ng_randolph
Bjorn H
The cam pulley has 42 teeth, so one tooth here is ~8.57° Edit: Corresponding to 17.14° of crank rotation. (Thanks Steve)
Last edited:
Tuning adjustment for performance mods.
- Thread starter lookforjoe
- Start date
fiatfactory
Steve Cecchele
But the cam spins at half crank speed, so one cam pulley tooth is 17.14 degrees of crank rotation.
SteveC
SteveC
lookforjoe
True Classic
These were Matt's words to me when I emailed him about running with one tooth advance on the setup:
"A full tooth advance is WAY too much advance. That's why you're
flat up high. Should never be more than 1/2 tooth advance and preferably between 1/3 and 1/2 tooth (about 2-4 degrees). If you cannot get it to index less than one full tooth off, you need an adjustable cam wheel to compensate."
So, I pulled the cam gear back to the stock reference marker, and it seems to perform well across the board. I honestly don't feel I have any reason to play with the cam timing, but I would like to have a more definitive answer to exactly where the cam timing ends up, in relation to the stock reference markings, using his .040" milled box & 35/75 cam, and head milled .075".
"A full tooth advance is WAY too much advance. That's why you're
flat up high. Should never be more than 1/2 tooth advance and preferably between 1/3 and 1/2 tooth (about 2-4 degrees). If you cannot get it to index less than one full tooth off, you need an adjustable cam wheel to compensate."
So, I pulled the cam gear back to the stock reference marker, and it seems to perform well across the board. I honestly don't feel I have any reason to play with the cam timing, but I would like to have a more definitive answer to exactly where the cam timing ends up, in relation to the stock reference markings, using his .040" milled box & 35/75 cam, and head milled .075".
Pete Whitstone
True Classic
Well the math is pretty simple...
Using some round numbers, each tooth is 8.6 degrees, and a rough measurement of the tooth spacing shows about .380 inches center to center.
You have moved your cam and crank centerlines .115 inches closer to each other, which would rotate your cam pulley counterclockwise by an equal amount. This equates to about 30% of a belt tooth. Since we know that a belt tooth equates to 8.6 degrees, we now know that you have changed your cam timing by 2.58 degrees (from the nominal factory settings).
The factory alignment marks are not all that precise and I'm guessing that the third of a belt tooth that it's off is not visually evident.
Like a previous poster said, degree the thing and you will know for sure.
Pete
Using some round numbers, each tooth is 8.6 degrees, and a rough measurement of the tooth spacing shows about .380 inches center to center.
You have moved your cam and crank centerlines .115 inches closer to each other, which would rotate your cam pulley counterclockwise by an equal amount. This equates to about 30% of a belt tooth. Since we know that a belt tooth equates to 8.6 degrees, we now know that you have changed your cam timing by 2.58 degrees (from the nominal factory settings).
The factory alignment marks are not all that precise and I'm guessing that the third of a belt tooth that it's off is not visually evident.
Like a previous poster said, degree the thing and you will know for sure.
Pete
lookforjoe
True Classic
Thanks for the math lesson, Pete...
...math is NOT my forte :grin:
So, with an adjustable gear, it is indexed off the locating pin to determine 0º?
I dunno, as I said, it runs great in terms of power band, but it would be nice to tweak the cam timing for the heck of it. Maybe I'll have to invest in a gear anyway...
...math is NOT my forte :grin:
So, with an adjustable gear, it is indexed off the locating pin to determine 0º?
I dunno, as I said, it runs great in terms of power band, but it would be nice to tweak the cam timing for the heck of it. Maybe I'll have to invest in a gear anyway...
Pete Whitstone
True Classic
The one I have
Does not have any markings on it to indicate what "straight up" is. I think the idea is, if you are going to use an adjustable cam pulley, you are going to degree the motor anyway.
Pete
Does not have any markings on it to indicate what "straight up" is. I think the idea is, if you are going to use an adjustable cam pulley, you are going to degree the motor anyway.
Pete
Matt Brannon - Midwest Bayless
Mad.Matt
Milling retards the cam timing....
