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FAT CAM spark tuning

fryea

New member
Joined
Mar 4, 2005
Location
Tacoma, WA
Put your K and H cams away.

Im looking to see if anyone has experience tuning a spark map for a FAT cam.

The cam I've got stuffed into my rebuilt b230f likes to idle at around 85kpa.

Power brakes are a joke with this thing:rofl::rofl::rofl:

It LOVES spark advance too.

Idleing. It can sit fine at 900rpm without touching it. The problem is that the idle wants to run away after that, chase itself up to 2400 on spark advance alone. Because I need to add ALOT of spark advance really fast after idle, the bins adjacent to idle are quite high. Then when I lightly press on the gas, it won't settle back down at my comfy 900.

The X axis bins are set up near idle at 700-900-1200-1700...

THEN... I remember reading a thread recently that stated that TOO MUCH spark advance can sometimes be a bad thing, even without knock. I guess the only real way to test this is at a load dyno. Just curious where if there are any ballpark figures to be safe.

Any similiar experience with any other 2v 1.8-2.5l engine?

Cam in question is based on an 8v Alfa 2.0 profile, grinded onto a Slotted T-cam base. 12mm Lift, 110.8 LSA, 47.6 overlap, 58.3 intake closing ABDC. Here is the chart

cam_alfagrind.gif
 
Well, that's hotter than a K cam, but not by much - same lift, almost the lame LSA, 15 degrees more overlap and duration.

What I'm saying is it should pull more vaccuum than that.

Perhaps it doesn't because your timing is ****ed though.

I assume you have done the obvious things like set the timing to where it pulls the most vaccuum, yeah? Otherwise go do that first.

edit: but yeah the hotter the cam gets the more agressive the timing curve gets.
Less charge density at lower rpms means more advance.
 
I feel like I've already advanced the piss out of it, I could try to go another tooth.

It has been advanced a fair bit. I did hack a bunch off the cyl head though, so that throws things off a bit, aye?

Edit: By my calculations it has alot more than the K cam. 33.4 MORE degrees of overlap, 11.5 MORE int close ABDC, 32 MORE intake duration at .050, and 18 MORE exhaust duration at .050

Referenced from http://turbobricks.com/forums/showthread.php?t=152021, and I KNOW you saw these because I was chatting with you in this thread ;-);-);-)
 
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Yeah if you've shaved the head you are already going to need to advance the cam to get it to where it would have been w/o. Do you have an adjustable cam gear?
 
I feel like I've already advanced the piss out of it, I could try to go another tooth.

It has been advanced a fair bit. I did hack a bunch off the cyl head though, so that throws things off a bit, aye?

No no no I am talking about the ignition timing. Have you set the ignition timing to where it makes the most vacuum at idle? yes? Don't just change the cam timing arbitrarily...
 
No no no I am talking about the ignition timing. Have you set the ignition timing to where it makes the most vacuum at idle? yes? Don't just change the cam timing arbitrarily...

Me either, im talking about cam timing.

When it was timed strait up it would barely drive.

Is there a formula that will tell you the amount you need to advance based upon amount taken off the head?

Edit: The 85kpa does sound a bit rediculous. I have no doubt that my cam timing needs some more adjustment.
 
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Me either, im talking about cam timing.

When it was timed strait up it would barely drive.

Is there a formula that will tell you the amount you need to advance based upon amount taken off the head?

Edit: The 85kpa does sound a bit rediculous. I have no doubt that my cam timing needs some more adjustment.

1 degree for every 10 thou is just about right.

best bet would be to get some proper measuring tools and make sure its right, not just a guess
 
1 degree for every 10 thou is just about right.

best bet would be to get some proper measuring tools and make sure its right, not just a guess

In that case, I had 2.5mm taken off of a stock head, so almost 100 thou. That's the most allowable by the stock timing belt. Does 10 degrees retarded sound right? Will double check cam timing when I get home. Otherwise, back to the tuning trenches.
 
In that case, I had 2.5mm taken off of a stock head, so almost 100 thou. That's the most allowable by the stock timing belt. Does 10 degrees retarded sound right? Will double check cam timing when I get home. Otherwise, back to the tuning trenches.

Welp, it was on the right tooth.

Timed the crank and cam at TDC, and the cam is 1 tooth advanced.

This gave me around 15 degrees at the crank advance.

Take into account the figure fidel gave (10thou = 1 degree, 10 degrees total retarded). However, is this for Cam degrees? Or Crank degrees? Could set me 5 degrees + or - TDC depending on the unit of measure (cam/crank).

For ****s and giggles I ran it +1 tooth and -1 tooth.

1 more tooth retarded and it ran REEEEEALLLLY rough

1 more tooth advanced and it wouldn't start.

So I'll have to live with my 80-85kpa idle until I get an adjustable cam gear. Actually there is much more spark and fuel tuning to be done, maybe I can make it hunt a bit lower on the map.
 
