Why so much inital timing???

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mopowers

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I've been playing with the tune on my 340 and it seems this engine for some reason likes a ton of initial timing. I've got it set at 28* now and it starts fine when hot. I've verified TDC on the balancer as well and have the total limited to 36* (which may or may not be too much).

Why does this particular engine like so much initial timing and is that an indicator of something that may be wrong? I've got the idle set at 800 in gear and it pulls 11" of vacuum.

Engine is a .030 over 340, 9.6 SCR, RHS heads, 231* @ .050"/.561" lift/108 LSA hydraulic flat tappet.

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I've been playing with the tune on my 340 and it seems this engine for some reason likes a ton of initial timing. I've got it set at 28* now and it starts fine when hot. I've verified TDC on the balancer as well and have the total limited to 36* (which may or may not be too much).

Why does this particular engine like so much initial timing and is that an indicator of something that may be wrong? I've got the idle set at 800 in gear and it pulls 11" of vacuum.

Engine is a .030 over 340, 9.6 SCR, RHS heads, 231* @ .050"/.561" lift/108 ICL hydraulic flat tappet.

View attachment 1715002382
I just built a 340 with 9.4 SCR and a 220 @ .050"camshaft, that was set at 22 initial and could have had a tad more. If it doesn't ping or start hard when hot, it isn't too much. Drag guys lock out their advance most of the time, because the engine makes the best power when at it's optimum timing number, and they are usually running enough cam to bleed off some of the cylinder pressure that causes hard starting anyway.
 
I just built a 340 with 9.4 SCR and a 220 @ .050"camshaft, that was set at 22 initial and could have had a tad more. If it doesn't ping or start hard when hot, it isn't too much. Drag guys lock out their advance most of the time, because the engine makes the best power when at it's optimum timing number, and they are usually running enough cam to bleed off some of the cylinder pressure that causes hard starting anyway.

Give the girl what she wants!
 
Because the cam is too big for the static compression. People too many times do not calculate the dynamic/cranking psi when deciding a cam and end up with less than optimal throttle response at low speeds and timing so high they may as well lock it out at full advance.
Ideally you wanna shoot for an 8.1- or better dynamic but depending on the chamber and head material try and keep at or below 8.5- 170'ish psi dynamic...however if you are experienced in tuning and building, you can run it higher like I do at 8.8 dynamic-185psi
In the future....don't stop thinking after the 10.1 compression pistons go in that its good , think about that cams intake closing, run it on a calculator , cause if you don't...you are building a dog and leaving yourself short on torque.
 
Because the cam is too big for the static compression. People too many times do not calculate the dynamic/cranking psi when deciding a cam and end up with less than optimal throttle response at low speeds and timing so high they may as well lock it out at full advance.
Ideally you wanna shoot for an 8.1- or better dynamic but depending on the chamber and head material try and keep at or below 8.5- 170'ish psi dynamic...however if you are experienced in tuning and building, you can run it higher like I do at 8.8 dynamic-185psi
In the future....don't stop thinking after the 10.1 compression pistons go in that its good , think about that cams intake closing, run it on a calculator , cause if you don't...you are building a dog and leaving yourself short on torque.

Well, considering the cam is a custom grind, I don't believe the cam is too big at all. I'll have to dig up my last compression test numbers. The motor's an absolute screamer. I can't wait to see what it does at the track. Seems to do alright on the street.
 
Well, considering the cam is a custom grind, I don't believe the cam is too big at all. I'll have to dig up my last compression test numbers. The motor's an absolute screamer. I can't wait to see what it does at the track. Seems to do alright on the street.
It's fine. I run mine at 25*/35* 9.3:1 stock 360 Magnum, 234@.050 108 LSA. Car hauls a$$. If it ever wears out I'll put a better piston in it.
 
Well, considering the cam is a custom grind, I don't believe the cam is too big at all. I'll have to dig up my last compression test numbers. The motor's an absolute screamer. I can't wait to see what it does at the track. Seems to do alright on the street.
Understand I'm not saying the cam is too big, its small actually, I'm saying the int close is killing your dynamic compression.
I'm sure its got power and a blast to drive, but its just not the best it could be.
 
It's fine. I run mine at 25*/35* 9.3:1 stock 360 Magnum, 234@.050 108 LSA. Car hauls a$$. If it ever wears out I'll put a better piston in it.
I'm sure yours runs great too, but if you need 35 degrees total under wot ...your compression is lower than it needs to be, and again...its not the best it could be.
 
Don't know who built your engines and wont knock them...because its widely known builders "knock" the cyl pressure down so Joe shmo doesn't crack rings or burn pistons and come crying about a refund.
 
