1970 340. Pistons .040 out of the hole. Would u try run a closed chamber aluminum head or the X heads. Any and all input welcomed. This is for a street car that will never be raced. Thanks. Kim
To quench or no quench
- Thread starter oldkimmer
- Start date
-
I’m at that cross road now. I could go ether way.
My J/U head can go with a thin gasket and have clearance.
If I move to the Edelbrock head, it’ll just take a thicker gasket. If it is not available off the shelf then Cometic gaskets will be ordered.
Measure your piston to head distance and order the gasket with the amount of quench your needing. It will be a while before I can race the car. It Needs a lot of work. Changing parts or the engine is much like socks for me. When the socks are done for the day, off they go!
(Both heads need work. The Edelbrock should be cheaper.)
As it is now, the 340 is more for just moving it around. The rebuild was stupid cheap as it mostly falls under a spare parts build. It’s not exactly race suitable.
My J/U head can go with a thin gasket and have clearance.
If I move to the Edelbrock head, it’ll just take a thicker gasket. If it is not available off the shelf then Cometic gaskets will be ordered.
Measure your piston to head distance and order the gasket with the amount of quench your needing. It will be a while before I can race the car. It Needs a lot of work. Changing parts or the engine is much like socks for me. When the socks are done for the day, off they go!
(Both heads need work. The Edelbrock should be cheaper.)
As it is now, the 340 is more for just moving it around. The rebuild was stupid cheap as it mostly falls under a spare parts build. It’s not exactly race suitable.
C130 Chief
Mechanical Genius
So you'd need something like a .075-.080 head gasket to run closed chamber heads. You may need thicker intake gaskets as well.
Yes I was thinking there will be intake sealing problems with thick head gaskets. I’m trying to help a buddy out. Of course he has lots into this build so far so he wants it done right, but don’t spend much on it. Lol
yellow rose
Overnight Sensation
I'm still cornfused. If the piston is positive .040 and you have X heads or similar, what the issue? Why the thick gaskets? Unless the heads are milled to nothing, being .040 out is actually probably pretty good.
I have a 340 on the stand out in the shop right now, with .030 68-71 TRW replacement Pistons. Should be 10.5:1 but they never are. With a 68 CC chamber and the piston .045 out of the bore it's at a measured 10.58:1. And that's a pump gas deal. And it won't rattle. And it won't need reduced timing to run. I'm not understanding what the issue is with the piston out of the bore, unless you are dead set on using a head with a closed chamber. There are very few closed chambers I like.
He has both sets. The X are done, and he has the alum Procomps that are CNCed. He would like to run them
yellow rose
Overnight Sensation
Well that's ok then. Like I said above the easy and cheap way to get it done is .080 gaskets. And they'll seal. Or get .040 off the top of the Pistons.
The latter being more expensive and time consuming.
He says his head is hurting from everybody’s input. I told him if he wants the best to get Cometic head gaskets. Kim
Unless he plans on porting the aluminum heads, I say it's splittin hairs. In other words the unported aluminum heads ain't "that much" better than the X heads, IMO so that leaves quench as "the difference". Jus thow much difference is "THAT"?
The alum heads are CNCed
Well that makes a difference. I say use um.
Hell yea!
Wyrmrider
Well-Known Member
sure
mock it up to get the quench below .040 maybe closer to .030 if pistons do not have a lot of clearance
you will be less sensitive to timing or octane
on what yr said
open chambers can give a little more top end hp
IMHO closed chambers better for pump gas street
you have to build either right and different for best results
mock it up to get the quench below .040 maybe closer to .030 if pistons do not have a lot of clearance
you will be less sensitive to timing or octane
on what yr said
open chambers can give a little more top end hp
IMHO closed chambers better for pump gas street
you have to build either right and different for best results
FWIW, I race .100 Cometic’s without issue.
Bakerlite
Well-Known Member
- Joined
- Nov 12, 2007
- Messages
- 6,431
- Reaction score
- 3,311
Your going to have to run at least .075 head gaskets. If you trim the pistons it will make your valve reliefs shallower, which in turn may limit valve events. Closed chambers can help ward off detonation or pre ignition even if it increases the compression ratio. Same with just switching to an allot head.
yellow rose
Overnight Sensation
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
- 24,870
- Reaction score
- 12,217
Every guy who responded so far is waaay smarter than me, but no one has as yet touched on the combo.
As a streeter, Part Throttle(PT) Torque us a really big deal to me.
Back in 1998,None of the local speed-shops would get on board with me as to what I was planning. They flat-out said it wouldn't work. Everybody said 9.5 was the ceiling for best gas. But I thought to myself, how does the engine even know what static compression ratio it is operating under? So I did the homework, and figured out, that it doesn't. AND, here's the tip-off; If I had listened to those guys, then the same 9.5Scr is good for every cam-size out there, and I figured that was patently bizarre.
