Walter R. Malik wrote: ↑Wed Mar 06, 2019 9:30 am
Way back almost 50 years ago, there is a small tidbit in the Bill Jenkins Chevrolet book where he says, "Anytime I do something which requires me to take cam out of it, I go slower".
What is the reasoning behind that...?
Been a long time since I read his book, but likely means if you are bandaiding something with less cam, it's likely not the right direction.
But, a lot has changed in 50 years.
Like this 383,.. would it be better to just reduce duration till reversion is gone, or get rid of the other problems and add duration ?
I don't know,... maybe it's more complex than I thought,..
Or........maybe people are curious as to just what was done to get a pile parts that on paper equate to mid-11’s CR up to 13:1.
Like this 383,.. would it be better to just reduce duration till reversion is gone, or get rid of the other problems and add duration ?
I think it would have been interesting to just try and “fix” whatever was the root cause of the need for 48* timing, and then seen how that affected the power output.
But that just ends up being a science experiment.
PRH wrote: ↑Wed Mar 06, 2019 11:11 am
I think it would have been interesting to just try and “fix” whatever was the root cause of the need for 48* timing, and then seen how that affected the power output.
But that just ends up being a science experiment.
I don't think there is a single root cause for that myself.
randy331 wrote: ↑Sat Mar 02, 2019 9:30 pm
I think the main reason the timing requirements were what they were is the ex residue in the chamber. I've seen that before.
Other reasons are,.. too much piston to head clearance, the radius in seats, it had non projected tip plugs,.. the plug is/was a little recessed in the threads,..too big of headers probably contributed to the ex residue problem. I agree with melway, I think there are better chambers than this one, but they are gonna be used for now.
paulzig wrote: ↑Sat Mar 02, 2019 6:49 pm
looking for a peak HP figure at or around 7500RPM??
Not sure it will peak that high, but if it does it will make some power.
Randy
A 7500 rpm peak would put it close to 700 hp by my crude calculation.
Like this 383,.. would it be better to just reduce duration till reversion is gone, or get rid of the other problems and add duration ?
I think it would have been interesting to just try and “fix” whatever was the root cause of the need for 48* timing, and then seen how that affected the power output.
But that just ends up being a science experiment.
I would have liked to see that. But for the power and rpm range i think first things would have been wider lsa and smaller header.
Like this 383,.. would it be better to just reduce duration till reversion is gone, or get rid of the other problems and add duration ?
I think it would have been interesting to just try and “fix” whatever was the root cause of the need for 48* timing, and then seen how that affected the power output.
But that just ends up being a science experiment.
I would have liked to see that. But for the power and rpm range i think first things would have been wider lsa and smaller header.
I thought the same thing about to much overlap and no lift. I seems a cam change and porting would have been a good improvement for the original combo when first built.
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
Not ever one is on that high level that some of you think you are.
Just keep making fun of people who do not know as much as you do and pretty soon you will just be talking to yourselves. But then again sometimes I think that all some of you are doing anyway.
/rant off
By the way that "best liquid for volume measurement of cc" thread has more views than this thread.
Stan Weiss wrote: ↑Wed Mar 06, 2019 2:28 pm
rant on
Some of you are really something.
Not ever one is on that high level that some of you think you are.
Just keep making fun of people who do not know as much as you do and pretty soon you will just be talking to yourselves. But then again sometimes I think that all some of you are doing anyway.
/rant off
By the way that "best liquid for volume measurement of cc" thread has more views than this thread.
Stan
The minefield is getting easy to see. It's better to avoid it all together
I’d someone had presented the parts list for this engine to you, would any of you come to the conclusion that it would likely need 48* ignition timing?
Forget 48*....... would anyone have anticipated 42+? 40+?
For me, this is real puzzle.
I cant think of anything I’ve tested in the 29 years I’ve been doing it that wanted that much timing, and just flat out didn’t run well when the timing was set at a more “normal” place.
I realize at this point “it is what it is”, but I don’t really see anything so out of place on the build where I’d be thinking it would want(need?) that much timing to make it run well.