Hey Hussein,
To beat the horse a bit more. Any time you mill the head or cam box and shorten the distance between the crank and the camshaft, the timing becomes retarded, meaning that with crank at TDC, the mark on the cam pulley will be some position counter clockwise from the pointer.
I carefully used the term counter-clockwise. On 1500 engines, this will make the cam pulley mark "to the left of the pointer". For the 1300 crowd with the pointer on the engine mount foot, it will appear to the right of the pointer.
As Pete said, a full tooth is approximately 8 degrees of rotation, so 1/2 a tooth offset is about 4 degrees, give or take.
The stock timing marks as established by the factory with a stock cam is at split overlap. Truely neutral, intake and exhaust valves are opened the same amount. The SOHC engine actually likes a few degrees of cam advance, usually between 2-4 degrees. They really don't work well with lagging or retarded cam timing. They will free rev fine but have much diminished power. Also, they don't usually like more than 4 degrees or so of advance either.
Now, the specific amount of cam advance an engine should be set to is different from camshaft to camshaft, based on the lobe separation specs and a few other things. An engine whose cam has 106 degrees separation will behave differently than one with 108, 110 or 112 degrees, so there is no single answer to where to set cam advance.
If you have performed a slight milling, such as straightening a head by .010, or straighening a cam box and not using a thicker cam gasket to compensate, you will find your settings between 0 - 3 degrees retarded, and there is nothing you can do to correct it except for investing in a vernier adjustable wheel. If you try to reposition the cam clockwise to the next tooth, you end up between 5-8 degrees advanced and that's no bueno.
If you have taken a lot of material off the head and cam box, (oh, say about .075 head + .040 cam box surfaces), you will end up lagging about 5-6 degrees or so.
In this situation you are past the half-tooth mark of cam position change, and if you reposition the cam clockwise to the next tooth on the belt, you will be advanced 2-3 degrees, right in the sweet spot.
Now, all that said, an adjustable timing wheel is really the way to go. 1 degree or more can make a big difference. If you get out your degree wheel and calculator, you can set it up in the shop. The more exciting way to set cam timing with an adjustable wheel is to take the car to a chassis dyno. Make a couple of baseline pulls, then loosen the pulley and nudge it forward 1/2 degee, then tighten and make a pull. If you found more power, then nudge it another 1/2 degree and do it again. If the power decreased, move the wheel back a full degree and try it there. You hunt around in very small increments till you find the sweet spot, and the sweetspot will be noticeable. Then, while you're at it, you can dial in ignition timing as well.
Hope this helps.
-Matt
Hey Hussein,
To beat the horse a bit more. Any time you mill the head or cam box and shorten the distance between the crank and the camshaft, the timing becomes retarded, meaning that with crank at TDC, the mark on the cam pulley will be some position counter clockwise from the pointer.
I carefully used the term counter-clockwise. On 1500 engines, this will make the cam pulley mark "to the left of the pointer". For the 1300 crowd with the pointer on the engine mount foot, it will appear to the right of the pointer.
As Pete said, a full tooth is approximately 8 degrees of rotation, so 1/2 a tooth offset is about 4 degrees, give or take.
The stock timing marks as established by the factory with a stock cam is at split overlap. Truely neutral, intake and exhaust valves are opened the same amount. The SOHC engine actually likes a few degrees of cam advance, usually between 2-4 degrees. They really don't work well with lagging or retarded cam timing. They will free rev fine but have much diminished power. Also, they don't usually like more than 4 degrees or so of advance either.
Now, the specific amount of cam advance an engine should be set to is different from camshaft to camshaft, based on the lobe separation specs and a few other things. An engine whose cam has 106 degrees separation will behave differently than one with 108, 110 or 112 degrees, so there is no single answer to where to set cam advance.
If you have performed a slight milling, such as straightening a head by .010, or straighening a cam box and not using a thicker cam gasket to compensate, you will find your settings between 0 - 3 degrees retarded, and there is nothing you can do to correct it except for investing in a vernier adjustable wheel. If you try to reposition the cam clockwise to the next tooth, you end up between 5-8 degrees advanced and that's no bueno.