Since No one would help me, I figured it out myself; that D-cr was the thing to make note of, and E-cr( Effective)was what the engine was actually seeing. Which meant you can just about run whatever Scr you want to or need to to get the Ecr you are targeting. The Effective compression ratio is constantly changing with throttle-opening, rpm, and load. The only one time your engine is operating at Dcr is at WOT (with a big enough carb), and 100%VE. And if the Dcr is set right, then the engine will never care about it's Scr. So those 9.5 naysayers of 1998 can kissmyazz.
But of course there was no data available in 1998 to support my thinking, I was on my own.
Eventually I just started looking at some hotrod builds to see what the racing community was doing, and sure enough, I could back- figure the Dcrs from the data, and it soon became apparent that 8.0 to 8.2Dcr was gonna be the limit for pump gas, with iron heads. But I wasn't satisfied with 160/165 psi. I mean all the hotrodders were running around there, but was I one of them? Heck no, a street engine has a pretty easy life. And the reason I thought 160/165 psi was not for me, was that with just 165psi, the part throttle, I reasoned, would have LOW E-cr, and the fuel efficiency was gonna suffer. This was very important to me cuz I was a broke-azz young father of 3, so this hotrod was gonna have to be a DD.
So after more research, I learned that the accepted scuttlebutt was that alloy heads could run a half a point more Scr. Says who? and why? Well that led me to thinking that alloys HAD to run more pressure, cuz they were gonna shed heat faster, and heat in the chamber is power.... or at PT it's torque.So if "they" said a half a point, I interpreted it as a full point... of Dcr.... lol
Ok so now Ima thinking I'm just gonna punch it up and see what happens. If I gotta run Water-Injection, so be it.
So, I had always, as a younger man, wanted a 7000 rpm engine, so the Mopar 292/292/108 was the cam I chose.
Then,doing the Dcr calculation longhand, I figured 11.3Scr was an easy target to achieve with an .028 gasket, leaving the .039,etc for back-ups if I aimed too high. This just happened to make my Quench right where I wanted it to be with the Edelbrocks I had chosen. With the pistons down .007 plus the .028 gasket. I was at .035 bingo.
And surprise surprise, the pressure came in at over 185 psi.
And hot-damn that engine was an animal, over the top.
But for a clutched DD, I didn't really like that Mopar cam; yeah it made a lot of power over the top. But at PT I wasn't real happy with it. It didn't have the bottom-end punch I was looking for (3.55s and A833) .
I had chosen the alloys for their supposed detonation resistance. This was a wild card for me, but right outta the gate it ran on 87E10, with 34* at 3400. Eventually I ran 32@3200 detonation-free.
So now, having successfully run 185psi, but not liking the "race cam", I flipped the other way and got me a 270/276/110. For the which I took the engine apart and decked it to use the FellPro .039s, cuz the .028s were about to pop, with only one summer on them. So this fell together now at .039 Q and 10.90Scr, and the pressure was again 185. And with the 3.55s and 2.66 low gear, that was exactly what I was looking for. Again, it ran on 87E10. And with the new Hughes springs and HD lifters, she was still hitting 7000s, albeit with noticeably less power. No biggie cuz 7200 with these gears was hitting over 60mph in first gear, so I was happy .
That cam died, and was replaced with a 276/286/110, and the block decked again for .005 pop up, and the Q now at .034 ( I didn't know the limit was further down yet), but I hadn't seen any evidence of the previous Qs being too tight, so I was game.) This cam immediately showed it's colors with more topend and a little less bottom, which I expected.
Long story short;
all three cams ran about the same pressure and about the same Q, and all with the alloys.And I just gotta tell ya 180/185 psi with .034Q is great place to be, and I'm still on 87E10. Over 100,000 plus miles, those heads payed for themselves in cost of fuel difference... a long time ago, and the 270 cam pulled a lotta lotta mpgs, For that, and other reasons, it was my favorite.
So I wouldn't tell a guy to rush out and get some alloys, expecting a bunch of power. But there is waaay more to alloys than absolute power. These things, at this pressure, with just 3.55s, are amazingly potent.
But if the guy already has them, and he has a high-compression short block, and he can do the work himself.......... well then... bam I would be on it; I don't even care about porting the heads cuz the pressure and Q are gonna take care of business, and I don't care about absolute power, cuz at most it's 5 seconds and change from zero to 60mph, and the tires are gonna be spinning most of the way. So whatever the porting might bring, can you justify the cash outlay? for the occasional blast to 60?..... for the milliseconds it might shave? IDK, your call. But tires and suspension are gonna be worth more.
And the Icing on the cake is that the car went 93mph in the Eighth with this combo, which at 3467 pounds is calculated to be 433hp.
But yeah, I solved the low-rpm issue with a 3.09Commando low gear.