PRH wrote: ↑Wed Mar 06, 2019 2:55 pm
Real question.......
I’d someone had presented the parts list for this engine to you, would any of you come to the conclusion that it would likely need 48* ignition timing?
Forget 48*....... would anyone have anticipated 42+? 40+?
For me, this is real puzzle.
I cant think of anything I’ve tested in the 29 years I’ve been doing it that wanted that much timing, and just flat out didn’t run well when the timing was set at a more “normal” place.
I realize at this point “it is what it is”, but I don’t really see anything so out of place on the build where I’d be thinking it would want(need?) that much timing to make it run well.
Who else has had a similar situation?
I saw this phenomena once in an alcohol drag race engine.
It seems the the intake port caused enough swirl to send the main stream of the intake charge right across the spark plug tip causing it to need a bunch more timing.
Changing the intake port criteria was necessary to cure this.
I don't see it being a happening with gasoline.
Though, I have been witness to some strange things throughout the years.
I guess what I’m getting at is, these are pretty generic main stream parts for the most part.
It can’t be the first time someone put some Track 1’s on a 383 with SRP dome pistons.
Is it really the cam that’s causing most of the issue?
As far as “drag race” cams go, it’s not even that big, and it’s not installed with a bunch of advance.
Even though the ramps are pretty fast, the motor isn’t using high rocker ratios.
So, a more “typical” catalog bracket race cam, like what many diy type guys would end up getting(something like a Comp 12-906-9), even though having slower ramps, would have more net overlap...... and would typically be installed at about the same icl as the combo tested here.
Would we still expect it to need the 48* timing if nothing were to happen but just swapping to a more “normal” cam?
If the answer is yes....... then is the cam really the problem?
I’ve run TK lobes in iron headed Dirt 355’s with flat tops....... about 10* shorter than the one in the subject 383........ no unusual timing needed on those builds...... and they made slightly more than the 560hp that the 383 in this thread tested at.
Last edited by PRH on Wed Mar 06, 2019 3:55 pm, edited 2 times in total.
How much cam does a 383 need to go to 7500RPM peak?
Can it be done with 255 or do you need 288 @50 ... For a certain short block there has to be a point where you are controlling pressures better with 1 cam vs another. then you call a head guy, and say give me a head to suit this cam. At least they wont ask you for flowz
PRH wrote: ↑Wed Mar 06, 2019 3:49 pm
I guess what I’m getting at is, these are pretty generic main stream parts for the most part.
It can’t be the first time someone put some Track 1’s on a 383 with SRP dome pistons.
Is it really the cam that’s causing most of the issue?
As far as “drag race” cams go, it’s not even that big, and it’s not installed with a bunch of advance.
Even though the ramps are pretty fast, the motor isn’t using high rocker ratios.
So, a more “typical” catalog bracket race cam, like what many diy type guys would end up getting(something like a Comp 12-906-9), even though having slower ramps, would have more net overlap...... and would typically be installed at about the same icl as the combo tested here.
Would we still expect it to need the 48* timing if nothing were to happen but just swapping to a more “normal” cam?
If the answer is yes....... then is the cam really the problem?
I’ve run TK lobes in iron headed Dirt 355’s with flat tops....... about 10* shorter than the one in the subject 383........ no unusual timing needed on those builds...... and they made slightly more than the 560hp that the 383 in this thread tested at.
Just look at some of the original parts of the build
Headers too big
Radius V'J
High low lift flow
Close lobe centers
Brodix chamber and Dome
Slow avr inlet mach
All of that creates reversion, and lots of it, anytime you have unauthorized EGR in the chamber temps go down and ignition advance goes up in an attempt to find tq
Tom
I understand all of that, and referred to most of it in my early posts on this thread.
My point was...... this can’t be the first time this type of situation has been assembled, yet it doesn’t appear that needing 48* of timing is very common.
Certainly less common than Track 1’s with there as delivered radius valve job being used on a motor with domed pistons and a tighter lsa cam.
If it was as simple as that(radius intake seat, dome, tight lsa)...... wouldn’t needing 48* of timing be more of a common occurrence....... along with the known solution?
