The picture clearly shows detonation damage to the piston.
340 Static Compression Numbers and Test Procedure
- Thread starter 340inabbody
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Wyrmrider
Well-Known Member
Interested in what you come up with YR
I used to find that my motors ran better when I advanced the cam and turned out I was doing what I had been doing for years- measuring down from the max lobe- or your actually better method of up from the base circle and using the printed ICL
Turns out that I was not even as advanced as the timing tags showed when measuring the .050 timing
running retarded
BOttom line today is to verify what method the cam grinder wants you to know
Now about all the quotes from old tech- I's left over from symetriclal days
Read their methods of getting correct geometry- also way out of date and note even accurate for motors were you can adjust the fulcrum height on a stud
One has one line indicating that you need to obtain a narrow witness stripe
with no clue on how to do it even on a stud rocker much less on a shaft
So hint two
ignore all advice to advance a cam unless you know it was installed incorrectly in the first place
Cheers YR
I used to find that my motors ran better when I advanced the cam and turned out I was doing what I had been doing for years- measuring down from the max lobe- or your actually better method of up from the base circle and using the printed ICL
Turns out that I was not even as advanced as the timing tags showed when measuring the .050 timing
running retarded
BOttom line today is to verify what method the cam grinder wants you to know
Now about all the quotes from old tech- I's left over from symetriclal days
Read their methods of getting correct geometry- also way out of date and note even accurate for motors were you can adjust the fulcrum height on a stud
One has one line indicating that you need to obtain a narrow witness stripe
with no clue on how to do it even on a stud rocker much less on a shaft
So hint two
ignore all advice to advance a cam unless you know it was installed incorrectly in the first place
Cheers YR
yellow rose
Overnight Sensation
7 and 8 are just pig rich. It's hard to see what WOT is with the shell on the plug.
What intake manifold is that? I'd be looking to do something to correct the fuel distribution issues you have. You have the tune for the lean cylinders, and you have two that are pretty fat.
You need to clean up the idle circuit a bit and the go after your cruise tune up. Once that's done, you can work on you WOT tuning.
Not sure what your ignition timing is and it's a bit hard to see from those pictures but it looks like you got too much total for my tastes and probably a bit too much initial.
Get a magnifying glass and look very close on the porcelain and see if there are any shiny, purple looking balls on there or in the shell. Black specs are carbon and not detonation.
Looks to me (and several others) like the Pistons have had their guts kicked out. I'm pretty sure the rings are now hammered, and any oil getting by them only adds to the detonation issue.
Time to do some very careful disassembly of your engine and see what you have. Before anything else gets ate up.
Don't have any close ups of the Plugs. Plugs are relatively new so may not be a great indicator of much. But it looks like most everyone agrees looks like detonation marks. If I correct the detonation is there any issues running the pistons as is? Clearly if I yank the motor I would replace the pistons. Was wondering if I could shim the heads to lower the compression which would be the easiest way but not sure if that would be enough to lower the count by 2 which maybe whats needed...... I have to find someone with a Whistler here in Phoenix.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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If I didn't already have alloys, I might follow you.
I built my combo for 185 with the alloys, not knowing where the ceiling was. When it burned 87E10 with no complaints, and drove like a cat on fire, I quit hunting pressure.
gzig5
Well-Known Member
If you pull it down you should be able to cut the domes off the pistons to lower compression but that will probably affect the balance of the rotating assy. So will new flattop pistons.
yellow rose
Overnight Sensation
If it didn't lift the ring lands you can still use the Pistons. They are pretty tough.
If you are going to pull the engine down, CC the heads and then measure how far the deck is either positive or negative relative to the block.
Then you need to figure out what cam you have.
Then you can start making informed decisions about what to do next.
You can mill the dome off of those Pistons. I've done it, many times. I use that piston in the engine in my car now. And I'm at 11:1 with it. And no issues. But I had a PLAN to do that before I started.