So somewhere in this story, you might find an answer to this question;
As a streeter, Part Throttle(PT) Torque us a really big deal to me.
Back in 1998,None of the local speed-shops would get on board with me as to what I was planning. They flat-out said it wouldn't work. Everybody said 9.5 was the ceiling for best gas. But I thought to myself, how does the engine even know what static compression ratio it is operating under? So I did the homework, and figured out, that it doesn't. AND, here's the tip-off; If I had listened to those guys, then the same 9.5Scr is good for every cam-size out there, and I figured that was patently bizarre.
Since No one would help me, I figured it out myself; that D-cr was the thing to make note of, and E-cr( Effective)was what the engine was actually seeing. Which meant you can just about run whatever Scr you want to or need to to get the Ecr you are targeting. The Effective compression ratio is constantly changing with throttle-opening, rpm, and load. The only one time your engine is operating at Dcr is at WOT (with a big enough carb), and 100%VE. And if the Dcr is set right, then the engine will never care about it's Scr. So those 9.5 naysayers of 1998 can kissmyazz.
But of course there was no data available in 1998 to support my thinking, I was on my own.
Eventually I just started looking at some hotrod builds to see what the racing community was doing, and sure enough, I could back- figure the Dcrs from the data, and it soon became apparent that 8.0 to 8.2Dcr was gonna be the limit for pump gas, with iron heads. But I wasn't satisfied with 160/165 psi. I mean all the hotrodders were running around there, but was I one of them? Heck no, a street engine has a pretty easy life. And the reason I thought 160/165 psi was not for me, was that with just 165psi, the part throttle, I reasoned, would have LOW E-cr, and the fuel efficiency was gonna suffer. This was very important to me cuz I was a broke-azz young father of 3, so this hotrod was gonna have to be a DD.
So after more research, I learned that the accepted scuttlebutt was that alloy heads could run a half a point more Scr. Says who? and why? Well that led me to thinking that alloys HAD to run more pressure, cuz they were gonna shed heat faster, and heat in the chamber is power.... or at PT it's torque.So if "they" said a half a point, I interpreted it as a full point... of Dcr.... lol
Ok so now Ima thinking I'm just gonna punch it up and see what happens. If I gotta run Water-Injection, so be it.
So, I had always, as a younger man, wanted a 7000 rpm engine, so the Mopar 292/292/108 was the cam I chose.
Then,doing the Dcr calculation longhand, I figured 11.3Scr was an easy target to achieve with an .028 gasket, leaving the .039,etc for back-ups if I aimed too high. This just happened to make my Quench right where I wanted it to be with the Edelbrocks I had chosen. With the pistons down .007 plus the .028 gasket. I was at .035 bingo.
And surprise surprise, the pressure came in at over 185 psi.
And hot-damn that engine was an animal, over the top.
But for a clutched DD, I didn't really like that Mopar cam; yeah it made a lot of power over the top. But at PT I wasn't real happy with it. It didn't have the bottom-end punch I was looking for (3.55s and A833) .
I had chosen the alloys for their supposed detonation resistance. This was a wild card for me, but right outta the gate it ran on 87E10, with 34* at 3400. Eventually I ran 32@3200 detonation-free.
So now, having successfully run 185psi, but not liking the "race cam", I flipped the other way and got me a 270/276/110. For the which I took the engine apart and decked it to use the FellPro .039s, cuz the .028s were about to pop, with only one summer on them. So this fell together now at .039 Q and 10.90Scr, and the pressure was again 185. And with the 3.55s and 2.66 low gear, that was exactly what I was looking for. Again, it ran on 87E10. And with the new Hughes springs and HD lifters, she was still hitting 7000s, albeit with noticeably less power. No biggie cuz 7200 with these gears was hitting over 60mph in first gear, so I was happy .
That cam died, and was replaced with a 276/286/110, and the block decked again for .005 pop up, and the Q now at .034 ( I didn't know the limit was further down yet), but I hadn't seen any evidence of the previous Qs being too tight, so I was game.) This cam immediately showed it's colors with more topend and a little less bottom, which I expected.
Long story short;
all three cams ran about the same pressure and about the same Q, and all with the alloys.And I just gotta tell ya 180/185 psi with .034Q is great place to be, and I'm still on 87E10. Over 100,000 plus miles, those heads payed for themselves in cost of fuel difference... a long time ago, and the 270 cam pulled a lotta lotta mpgs, For that, and other reasons, it was my favorite.
So I wouldn't tell a guy to rush out and get some alloys, expecting a bunch of power. But there is waaay more to alloys than absolute power. These things, at this pressure, with just 3.55s, are amazingly potent.
