340 street build help from experienced input

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Cmanhattan

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Building a 340 for my ‘69 fastback. Have a ‘69 block and crank. Srp 310725 slugs on scat rods. A833 and 3.55 gears. Want to use trickflow heads ootb at 60cc. Need cam selection help for a daily street car. Wanted a hydraulic roller utilizing 5321 morel lifters. Two cams that were researched were comp xr268hr and Howard’s 713175-10. Would love to hear about some better choices from those that have ran a similar bottom end and or those that know from more experience than I. Thanks for any and all help.
 
I use this cam with 1.6 rockers in a .030 over 360 with slugs at zero deck height and a .028 Cometic head gasket and trick flow heads. TTI exhaust stem to stern. A 904 & 3.55’s with 26 X 10 tires.
F303A0BF-A43C-48FE-8EF7-7790D890F076.jpeg
 
Cmanhattan said:
Building a 340 for my ‘69 fastback. Have a ‘69 block and crank. Srp 310725 slugs on scat rods. A833 and 3.55 gears. Want to use trickflow heads ootb at 60cc. Need cam selection help for a daily street car. Wanted a hydraulic roller utilizing 5321 morel lifters. Two cams that were researched were comp xr268hr and Howard’s 713175-10. Would love to hear about some better choices from those that have ran a similar bottom end and or those that know from more experience than I. Thanks for any and all help.
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What are the actual specs of the two cams you mentioned? It makes it easier...so imo you would get more answers.
 
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Thanks for the response. Have that cam saved as a step up from the 268. May I ask what lifters, valvetrain and pushrods you use on that setup? Thanks again, I’m using 255/60 cop wheel, 27x10 tires
 
Cmanhattan said:
Thanks for the response. Have that cam saved as a step up from the 268. May I ask what lifters, valvetrain and pushrods you use on that setup? Thanks again, I’m using 255/60 cop wheel, 27x10 tires
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Are you taking to me?
 
I understand that head is meant for more lift and am open to roller solid daily driver inputs from members ,Rusty. Moparofficial, xr268hr is 268/276 .535/.531 and Howard’s is 272/278 .525/.525. Looking for inputs and or recommendations based on the 340 short as described and members successful combos. All help is greatly appreciated.
 
Yes to rumblefish, you were kind enough to share your cam choice. Thanks and wondered what components you also utilized.
 
Welcome aboard!
Click on the button labeled “Reply” as to quote the person your conversing with.
Well, I gave my account and I used 1.6 rockers for the increased valve lift. .573/.569 lift. Stock lifters, PRW rockers, custom pushrods available from many places.
Cmanhattan said:
Yes to rumblefish, you were kind enough to share your cam choice. Thanks and wondered what components you also utilized.
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Crap... valve springs by PAC. 1.800 height installed.
I forget the part number. Sorry about that. But it’ll be easy enough to look up for yourself.

With the 3.55’s and a 27 inch tire, that thing will have long legs and pull far. You’ll have a really good top end. It’ll just take a little bit to get there. The cylinder head being very good will extend the rpm range of the cam a little bit.
 
Cmanhattan said:
I understand that head is meant for more lift and am open to roller solid daily driver inputs from members ,Rusty. Moparofficial, xr268hr is 268/276 .535/.531 and Howard’s is 272/278 .525/.525. Looking for inputs and or recommendations based on the 340 short as described and members successful combos. All help is greatly appreciated.
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I was asking merely from a power standpoint. Even with similar lift, a solid will make more power by a good margin. Just my personal observation.
 
IIRC, the problem is getting a cam that small in a solid grind. As it is slated for a street driver,
Need cam selection help for a daily street car.
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a Hyd grind is fine for this endeavor. This is why I got it for the wife’s ride. Her ‘67 Cuda is a similar build and she wanted the ability to drive it everyday without a big cam but make good street power.

The 1.6 rockers add a minor duration bump and the added lift makes it a little more intense. The car clearly pulled past the listed rpm range to approximately 6100/6200 rpm. By then, we were really picking up the mph. The drum brakes are not up to par for these speeds. LOL!!! (~SCAAAAARRYYYYYY~)
 
rumblefish360 said:
IIRC, the problem is getting a cam that small in a solid grind. As it is slated for a street driver,

a Hyd grind is fine for this endeavor. This is why I got it for the wife’s ride. Her ‘67 Cuda is a similar build and she wanted the ability to drive it everyday without a big cam but make good street power.

