'68 4-speed cam?

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MopaRobey

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Please humor me, as I'm new here, but I've always wondered if Mopar etc. ever released the power difference from using the one year only cam in the 340? It would not be earth-shattering, but it no doubt would have made more power. Thanks
 
Never really seen anything concrete, I would guess around 5HP. The 71 340 has been considered the best in HP with the better intake and big t- quad
 
That said, it's a 46 year old cam design and cam tech has come a long way since then. Look for a modern day cam design and get more out of that motor. It what I did in my 340.
 
they kept the 340 rated at 275 hp from 68 to 71 no matter which trans you had...
 
1970Duster said:
That said, it's a 46 year old cam design and cam tech has come a long way since then. Look for a modern day cam design and get more out of that motor. It what I did in my 340.
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I asked Rick Ehrenberg of Mopar Action the same question about the 68 340 4 speed cam and he said go with a modern fast rate cam for more power and streetability instead of a 45 year old grind.

I was looking at the Comp Cams XE268H which is their modern fast ramp rate grind which is the biggest cam possible in the XE line with the factory valve springs.

What cam did you go with?
 
Are you saying you could put that 268 cam into a good engine with stock valve train and springs without any harm?
Looking for a slight extra bump in mine without doing a complete tear down.
Ron
 
scatpackbee said:
I asked Rick Ehrenberg of Mopar Action the same question about the 68 340 4 speed cam and he said go with a modern fast rate cam for more power and streetability instead of a 45 year old grind.

I was looking at the Comp Cams XE268H which is their modern fast ramp rate grind which is the biggest cam possible in the XE line with the factory valve springs.

What cam did you go with?
Click to expand...

I stuck a hyd roller cam in mine (roller cams bring you into the power curve/band sooner and keep you there long vs a flat tappet cam).
My cam specs are: @50

231in/239ex
.535"in/.550"ex
110/106 lobe
2400-6200 Rpms
Requires 3.42 or num higher rear gears and
2500 stall for autos.
 
RJS said:
Are you saying you could put that 268 cam into a doesn't haveengine with stock valve train and springs without any harm?
Looking for a slight extra bump in mine without doing a complete tear down.
Ron
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The recommended valve springs for the XE268H are very similar to the factory 340 valve spring pressures according to the CompCams catalog and the Mopar Performance Engines book, so I feel it would be a good modern cam as a replacement to a factory 340 cam.

The next cam up the XE274H requires double valve springs which the factory 340 doesn‘t have.
 
EL5DEMON340 said:
Never really seen anything concrete, I would guess around 5HP. The 71 340 has been considered the best in HP with the better intake and big t- quad
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Years ago Rick Ehrenberg wrote the 2 best 340's were the 68 4 spd and the 71 Thermoquad engines.
 
scatpackbee said:
I asked Rick Ehrenberg of Mopar Action the same question about the 68 340 4 speed cam and he said go with a modern fast rate cam for more power and streetability instead of a 45 year old grind.

I was looking at the Comp Cams XE268H which is their modern fast ramp rate grind which is the biggest cam possible in the XE line with the factory valve springs.

What cam did you go with?
Click to expand...

Much as I like Rick, he's wrong here, IMO. Faster rates of lift may equal more power, but they beat on the valve train. Those 45 year old grinds still work today. Ask any Stock or Stock Eliminator racer. Those slow rate cams are easy on the valve train and make things last a long time in a street car.
 
RJS said:
Are you saying you could put that 268 cam into a good engine with stock valve train and springs without any harm?
Looking for a slight extra bump in mine without doing a complete tear down.
Ron
Click to expand...

Yeah, on NEW factory 340 springs. I consider springs in the same way as lifters. I won't put a new cam in anything without knowing the springs are in good condition and adequate for the lift. The Comp 268 list a stronger spring than the factory 340 spring anyway. As cheap as springs are and as easy as they are to replace, there's no reason not to do it right.
 
