Everybody talks about how you have to adjust the timing for different size engine bore but no one says anything for the long stroke engines. My engine (F23) is 3.39 Bore by 3.82 stroke and seems to like low timing. A longer stroke engine turning at 6000 rpm can have the same piston speed as a more over-square engine at 8000 rpm, so timing will obviously be different to account for the difference in piston speed in relation to rpm.

So how would you say the timing retard be applied in this case? (Long Stroke)

 

actually your stroke is 95mm (3.74in)

 

I would imagine that piston speeds on a motor with such a low R/S ratio would be awfully high at say 7k rpm, so you have to take into consideration dwell time (or lack thereof). I'd like to hear a little on this too, good question for the likes of Ben Strader

 

Bump, I am highly interested as well.

 

ttt

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by B20luda &raquo;</TD></TR><TR><TD CLASS="quote">actually your stroke is 95mm (3.74in)</TD></TR></TABLE>

No.... Actually he does have a 97mm stroke....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Sam1am26 &raquo;</TD></TR><TR><TD CLASS="quote">

No.... Actually he does have a 97mm stroke....</TD></TR></TABLE>

i also agree, the f23 has a 97mm stroke ,

this is an interesting question, what makes you say your motor likes lower timing ?

 

Because the engine detonates around 4000 rpm at 14 psi at 18 degrees BTDC.
It's 86 x 97 mm.

 

Timing should be lowest at peak torque, remember that. That timing numbers sounds about normal for that rpm even on a b series like that.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tony1 &raquo;</TD></TR><TR><TD CLASS="quote">Timing should be lowest at peak torque, remember that. That timing numbers sounds about normal for that rpm even on a b series like that.</TD></TR></TABLE>
My peak torque is at 4700rpm. The thing is, I had to get down to 11 deg at 4000rpm to stop the detonation. From 4000-6000 I give it 2 more deg. This would be way too low for a B and D engines. I do not know about H series timing since I have never done one.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VTC_ohgodnotagain_CiViC &raquo;</TD></TR><TR><TD CLASS="quote">I would imagine that piston speeds on a motor with such a low R/S ratio would be awfully high at say 7k rpm, so you have to take into consideration dwell time (or lack thereof).</TD></TR></TABLE>

Where is the relationship between piston speed and dwell time?

 

Someone...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by coocoo32 &raquo;</TD></TR><TR><TD CLASS="quote">Because the engine detonates around 4000 rpm at 14 psi at 18 degrees BTDC.
It's 86 x 97 mm.</TD></TR></TABLE>

How have you tuned the engine?

Also timing is not the only thing that cause detonation. Adding more fuel and colder spark plugs might help as well as pulling timing.

You should watch your EGT.

 

I'm not sure if I am right or wrong, but here is how I see it.

Left Cylinder = Stock Stroke
Right Cylinder = Stroke has been doubled

Black block = Piston

They are both churning at 6,000 RPM. Although the RPM is the same, the piston speed is different (It's moving about twice the speed of the stock stroke. At about .008 second, the spark plug fires and takes about .002 to burn the air/fuel mixture. Lets just say taht the left piston has "perfect timing", so right when the piston is at Top Dead Center, the air/fuel mixture is combusted completly. However, notice how the ignition timing is TOO ADVANCED on the stroked cylinder to the right. The air/fuel mixture is burning too early so the combustion will PUSH down on the piston, while the piston is still moving UP and that means bent rods or blown pistons. So the ignition timing on the stroked motor has to be retarded.

 

The whole idea that they go faster means that they start at the same time. The way you have the stroked piston startin gupward first would lead one to believe the piston speeds were the same. The piston on the right should have to travel twice the distance in the same time.

 

Great explanation, that is awesome. That pretty much explain why I could not get such high timing with the F series.

 

I think it comes down to cylinder volume filling. A big bore short stoke will be less prone to detonation because it gets out of peak pressure cylinder faster than the small bore long stoke engine even though the piston speed is faster for the long stroke at the same rpm for the two engines.

 

the higher the piston speed, the less time you have for the flame front to propagate.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TurboSmart &raquo;</TD></TR><TR><TD CLASS="quote">so right when the piston is at Top Dead Center, the air/fuel mixture is combusted completly </TD></TR></TABLE>

If that happend, you'd have problems. I don't remember the exact number off the top of my head, but its something like 40% or 60% of the mixture is burned at peak cyl. pressure, say 12-18* ATDC. I need to refresh my memory with 'the book'.

 

I just wanted to add that my timing numbers all also pretty low on my f22b2 (according to others). I'm not completely finished tuning, but I hear a tad of detonation in higher load gears (4th+) at the top of my boost (7psi currently). My engine is 85.5 bore x 95 stroke.

Although, I was doing some calcuations, and according to c-speed's calculator, my c/r is around 10.7:1 - higher than I was initially shooting for. Water injection here I come.

Btw, I run 580cc injectors

I've modified these maps a little, but was initially using the following with decent results:

 

Your timing looks a lot like mine. But in my 7.5 psi column it goes like that:

8 deg at 2100 rpm
9 at 2500
11 at 2800
12.5 at 3100
14 at 3500 and
15 at 3800.

Works very well that way.