But if the guy already has them, and he has a high-compression short block, and he can do the work himself.......... well then... bam I would be on it; I don't even care about porting the heads cuz the pressure and Q are gonna take care of business, and I don't care about absolute power, cuz at most it's 5 seconds and change from zero to 60mph, and the tires are gonna be spinning most of the way. So whatever the porting might bring, can you justify the cash outlay? for the occasional blast to 60?..... for the milliseconds it might shave? IDK, your call. But tires and suspension are gonna be worth more.
And the Icing on the cake is that the car went 93mph in the Eighth with this combo, which at 3467 pounds is calculated to be 433hp.
But yeah, I solved the low-rpm issue with a 3.09Commando low gear.
So somewhere in this story, you might find an answer to this question;
If not, then sorry if I wasted your time,lol.
Last edited:
Wyrmrider
Well-Known Member
Well said
DCR and cranking compression are just tools
REmember Bruce Crower and his high compression builds with late closing cams and long expansion ratios?
lessons to be learned there
DCR and cranking compression are just tools
REmember Bruce Crower and his high compression builds with late closing cams and long expansion ratios?
lessons to be learned there
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
- 24,870
- Reaction score
- 12,217
If by long expansion ratio, you mean the "power-stroke" or I like to call it extraction duration,then;
yeah after the intake and exhaust durations are selected and
the LSA is set,
then you have a fixed number of degrees left to split between compression and power-extraction.
And it always surprises me to see a streeter sacrifice extraction for compression, when the cure is just to increase the Scr, and give up the compression degrees instead.
I mean you can get away with that, often have to, at the racetrack, but on the street once you get to a certain size cam, it just sux gas big time, on account of all the energy that goes right down the exhaust pipes. That is why I pulled the 292 cam very early on. I hadn't thought that the price of gas was about to skyrocket.
And the more I advanced it, to get the pressure, the more energy came out the back. When I noticed that (I was still learning) I even tried that cam straight up and retarded. WTH, I had 11.3 Scr to play with,lol. For me it was just the wrong choice.
It was however, a pleasure to listen to. If I couldda bagged the sound, I might made a million bucks.
yeah after the intake and exhaust durations are selected and
the LSA is set,
then you have a fixed number of degrees left to split between compression and power-extraction.
And it always surprises me to see a streeter sacrifice extraction for compression, when the cure is just to increase the Scr, and give up the compression degrees instead.
I mean you can get away with that, often have to, at the racetrack, but on the street once you get to a certain size cam, it just sux gas big time, on account of all the energy that goes right down the exhaust pipes. That is why I pulled the 292 cam very early on. I hadn't thought that the price of gas was about to skyrocket.
And the more I advanced it, to get the pressure, the more energy came out the back. When I noticed that (I was still learning) I even tried that cam straight up and retarded. WTH, I had 11.3 Scr to play with,lol. For me it was just the wrong choice.
It was however, a pleasure to listen to. If I couldda bagged the sound, I might made a million bucks.
yellow rose
Overnight Sensation
MOPAROFFICIAL
Oogliboogli
Some assume way too much. It could rattle...and no one knows if it will or wont till the cam is spec'd.
I'd run the x heads if the cam is right.
Otherwise it could rattle
I'd run the x heads if the cam is right.
Otherwise it could rattle
It a 73 Cuda 4 gear with 3.23s. An old comp 270/470 grind. LD340 intake. 650 dp Holley. May use 1.6 rockers if the stock stamped won’t work. Stock dual exhaust. likely will be getting a GearVenders OD at some point. Kim
PRH
Well-Known Member
If the short block is done, assembled, and ready to put heads on, and the CNC SM heads are the first choice....... get some .080 gaskets and forge ahead.
If the short block isn’t assembled yet, then there would be other options to explore...... budget and time permitting.
You might still decide the thick gaskets make the most sense.
If the short block isn’t assembled yet, then there would be other options to explore...... budget and time permitting.
You might still decide the thick gaskets make the most sense.
PRH
Well-Known Member
Eh....... not the best place for the cnc heads imo.
Bowl blended X’s with hardened ex seats would be a more suitable choice imo.
MOPAROFFICIAL
Oogliboogli
The more airflow available...the more chance of it rattling.
So just keep in mind that if you feel you are on the edge compression wise already... putting a high flow in head on there is going to fill it even more. You end up with the actual being more than it shows on paper.
I havent read what cc the x heads are..
But a 600 carb WILL have a restrictor plate effect on this combo and help fight against pinging. Lol
541sd .054 thick, I think, that would leave you plenty and the heads can be 68-72cc who knows.. you surely wont be hitting the heads
So just keep in mind that if you feel you are on the edge compression wise already... putting a high flow in head on there is going to fill it even more. You end up with the actual being more than it shows on paper.
I havent read what cc the x heads are..
But a 600 carb WILL have a restrictor plate effect on this combo and help fight against pinging. Lol
541sd .054 thick, I think, that would leave you plenty and the heads can be 68-72cc who knows.. you surely wont be hitting the heads
-
