bigger exhaust cam than intake

[jeffro ra28]

Basically, you need the intake to be open long enough to allow max cylinder filling, but not too long that the piston is not able to achieve max cylinder pressure and the exhaust open long enough to allow quality scavenging, but not fresh intake to escape at revs.

Not trying to have a go. but that really doesnt make much sense.

I think what you are trying to say is that if the duration is to excessive for the desired revs then the intake gas will end up reversing direction as the intake valve closes to late after BDC and the rising piston starts pushing the intake air back out the intake valve = reversion.


Good work on the actuall figures tho but at wahts revs where these powers acheived?

[w810sc]

As stated above, the greater the duration, the longer the valve stays off it's seat. For an exhaust cam it's benefit would be keeping the exhaust valve open longer allowing the piston to expel more exhaust gas.

For a forced induction setup, I would increase the cams duration slightly and would pay attention to the lobe separation angle and intake centerlines. The wider the angle between cams the less over lap at TDC, the narrower the angle between cams the more over lap at TDC.

Top Dead Center - end of the exhaust stroke and beginning of the intake stroke
lobe separation angle - the angle between max lift of intake and exhaust cam
intake centerline - the angle between TDC and max lift on intake cam

Here are some intake centerline figures I use on my 2T-G

(intake cam* - exhaust cam*)
low end gain
108* - 112*
mid range gain
106* - 110*
high end gain
100* - 106

my 2 cents
fonz

[DeftAnesthetik]

Some of the drift cars in Japan frun mixed cams in their 4age's and make around 200hp. Having said that, most of them don't and still make the 200hp, in many cases using approx 270deg both sides. Altering the duration seems to have more effect on where the power is made than how much is made (beyond 290 deg), and getting your overlap/timing correct is crucial. Basically, you need the intake to be open long enough to allow max cylinder filling, but not too long that the piston is not able to achieve max cylinder pressure and the exhaust open long enough to allow quality scavenging, but not fresh intake to escape at revs.

I have found some specs.
In/Ex 272/272 deg 192.5hp, stock bores
In/Ex 272/288 deg 185 hp, 81.25mm pistons
In/Ex 288/288 deg 196 hp, 81.25mm pistons

Also, most cams under 290 seem to make peak power at 8000rpm or less, whilst 300 deg cams need 9000 rpm to make peak hp.
I'm still translating these specs, i'll see if I can work out what the comp ratios/lobe centres are.

HP numbers are nice but its more interesting to be looking at torque at specific RPM. As a guestimate I am currently running in the 150HP range, enough to take just about anything on the street (MR2). as long as i can get wound up and into 3rd gear..... VROOOOOM...... gone. in 100' though i dont think 3rd gear would see much if any action. personally i would rather have a 4a with low(er) hp and high torque to a 4a with high hp and low torque. That being said, we all (should) know that a 1.6l inline 4, is not a torque generating beast.

My memory is a little fuzzy but it seems to me my Tercel running a 3A SOHC would walk on the 4AGE in the MR2 in 100'. Ive actually considered putting the 3A in the MR2 for the shootouts. now in 1000' forget it, MR2 all the way.

as the conversation is going, is it fair to make theses statements?:

more duration=more hp
more lift=more torque.

so one could possibly lower shim clearances (a little) to gain extra lift, thus gaining torque?

PS someone tell me when im rambling about something i dont need to.

[oldcorollas]

shim should be "correct" spacing. lift should come from lobe with the obvious limitation of shims spitting or hitting head.

but yeah, lift = maximising torque, duration+overlap = where you make that torque

[oldeskewltoy]

HP numbers are nice but its more interesting to be looking at torque at specific RPM.......
......personally i would rather have a 4a with low(er) hp and high torque to a 4a with high hp and low torque. That being said, we all (should) know that a 1.6l inline 4, is not a torque generating beast.

EXACTLY what I'm after..... now from my POV.... I'm not looking to choke the hp output... but my goal is NOT the very last hp... but to achieve the best, fattest(longest lasting) torque curve.

[DeftAnesthetik]

EXACTLY what I'm after..... now from my POV.... I'm not looking to choke the hp output... but my goal is NOT the very last hp... but to achieve the best, fattest(longest lasting) torque curve.

yeah ive been following your thread as well.....