Have you actually set the base/idle timing for max vacuum yet? You are wasting your time just changing cam gear timing randomly dude...
 
Have you actually set the base/idle timing for max vacuum yet? You are wasting your time just changing cam gear timing randomly dude...

I've never really messed with any other cams than the B/K cam in megasquirt, so no, I probably have not set my idle for best vacuum. How does one go about that?

As for the cam gear timing, again, first time messing around with it, might as well play around with the various settings to see what works best, and to learn what too far one way or the other feels/sounds like. One tooth advanced past TDC is as good as it is going to get until I can get my hands on an adjustable timing gear (round tooth cogs)
 
2.5mm111 Thats a **** ton. You mean 1.5mm/60thou maybe??? that is about teh max I could get on the stock t-belt tensioner and need to advance a whole tooth basically at that point. I'm shocked that the t-belt tensioner even holds the belt at that point. My H-cam ~12:1 compression B23 with a cometic leaves a bit left on the t-belt tensioner, but not a ton...just barely enough for normal service life of a belt.

It is about 1 cam degree of retard for every 10 thou, but you should do the calculations for your own self. The good news is that on a sohc volvo the t-belt is basically perpendicular to the block/head deck surfaces, so if you know the approximate diameter of the cam pulley/sprocket (do we have consensus as to what to call the thing lol for all your "gear" or "pulley" or "sprocket" nazis) and measure the head on the corner and look in the book for a new uncut head, you then know how much your timing is changing in relation to shaving the head and how much your head is shaved from a perfect new one...don't assume here.

I have to advance my camshaft just a hair less than one belt tooth (9 camshaft degrees), though I gained a fair bit of SCR so I'm running my camshaft near steaight up or a hair retarded theoretically and the powerband winds up in more or less the same place.

That cam should drive/make power about the same as an H. I'm using a slightly recurved volvo H/K cam ignition distributor. It starts out at 4 degrees at idle an climbs pretty sharply. Can't run much timing at idle without a spark miss and really most OEMs just want to get the thing TO idle at all. That means not richening it so it wants to foul/flood out and not running too much timing to wind up with a spark miss, but enough to keep the plugs warm and get the thing to run.

A spark miss reads as lean on a wideband 02 sensor. You need to make this easier on yourself and eliminate variables.

1: Establish where the camshaft timing should be to at least restore it close to stock (which could be complicated if the shapes of your lobes are way off "normal" offset from the pin in addition to the shaved head...the cam grinder will have to answer for some of that and check it with a degree wheel (or you will)....see "mushroom effect" and other issues...cams are complicated beasts to design to even work with the valvetrain, let alone produce the kind of power you want where you want it)

2: Run nice conservative ignition timing to start and conservative warmish plugs...make this easier on yourself starting out. We don't want a nasty spark miss if you are tuning off the wideband 02, and we want it to be harder to foul out if you are trying to smooth it out and things are less than ideal. Start with something like volvo did at idle...5 degrees BTDC or so. I start with like plugs 1 or 2 steps warmer sometimes (when I have no idea what to expect), conservative timing, conservative spark gap etc. Then, when it comes time to really dial more out of it, start dialing that stuff in in systematic steps. Most t-brickers use a shotgun approach for anything...change tons (shoot tons up on the board) and see what sticks lol.

3: Start to stabilize the AFRs and really get things smooth from idle-redline.

4: Last but certainly not least, dyno tune it and triple check any maintenance or other dumb stuff...heck you should test all that stuff all along...plug readings, possible soot reversion into the intake, anything and everything you can log should be logged and dead reliable (if not slow) before it gets strapped on the dyno to actually make power.

Anyway, you have a lot of unknowns and variables here. I suspect between potential spark miss, cam lobe shape offset and god only knows what else you have no chance of making it run right without checking/correcting all of that. I've run cams wilder than that in a volvo redblock sohc with no problems.

I should also mention, many people tune their megasquirt volvos very strangely. They put all their bins evenly for RPM and load like every 500rpm from idle to redline and from idle to WOT. This is contrary to just about all sane tuning philosophy. Think back to your lawnmower...it has maybe a small finer tuned adjustment for "turtle" on the carb/magneto and a radically different set for "rabbit." Well, graduate up to your k-jet B23E...same thing is happening...there is a spring in the dist for "turtle" (lower RPMS and load) and "rabbit." I guess what I'm saying is that you guys should have a lot of bins in places where the behavior of the engine transitions more rapidly/on the bottom and just try to keep things holding steady as you scream through "rabbit" to redline. I know that doesn't make a lot of sense how I have it typed, but as an overall theme, that is how most people approach this, from lawnmower, to OEM automotive, to racing (though in racing we mostly want to just make the thing idle and don't much care if it isn't that smooth under 3000 or whatever). It has worked well for me in practice.
 