I wouldn't be worried about that much initial. Give it as much initial timing as possible before any hard starting and such problems. Limit your total based on that. That gives you the best running possible. Small blocks love lots of initial timing. The less mechanical timing, the better. You seem to have done this.

I wouldn't exactly listen to moparofficial. He says your intake valve closing angle is killing your dynamic. Without actually knowing what your dynamic is. Based on the limited cam specs you gave, I'm making a guess that your IVC is somewhere from 58-60. Putting your DCR (dynamic compression ratio) a hair under 8:1 (7.98 if your LSA is 108, 7.85 if its 110). 8.5:1 is the limit for 91 pump premium on iron heads. So while yes, you could squeeze another .5 DCR out of it, in my opinion it's not worth it. That's maybe 5 horse? And when you are right on the edge like that, your tuneup better be SPOT on. And if you get a bad batch of gas from some sleezy gas station owner? Kaboom. It's a lot better to run a half point of DCR less, not worry about the whole 5 horse you lose, and not have to constantly worry about detonation. Especially on a street driven car. Especially in Cali, I hear you guys get **** gas out there.

If you got the cam card, let me know the IVC and we can calculate your DCR and see what we come up with. As for your timing? Sounds fine to me.
 
I have a mopar performance 410 CI "crate motor" purportedly built by Stanton race engines, it has a "509" purple shaft in it, alum heads....I run it at 34 total, starts fine hot, and actually runs pretty strong. I do think a modern custom solid flat tappet would run better in it, but I don't feel like opening it back up..
 
So while yes, you could squeeze another .5 DCR out of it, in my opinion it's not worth it. That's maybe 5 horse? And when you are right on the edge like that, your tuneup better be SPOT on. And if you get a bad batch of gas from some sleezy gas station owner? Kaboom. It's a lot better to run a half point of DCR less, not worry about the whole 5 horse you lose, and not have to constantly worry about detonation. Especially on a street driven car. Especially in Cali, I hear you guys get **** gas out there.

That is exactly why the shop that built the heads opened up the heads to 65 CC's to give me under 10:1 and spec'd the cam he did. I'll dig up the cam card. If I recall, IVC was around 60 ABDC, which would put the DCR near 8:1, right. That's what we were shooting for. Cam has a 108 LSA and 104 ICL. I'll happily give up a couple HP numbers to run on crappy 91 CA pump gas in the middle of summer.
 
I'm sure yours runs great too, but if you need 35 degrees total under wot ...your compression is lower than it needs to be, and again...its not the best it could be.
please explain this logic.
 
That is exactly why the shop that built the heads opened up the heads to 65 CC's to give me under 10:1 and spec'd the cam he did. I'll dig up the cam card. If I recall, IVC was around 60 ABDC, which would put the DCR near 8:1, right. That's what we were shooting for. Cam has a 108 LSA and 104 ICL. I'll happily give up a couple HP numbers to run on crappy 91 CA pump gas in the middle of summer.

Was it 104 or 108 ICL? You list 108 in your first post. I'm just curious.

Assuming your 60 is correct (and look at that, my guess was close!). Gives us:
Your dynamic compression ratio is 7.90:1 .
Your dynamic cranking pressure is 157.29 PSI.

So yeah. You COULD squeeze a little more out of it. RHS iron heads have closed chamber. Which is a big plus against detonation. And if you planned it with great quench. You could definitely run the max DCR. But once again, you'd need to stay on top of the tune. Watch timing closely. Be careful where you fill up. Etc etc. Which is fine if you're like some of us (me) and don't mind that sorta thing. But in a daily driver and average street car. It's a lot to worry about. And like I said. That shitty CA gas? One bad tank and that engine is cooked before you can turn it off. I think the setup you got is fine. And timing doesn't surprise me at all. Almost any 340 with a 230 @.050 or bigger cam is over 20 initial.
 
Was it 104 or 108 ICL? You list 108 in your first post. I'm just curious.

Assuming your 60 is correct (and look at that, my guess was close!). Gives us:
Your dynamic compression ratio is 7.90:1 .
Your dynamic cranking pressure is 157.29 PSI.

So yeah. You COULD squeeze a little more out of it. RHS iron heads have closed chamber. Which is a big plus against detonation. And if you planned it with great quench. You could definitely run the max DCR. But once again, you'd need to stay on top of the tune. Watch timing closely. Be careful where you fill up. Etc etc. Which is fine if you're like some of us (me) and don't mind that sorta thing. But in a daily driver and average street car. It's a lot to worry about. And like I said. That shitty CA gas? One bad tank and that engine is cooked before you can turn it off. I think the setup you got is fine. And timing doesn't surprise me at all. Almost any 340 with a 230 @.050 or bigger cam is over 20 initial.


