Why does this car like so much timing?

[cdigerlando]

Originally Posted by oab_au

Chuck, what numbers are you looking at for the advance curve. I would reckond that it would run about 10*BTDC at idle, about 36*BTCD at full throttle/power, and probably 55/65*BTDC at a light throttle cruise. Boost pressure would reduce the advance.

What do you see?

Harvey.

Harvey:

Look at the second posting on this page

http://www.subaru-svx.net/forum/show...=25555&page=42

Look at the last map (Stg 3) Essentially I am running a map like this. I do not have the resolution though, but its a good extrapolation. I am running 30* of intitial timing at startup, which according to the listed map is too low, but close, and its as high as my software will let me go. I do go slightly above 50* where you see his curve peak. The map works. I have not pushed it at all. I'll wait for the experts and the dyno. Problem is I don't think anyone is going to want to touch a car with this much timing. We shall see.

Chuck D.

[dieingSVX]

hey chuck,

long time no talk. i quit my old job and now i'm a bartender. new hours are killing me and i've been working about everyday. that's the reason for the short pms and no responses.

you are seeing 50 degrees of timing? shouldn't you be falling off the map for timing advancment? i don't think the compression is the reason for having to run such high timing. on my cobra i was running 26-27 degrees of total timing. its also a 10:1 engine. that was on race gas to. hmm. do you think there is any way something could be hooked up wrong? iono. i'll give you a shout later tonight.

[TomsSVX]

No there is nothing wrong, the car loves timing and for some reason loves it on boost as well. It makes no real sense to anyone, but it is working really well

Tom

[cdigerlando]

Originally Posted by dieingSVX

hey chuck,

long time no talk. i quit my old job and now i'm a bartender. new hours are killing me and i've been working about everyday. that's the reason for the short pms and no responses.

you are seeing 50 degrees of timing? shouldn't you be falling off the map for timing advancment? i don't think the compression is the reason for having to run such high timing. on my cobra i was running 26-27 degrees of total timing. its also a 10:1 engine. that was on race gas to. hmm. do you think there is any way something could be hooked up wrong? iono. i'll give you a shout later tonight.

When I get done rearranging the battery and rehooking up the engine management, I'll give you a call. Better yet, I could come up your way. Got any long abandoned streches of road in Eustis? I'll show you. This time we'll be moving a lot faster. Not as fast as your Cobra though I'm afraid.

You need to check out page 42 of the stage III supercharger. I'm using a map simulated from that. It works great.

I'll talk to you soon.

[dieingSVX]

cobra's gone. the black car is nearing it's final assembly of the engine. just one more time to put it together and it will be done and ready to go back in the car. i'm not sure if i told you i dumped my huge procharger f1 for a turbo. i'm hoping to break the 1krwhp mark with my newest changes and only 22lbs to do it out a 283ci motor. here's a pic of something that is going to be hard to fit under the stock hood.



what do you think of that?

[oab_au]

Originally Posted by cdigerlando

Harvey:

Look at the second posting on this page

http://www.subaru-svx.net/forum/show...=25555&page=42

Look at the last map (Stg 3) Essentially I am running a map like this. I do not have the resolution though, but its a good extrapolation. I am running 30* of intitial timing at startup, which according to the listed map is too low, but close, and its as high as my software will let me go. I do go slightly above 50* where you see his curve peak. The map works. I have not pushed it at all. I'll wait for the experts and the dyno. Problem is I don't think anyone is going to want to touch a car with this much timing. We shall see.

Chuck D.

This map looks like a fairly normal advance map.

Hits about 34*BTDC at full throttle, which is what a combustion chamber this size would need, to achieve maximum pressure by 13/15*ATDC. As the boost pressure goes up, the advance needed is less, due to the higher pressure that increases the burn speed.

Exhaust gas temps are at their max at about 14.7:1 A/F, but are also the result of the burn time. A late burn produces high EGT.

Harvey.

[cdigerlando]

Harvey:

I don't know where you are getting 12-15*. Please explain. I am seeing about 34* at max load and max RPM. Are you familiar with the scale he is using?

Thanks

Chuck D.

[oab_au]

Originally Posted by cdigerlando

Harvey:

I don't know where you are getting 12-15*. Please explain. I am seeing about 34* at max load and max RPM. Are you familiar with the scale he is using?

Thanks

Chuck D.

Yes Chuck the maximum fully throttle advance is about 34*BTDC, and really this is the figure that is the important one.