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1: Establish where the camshaft timing should be to at least restore it close to stock (which could be complicated if the shapes of your lobes are way off "normal" offset from the pin in addition to the shaved head...the cam grinder will have to answer for some of that and check it with a degree wheel (or you will)....see "mushroom effect" and other issues...cams are complicated beasts to design to even work with the valvetrain, let alone produce the kind of power you want where you want it)


Nice Post James.

To elaborate on the above-
He has a cam card so timing the cam should be easy.

Dial indicator on the #4 intake cam lobe.

0.100" is at 12 deg BTDC.

Turn the crank 12 degrees BTDC using the timing marks, based on the dial indicator the lift will be more or less than that. If it's more, retard the cam. If it's less, advance it until the dial indicator readings correspond with the card.
 
just curious: what is the valve lash clearance?

also: when running a camshaft with a considerable amount of overlap, the idle is going to be rough, lopey, and tend to act like the motor is misfiring.

you might open up the lash clearances a few thou; and you may need to raise the idle speed up to ~1000 or so. possibly 1200 or more. I've had V8s that would not idle anywhere near smooth under 1200.

and yeah, you are going to need to find out just where that cam is actually at....vis a vis the cam dowel pin vs "TDC", and use an adjustable gear [sorry, James, I call them gears] to get that cam closer to actually being 'straight up' as a starting point.

cutting back a bit on the overlap via more lash might assist you in getting to a baseline. From which you can more logically proceed.

TF
 
Very true. The k/H-cam B23E idles at 900rpm (in theory if the idle slide is working on that day lol), low 13s AFR and 5 degrees btdc in perfect repair and will do that for 400K miles smoothly and effortlessly.

I can get an R-cam B20 on dual weber 45s with basically no choke to do the same. With all your mega-****-you er...megasquirt you ought to be able to do at least as well...in theory.

Volvo didn't make the camshafts they way they did and actuate the valvetrain the way they did just because they felt like it. Granted, volvo and TF (usually based on what he writes here) are heavily longevity oriented (which is fine...I know volvo wouldn't shave 60 thou off a head and they are smart not to), but even so, they DO WORK...for a long time.
 
cutting back a bit on the overlap via more lash might assist you in getting to a baseline. From which you can more logically proceed.

TF

I would really time everything first and try that before i started re-shimming everything though...
 
Thank you all for the very well written posts, this has been very helpful.

I sent dave an email seeing if he has any round tooth adjustable cam gears available. Last time I checked he was out. First step towards getting things all lines up again (after measuring).

I'll load up a stock timing map from a B23F-LH Manual. This should put me in the ballpark of a conservative timing map for this setup.

b23f-LH-M.jpg
 
How do you figure? M-cam B23F and low compression B23F? Not exactly the the conclusion I draw.

K/H-cam B23E ignition dist is bosch part#
0 237 002 017

Bosch is so kind as to make everything they make have such nice logical numbering stamped right on it. R-sportinternational.com has the k-jet ignition dist curves. "picture 4" in the zip file contains the K/H-cam ignition dist map for low RPMs. Many other ignition dists can be examined and guts from many other bosch ignition dists can be transplanted into others and modified from there with care. More old school and less digital than the keyboard perhaps, but it does work and works great for years.

Square tooth gears work just fine *shrug*. I'm too lazy to take the gear off to adjust it on a more radical engine that is rather experimental or that is adjusted for different uses often. I like the RSI gear, but also like Dale's style gear...can't beat OEM qualtiy, just not as easily adjustable.
 
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How do you figure? M-cam B23F and low compression B23F? Not exactly the the conclusion I draw.

M-Cam should be on the conservative side. Similiar compression ratio as well to b23f.

I've seen that dizzy map before. I usually check out the .pdf version on k-jet.org, it has all of those in much higher resolution.

Here is comparing the two back to back:

Assuming the 2017 has a base timing of 5*, I get:
RPM - Advance*
2600 - 31
4000 - 35
6000 - 33

Interpolating the same points on the B23F-M chart with a base timing of 12*, I get:
RPM - Advance*
2600 - 22
4000 - 32
6000 - 36

So significant difference in the sub 3000 rpm range, but the B23F chart is slightly more aggressive on the top end. I chose the B23F chart based upon the more conservative nature of the M cam and the data points look more refined. Would you suggest using the 2017 dizzy to start out with?
 
Yes, I'd use the 002 017 to start with with a base timing of 5* at 900rpm. The B23F one has a base timing of 12 +- 2 at 750-800rpm.

One needs less timing and more air to not get the thing to have a partial misfire at idle. Set the idle at 1000, set the timing to ~5 with all the trigger angle correct and good rotor spark contact and go from there with something more akin to the 017 map.

The k-cam ignition dist will be more "correct" for the cam you have. I just mean conservative at an idle and so on and not hammering it or pinging it as you fine tune it with warmer plugs and everything figured out. Make sense? It would make sense to establish all the other stuff I outlined first...kind of pointless to do anything without knowing where the camshaft is timed up and how it opens the valves. The measuring technique kenny outlined should establish some basis for knowing where you are at.
 
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