FWIW- When I purchased my car, the PO had some dyno sheets that i peeped at. Average of the four sheets he had was ~135hp. I was uninterested in the torque at the time so i have no recolection of those numbers. mods: overbore (i still have to crack open the top end to see what to but its only a 3rib so i would say it was kept back to 81.5mm.) "full race porting" whatever that exactly means, i don't know. i need to get the head off and have a good look at it. full balance of the bottom end. upgraded to forged pistons, unknow compression (again i need to get in and see) but i can run regular octaine no problems (not that i do). and a cone filter (aka powermax intake mod) stock cams, timing and managment. Seeing what you've done to your head so far, i think your going to hit your goals easily. whats going to mess with you is the emisions stuff.

as it sits (without adj. cam gears) HKS 264/8.35 on the intake puts the power higher in the rpm's than i want it to be. and it sounds like we are aiming at the same target.

IF, and its a BIG IF (my wife is 10 days past due and counting), I can get the cam gears in, i may change my tune on 264 being to big.

[oldeskewltoy]

Well... I don't know why you'd have a longer duration in the exhaust...


But I've been told (very recently) by some VERY competent 4AG specialists that running the larger cam on the intake MAY benefit the torque curve (it depends on the camshafts). You will lose one or 2 hp, but you could gain twice as much in the low end torque as you lose in the high end HP.

[oldcorollas]

and if you match that with bigger exhaust cam?

intake will always be the "tap" that lets air into engine.. and exhaust is the "drain" that lets it out...
bigger "tap" should always allow more flow, although maybe not as much as a proper sized "drain will allow.

bigger drain will make sure that the chamber is more empty, but too much will not make it much more empty..

besides.. some EGR from exhaust will increase fuel economy

[qcautosports]

(exhaust cam* - intake cam*)
low end gain
108* - 112*
mid range gain
106* - 110*
high end gain
100* - 106

my 2 cents
fonz

Good work. The 3rd setting will probably run better with a 110 deg. LC on the EX and keep the intake at 100. The first setting however would have given you better low end if you set it at 94 in - 106 ex. The 2nd setting, try a 96 in - 112 to 114 ex. These are numbers I've tried like 20 years ago, it should work for you.

Switching the cams is worth trying , at least you'll get to see results weather it's gonna be bad or good. I've done it back in the days with my 2TG running 320/304. I switched the cams but wasn;t very happy with the results so I switched them back.

Always time your cams so that you know where your starting points are. And (4AG,2TG,3TG,18RG,3SG and other similar engines with same configuration) always start with the...which cam...IN or EX?

Your cylinder head will also play a big part if it was or wasn't done correctly, assuming it is a ported head.

[w810sc]

Good work. The 3rd setting will probably run better with a 110 deg. LC on the EX and keep the intake at 100. The first setting however would have given you better low end if you set it at 94 in - 106 ex. The 2nd setting, try a 96 in - 112 to 114 ex. These are numbers I've tried like 20 years ago, it should work for you.

Switching the cams is worth trying , at least you'll get to see results weather it's gonna be bad or good. I've done it back in the days with my 2TG running 320/304. I switched the cams but wasn;t very happy with the results so I switched them back.

Always time your cams so that you know where your starting points are. And (4AG,2TG,3TG,18RG,3SG and other similar engines with same configuration) always start with the...which cam...IN or EX?

Your cylinder head will also play a big part if it was or wasn't done correctly, assuming it is a ported head.

QC, what cams do you use for those figures? I use 300*in 300*ex. I'm about to give those figures a go right now.

fonz

[qcautosports]

QC, what cams do you use for those figures? I use 300*in 300*ex. I'm about to give those figures a go right now.

fonz

I use those numbers for any combination. Most of the test were done using TRD cams but they will work with any as most cams for the 2TG and 18RG have almost similar LC as per manufacturer, the differences are very small (+/-2 deg being the biggest) between manufacturer. All the settings you've tried are split timing configurations in which, it will give you a broader power band.

Sorry for hi-jacking the thread but this is also applicable to the 4AG although the numbers are going to be different. Use 100 degeesATDC for IN cam and 98 degrees BTDC for EX, +/- 2 degrees for both. (for 7.5 lift TRD cam 272/272 rally setting). 304/304 is 100-100 deg. for race (road course). As far as I can remember, TRD sells their cams without giving any cam cards, so here you are.

And always start with the ______ cam when cam timing.

[oldeskewltoy]

As far as I can remember, TRD sells their cams without giving any cam cards, so here you are.

Where???????

[qcautosports]

Where???????

Those are the numbers. My last post before this one. hose are the numbers they use for all there 7.5 lift cams from 272 to 288 to 304.
Easy with the question marks. I don't know if you're excited, demanding or pissed.