Gain from cam gear Vs. gain from camshaft

[cobrAA]

Basicly, the aussies are telling me, price-wise, on a budget, the gain I will get from a camshaft approx. 40whp ( considering cams are worth 800$,+ labour + shim + springs) is not worth Vs. the approx. 20whp gain I should see with a cam gear tuning.

Anyone played with their cam gears and would like to give more info about this. I already have Tomei cam gear on my car so.. if it will cost more 1000$+ for only 20whp more, I better put my money elsewhere since I'm on a tight budget.

[GTR-Dad]

If cam timing is set to OEM specs, you won't gain a bunch of power, but if it's off you can make large gains. When block and head is decked it changes the distance between cam gears and crank, which, when the timing belt is tensioned, alters cam timing. For reference, running Jun 264/264 x 9.7mm lift cams I gained about 100 hp by correcting an intake cam timing error of 3 deg and an exhaust error of 10 deg.

Remember that efficiency gains are based on reducing resistance to flow. Thereofore, for a given change your gains will depend on how much of a bottleneck your upgraded part had been. For instance, if you fit a new cam to an otherwise stock car you'll get only modest gains. If you leave the cams til last on a full build where you've done intake, hard piping, intercooler, turbos, and exhaust you'll see much greater gains from a cam upgrade.

Dan

[GTRADDICT]

If cam timing is set to OEM specs, you won't gain a bunch of power, but if it's off you can make large gains. When block and head is decked it changes the distance between cam gears and crank, which, when the timing belt is tensioned, alters cam timing. For reference, running Jun 264/264 x 9.7mm lift cams I gained about 100 hp by correcting an intake cam timing error of 3 deg and an exhaust error of 10 deg.

Remember that efficiency gains are based on reducing resistance to flow. Thereofore, for a given change your gains will depend on how much of a bottleneck your upgraded part had been. For instance, if you fit a new cam to an otherwise stock car you'll get only modest gains. If you leave the cams til last on a full build where you've done intake, hard piping, intercooler, turbos, and exhaust you'll see much greater gains from a cam upgrade.

Dan

+1 I saw your post in SAU and was impressed by the gain!

[Dragon Humper]

Anyone who says that you only get about 20 to 40 hp from cams is drunk as hell.

At the same boost level (remember larger cams will remove a sizable restriction) you will make at least 100 more HP. If you were running a positive displacement supercharger your boost pressure will go down after an increase in cam size, why? You are now allowing the engine to move more air in and out which removes some restriction and will lower boost pressure at the same HP level (usually slightly more). You are now making more power with less heat. Turbos, though, have a wonderfull way of self adjusting via the boost controller and will still run 10psi (if that`s where it was at before the cam change) vs 6 to 8 psi that the supercharger will make.

If you are stock now with a decent cat-back, properly tuned with 270`s you would make at least 100 more HP with less heat to boot. Crank her up to 14 psi and 150HP is easily had. If you went from 10 to 14psi on stock cams you would make about 40 to 50 HP more as well but at a level 100HP less than with cams and with more heat which we all know is a bad thing.


One of the reasons the Aussies have a tough time making HP is their fuel is 2 steps above donkeypiss, it`s even worse than the US fuel. You can add at least 20% to anything they predict because of that. You can`t make torque without a decent ign. timing curve and you can`t crank her up when you are trying to do it with Bunker C (SuperTanker fuel....LOL).






Jon.

[cobrAA]

i think those gains are pretty step. Well to give you a better idea.. I have 400whp with all the usual external mods you would see on a 400 gtr but my engine is stock and 20yr old.

Im also talking about regular camshaft 260 not extreme 280 cams.

[archaeic_bloke]

ok, So here's a scenario for you cam and head gurus...

lets say my goal is 450 Whp... and i have all the usual upgrades including -5 turbos, fuel mods, intake exhaust, but like cobraa, stock pistons and rods and head.

so lets "assume" I can hit 450 whp by running 17 PSI of boost (just for arguments sake) on stock head.

now if i wanna drop in pon cams or grex easy cam, say 264/264 IN/EX 9.x mm lift.

are you saying I could reach 450 WHP easier due to cams?
so effectively after cam install, i could lower the boost pressure and still hit 450 WHP?

does that mean that upgrading cams might be an effective way of reducing wear on the pistons and rings since we don't have to run as much boost to make as much power?

or do cams change the heat cycles and combustion, and possibly put more stress on rings and pistons?

basically the goal is to reduce stress on pistons and rings, will cams help do that?

[cobrAA]

Interesting question!!

[nelsonmxmarc]

do cams change the heat cycles and combustion, and possibly put more stress on rings and pistons?

basically the goal is to reduce stress on pistons and rings, will cams help do that?

This is simply speculation, but by increasing lift and lobe duration, you're effectively moving more of the same volume of air in the cylinder allowing you to decrease boost due to this supplemented increase. Your cylinder volume doesn't change, it simply moves more of that air effectively allowing more air and fuel to be mixed (larger lift) complimented to a larger volume of exhaust gas release.

Wear on pistons and rings isn't necessarily based on increased boost - moreso it's a constant variable that has to do with heat saturation and time. Engines wear, its not possible for an engine to work as effectively as the day it was produced, so it's a given that in time it will need to be rebuilt. Heat is the number one cause, so if you can keep heat down (water meth for instance), you can increase hp by simply keeping the block cool. Cams technically do this, but rather than keep the motor cool, youre simply moving a larger volume of air on each stroke. And since we know turbo spool is a function of exhaust gas, we can say that the larger volume of air expelled due to your larger lift and duration will enable you to run the same, or lesser boost per se, to achieve the same power.

