Small block combo suggestions

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Except his issues are not at wide open, unless I misread the first post. Once detonation starts it will not stop until the throttle closes down. I think it's lean at cruse and light throttle cruise, and the vacuum advance doesn't have enough preload cause of the surging. Least that's how I read it.
 
I really have to believe the single exhaust and "high performance 1967 exhaust?" is a major contributing factor.
 
If I recall correctly the 273 was the only available small block in 1967. There was the version that came with factory headers but I doubt this is the exhaust we are referring to. I cant help but think you are running small port 273 exhaust manifolds on a 360.
 
Bodyperson said:
If I recall correctly the 273 was the only available small block in 1967. There was the version that came with factory headers but I doubt this is the exhaust we are referring to. I cant help but think you are running small port 273 exhaust manifolds on a 360.
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Actually I'm running 340 hp manifolds the exhaust system is the hp exhaust from factory in 1967. And yes it's a single exhaust wt muffler and resonater
In 67 no dual exhaust offered.
The gas tank retention strap is in the way on passenger side
The top end of the engine is all six pack stuff.
 
jeff1 said:
Actually I'm running 340 hp manifolds the exhaust system is the hp exhaust from factory in 1967. And yes it's a single exhaust wt muffler and resonater
In 67 no dual exhaust offered.
The gas tank retention strap is in the way on passenger side
The top end of the engine is all six pack stuff.
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I'm curios, not to undermine all of the good information in this thread, what makes the 1967 single exhaust with resonator high performance?
 
Bodyperson said:
I'm curios, not to undermine all of the good information in this thread, what makes the 1967 single exhaust with resonator high performance?
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Not a clue it's listed like that in brochures , and by some of the exhaust vendors. Remember it was behind an almighty 273
 
jeff1 said:
Not a clue it's listed like that in brochures , and by some of the exhaust vendors. Remember it was behind an almighty 273
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and 1/3 less cubes than a 360. I cant believe this discussion has gone this far ignoring the exhaust. And are yo sure they are HP manifolds . Pretty rare.
 
Bodyperson said:
and 1/3 less cubes than a 360. I cant believe this discussion has gone this far ignoring the exhaust. And are yo sure they are HP manifolds . Pretty rare.
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And expensive I've had them for 20 plus years. Just recently had to swap out the pass side for a modified magnum manifold. If you know anyone that is really talented at old cast iron welding I have a couple that need help. Lol
 
jeff1 said:
And expensive I've had them for 20 plus years. Just recently had to swap out the pass side for a modified magnum manifold. If you know anyone that is really talented at old cast iron welding I have a couple that need help. Lol
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My people only weld "new" cast iron. LoL
 
Bodyperson said:
and 1/3 less cubes than a 360. I cant believe this discussion has gone this far ignoring the exhaust. And are yo sure they are HP manifolds . Pretty rare.
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I am not sure why exhaust would effect this knocking but am open to hear. I would expect back pressure to lower exhaust efficiency and leave more residual exhaust in the cylinders, which tends to slow the combustion process.
 
Actually, AJforms does address the exhaust concern in post number 17.
I'm not professing to be an authority here. Just an observation most others seem to be dismissing.
 
nm9stheham said:
Very interesting.... maybe tThe big cam is saving you. Which cam, SCR?
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comp 20-249-4, 306/306 260/260 .555"/.555" in at 107*. blueprinted to 11.5:1 with quench. 4.56 rear gear and 28" tire. 1.75" headers and 2.5" dual exhaust. 195 cranking psi, AVS carb, exhaust crossover blocked ld340. will ping for a second at low rpms until the revs come up if I am in too low of a trans gear, no vacuum advance
 
some people get too hung up on theory, where does like "oh, you can only run blah blah on whatever with blah blah" dcr etc. com from ? real world examples are where it is at!
 
Marcohotrod said:
comp 20-249-4, 306/306 260/260 .555"/.555" in at 107*. blueprinted to 11.5:1 with quench. 4.56 rear gear and 28" tire. 1.75" headers and 2.5" dual exhaust. 195 cranking psi, AVS carb, exhaust crossover blocked ld340. will ping for a second at low rpms until the revs come up if I am in too low of a trans gear, no vacuum advance
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Interesting... that combo comes up with a DCR of 7.95; I sure would not expect 195 psi cranking; more like 160. Buuuuut, I am sure that could be a bit higher with a large lash setting and the resulting shortened duration.
Your low RPM, high load knocking sounds like my '76 Dart Lite LOL

Edit to add: You sure the cam is not jumped a tooth advanced? I imagine not but if it was, then it would get to 190 psi cranking with your cam, etc.....
 