I'm not a guy who will lose my marbles if I don't have a quench distance of .035, but I also don't want a dome bigger than I need. That's why my piston is out of the bore .045 so I can get the CR I wanted with a dome that is about .187 high.
Wyrmrider
Well-Known Member
cut domes down/ off lots of times without reballancing with street rpms
heavier is worse than lighter IMHO and those are not light pistons
depends on your heads if you should run thicker gaskets
ok with stock heads but I'd work on my combination if I had wedge heads
YR and I have different applications
No quench ok if you are reved up
If around town or towing then quench is esier to live with
cheeers
heavier is worse than lighter IMHO and those are not light pistons
depends on your heads if you should run thicker gaskets
ok with stock heads but I'd work on my combination if I had wedge heads
YR and I have different applications
No quench ok if you are reved up
If around town or towing then quench is esier to live with
cheeers
yellow rose
Overnight Sensation
I have to read this in years and it's a damn shame. There is so much quality information in there I had my wife print off the entire 51 pages so I can makes notes and reference it.
I love the fact that RB explains why R/S ratio DOES make a difference, especially in induction limited applications. But IMO it makes a difference in how you select your timing events. A higher R/S ratio affects when the piston reaches max velocity and how it moves around not only BDC but TDC.
If anyone wants to gain a better understanding of cam timing, you can't beat this article.
Reading between the lines you can start to realize why there is a benefit to more agressive lobe profiles, and power output is not at the top of the list.
Thanks for the link Wyr. Great stuff.
yellow rose
Overnight Sensation
I agree. I wouldn't leave the quench at .080 or even .060 but once I get to .050 I call it good, especially on the Chrysler stuff.
I'd rather be at .040 than .060 but I wouldn't lose sleep over it. The OP has the chance to fix what he has for relatively little money and have something really cool.
I've long been a HUGE proponent of higher compression ratios for street engines. Some of the most miserable junk I've had to tune was low compression pump gas crap. Especially with a carb. To me, especially for a situation like the OP has, my minimum CR would be 10:1 and 11:1 wouldn't scare me IF the OP is willing to do the work to make it happen...like a custom cam, high quality cooling system, high end ignition system, a quality, tuneable carb and then tune the stuff.
To me, that is just cool stuff.
Again, thanks for the link Wyr.
Shrinker wrote about this and it really got my attention. The discussions you guys have been having here have really helped get a better grasp on what he was talking about.
Motorsports Village • View topic - Initial timing
Wyrmrider
Well-Known Member
Thanks YR but I just remembered the article and my link was broken some other good person posted the new link
about rod and TDC and around BDC
just the opposite of SBC and BBC and SBF which screws up us long rod people
we have been focusing on intake valve closed for Dynamic Compression
but
UD Harold thought that exhaust valve closed was more important as it controlled how much residual pressure was i n the chamber when the intake opened
dilution, reversion lots of issues
we have it much easier than the short rod engines around tdc for two reasons at least
we can close the exhaust earlier degree wise and open the intake later than a chevy for the same
result
and the max piston velocity is a few degrees later on the intake stroke
it's easier to open the intake too early and/or too quick on a mopar and stall the flow
(fast rate cam with chevy timing)
one reason to get .050 flows so you can see the overlap flows...
I try and avoid sinking the intake to kill low lift flow but..
and you know I sometimes use 30 degree seats on low lift builds but you have to BVVC as the reverse easier --the opposite of a 50 degree or sunken seat\
I think I'll start a new thread on this cam timing issue so that it;s searchable
and ask everyone to ask their camgrinder _ what do I do with this tiiming card
,050 or max lift center
about rod and TDC and around BDC
just the opposite of SBC and BBC and SBF which screws up us long rod people
we have been focusing on intake valve closed for Dynamic Compression
but
UD Harold thought that exhaust valve closed was more important as it controlled how much residual pressure was i n the chamber when the intake opened
dilution, reversion lots of issues
we have it much easier than the short rod engines around tdc for two reasons at least
we can close the exhaust earlier degree wise and open the intake later than a chevy for the same
result
and the max piston velocity is a few degrees later on the intake stroke
it's easier to open the intake too early and/or too quick on a mopar and stall the flow
(fast rate cam with chevy timing)
one reason to get .050 flows so you can see the overlap flows...