If you have taken a lot of material off the head and cam box, (oh, say about .075 head + .040 cam box surfaces), you will end up lagging about 5-6 degrees or so.
In this situation you are past the half-tooth mark of cam position change, and if you reposition the cam clockwise to the next tooth on the belt, you will be advanced 2-3 degrees, right in the sweet spot.
Now, all that said, an adjustable timing wheel is really the way to go. 1 degree or more can make a big difference. If you get out your degree wheel and calculator, you can set it up in the shop. The more exciting way to set cam timing with an adjustable wheel is to take the car to a chassis dyno. Make a couple of baseline pulls, then loosen the pulley and nudge it forward 1/2 degee, then tighten and make a pull. If you found more power, then nudge it another 1/2 degree and do it again. If the power decreased, move the wheel back a full degree and try it there. You hunt around in very small increments till you find the sweet spot, and the sweetspot will be noticeable. Then, while you're at it, you can dial in ignition timing as well.
Hope this helps.
-Matt
lookforjoe
True Classic
Thanks, Matt.
So, I'm likely running several degrees retarded now. But... it pulls very strongly over 4K. Highway driving in 4th/5th is much more pleasurable now!
When I installed the cam gear one tooth advanced initially, the engine did not idle well, it was very "lopey". Did not seem to have much top end, either.
Anyway, I'll get an adjustable gear & play with it. I don't have a degree wheel to check base cam timing, and dyno pulls around here tend to run $200+ for three pulls, so even though I've considered doing it just to get some numbers, I think I'll wait till I have played with the cam timing myself & driven it in between changes.
So, I'm likely running several degrees retarded now. But... it pulls very strongly over 4K. Highway driving in 4th/5th is much more pleasurable now!
When I installed the cam gear one tooth advanced initially, the engine did not idle well, it was very "lopey". Did not seem to have much top end, either.
Anyway, I'll get an adjustable gear & play with it. I don't have a degree wheel to check base cam timing, and dyno pulls around here tend to run $200+ for three pulls, so even though I've considered doing it just to get some numbers, I think I'll wait till I have played with the cam timing myself & driven it in between changes.
Pete Whitstone
True Classic
Matt, my math comes up with a different answer...
I come up with ~2.6 degrees retarded with a .115 cam-to-crank-centerline reduction. Can you walk me through the math that arrives at your number?
Not trying to challenge you, I would defer to your knowledge if we thought differently. Just trying to learn something.
Or are you talking crank degrees, in which case our numbers would match?
Thanks,
Pete
I come up with ~2.6 degrees retarded with a .115 cam-to-crank-centerline reduction. Can you walk me through the math that arrives at your number?
Not trying to challenge you, I would defer to your knowledge if we thought differently. Just trying to learn something.
Or are you talking crank degrees, in which case our numbers would match?
Thanks,
Pete
lookforjoe
True Classic
This arrived today....
.... now that I have the wideband, I decided it was worth playing with improving the biggest restriction on the intake side :grin:
RX7 AFM 3"
arrow indicates wheel adjuster
Tomorrow I'll install it, and see what kind of AFR's I see with it
.... now that I have the wideband, I decided it was worth playing with improving the biggest restriction on the intake side :grin:
RX7 AFM 3"
arrow indicates wheel adjuster
Tomorrow I'll install it, and see what kind of AFR's I see with it
Black-Tooth
Tony Natoli
Yur gettin' kinda sceery, Hussein!
... and that ain't even a Volvo part!
Hey... pick up the OCTOBER issue of Hot Rod when ya get a chance... featuring a Volvo 240 with an LS Chevy aboard! Nice piece of engineering!
... and that ain't even a Volvo part!
Hey... pick up the OCTOBER issue of Hot Rod when ya get a chance... featuring a Volvo 240 with an LS Chevy aboard! Nice piece of engineering!
lookforjoe
True Classic
Found this Miata thread on AFM tweaking for 1.6l
I've seen several LS implants into RWD Volvos - 'Volvette" was a high output turbo-charged 740, it was at Carlisle a couple of years ago, along with a 'vette modded to look like a P1800.. I'll check it out!