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8 cylinders range from 190-200 psi, lash set at recommended .022", in at 107* and with a Cloyes true double roller not jumped a tooth. this is real world, sometimes theoretical stuff is off
 
Yeah I got some pretty disappointing numbers too out of the calculator. After double-checking my work and getting the same numbers, I began hacking off duration, by the time the numbers were coming into line, the net cam duration was getting so small, I knew I was in trouble, so that's when I posted #92 my calculator quit working. I can make the calculator work @ -5000 ft altitude. Not a typo;-5000
It's funny tho, cuz it still works pretty good on my combo. It's a little shy (within 2%,or so on my gauge,lol),but I just figured my tester was a little off; that can happen after a few years.
So my obvious conclusion was Marco ain't telling us everything, or Marco really knows his stuff, and, I'm really glad I don't share track time with him,lol!

I think that Wallace calculator doesn't work with mechanical cams. That 249-4 cam specs out at 306* at .015 valve lift. And it specs out at 260* at .050. Where the valve actually closes is anybody's guess.
However, we can guess! We see that the cam takes 46* to go from .015 to .050, which is a constant rate of 46/.035= .00076 " per degree. I suppose one could extrapolate backwards .015/.00076 and get 19.73*. These degrees would need to be added to the 306, and then those degrees used up by the lash would need to be subtracted. Doing all that, I get; 306+19.73-28.95=298* as the actual seat to seat. Yeah I know, that's a best mathematical guess, and overlooks all kinds of important things. but Marco (I think it was Marco), gave us a clue a while back; He said something along the lines of, the valve lash could eat up 12* of duration, from the seat to seat. But we can only imagine the seat to seat of this cam.
Elsewhere I seem to remember that the rule of thumb when ordering a mechanical cam was to order the next size bigger cam as compared to a hydraulic. Well backtracking from the 306mechanical, the next smaller hydro cam might be a 298.
Surprise,surprise, surprise!
In this case at least, the numbers want to agree. So if we use a 298* as the theoretical seat to seat, then, in at 107, we get an intake opening angle of; 298/2-107 =42BT, and then;
180-(42 +360 -298)=76*AB, the ICA.
And with that 76* number, we can hit the Wallace, which spits out a pretty good number; 8.25Dcr/166psi in a 30over 360 @sealevel. We know this works with iron heads. We also know that 11.5Scr can be made to work with the best gas and careful manipulation of the timing,fueling,and loading.
But like I said, the only way I could get the Wallace to spit out 195psi was to input -5000 ft altitude.lol
And the 298* seat to seat cannot possibly be correct, it is pure speculation on my part. I just love math......
 
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Getting the math to work out is a good thing.... I sure don't ignore it. Figuring out why this case is so far off is a good exercise on improving knowledge IMHO.

The .022" lash is larger than the .015" lift used for advertised duration for this particular cam. So that explains part, and the 298 makes sense, but the final cranking pressure number is still pretty far off in this case. The math worked out well within 10 psi for our last build.....

Cam ramp shape with a very slow ramp around the lash point? Total Seal rings? Rhodes lifters being used a solids LOL? Reeealy goofy valvetrain geometry? Bad compression gauge?
 
Well I thought of those things too, but we both know Rocco is well beyond rookie, so I'm very interested to hear more about his recipe.
And I'm the new guy here, so there was no way I was gonna go where you went.lol
 
[Cam ramp shape with a very slow ramp around the lash point? Total Seal rings? Rhodes lifters being used a solids LOL? Reeealy goofy valvetrain geometry? Bad compression gauge?]
My guess is the 25 year old Comp cam has an average ramp, not very slow. Sealed Power rings-.018" top gap, .017" second. flat solid lifters. Harland Sharp 1.5 rockers-decent geometry. 4.06" bore, 3.48" stroke, .045" quench, 2.055" / 1.625" valves, 3200lbs. with driver, 4.56 gear, 28" tire, water temp 170-200, good gauge, compression checked every time plugs are changed-53 autolite or N9Yc-about 4 times in 20 years. no secrets
 
Marcohotrod said:
[Cam ramp shape with a very slow ramp around the lash point? Total Seal rings? Rhodes lifters being used a solids LOL? Reeealy goofy valvetrain geometry? Bad compression gauge?]
My guess is the 25 year old Comp cam has an average ramp, not very slow. Sealed Power rings-.018" top gap, .017" second. flat solid lifters. Harland Sharp 1.5 rockers-decent geometry. 4.06" bore, 3.48" stroke, .045" quench, 2.055" / 1.625" valves, 3200lbs. with driver, 4.56 gear, 28" tire, water temp 170-200, good gauge, compression checked every time plugs are changed-53 autolite or N9Yc-about 4 times in 20 years. no secrets
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How fast is this combo?
 
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