Can you expound on how the rest of this engine will go? Static compression ratio, what heads, intake and exhaust? Automatic? Gear ratio?
Camshafts: What effect does increased lift have on performance?
- Thread starter Kern Dog
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mopowers
Well-Known Member
I forget, what rockers were on that motor? I'd think that cam would need something more than stock stamped rockers.
Absolutely.
It appears to have been approximately .010 below deck with 5 cc valve reliefs. .020 over, stock 3.58 stroke. I don't know the exact chamber size but online sources show between 63-72 ccs for a '308 head.
The first and worst case scenario comes in at 10.52 to 1, way too high for an iron head engine on 91 octane. If the pistons were .020 below deck, it gets slightly better:
If the heads are closer to 65 ccs AND if I used a piston with an 18 cc dish, the C/R gets around where I'd feel comfortable.
I don't want to always have to run 91 octane with this car:
The Dart has a 4.10 gear SG 8.75 axle. The intake that came with this engine will go back on it.
Buried in that is the RPM Air Gap. I'll also use 1 5/8" headers and 2 1/2" pipes with an H pipe and Flowmaster mufflers.
It appears to have been approximately .010 below deck with 5 cc valve reliefs. .020 over, stock 3.58 stroke. I don't know the exact chamber size but online sources show between 63-72 ccs for a '308 head.
The first and worst case scenario comes in at 10.52 to 1, way too high for an iron head engine on 91 octane. If the pistons were .020 below deck, it gets slightly better:
If the heads are closer to 65 ccs AND if I used a piston with an 18 cc dish, the C/R gets around where I'd feel comfortable.
I don't want to always have to run 91 octane with this car:
The Dart has a 4.10 gear SG 8.75 axle. The intake that came with this engine will go back on it.
Buried in that is the RPM Air Gap. I'll also use 1 5/8" headers and 2 1/2" pipes with an H pipe and Flowmaster mufflers.
Let's dispel that myth. 10.2 isn't too high for pump gas and iron heads. I run 10.6 on premium all the time when I drive Vixen. It's all in the tune. So yeah, you can do it just fine. And not with a large by huge cam, either.
mopowers
Well-Known Member
Your 308 heads probably have 72 cc chambers. Not that I have measured a set, I gave up trying to find a set that wasn't cracked. J head chambers measured 74 to 72 cc if i am remembering correctly. With that hardware on the engine you bought I'd measure the chambers and deck measurement myself before you buy pistons. You can also adjust CR with thinner or thicker head gaskets available today.
That is true. I have really mellowed with age, and I've seriously detuned the 273. But once you've been bitten by the high performance bug you can only go back so far.
I can’t find the flow sheet this instant but my OEM Magnum heads do this. I didn’t go to .600, IIRC Between 500-600/650, it floated in the 210 area.
Valve timing events.
That nano second, is the difference between an advertised 252/.425 & a 208/.600.
The difference between a OEM .410 lift and a 252/.425 can be 5-20 hp, all things being equal, good question. The variables are to many. Interesting question. I know with rebuilt engines it has been done and tested. Steve Dulchich did this before.
Like an X coworker of mine. “.500 is big lift….”
Me: “Ummm, noooooo, I’m daily driving a .575 right now.”
Him - Mind explodes!
That cam you have circled is a fine everyday driver. I e used very similar specs on a HFT with very good results. Even in low compression 318’s that turned high 14’s in the 1/4 w/3.21 gears on stock size tires.
Holy crap...Really? That ought to be fun!
It was. Even more so the comp ratio spaced in at 7.8-1 on the 318. It also got headers, Jets exhaust, LD4B and a 600. Orange box ignition. Tires, IIRC, were BFG’s OEM size. No shift kit in the transmission, no recurved distributor. Just a cam and bolt on parts. Not to shabby. Spun a lot at the starting line at Atco NJ.
