To quench or no quench
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;
1970 340. Pistons .040 out of the hole. Would u try run a closed chamber aluminum head (yes I would try the alloys) or the X heads
If not, then sorry if I wasted your time,lol.
