I built a KA24DE!!!!! Cam timing? Whats that??!! *Discussion Thread*

[OddyseusDSM]

This is in no way a knock on 248/248 swaps and the like, but they may not be the be all end all of cheapy cams.....read on. BTW, I'm also not the most eloquent writer, feel free to skip ahead also.


The Story in 3 minutes:
buy car from florida (2007)
blow up car from florida in jersey
tow to ct
replace engine
blow up transmission (2009)
replace transmission with manual
blow head gasket (2012)
replace.......wait a minute I CAN DO A SWAP!!!!
no money for swap
2014.....REBUILD KA --- i can do this right?


The Motor:
So in my typical fashion I get completely obsessed. Lets find out how this motor really ticks. I mean, I have pages upon pages of math, excel programs calculating what happens when and how much etc. I mean my perameters are pretty tight….rebuild…..but can I just make it that much better, that much more fun, even if it still has only 150 hp at the crank…..most.

I settle on a SOHC piston swap, some S13 cams, and new gaskets and bearings for all. Heres where all the cam crap comes in.

When going with higher compression, your effective compression (i.e. when your intake valve closes) has an effect on your cylinder pressure. This all in turn has an effect on youre low end and peak torque and even the octane you are using. Through my efforts creating calculators, doing it by hand etc… I find a nifty excel spreadsheet calculator that put it all together. Great! Now I can calculate my Effective Compression Ratio (CRE) easier.

But wait theres more!

Overlap creates a scavaging effect which will help draw or jumpstart the intake charge. Whats overlaps effect on the KA. Back to the math… that is until I get my hands on a copy of Desktop Dyno. You may notice the power numbers look a little low but the peaks and drop are right where they are on the car. Score! A little less playing with the motor more on paper, at least point me in the right direction.

So the CRE for my engine I’m putting together falls between 60 and 65 degrees Before Top Dead Center (BTDC) for the Intake Valve Closing event (IVC). I would have to retard a 232 camshaft for that to work and the IVO (intake valve open) for that cam is just after TDC. 13 degrees if I aimed for 65 degrees IVC. I need something longer duration if this 11:1 is gonna work safely…..an S13 intake cam closes at 61 degrees, awesome, and I wont even really have to clock anything. Set ordered.

Rip apart my head and start rebuilding. WHAT!? I have S13 cams in there. Bonus! With the new head (old warped) and the S13 cam set I got I have a full compliment of cams that I can play with, 248/248 here I come. I shim everything up for .010” and do the 3/4 teeth method for the cam and check my timing events. 70ish degrees with one method, 30ish with the other. No Wonder why people doing these 3/4 tooth clocks see such wild variations in the 248 swap. Take 2 gears do some math and start drilling on my drill press (that’s the blood in blood,sweat, and tears).

Now, long story short, cars together, has a nice lope not not really like you see in the youtube videos, little more stock than that. NO loss of low end except for off idle to 1500 and pulls to redline and doesn’t fall flat after 4500 like all S14s feel like. If you don’t think yours does you need to drive some more cars.
But this all got me thinking…..

What if I never swapped my pistons….. or my cams for that matter, what could I gain…..
Heck even a flat power band at our current power level would be a drastic improvement. There had to be a reason why the cams in newer cars even without VVT and the sort make better power than we do.
Back to the computer…..

Now obviously I hadn’t done much in the way of physical testing on this, but even putting aftermarket cams in the program yields the desired results even though stage 1 seems nothing more than 2 exhaust cams clock to the manufacturers spec, which is really just more overlap (narrower Lobe Separation Angle if you’ve ever looked into it).

I took a series of screenshots to highlight the differences and in some cases its peanuts and subject to your personal preference. OBD2 cars may have negative effects if you go to crazy, I’m not OBD2. Part throttle performance may be better with some cams rather than others, I do not know. I stayed with 248/248 solely due to the compression ratio I am running.

Intro to engine calc page, we are concerned with CP and CRE. My CRE is in the high 8s and I don’t knock on 93 octane. I propose no issue on 87 octane from 7.5-8, 91 for 8-8.5 and 93 for 8.5-9+ or race gas. There are 5 million different views on this and I think our combustion chambers are not as sensitive to knock as other cars but I digress, I err on the safe side. I don’t make money with my ride, I just have fun with it.



advanced 5 degrees


advanced 10 degrees


advanced 15 degrees


mine at 65 degrees BTDC IVC


mine at 60 degrees….mind you I used these numbers as a target so I’m somewhere in between



The stuff you’re really interested in….how does it compare? These are all cams in a 9.5:1 compression motor, I cobbled the specs from countless hours scouring forums builds and the lot to get CFM rate of intakes etc. its not perfect, but the peaks are right, the drops are right, the feel is right. Therefore I think this is a decent comparison.

S14 VS S13 stock for stock. Not much different, eh?
Note the white numbers on the right in the cam spec box, which are hard to see as they are for me too, are the true valve open and close events. Yes I had to fudge it but its all right, its what numbers the program will accept.


This is everything set to the same IVO and EVC as are stock spec’d by the FSM, look I even threw in a 248/248 swap properly timed. They are close! This can't be right!!! I left out S13 stock for obvious reasons


Heres where the fun begins. You’ll notice the file names for each trace, I will explain them and allow you to decipher them further since I don’t wanna type every one of them out every time. I assume if you use cam gears you will clock at 5 degree on crank intervals, so up to 20 degree advance and 20 degree retard. Remember, 1 tooth on cam is 37.9 degrees on crank. So if you have a 232 5r 248 15e overlap that equates to 232 intake retarded 5 degrees and set with 15 degrees overlap added, on gears the intake would be clocked 5 degrees retarded and exhaust a full 20 retarded. Its how the program would let me do it because they designed it for SOHC or cam in block for SBC and the like.






The best of each of the sets


The 2 best (IMHO) out of these groups, with comparison to stock S14


Heres what I considered the best one compared to a 248/248 swap clocked at a 50 degree IVC and 37 degrees overlap exhaust retarded 15 degrees. That said I figure drivability on the 232s with only 15 degrees overlap would be better than the 2 hp increase the program shows. Where you drive more? 1500-3000 or 4500-6000?


This is all to get you to think, you want 5 peak hp most or a flatter power band, more up top or a nice daily that never winds out. I promote discussion on this, no flame wars about “248 rock socks and anything else blows” or “I once beat a vette…”. I live on curves, and I’m poor (bought a house, so, really really poor). If I can snark a friends car and mess with his cams I will. But otherwise this is bench...err...dynoing.

All suggestions will be taken, modifications to the numbers, I once did and it seemed to work but I wanna see how the numbers panned outs….. I’ll throw em in and see what happens. I work…A LOT… and wont be on the thread often, though.

[OddyseusDSM]

look cams!



and cam gears!



This is how I made them, used an EG Civic rotor as a jig to set the angle, a headbolt through a socket that just so happened to be like .003" smaller in diameter than the inside hole on the cam gear. Clock the rotor, clamp, clock the gear, clamp, drill, repeat. Id place my error at 2-3 degrees on crank most.

[Sleepy_Steve]

Neat! I should degree my BCV2's