67 Cuda: disappointing dyno numbers, need some advice!

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72bluNblu said:
My 340 has a static compression at 9.8:1 and cranks between 175-180 on all cylinders
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....and I am sure has "lots? more camshaft than what we're talkin about "here". I thought I was actually bein kinda conservative with my number at 11:1 with his cam.

Unrelated, but the 360 I had in my 65 Valiant with the FIVE OH EIGHT 108 MP cam had 205 cranking pressure. LOL When I built it, I kept advancing it until the pressure fell off and backed it up one. I think I ended up at 101 ICL.
 
Brandt Fonda said:
awesome thanks for the responses guys, I'll get a compression gauge and see what it looks like. Based on that hughes cam is there any intake manifolds that would work well with it?
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Edelbrock Air Gap seems to be about the best for hot street setups. There are some good vintage choices such as the Holley Street Dominator you might could find at a decent price if you're on a budget. Yes, that's a single plane intake, but it loses nothing on the bottom end because of its design. It's a well known and very good vintage intake. I would find one of those before I plunked down 350 clams for the Edelbrock........but the Edelbrock IS a good piece.
 
72bluNblu said:
Yeah, I mostly agree. The biggest thing with the “swirl port” deal is that all kinds of people misapply that label anyway.

The guy that ported the 308’s for my 340 said the exhaust port floor looked better than some of the earlier heads. It wasn’t a huge difference but the 308’s did flow better on the exhaust side than the J’s.
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I agree 100%. I was just tryin to keep it simple for the sake of discussion.
 
the M1 will work good for street/strip ,why switch ? IF you gear lower and up the stall then a single plane may work better.
 
72bluNblu said:
Yeah, I mostly agree. The biggest thing with the “swirl port” deal is that all kinds of people misapply that label anyway.

The guy that ported the 308’s for my 340 said the exhaust port floor looked better than some of the earlier heads. It wasn’t a huge difference but the 308’s did flow better on the exhaust side than the J’s.



It may come to that, but a simple cranking compression check will tell you some things without tearing all the stuff down first. Like Rusty said, we know the cam, we can ballpark the cranking compression to the static.





My 340 has a static compression at 9.8:1 and cranks between 175-180 on all cylinders
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That sounds about right, my low compression 340 has 9.0 static, measured, and 160 psi.
It still runs decent for a street car.
 
fishmens67 said:
the M1 will work good for street/strip ,why switch ? IF you gear lower and up the stall then a single plane may work better.
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Yeah is that what he has now? I didn't even look. lol The M1 is a good one too. If you have it, use it.
 
fishmens67 said:
the M1 will work good for street/strip ,why switch ? IF you gear lower and up the stall then a single plane may work better.
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I thought maybe the intake was killing the HP because it is more of a torque intake? The M1 that is on it is the one from the 90's
 
RustyRatRod said:
Sounds like it's runnin outta camshaft and or valve springs. It probably is. But before you make changes, run the compression test and tell us what you come up with. We can then come up with some parts to optimize your combo if that's what you want to do. As usual, we won't all agree on what camshaft, BUT you will see a good enough pattern with our recommendations that you will be able to make a decision.
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Friend said they were good springs I don't know here is a pic:
spring.jpg


and a link to the dyno pull:
 
thesiren74 said:
How does feel on the street?
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feels ok the torque is great, pulls right off idle. But just doesn't have anything past 5100, takes for ever for the HP to peak. And the few pulls I've had against other cars have been less than impressive.
 
RustyRatRod said:
....and I am sure has "lots? more camshaft than what we're talkin about "here". I thought I was actually bein kinda conservative with my number at 11:1 with his cam.

Unrelated, but the 360 I had in my 65 Valiant with the FIVE OH EIGHT 108 MP cam had 205 cranking pressure. LOL When I built it, I kept advancing it until the pressure fell off and backed it up one. I think I ended up at 101 ICL.
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I dunno about "lots", but more. Mine's .513"/.533", advertised 276/284, duration @ .050" 234/242, 110° lobe separation, RPM 2200-6400

Calculated static is 9.8:1, dynamic with that cam is 8.2, and I still pull a couple degrees of timing to keep it happy on 91 octane in the summer with those iron 308's.

sireland67 said:
That sounds about right, my low compression 340 has 9.0 static, measured, and 160 psi.
It still runs decent for a street car.
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I would suspect that has a fairly small cam too yeah?