I try and avoid sinking the intake to kill low lift flow but..
and you know I sometimes use 30 degree seats on low lift builds but you have to BVVC as the reverse easier --the opposite of a 50 degree or sunken seat\
I think I'll start a new thread on this cam timing issue so that it;s searchable
and ask everyone to ask their camgrinder _ what do I do with this tiiming card
,050 or max lift center
yellow rose
Overnight Sensation
DAYUM!!!! Stuff I've been saying since I bought my first Dodge. Long rods, short strokes, tall decks, wide pan rails, higher cam placement...and more. My dad made me do the same research before buying a car that he made me do before he bought my dirt bikes.
I'll take a long Rod, short stroke deal any day. Look at a Pro Stock deal. They are pretty damn close to a 1.8:1 R/S ratio. Even with unlimited induction.
Shrinker was a right on dude.
512Stroker
We are all here because we are not all there.
That would be me.
Great paper, maybe to technical for the average Joe.
A must read for any engine builder.
MopaR&D
Nerd Member
Yes you are right but that is specifically due to the drawbacks of a typical 4-stroke gas engine running on liquid fuel. Heat is needed to vaporize and mix the fuel and air before it's burned especially in carb'd engines. If it is possible to get the fuel completely vaporized and mixed with the air inside the cylinder without using any heat you will have a much more efficient and clean-burning engine. That's why I mentioned the HCCI, in theory it uses no spark plug and compared to conventional engines has a very cold combustion with rapid but controlled burn. Basically in one of those engines the mixture is compressed to where it auto-ignites but the ignition doesn't start at one "point" (spark plug, or injector tip in a diesel), the entire mixture lights off simultaneously.
As you can probably guess the main problem with its application right now is how to control it since there is no device to initiate the combustion process and we all know how tricky and persistent uncontrolled detonation can be when you're pushing the envelope... Really tough to not make things go BOOM
Yes. If it can be done. I've had hopes on technolgy before - such as stratified injection - that didn't/couldn't be implemented widely. 
My takeaway for our stuff is that we need to get sufficient heat in at idle - especially when we've mucked up the vacuum which normally aids in partial vaporization and distribution.
Shrinker wrote alot about fuel conditions and reactions. He was always investigating, asking and learning - and sharing. I understand enough of what he wrote most of the time to get the gist. Sometimes I get a little more when I go back and read again...
here commenting on dyno testing of a 440
Motorsports Village • View topic - Dyno time
I've posted this one before
Motorsports Village • View topic - How a Wideband gets tricked to read wrong AFR
and way deep relationships of fuel, heat, pressure, products of combustion...
Motorsports Village • View topic - Timing/jetting Shrinker
One thing that I really have come to appreciate is that he tried to get us to see things from the combustion perspective, and then work back to what needs to be done. It's the totally the opposite of the way most of us got into this. We were advised 'change jets' or 'change timing' or 'add squish' etc etc. and see what happens. Shrinker says - try to understand what is happening in the cylinders and then make the changes that ought to correct the situation. I think that's what some of you guys who have worked with engine tuning alot do. But those of us who did not have to make a concious effort to think that way.
My takeaway for our stuff is that we need to get sufficient heat in at idle - especially when we've mucked up the vacuum which normally aids in partial vaporization and distribution.