I've seen several LS implants into RWD Volvos - 'Volvette" was a high output turbo-charged 740, it was at Carlisle a couple of years ago, along with a 'vette modded to look like a P1800.. I'll check it out!
lookforjoe
True Classic
wiring between the two is different..
4th from left feeds flap track
3rd from left feeds flap track, 4th pin is for altitude pressure sensor
hard to read wiring diagram - the Fiat ones don't show current path clearly, Mazda diagram is worse!
it says connectors are viewed form harness side, but that doesn't jive with the connector..
4th from left feeds flap track
3rd from left feeds flap track, 4th pin is for altitude pressure sensor
hard to read wiring diagram - the Fiat ones don't show current path clearly, Mazda diagram is worse!
it says connectors are viewed form harness side, but that doesn't jive with the connector..
Last edited:
mx5rush
True Classic
I actually bought a RX7 AFM for my supercharged 1.6 Miata like those guys are messing with. I don't plan on putting it on till I have access to a wideband O2 sensor to play with it. I've read a bunch of threads about the Rx7 AFM swap and lots of guys totally rag it because it does require 'tweaking'... and it has been noted that they don't all respond the same. There is no set "6 clicks" rule or anything like that... Lots of good info on what your adjustments are doing, and how to correct problems, etc.
The miata site is HUGE and there is tons of good stuff there. There are so many people on there each day, you can find info on anything, automotive or not. (need to know how to set the ignition timing on your Cessna 172? Probably 3 guys on there who did that last weekend and 2 or 3 who do it for a living!!!) Seriously, I've gotten more reliable info for repairing my 91 Toyota pickup on Miata.net than on a large toyota board I go to. (bunch of fanboy kids on the toyota site!).
But, one complaint I have about miata.net forum is you'll notice if you read much is there sure are a lot of guys over there who want things to be perfect right out of the box. I guess having a typical Japanese car that you don't have to fidget with in day to day usage has spoiled them. There are a few guys who don't mind playing with the cars, but lots of them expect to put on a turbo kit and drive it like a Civic for the next 60,000 miles. Anything that doesn't perform like that often gets slammed as crap.
lookforjoe
True Classic
Thanks for the input. I found this old page yesterday, which pretty much explains that there is no way to work with the larger housing without major changes. Without a spare stock AFM to play with, I'm unwilling to dismantle my only AFM. Looking at the link, early RX7's used an AFM that is identical to that of the X, the cheapest I've found one for online is about $40.
He talks about swapping the guts from one to the other, but I would have thought the mechanism calibrated to the cfm rate, so not sure if doing that makes any sense. Rewiring would require at a minimum dropping the reference voltage signal to 5v, and dealing with the altitude sensor signal, which is not present on the later AFM. Apparently the scale values are different, but that may be due to the higher CFM rate? I dunno.
EDIT: after reviewing several diagrams - this one included....
early (same as Fiat version) followed by 86-88
39 36 6 9 8 7 27
....it seems that the major difference in terms of wiring the connector is that the reference voltage feed to the 'wiper" is reversed in the later AFM ("9"), and the signal that goes to the altitude sensor on the Bosch unit, would go to "8" in this case. So, I may be able to switch pins "9" & "8", and pins "39" & "36" (pump ground circuit) to at least give the AFM a try.
He talks about swapping the guts from one to the other, but I would have thought the mechanism calibrated to the cfm rate, so not sure if doing that makes any sense. Rewiring would require at a minimum dropping the reference voltage signal to 5v, and dealing with the altitude sensor signal, which is not present on the later AFM. Apparently the scale values are different, but that may be due to the higher CFM rate? I dunno.
EDIT: after reviewing several diagrams - this one included....
early (same as Fiat version) followed by 86-88
39 36 6 9 8 7 27
....it seems that the major difference in terms of wiring the connector is that the reference voltage feed to the 'wiper" is reversed in the later AFM ("9"), and the signal that goes to the altitude sensor on the Bosch unit, would go to "8" in this case. So, I may be able to switch pins "9" & "8", and pins "39" & "36" (pump ground circuit) to at least give the AFM a try.