I think the OP meant it was ground on a 108 LSA and has a 104 ICL.
Someday, hopefully, we will start diffentiating the two.
 
Was it 104 or 108 ICL? You list 108 in your first post. I'm just curious.

Assuming your 60 is correct (and look at that, my guess was close!). Gives us:
Your dynamic compression ratio is 7.90:1 .
Your dynamic cranking pressure is 157.29 PSI.

So yeah. You COULD squeeze a little more out of it. RHS iron heads have closed chamber. Which is a big plus against detonation. And if you planned it with great quench. You could definitely run the max DCR. But once again, you'd need to stay on top of the tune. Watch timing closely. Be careful where you fill up. Etc etc. Which is fine if you're like some of us (me) and don't mind that sorta thing. But in a daily driver and average street car. It's a lot to worry about. And like I said. That shitty CA gas? One bad tank and that engine is cooked before you can turn it off. I think the setup you got is fine. And timing doesn't surprise me at all. Almost any 340 with a 230 @.050 or bigger cam is over 20 initial.

I apologize. The cam was ground on a 108 LSA and installed at 104 ICL. I fixed the first post. Thanks for catching that.
 
I wouldn't be worried about that much initial. Give it as much initial timing as possible before any hard starting and such problems. Limit your total based on that. That gives you the best running possible. Small blocks love lots of initial timing. The less mechanical timing, the better. You seem to have done this.

I wouldn't exactly listen to moparofficial. He says your intake valve closing angle is killing your dynamic. Without actually knowing what your dynamic is. Based on the limited cam specs you gave, I'm making a guess that your IVC is somewhere from 58-60. Putting your DCR (dynamic compression ratio) a hair under 8:1 (7.98 if your LSA is 108, 7.85 if its 110). 8.5:1 is the limit for 91 pump premium on iron heads. So while yes, you could squeeze another .5 DCR out of it, in my opinion it's not worth it. That's maybe 5 horse? And when you are right on the edge like that, your tuneup better be SPOT on. And if you get a bad batch of gas from some sleezy gas station owner? Kaboom. It's a lot better to run a half point of DCR less, not worry about the whole 5 horse you lose, and not have to constantly worry about detonation. Especially on a street driven car. Especially in Cali, I hear you guys get **** gas out there.

If you got the cam card, let me know the IVC and we can calculate your DCR and see what we come up with. As for your timing? Sounds fine to me.

Whoa whoa wait a second genius, you just told the op not to listen to me , then guesstimate the same conclusion.
 
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Whoa whoa wait a second genius, you just told the op not to listen to me , then guesstimate the same conclusion.



You said he killed his DCR with that cam. I said he didn't. I guesstimated (a very educated guess, as I was right) what his IVC/DCR would be. You said his cam was too big for his setup. That he should shoot for 8:1 DCR. Guess what? He's there! You made the statement that his cam was too big, that he killed DCR with a bad IVC. Without actually bothering to figure out his DCR. That's called bad advice.
 
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I'll guess about 8.25:1 for dynamic, if the IVC is in the 60* range and a true 10:1 static compression.
 
Is IVC measured at .050" lift or something else?

IVC can be measured at any point along. Just like duration. But for best DCR calculation, you want it at the seat. This will give you the "full" angle of the intake valve closing. And the most accurate calculation. If you use IVC at .050, it's going to be a lot smaller, and give you a false DCR.
 
IVC can be measured at any point along. Just like duration. But for best DCR calculation, you want it at the seat. This will give you the "full" angle of the intake valve closing. And the most accurate calculation. If you use IVC at .050, it's going to be a lot smaller, and give you a false DCR.

I understand that. I'm just wondering what the calculators use. If they don't say, is it safe to assume they are using the "at the seat" IVC event?
 
I understand that. I'm just wondering what the calculators use. If they don't say, is it safe to assume they are using the "at the seat" IVC event?

I would think so. That will always give the best and most accurate result. IVC can be a lot different on two different cams from seat to .050. They might have the same at .050 but be different at seat. Depending on lobe shape, style, ramp rates, roller vs flat, etc etc. The cylinder starts building pressure at seat, not .050, so that's the best. Personally I use:

Wallace Racing: Dynamic Compression Ratio Calculator

And it even mentions at the top, use seat value.
 
All assuming it is a true 10.1 motor which I see no evidence of, he has no real idea for he didn't measure it himself. I bet its more like 9.5 or so, but only way to really know is by taking it apart and measuring everything.
The question was undoubtedly answered as to why he can crank up the intial so high...but yet you argue that.
You can all build how you like, or claim to at least, but don't for one minute assume you do it better than everyone else.
 
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