Shrinker wrote alot about fuel conditions and reactions. He was always investigating, asking and learning - and sharing. I understand enough of what he wrote most of the time to get the gist. Sometimes I get a little more when I go back and read again...
here commenting on dyno testing of a 440
Motorsports Village • View topic - Dyno time
I've posted this one before
Motorsports Village • View topic - How a Wideband gets tricked to read wrong AFR
and way deep relationships of fuel, heat, pressure, products of combustion...
Motorsports Village • View topic - Timing/jetting Shrinker
One thing that I really have come to appreciate is that he tried to get us to see things from the combustion perspective, and then work back to what needs to be done. It's the totally the opposite of the way most of us got into this. We were advised 'change jets' or 'change timing' or 'add squish' etc etc. and see what happens. Shrinker says - try to understand what is happening in the cylinders and then make the changes that ought to correct the situation. I think that's what some of you guys who have worked with engine tuning alot do. But those of us who did not have to make a concious effort to think that way.
yellow rose
Overnight Sensation
I know David Vizard is a HUGE proponent of heating an intake manifold to promote vaporization, but on the other hand, he spends a ton of time on booster design and booster gain!! Contradictory in my mind.
I'm all for the most booster gain you can get (to a point...I'm still not a fan of annular boosters in a Venturi under 1.50ish inches because the signal can be hard to control. Ive also had issues with those boosters getting a hole in the fuel curve (well...a big dip) that I could never clean up.
All that to say that IMO, the best way to get a homogenous fuel/air mixture is with the booster and carb. Even with heat you'll still have wall flow when you slam the butterflies on end.
I've been running cold air intakes since 1980. I drive my junk year round. I've never iced a carb (a fear for many but I've never had it happen...yet) but I don't just hit the key and drive down the driveway on a 15 degree day. I give myself 4-5 minutes to build a bit of heat. I do that with all my junk, not just the hot rod stuff.
Followed Vizard down the rabbit hole once - that was an interesting, confusing journey. Never would have made it back out without Tuner, Shrinker, and some of the others that contributed to the Innovatemotorsports forum. DV is a good writer and smart cookie but ....
Sometimes we just got to make work what we've got. Or at least we think we do. Often we can do that messing with timing and fuel mixtures etc. That's basically what @340inabbody was hoping to do here. Get some understanding of the engine build and work around it, and tune it to work better, as good as we can.
However at some point there is a limit. Shrinker always was always saying that everything can't be fixed with fuel preparation. Build the engine 'right' and the related systems fall into place.
So that really does tie back to 340inabbody's engine. The valve events as well as the compresion, the piston and cylinder shapes etc are all related to how the fuel gasifies and burns at different rpms and loads.
The question at this point seems to be what is the best plan for @340inabbody ?
Continue on current path?
..that is, measure the cam timing events, then pull the intake and heads
..or, take the engine out.
Then do some measurements and a partial or full teardown
Sometimes we just got to make work what we've got. Or at least we think we do. Often we can do that messing with timing and fuel mixtures etc. That's basically what @340inabbody was hoping to do here. Get some understanding of the engine build and work around it, and tune it to work better, as good as we can.
However at some point there is a limit. Shrinker always was always saying that everything can't be fixed with fuel preparation. Build the engine 'right' and the related systems fall into place.
So that really does tie back to 340inabbody's engine. The valve events as well as the compresion, the piston and cylinder shapes etc are all related to how the fuel gasifies and burns at different rpms and loads.
The question at this point seems to be what is the best plan for @340inabbody ?
Continue on current path?
..that is, measure the cam timing events, then pull the intake and heads
..or, take the engine out.
Then do some measurements and a partial or full teardown
Last edited:
yellow rose
Overnight Sensation
Yes. If it can be done. I've had hopes on technolgy before - such as stratified injection - that didn't/couldn't be implemented widely.
My takeaway for our stuff is that we need to get sufficient heat in at idle - especially when we've mucked up the vacuum which normally aids in partial vaporization and distribution.