[nelsonmxmarc]

And Josh, when you talk of "stress" on pistons and rings, take into account that the force exerted due to combustion is placed primarily on the rods. Rods will sheer/bend due to stress, pistons will give way as well, but most likely in the case of detonation or old/faulty ring lands.

[nelsonmxmarc]

Damn triple post..

I have a quick question to add to this now;
can nistune account for the variation between both cams (ie, instead of physically varying intake and exhaust gears) or is the timing limited to a specific value for BOTH?

[frankiman]

like marc said, changing cam timing only changes the mouvement of the air in the cylinder head

cams don't change the combustion cycle at all, that is determined by the ignition timing

cam timing and lift will let inlet air IN and exhaust gasses OUT at different time and flow rate than stock

its all about "how much air" you can cramp into the cylinder before the combustion cycle

i.e.
cams that add lift, means the valves will open further out in the cylinder head, resulting in a larger opening for the air and gasses to move in out in their allowed time frame

its very important to understand that its just as important to get the exhaust gasses out as quickly as possible so that none is left when the exhaust valves close and cold air/fuel is let in
also, the quicker and the more exhaust gasses you expell from the cylinder head, the quicker the turbos will spool, better response

now with timing, you can change the allowed time each side can move their volume of whatever gasses
its always best to have a good amount of overlap between each side

this is acheived my retarding the exhaust cam, and advancing the intake cam
this will create overlap,
meaning, that the intake valve will start opening before the exhaust valves have closed, creating a fully open flow in the cylinder head,
the incoming air will help push out the exhaust gasses, leaving no exhaust gas in the combustion chamber afterwards, and making the exhaust gasses coming out at a much higher flow rate (it will likely be mixed with some of the inlet air) and faster, making turbos spool a lot faster

think of it has car doors, in the winter, when the air inside the car is hot 25deg C, but outside its -10deg C
if you open one door, what happens, the hot air inside is taken outside at a certain rate, an exchange rate because something has to fill the space created by the hot air leaving, so the flow rate is low
but what happens if for a short period of time you also open the other door, then there is 2 openings, this will automatically create a good flow rate because cold air will come in from one side and push the hot air out the other
(thats why you should never open both doors at the same time in winter if you don't want to freeze to death)


also,
with every single modification you make to your engine, intake system, exhaust system, boost, better ignition, turbo sizes, etc etc
it keeps changing the engine's flow caracteristics (and air/fuel ratios)

it is the one reason it is very important to tune cam timing (via cam gears) to match those caracteristics and use the full potential of all the modifications
gains from tuning cam timing on a stock engine is minimal, because it is already optimized

but when you modify everything else, the cam timing can be wayyyy off from its optimal setting

the longer you can keep those intake valves open, the more air you can cramp into each cylinder
also,
its not because you are running 17psi of boost, that actually 17psi of positive pressure will be created into the combustion chamber, if theres not enough time to fill it, it won't reach you manifold absolute pressure (what a boost gauge indicates)

thats why with better cam timing you can run less boost and still make the same power,
i.e.
with lets say you run 17psi, but have crappy timing, the combustion chamber might only pressurize to 14psi
whereas, if you run 15psi of boost with muc better timing, you might still get that 14psi of positive pressure actually into the chamber

thats how gains of over 100hp are acheived JUST with cam timing

[evilgtr]

Frankiman thank you very much that was very detailed and a great read ! What do you think is a optimal cam gear set up that you hae found for say 264 degree cams ? I believe my cams are still set at 0 and 0. When I retune in the spring I would like to maybe have my cams set up to maximise power and effiency of my engine.

[frankiman]

like a said, the optimal cam timing will be different for every engine,
last time i went on the dyno, we didn't have time to fiddle with the cam timing, as it was a saturday night and i left the shop at 9;30pm
but since i changed the timing belt this summer, and the intake system, and coilpacks, the timing as been off which made me loose some power (15hp) at the same boost i got it tuned last year, it took 1,2psi to regain that power

next year though, if it takes 10 hours to get it right, we'll do it right, i want my 425whp/500bhp

also, i haven't talked about the duration of aftermarket cams, thats another story


the only downside to changing timing, is how the engine will feel,
too much overlap and it will be impossible to keep the engine idling

thats why cars running "big" cam of 280+ deg, have a hard time idling, sometime idle RPMs have to be set at 1500rpm+, just to keep a regualr flow in the head so the engine doesn't die,
an engine at idle has no load at all, so the flow caracteristics have VERY different than at WOT / full load
those big cams, have high (or long) duration so they automatically create overlap between the valves

[cobrAA]

umm thanks frank.. I don't have times right now, I will read it friday nigth after my last exam with a pack of beer around me :P

[mikes_ca]

Just for arguments sake, and since Vex just got done tuning my car last week, here is a dyno graph that shows before and after adjusting the cam timing. Red lines are pre-cam timing, blue are post. Max hp was actually high before, but the curve is much better with the cam timing. Boost was held steady at 19-20 psi in both cases.

/Users/michaeljames/Downloads/Final Tune Cam Adjusted.jpg