The 1.6 rockers add a minor duration bump and the added lift makes it a little more intense. The car clearly pulled past the listed rpm range to approximately 6100/6200 rpm. By then, we were really picking up the mph. The drum brakes are not up to par for these speeds. LOL!!! (~SCAAAAARRYYYYYY~)
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So based on your xr274hr cam choice and my tire/gear selection It’d be a bit dog off the line where a 3.91 may better suit that choice of combo?
 
A dog off line? Not really a dog.... yea, more gear is always quicker... PM coming...
 
You don't mention your exhaust system, so I will assume it is a good free flowing system. IMO, a cylinder head with a good exhaust to intake ratio like the Trick Flow, would benefit using a cam with less split in the duration between the lobes. The wider split durations favor a restrictive exhaust system, or a head with a less efficient exhaust side. I would personally call a cam grinder and have them make a recommendation based on your specific parameters. The cost is really not much more and it will be tailored to your needs. My W2 head 408 runs a hydraulic roller with a 4 degree split in the lobes. You may also consider tightening up the lobe separation angle, I assume these shelf cams are likely 110 degree LSA. I recommend taking the time to call a cam grinder like Mike Jones, or Jim Dowel. There is a lot to be learned from guys like that.
 
Cmanhattan said:
A833 and 3.55 gears.
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I checked with Wiki and she says your location is at close to 6000 ft elevation. Up there, you are gonna need some serious Compression ratio, to get some serious cylinder pressure, to get moving off the line; cuz the 69 Barracuda is kindof the Tank of A-bodies (see note-1) but with iron heads you are sorta limited to 160/165 on pump gas.
With a starter gear of 2.66 x3.55= just 9.44; and
3.55s and 27s will get you 60=5140 in 1.92 second gear, 65=5570.. This is about right for a fast-rate 224/230/110 cam; but again, you will need to keep the pressure up or get a heavy flywheel.
With an Scr of about 11.2/1, and with an Ica of 63*, the Wallace calculator is predicting that the bottom end will be similar to a 5.2M at take-off.
To get to 11.2 with a 4.06 x3.315= 42.92 cubes/703.276 swept, will require a maximum total chamber size of 703.28/(11.2-1) =68.95cc, with a Tight Quench of about .040 or a lil less. That will take care of the bottom end, but the cranking cylinder pressure is predicted to be 157psi, so getting the ignition timing exactly right might be a lil tricky. I'll say start of with 12* at idle, increasing to 28*@2800, and delaying the all-in to 34* at 3600. That will get you in the ballpark. She will want a big V-can of at least 20*
Happy hotRodding

note-1;
My 68 weighs 3450 me not in it, with an aluminum top-end and an aluminum trans case but with a GVod (advertised 23 lbs) and full-length, dual 3" exhaust (measured 72 pounds), and very light kidney-slot mags.
I ran about the same sized cam in my 360, namely
223/230/110@.008
but my 367 is pushing 180psi with alloy heads so I have bottom-end to spare. I was exceedingly happy with that set-up.
 
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cpearce said:
You don't mention your exhaust system, so I will assume it is a good free flowing system. IMO, a cylinder head with a good exhaust to intake ratio like the Trick Flow, would benefit using a cam with less split in the duration between the lobes. The wider split durations favor a restrictive exhaust system, or a head with a less efficient exhaust side. I would personally call a cam grinder and have them make a recommendation based on your specific parameters. The cost is really not much more and it will be tailored to your needs. My W2 head 408 runs a hydraulic roller with a 4 degree split in the lobes. You may also consider tightening up the lobe separation angle, I assume these shelf cams are likely 110 degree LSA. I recommend taking the time to call a cam grinder like Mike Jones, or Jim Dowel. There is a lot to be learned from guys like that.
Click to expand...
Dougs d453 1-5/8 headers to a pypes 2.5” x pipe. Lotta good info. Thanks
 