Shrinker wrote alot about fuel conditions and reactions. He was always investigating, asking and learning - and sharing. I understand enough of what he wrote most of the time to get the gist. Sometimes I get a little more when I go back and read again...
here commenting on dyno testing of a 440
Motorsports Village • View topic - Dyno time
I've posted this one before
Motorsports Village • View topic - How a Wideband gets tricked to read wrong AFR
and way deep relationships of fuel, heat, pressure, products of combustion...
Motorsports Village • View topic - Timing/jetting Shrinker
One thing that I really have come to appreciate is that he tried to get us to see things from the combustion perspective, and then work back to what needs to be done. It's the totally the opposite of the way most of us got into this. We were advised 'change jets' or 'change timing' or 'add squish' etc etc. and see what happens. Shrinker says - try to understand what is happening in the cylinders and then make the changes that ought to correct the situation. I think that's what some of you guys who have worked with engine tuning alot do. But those of us who did not have to make a concious effort to think that way.
Those are some cool links. It's amazing how some of this stuff comes about. I've known for a long time that low compression was mostly a bad thing. As Shrinker explains it, it makes more sense to me.
And as we both know, living a dying by an O2 sensor is a bad, bad way to tune. You can get lied to.
Pump gas is its own deal. Just like alcohol. Or race gas. I know pump gas is doable at 11:1 and I think I can do it at 12:1 (or I'm going to make a fool of myself).
To me, if you can get 92-93 octane pump gas, even with 10% ethanol, you should be able to do 10.5:1 even on a very mild build and be successful. And have a cleaner, more powerful engine that should be easier to tune.
Duane
Well-Known Member
Should be all in by 3000 rpm max I would think.
nm9stheham
Well-Known Member
Thanks for the links, Mattax. Last time I mentioned flame kernal on FABO, I got a hard time. I'm gonna have to bookmark those links for the future. Plenty of good things to learn are out there: flame speed; flame initiation from the kernal; lack of exhausting all the old gases and diluting the new charge simply due to having low compression ratio ('specially at lower RPM's when the exhaust pull through effects craps out); the fact that not all the O2 ever gets burned up... all these things help us to understand better.
There is so much of this type of stuff that is available online in research papers that may take a few reads to absorb, but so few take advantage of the info to help their understanding.
There is so much of this type of stuff that is available online in research papers that may take a few reads to absorb, but so few take advantage of the info to help their understanding.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Every engine is different.
The better the chamber the sooner you can bring it in.
But for what it's worth, on a streeter, I never push power timing on the engine...... cuz they always have more power than the chassis can deal with anyway. If the car is running typical 3.55s then 3000 will be about 26mph with an automatic.... and if it don't lite up the tires when you whack it open, then 2 to 4 degrees more timing is not gonna solve that little problem.
But I push real hard to get the Vcan working, to pump up the Part-Throttle power.
And the bottom line is that you only go thru that low-rpm zone once on the way to anywhere at WOT. So if the power-timing is adequate at 3600, that matters more to me then if it's a lil slow getting there.
For the life of me I can't figure out why so many guys want to force-feed power-timing on their engines.......... and/or then not run any Vcan. I mean there are times and combos that might run that way, but not a typical streeter, which is all I work on.
Guys’s Never calculated the stack up but was wondering how much compression loss could be achieved with either thick head gaskets or “shims”. Is it on the order of a point or tenths of points?
Duane
Well-Known Member
Maybe play around with the Wallace calculator. Punch in all your variables and then play with the gasket thickness to see what you get.
nm9stheham
Well-Known Member
As a rule of thumb, you can count on approximately 0.1 point loss of compression ratio for every .005" increase in head gasket thickness for these engines, in the typical compression range we run. For a specific amount of thickness increase, the changes in CR will be a more on higher compression engines and a less on low compression engines
So it would take a lot to make a whole point change. But Cometic makes these heads gaskets up at least .125" thick so it can be done. Of course, you'll quickly ruin any sort of quench/squish gap you may have had when you thicken up the head gasket.
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