Brandt Fonda said:
awesome thanks for the responses guys, I'll get a compression gauge and see what it looks like. Based on that hughes cam is there any intake manifolds that would work well with it?
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Nothing wrong with the M1. I don't think you're going to find a ton of compression to warrant some big single plane intake and a big cam for a big high end number. I like the Eddy Air Gap better than the dual plane M1, but it's not a huge difference. Not worth swapping over I wouldn't think.

Brandt Fonda said:
feels ok the torque is great, pulls right off idle. But just doesn't have anything past 5100, takes for ever for the HP to peak. And the few pulls I've had against other cars have been less than impressive.
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"doesn't have anything past 5,100" is probably a few things

First, the operating range of your cam is 1,500-5,800. So, not a giant cam to expect a big top end number, it's supposed to be all in at 5,800. I'm assuming this is the MP cam you've got- .450"/.455", advertised duration 268/272, duration @ .050" 228/231, 110°. The MP cams are ok, but there are newer grinds that perform much better than the old "purple cam" grinds. I like the Lunati Voodoo cams personally, but people are funny about camshafts.

Heads are next. You still have the small valves so 1.88/1.60, plus maybe some kind of porting that might actually be hurting you. A badly ported head will flow worse than stock. "Some porting" for me is code for "some previous owner screwed around with a dremel". Maybe not. But if it was professional they usually give you a number. IE, stage II porting, flows 264 cfm @ .500", that sort of thing. And if someone payed for that they usually know what they got. Anyway, if they left the small valves in there they probably didn't do much porting either.

The valve springs are singles with dampeners. There's a few varieties with varying spring pressures, but any of the singles are going to be kinda borderline with that cam. The Lunati I listed above that I run in my 340 requires doubles and more seat pressure than any of the MP singles with dampeners can give. The video didn't sound bad like you had a ton of valve float, but they may not be helping your situation either.

Compression ratio. You obviously don't have an 11:1 static. If you put 11:1 pistons into a 360 and they sit close-ish to the deck and then you use a set of heads with 67cc chambers (which the 308's could easily be), well, your compression ratio isn't even 10:1. The 308's on my 340 are 65cc chambers after everything was done and the heads were cut, and the pistons I run are .018" proud of the deck. And I'm at 9.8:1. If you don't have a ton of compression, you don't want a bigger cam to blow off more compression.

Report back after the compression check, if it doesn't crank at 160 psi or better you're going to have some work to do if you want add a bunch of power.
 
My 2 cents FWIW.
That's pretty good numbers on a chassis dyno as yellow rose already said. It's not dying at 5300, so your shift point will be around 5600 or so..
I don't beleive an intake manifold is going to make a big change. I know you're not satisfied for your purposes which I'm guessing is mph at the track. In which case maybe a street dominator with spacers will be some help with cam and head work.

Heads. Need to have valve cuts that will help the flow. The old approach was to use the larger valves and that still works but I've seen some impressive results done with smaller diameer valves. The problem here is no one knows.

Pistons. Remove a spark plug that's easy and look in. Many times I've been able to see enough to figure out what piston is it by the shape, valve notches and numbers.

Rockers. Don't see anything to be gained here with rollers.

Timing at WOT. Timing is RPM dependent. Map this out. In other words, check and plot the timing from slow idle (hot) to at least 3000 preferable 4000 rpm. Be careful! Just need need a couple measurements at the high rpms to be sure the timing is steady or slightly climbing.

Fueling. It would be good to have the AFR plots for the dyno pulls. Mixture should stay steady when at full load.

Compression check. You'll need to crank it through at least 3, probably 4 cycles to get the reading. Throttle open is best.
 
It’s not going to be all that easy to find another 50-70 rwhp....... and you have to decide how much of that nice driveability and low end grunt you’re willing to give up to get more up top.

For “mid-300’s” at the wheels...... you’re talking about a 400hp at the crank combo.