AJ/FormS said:
I checked with Wiki and she says your location is at close to 6000 ft elevation. Up there, you are gonna need some serious Compression ratio, to get some serious cylinder pressure, to get moving off the line; cuz the 69 Barracuda is kindof the Tank of A-bodies (see note-1) but with iron heads you are sorta limited to 160/165 on pump gas.
With a starter gear of 2.66 x3.55= just 9.44; and
3.55s and 27s will get you 60=5140 in 1.92 second gear, 65=5570.. This is about right for a fast-rate 224/230/110 cam; but again, you will need to keep the pressure up or get a heavy flywheel.
With an Scr of about 11.2/1, and with an Ica of 63*, the Wallace calculator is predicting that the bottom end will be similar to a 5.2M at take-off.
To get to 11.2 with a 4.06 x3.315= 42.92 cubes/703.276 swept, will require a maximum total chamber size of 703.28/(11.2-1) =68.95cc, with a Tight Quench of about .040 or a lil less. That will take care of the bottom end, but the cranking cylinder pressure is predicted to be 157psi, so getting the ignition timing exactly right might be a lil tricky. I'll say start of with 12* at idle, increasing to 28*@2800, and delaying the all-in to 34* at 3600. That will get you in the ballpark. She will want a big V-can of at least 20*
Happy hotRodding

note-1;
My 68 weighs 3450 me not in it, with an aluminum top-end and an aluminum trans case but with a GVod (advertised 23 lbs) and full-length, dual 3" exhaust (measured 72 pounds), and very light kidney-slot mags.
I ran about the same sized cam in my 360, namely
223/230/110@.008
but my 367 is pushing 180psi with alloy heads so I have bottom-end to spare. I was exceedingly happy with that set-up.
Click to expand...
Yup, sadly 6k ft here in the Springs. No air to make power. The bottom end and intended heads are 10.6:1 with 60cc trickflow heads. I am using a McLeod 22lb steel flywheel with the current 318.
 
I think either of the cams you mentioned in your initial post would be as big as you should go with TF heads. Those heads have bigger ports & 340 cubes is, well, not huge, & easy to over-cam it & convert it turd status as a daily driver.
I agree with posts that suggest a single pattern cam [ int & exh duration the same ]. It will reduce overlap & help idle/low end tq. Something in the 225-228 @ 050 range, 108-110 LSA would be good.
 
At 10.5Scr, and with an Ica of 63*, your pressure is predicted to be about 145psi and the bottom end is weaker than a 318LA. For me, this will suck with that 9.44 starter gear, all the way to at least 3000 rpm/25 mph. In Second it will suck below 35, and in third below 48, and forget passing in Fourth.
So the cures for this are More compression, A shorter Ica, or bigger rear gears.
The next smaller cam will get you about 5 psi (now 150psi)and a bottom end that feels more like a 5.2M.
2.5cc less gasket will get you 10.8 and another 5psi, now 155psi.
switching to a 108LSA cam will get you an Ica of 58*, and 158psi and a much stouter bottom end.
So if you wanna keep this cam, I highly recommend a 3.09 low gear, and probably yur gonna need 3.73s or more. But you can at least try the 3.55s (with the 3.09low), cuz I mean, the 3.09 offers 16% more torque than the 2.66.. But you will have to rev it a lil higher before shifting into second, cuz what it gains in first, it loses on the 1-2 shift. 3.73s will get you 5% back, and 3.91s would get you 10%. Do not even consider the overdrive box.

But at your altitude I would highly recommend a solid lifter tight LSA cam, to get the pressure up to 160 at least; Then you can run the 2.66x3.55.
A solid lifter cam might have longer acceleration ramps, but from when the lash is taken up to .050, tappet rise, the solid will have fewer degrees; soooo at low-rpm, she will act like a smaller cam, than the same .050 hydraulic cam. The difference could be more than six degrees in total, so on the lifting side, the Ica would be about half of that, smaller; which is good for ~5psi pressure. Which is a lot! with a minor penalty of annual lash adjustments. But the added expense of adjusters.
If you did go to solids, I suppose you could go one size bigger at .050, but at your altitude, I wouldn't. 340s were never really known for torque with the 268/276/114 factory cam, and at 6000 they would be miserable, with a predicted pressure of just 130, and take-off power like a 273. So losing pressure would be a bad thing.
 
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