Last edited:
lookforjoe
True Classic
After checking voltages at the connector both connected & disconnected from AFM, pin 9 is the reference voltage. so, the changes are internal to the (larger) AFM, not in the wiring to the AFM. I've made a plug-in 5v regulator, so I'll try connecting that & see if the larger AFM provides the appropriate signals when connected.
Key On:
Stock AFM pins:
39 -36 -- 6 -- 9 -- 8 -- 7 -- 27
12v 00v 00v 11v 00v 00v 10v AFM unplugged
12v 00v 00v 11v 6.8v 1.5v 10v AFM connected
12v 12v 00v 11v 6.8v 6.6v 10v Flap opened
Key On:
Stock AFM pins:
39 -36 -- 6 -- 9 -- 8 -- 7 -- 27
12v 00v 00v 11v 00v 00v 10v AFM unplugged
12v 00v 00v 11v 6.8v 1.5v 10v AFM connected
12v 12v 00v 11v 6.8v 6.6v 10v Flap opened
lookforjoe
True Classic
That didn't work....
,,,cos the scale it uses is reversed - closed/open throttle voltages are reversed, so I rewired the AFM to match the Bosch circuitry, which involves flipping the voltage supply & ground of the 'wiper"
desoldered pin 9 from the board
1) cut board connection of pin 8 to 6
2) moved (9) board contact to pin 6 (ground)
3) add diode to prevent feedback to ground circuit
4-5)bridge input voltage (pin 9) to pin 8 via 200ohm resistance
add shrink wrap to temp sensor connectors to prevent any potential shorts
readjust tension of wiper stop for pump cutoff (gets flaky as clock tension is relieved)
plugged it in to the harness, and checked I/O voltages
39 -36 -- 6 -- 9 -- 8 -- 7 -- 27
12v 00v 00v 11v 6.8v 1.24v 4.3v
12v 12v 00v 11v 6.8v 5.36v 4.3v open flap
pin 7 output signal range is slightly different (lower voltage), but since the resistance values are tied to the increased air flow, that makes sense, I think. I may have to tighten the clock spring to lean it out, if the lower voltages make it run too rich.
Tomorrow I should have time to remove the stock AFM & mounting bracket, and try the modded unit.
,,,cos the scale it uses is reversed
- closed/open throttle voltages are reversed, so I rewired the AFM to match the Bosch circuitry, which involves flipping the voltage supply & ground of the 'wiper"desoldered pin 9 from the board
1) cut board connection of pin 8 to 6
2) moved (9) board contact to pin 6 (ground)
3) add diode to prevent feedback to ground circuit
4-5)bridge input voltage (pin 9) to pin 8 via 200ohm resistance
add shrink wrap to temp sensor connectors to prevent any potential shorts
readjust tension of wiper stop for pump cutoff (gets flaky as clock tension is relieved)
plugged it in to the harness, and checked I/O voltages
39 -36 -- 6 -- 9 -- 8 -- 7 -- 27
12v 00v 00v 11v 6.8v 1.24v 4.3v
12v 12v 00v 11v 6.8v 5.36v 4.3v open flap
pin 7 output signal range is slightly different (lower voltage), but since the resistance values are tied to the increased air flow, that makes sense, I think. I may have to tighten the clock spring to lean it out, if the lower voltages make it run too rich.
Tomorrow I should have time to remove the stock AFM & mounting bracket, and try the modded unit.
Black-Tooth
Tony Natoli
SOOOOO... What happened???
... or aren't you back home yet?
Hope all is well!
... or aren't you back home yet?
Hope all is well!
lookforjoe
True Classic
Car runs with the modded AFM, but waaaayyy to lean. Beyond loosening the clock spring lean. I will need to revise the resistor values to make it work, or try swapping the stock circuit board over. I bought an older RX7 AFM (that has the same design circuit as ours, just NipponDenso) to try that.
Back to school now, so not sure when that will happen. Car runs great as is, just want more, of course!
Back to school now, so not sure when that will happen. Car runs great as is, just want more, of course!
ng_randolph
Bjorn H
Do you think changing the fuel pressure (adjustable FPR) would be an easier way to get the mixture you want?