First run fresh off the road was a 15.01. Literally, I came off the highway turned in paid my fee and the guy says you better hurry up they just called but you’ll be running in. I drove directly to the study line and wait a less than five minutes. Engine was hot and toasty borderline of overheating. It was hard to start back up that day. Hot outside.
A member way back, Mike Beck, ran the same Crane HFT @216/228-.454/.480-112 in his drag on well lightened Duster into the 12’s with that cam and a well put together car.
A friend who does port work flowed my J heads whe I got done with them. Just as a favor and I didn’t get a full written report. He said he got 262 at 500 and the same at 600. I had heard that these heads don’t improve past .500. Just my experience. I put 1.6 rockers with my .484 lift Mopar Performance cam to up the lift a bit and quicken the opening. Duration at fifty as I remember is 238. My performance goal is to be respectable. Not a race car.
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Newbomb Turk
Well-Known Member
And I’m going a cam for a street car right now that will be in the .550-.560 lift range depending on the lobe.
It will be reliable and make more power than if I gave up .030ish in lift. In fact, I may look at some lobes in the .580 lift range so my net lift is closer to .550.
This nonsense that when a head breaks over you stop lifting the valve. That’s incorrect.
If more guys were flowing heads with the intake manifold on they’d learn the heads don’t break over nearly as much or not at all.
And…never mind.
Howard’s has a 266/.558 solid. 238@.05. Builds a lot of torque, but it’s over at 5400 in a 360.
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Thanks but that WAS confusing. It reminds me of the old saying....I asked him what time it was and he told me how to build a grandfather clock.
How about boiling it down to simple terms?
360 that is .040 over, 9.5 to 1 compression, stock '308 heads, RPM Air Gap intake, 1 5/8" headers and 2 1/2" exhaust.
This is a roller cam block with a Hughes 218-228 with .544 lift @ 1.6 rocker arms. I might swap back to stock stamped steel rocker arms for simplicity. That would put me back around .510 lift.
I haven't read the 4 pages worth of replies, but if you're thinking you'll gain a bunch of performance from increasing the lift, aka: like going from a 1.5 to a 1.6 ratio like a lot of guys do thinking they'll gain 30 HP it's not going to happen. Duration has far more to do with increased performance than .050" -.100" extra lift. Hanging the valve open longer is where you'll get more substantial power gains.
Tom
Tom
I have a set of 1.6 rocker arms that came with an engine that I am rebuilding. I was wondering if at my level, did the extra bit of ratio make measurable amount of power.
If not, I’d just sell off this rocker arm set.
If not, I’d just sell off this rocker arm set.
That is a damned good guess.
Last week I cc’d another ‘308 casting and came up with 72 ccs right on the nose.
Not really a guess, same as most all as cast 340/360 heads. Although most of my work was with "J" heads.
BSB67
Well-Known Member
Define measurable.
Engine dyno, probably. Well controlled track testing maybe. Street butt dyno - absolutely not.
Newbomb Turk
Well-Known Member
I was doing some testing on a 340 last week. It has a very small cam in it. Too small but it was picked for “drivability”.
Anyway, when it was last in the car we installed 1.6 rockers. With a geometry correction kit.
The cam was supposed to lash at .028/.032. I never lash anything that loose. But when the rockers went on, I did the math and it came back some big number.
So set them, against my better judgment at .028/.032 and went to the track and it was Sloooooooooooooow. I didn’t want I work on it at the track so we finished the day and left it alone.
On the dyno it was a P-I-G PIG.
I decided since it was on the dyno I’d tighten them up.
I could tell when it lit off it was much happier. Idled better, took load better. It was just better.
First pull was up 40 hp.
In this case the cam is so small that it will respond to anything that makes the cam bigger.
I killed any power gain by opening up the lash more than it should have been, regardless of what the math says.
So between the lash decrease in the lash and the 1.6 rockers it showed a nice gain.
Obvious had the cam been correct, or at least been closer the gain wouldn’t have been as big. If any.
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