The main objective of advancing the spark is to give time for the burning gas to heat up the air in the cylinder, so that the maximum pressure in the cylinder is developed, when the piston is about 13/15* ATDC. At this angle the pressure acting on the con rod, can turn this pressure into rotational force at the crankshaft.

If the maximum pressure is developed too early (too much advance), the con rod is too vertical, and the pressure just pushes the crank down, instead of rotating it. If it is too late( too much retard), The con rod is past the point of angularity, and the combustion chamber is growing too big to develop the maximum pressure.

So the spark advance is tied to the burn time. The burn time is affected by;
The mixture strength, lean burns longer.
Compression pressure, more pressure burns faster.
Con rod length, short rods burn faster.
Combustion chamber shape. High turbulence burns faster.

So the advance for the engine is set to the point that will have the maximum burn pressure arrive at 13/15*ATDC.

Harvey.

[cdigerlando]

Originally Posted by dieingSVX

cobra's gone. the black car is nearing it's final assembly of the engine. just one more time to put it together and it will be done and ready to go back in the car. i'm not sure if i told you i dumped my huge procharger f1 for a turbo. i'm hoping to break the 1krwhp mark with my newest changes and only 22lbs to do it out a 283ci motor. here's a pic of something that is going to be hard to fit under the stock hood.

what do you think of that?

I think I'm not going to get in your car again for fear for my life.

[dieingSVX]

what? this car is setup up right. you will have to wait and see what i'm talking about. i think you will be suprised on how well i put it together

[cdigerlando]

Originally Posted by dieingSVX

what? this car is setup up right. you will have to wait and see what i'm talking about. i think you will be suprised on how well i put it together

I'm not used to driving that fast is what I meant. I'm sure its set up well. I liked the cobra too. To bad you had to sell it. Its hard to justify multple cars. I'm still trying to convince my wife.

[Phast SVX]

Originally Posted by cdigerlando

I'm not used to driving that fast is what I meant. I'm sure its set up well. I liked the cobra too. To bad you had to sell it. Its hard to justify multple cars. I'm still trying to convince my wife.

I have the same dillema. I have always wanted to buy a supra when i graduated college, now i have secured a full time position for january but i a mgoing to be proposing to my GF in the next few months, so there goes the supra...its ok though, it would be rediculous to have 3 cars, two of which are money pits. Ill just have to focus on the SVX and not be rediculous and buy a 18-25k car that i couldnt drive very often anyways.

phil

[cdigerlando]

Originally Posted by Phast SVX

I have the same dillema. I have always wanted to buy a supra when i graduated college, now i have secured a full time position for january but i a mgoing to be proposing to my GF in the next few months, so there goes the supra...its ok though, it would be rediculous to have 3 cars, two of which are money pits. Ill just have to focus on the SVX and not be rediculous and buy a 18-25k car that i couldnt drive very often anyways.

phil

Kind of getting off topic but.....we have three cars in our family. The wife drives the '06 FXT. Its great because its safe and comfortable for her and the baby. My "justification" is that I put a lot of miles cars commuting and need a backups when I use old cars, while another is being repaired. What sucks is having to pay more in insurance when you don't drive them any more than if you had one. You know what I mean? Selling a car would not put that much money in my pocket. Especially a '92. So in my mind it's worth it. I wish the insurance company would just get their hands out of my pocket. Fortunately the only accident I have had was when I got run over on my bike. Believe it or not, in Florida, that is covered by car insurance. Is that wacked or what. I would have prefered my health insurance covered it.

[svxfiles]

Originally Posted by oab_au

Con rod length, short rods burn faster.
Combustion chamber shape. High turbulence burns faster.


Harvey.

Hi Harvey.
It's been a while.

Would you say, our engines are equipped with short length connecting rods?

And would you say we have a high turbulance combustion chamber?

[oab_au]

Originally Posted by svxfiles

Hi Harvey.
It's been a while.

Would you say, our engines are equipped with short length connecting rods?

And would you say we have a high turbulance combustion chamber?

Gid'ay Tom, yes the length of 130mm is short. 145mm would be about the norm, but they did need to keep the engine width down to fit in.
The shorter the rod, the faster the piston moves across TDC. This causes the compression space to change, through the burning phase. The longer rod keeps the combustion space, pretty much the same during the burn.

The shorter rod length, suits the high speed, high compression engine, better than the longer rod.

The ample squish area provides the turbulence that is needed to keep the burn time reducing, as the engine rpm increases, otherwise we would need to keep advancing the spark timing as the engine speed increases.

Harvey.

Shouldn't you be putting sheets up on your erection?