If that’s really the goal, then I agree with pulling a head to verify the compression and overall hp potential of the heads.

If you don’t want to dig that deep into it....... cam swap, retest..... see where you’re at.

Which m1 manifold are you using now?
If it’s the aluminum dual plane that looks about like a 68-70 340 intake, I’d step up to an RPM A/G.
 
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I don't recognize the number of that cam what are the specs
If you go roller rockers you need B3's kit factor that in I also do not see a gain with 1.5 maybe some with 1.6 on the intake
IDK about a 8 degree in/ex split with the late heads and headers
the new cam has a lot more lift so check the keeper to stem seal clearance
did you describe your exhaust? any restrictions will bleed off the top end
308s a great head for the HP you have may take major work to get to 400HP
 
Wyrmrider said:
I don't recognize the number of that cam what are the specs
If you go roller rockers you need B3's kit factor that in I also do not see a gain with 1.5 maybe some with 1.6 on the intake
IDK about a 8 degree in/ex split with the late heads and headers
the new cam has a lot more lift so check the keeper to stem seal clearance
did you describe your exhaust? any restrictions will bleed off the top end
308s a great head for the HP you have may take major work to get to 400HP
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the purple cam is the old grind .450/455 268/272 , I thought with the stamped rockers I may not even be getting a full 1.5 ratio and not seeing all of current cam. My exhaust is TTI 3/4 step headers into 3" TTI X pipe into dual 3" all the way out.

PRH said:
It’s not going to be all that easy to find another 50-70 rwhp....... and you have to decide how much of that nice driveability and low end grunt you’re willing to give up to get more up top.

For “mid-300’s” at the wheels...... you’re talking about a 400hp at the crank combo.

If that’s really the goal, then I agree with pulling a head to verify the compression and overall hp potential of the heads.

If you don’t want to dig that deep into it....... cam swap, retest..... see where you’re at.

Which m1 manifold are you using now?
If it’s the aluminum dual plane that looks about like a 68-70 340 intake, I’d step up to an RPM A/G.
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it is indeed the aluminum m1 dual plane. I'm starting to see a general consensus that my heads may be sub par, though I have heard that the 308's flow better than x, j heads. The engine was built by Barnes and Reece in NC. which I have heard is a reputable builder, however they may have just put the engine together how they were asked and may or may not of ported them. ​
 
Are any of you opposed to this: put the Hughes cam in and install the roller rockers keep the M1 manifold and dyno again? If I get into reworking these heads I believe it might be better to just get some good aluminum ones.
 
Brandt Fonda said:
the purple cam is the old grind .450/455 268/272 , I thought with the stamped rockers I may not even be getting a full 1.5 ratio and not seeing all of current cam. My exhaust is TTI 3/4 step headers into 3" TTI X pipe into dual 3" all the way out.



it is indeed the aluminum m1 dual plane. I'm starting to see a general consensus that my heads may be sub par, though I have heard that the 308's flow better than x, j heads. The engine was built by Barnes and Reece in NC. which I have heard is a reputable builder, however they may have just put the engine together how they were asked and may or may not of ported them. ​
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Yeah the stamped rockers probably aren’t a true 1.5”. But a lot of them aren’t and that’s not really the issue.

308’s were a minor rework of the earlier design. Minor. On the intake side they flow almost identically to the J’s, remember the X heads had 2.02’s and the 308’s won’t beat them on the intake side with 1.88’s in stock form. On the exhaust side they flowed better than the J’s. But not amazingly better, just a little better. They had a better exhaust port design, but think along the lines of improved efficiency- not a massive rework or improvement.

308’s in stock form will not easily get you to 400 hp at the crank.

Brandt Fonda said:
Are any of you opposed to this: put the Hughes cam in and install the roller rockers keep the M1 manifold and dyno again? If I get into reworking these heads I believe it might be better to just get some good aluminum ones.
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I mean do what you want, but like I said, the first thing I’d do is a compression test. Takes 15 minutes. Otherwise you’re just throwing parts at it. If you’re weak in the compression department a new cam isn’t going to be a magic bullet.

And yes, if you need to do a full rework and port on those 308’s it’ll be even money with a new set of aluminum heads if you’re paying someone for porting.
 
