actually a lot more "free" and by being more "free" hasnt actually made us any more able to produce "power" what it has done is help us "rev" higher. and as i said earlier:

horsepower=torque x RPM / 5252

doesnt matter if you made more POWER [read: torque] youve made more RPM. which has given you more horsepower. which is not actually POWER. its just horsepower. a magic number devised to show off to your mates about.

NOW, here is why it wont ever work.

namely:

overlap is gonna SUCK. why the fk would you want to build pressure just to force it out the exhaust when youre at the top of your intake cycle? overlap will not be your buddy. itll be the opposite of your buddy. itll be that arsehole thats better looking than you and chatting to your ex at a party. thats how **** overlap would be.

not only that, but people dont think of lift. ok lift. lift right? thats free HP right? isnt that what all the 6 banger fanbois say about mace rockers? yeah man, cam in a box.

guess what? a valve spring isnt easy to compress. when you have 16 of them theyre a lot less easy, and when you have 16 that used to compress to .430" and now compress to .600" they become a LOT LOT less easy to compress, which in turn causes friction and drag.

"who cares? its a 400hp engine, itll compress it no probs! its got oil and **** in there, lubed to fk"

yeah, for an NA engine, we use lift as a sacrifice the longer you can spread out a valve and the slower the ramp, the less strain on the valvetrain, than thus *free hp* les heat, less wear, less strain, less work= more horsepower cos' can rev longer.

now, if you can just explain to me why you would need these things when air is actually waiting at the throttle body at a 1 atmosphere, then +1 atmosphere at all times, thats'd be great.


(i got bored with typing)

XXX

also id just like to state that ive had a few largers, and this probably wont make any sense to me tomorrow morning.

 

[07GTS]

07GTS can you throw up a link to your build thread or some details on what you got please

i dont have any good data yet my last run was at 640rwhp and that was not full throttle because it was running lean and found my fuel system couldnt handle any more than 600hp, im now in the process of tuning at the moment with a big fuel system and E85 once ive done what i can do on the roads ill give it to my tuner to tweek the rest on the dyno and see what i get, i am happy with the hp so i dont care if that goes up or down im gonna see what torque i can get out of E85 and fingers crossed it dosnt stick a leg out of bed

 

[JETURBO]

666 iam hearning you to a "Tee" and you done a bloody good job of describing "scavenging" to the less un informed !

I fully admit iam on the learning side of things with what works on a LS and what does not so i do appreciate everything thats being said, i may need to divulge a bit further to make sense to why i have asked the original Q

Now i dont know how much people know on tuning and cylinder events but i will "assume" the LS is exactly like any other ICE, you pointed right to why i need ( or feel like i need ) a cam with overlap ( or greater than stock )
With this information why do u think i may need this vs close LSA to maintain cylinder pressure ?

As you know the greater cylinder base bressure ( compression ) the greater "potential" hp that engine can create ......

When we add positive than atmospheric pressure what effectively happens to compression ?

What takes a toll in this balance when we do increase pressure, advance timing, yeh ?

This is where it gets interesting ( for some ) if we take 1 degree of advance timing and add it to a base timing map at say 6000rpm it may give us a gain of say 5hp ( loose measurements here guys ) and say we add 1psi of boost pressure ( and for arguements sake at a constant delta density) and it makes 10hp
You could argue that boost pressure is greater than timed cylinder pressure? Yes ?

Sometimes...... Is the answer its a fine "seasaw" effect and largely a hi comp N/A engine will "happily" take less boost pressure than a low comp engine,

You may know this already..... What are we now looking to do up top with my big/ish LSA cam ?

Bleed off pressure to a slight degree, why well timing pressure ( IMHO and a chunk of data suggests ) that at certain RPM points it can be greater than Boost pressure .....true story.....

What some very well in the know chaps have already pointed out and as many will know that you need a "blower cam" or a "turbo cam" when going FI
I agree but what i want to do is TRY ( yes i realise i cant re invent the wheel ) to make that "blower or turbo" cam and TRY to give it some characteristics of a mild N/A cam.

I understand it might not just happen, thats cool but i want to see what people have gone with so far and hear their thoughts on that cam

If its not to be i wont cry about it but at least ill know

It might make sense if i gain 20rwkw across the rpm range even the top half but then that same cam can remove some boost/timing pressure up top to leave some "head room" for the stock hi comp engine

Just seeing if theres a balance somewhere, i cant be the first to think this way, maybe for good reason as to why it wont work but no biggy if it falls flat on its arse

Coming from tuning DOHC with independent control the world is the tuners oyster and i may be bringing to much practically to an old slug

 

[JETURBO]

LSA small but overlap enough to pass as a N/A "cam" to the average joe ( 112-114 )
Must maintain P-V still in .100 no less
Must have decent lift still but low to mild say 223/224 there abouts
Must have manners ( 600-700rpm idle )
Must suit stock stall
Would love it to be an off the shelf item ( i realise this is a long shot )

Ultimately it would seem like a "baby" cam to the N/A crowd, yet lift gains around 10-15rwkw from across the range ( maybe less )
Would have enough to support the FI in regards to dropping cylinder pressure a touch with the overlap making adding PSI a touch easier.

Well lads i think this may be a bloody good starting point, looks like its a very real possibility...............

Bring on that AC powered DC motor ! Hahaha

Have a read lads, i know its the LSX 383 with a whipple 4.0 but its end result will be simular ( big pushrod cubes,cammed,added boost )

LSX Blower Cams Tested

 

[ari666]

you done a bloody good job of describing "scavenging" to the less un informed

ah good, i was more aiming that post at others, rather than you

id also very much be interested in follwoing your quest, this type of "thinking outside the box" is exactly what my mind craves.

 

[JETURBO]

Well hang on to ya knickers as iam liking what reaserch iam coming across now and it is apparent this is a fully achieve able path !

P.s love a good drunken rant

 

[ari666]

well thats good cos' they happen a lot