Do the cam, rockers, and RPM A/G.

“If it were me”........ and I were buying rockers anyway....... I’d put a solid lifter cam in it.

Like mentioned above...... compression test first.
 
The stamped rocker ratio is right at 1.5 based on my direct measurements of the rockers alone, up to .500" lift at least, and even with the pushrod angle effects thrown in, the overall ratio is not that much below 1.5. The roller rockers per se are not going to buy you any lift.... they do nothing to change the pushrod angle effects on lift. So unless you just want the roller rockers, you'll be spending money for no effect on the present issue unless you go to 1.6 ratio ones. Plus rollers get into other issues that you are not addressing by just swapping them on, and those issues get worse with higher lift. Working on the rockers later is easy, so I would recommend setting that aside for now.

I'd do the cam alone first, but agree with others that there are other and probably better cam choices out there. I do realize that each time on the dyno costs money. But if you have some place to do your own butt dyno test with each change, you can judge each change on your own, and then go back to the dyno when you are happy with the changes.

BTW with the compression tests, prop the throttle open, pull all plugs for best cranking speed, and cycle each cylinder under test 5 or 6 times.

Valve springs are certainly non-stock but who knows what they are exactly. If someone could measure the force on one at stock installed height and some lift like .400" then the spring rate could be computed and you would have an idea what they really are. Would be a good thing to do when a head is off, if you get to that point.
 
nm9stheham said:
The stamped rocker ratio is right at 1.5 based on my direct measurements of the rockers alone, up to .500" lift at least, and even with the pushrod angle effects thrown in, the overall ratio is not that much below 1.5. The roller rockers per se are not going to buy you any lift.... they do nothing to change the pushrod angle effects on lift. So unless you just want the roller rockers, you'll be spending money for no effect on the present issue unless you go to 1.6 ratio ones. Plus rollers get into other issues that you are not addressing by just swapping them on, and those issues get worse with higher lift. Working on the rockers later is easy, so I would recommend setting that aside for now.

I'd do the cam alone first, but agree with others that there are other and probably better cam choices out there. I do realize that each time on the dyno costs money. But if you have some place to do your own butt dyno test with each change, you can judge each change on your own, and then go back to the dyno when you are happy with the changes.

BTW with the compression tests, prop the throttle open, pull all plugs for best cranking speed, and cycle each cylinder under test 5 or 6 times.

Valve springs are certainly non-stock but who knows what they are exactly. If someone could measure the force on one at stock installed height and some lift like .400" then the spring rate could be computed and you would have an idea what they really are. Would be a good thing to do when a head is off, if you get to that point.
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That’s the other thing I was gonna say. Those springs may be “ok” for the cam you have now. Maybe not, we don’t know for sure without knowing what they are.

But they will not be enough to go to a more aggressive cam. You’ll need new valve springs if you go with more cam.
 
PRH said:
Do the cam, rockers, and RPM A/G.

“If it were me”........ and I were buying rockers anyway....... I’d put a solid lifter cam in it.

Like mentioned above...... compression test first.
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^^^^^^^THIS^^^^^^^^^

Just know you are on the edge of a mighty precipice. Once you start digging into the engine it may require more than you want to do. You never know what you'll find.

You've already been told it was 11:1, and I can honestly say that I've pulled apart dozens of 10.5:1 small block Chrysler's and not one of them was over 9.8, and that 9.8 was an engine that came in my car.

Beware the pitfalls of trying to piece something together. It sounded pretty good in the video. Maybe leave it alone until you are ready to pull it and fix it all at once. 10.5:1 on pump gas is pretty easy if you can do a little tuning and get your combo correct.
 
It is a fun car and reliable atm, maybe best option is to concentrate on some other areas and save up for a crate engine from a reputable builder with build sheet and engine dyno already done.
 
The other way to approach it is...... have a couple springs tested, and(if they’re suitable) swap to a longer duration cam that will work with whatever they are....... and not buy the new rockers yet.
Cam swap & a manifold.

I def wouldn’t go to the trouble and expense of rockers, pushrods, and springs without upgrading to a solid lifter cam.
 
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