RustyRatRod said:
Much as I like Rick, he's wrong here, IMO. Faster rates of lift may equal more power, but they beat on the valve train. Those 45 year old grinds still work today. Ask any Stock or Stock Eliminator racer. Those slow rate cams are easy on the valve train and make things last a long time in a street car.
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Agreed. Without head work, A waste unless you are a aggressive in looking for power.
 
RustyRatRod said:
Yeah, on NEW factory 340 springs. I consider springs in the same way as lifters. I won't put a new cam in anything without knowing the springs are in good condition and adequate for the lift. The Comp 268 list a stronger spring than the factory 340 spring anyway. As cheap as springs are and as easy as they are to replace, there's no reason not to do it right.
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I'm hearing you but to go one step further would you throw new springs on like I did in the old days?
By that I mean in the street with a spring compressor from KD tools and a bent screw driver to hold the valve up? No checking this and that etc...

Did that in the winter of 79-80 in my stock 400 and a 509 cam/lifter and spring package. with a 4speed and a lot of gear it ran very well.
Ron
 
They are easy on valve train because they made their power with duration and not with lift. It's the acceleration ramps on the lobes and the maximum lift that is tough on valve train parts. Back then it was a great combination for a factory built hot rod.
 
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RJS said:
I'm hearing you but to go one step further would you throw new springs on like I did in the old days?
By that I mean in the street with a spring compressor from KD tools and a bent screw driver to hold the valve up? No checking this and that etc...

Did that in the winter of 79-80 in my stock 400 and a 509 cam/lifter and spring package. with a 4speed and a lot of gear it ran very well.
Ron
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Sure, I see zero wrong with doing that at all. That's how I would do it myself. Not like you're racing for trophies, money or poontang.
 
RustyRatRod said:
Much as I like Rick, he's wrong here, IMO. Faster rates of lift may equal more power, but they beat on the valve train. Those 45 year old grinds still work today. Ask any Stock or Stock Eliminator racer. Those slow rate cams are easy on the valve train and make things last a long time in a street car.
Click to expand...


Not that I always agree with Rick E. there is no comparison if you're referring to NHRA or IHRA Stock Eliminator entries. The cams they run have much faster rates than the XE line, the Lunati line, or anything street oriented from anybody. Look at the claimer lobes and you'll see what I mean. They cannot exceed factory lift but duration is wide open and they make use of it by slamming the valve open and closing it fast while setting it on the seat without bouncing.
The '68 4sp cam is good, but "slow and steady". The OP can do a bit better, and get more driveability with something more modern. Not massive, but modern. the XE268 runs great with the Comp 901-16s which are a drop in.
 
Thanks for the replies, and additional discussion. I wasn't considering running the '68 stick, but just always wondered how much extra power it made. Believe it was 276/284 444/453, so it might come alive with 1.6 rockers; just saying..................
 
toolmanmike said:
I think the 1968- 340/4/speed cam was a 276/284-.429/.444 with a 114° lobe separation.
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No, I think that was the auto cam.


In 68 the auto cam was: .429/.444 268/276 44 O/L

the manual cam was: .444/.453 276/284 52 O/L


Then in 69 and later all 340's had the 68 auto cam.
 
toolmanmike said:
I think the 1968- 340/4/speed cam was a 276/284-.429/.444 with a 114° lobe separation. They are easy on valve train because they made their power with duration and not with lift. It's the acceleration ramps on the lobes and the maximum lift that is tough on valve train parts. Back then it was a great combination for a factory built hot rod.
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That will teach me to trust specs I learned from Moparts! lol
 
I know power wise it may not be worth much but does anyone make or could a roller cam be made around the same specs as the 68 cam? something that would sound and idle like a factory 340 but be more modern.
 
RCK850 said:
I know power wise it may not be worth much but does anyone make or could a roller cam be made around the same specs as the 68 cam? something that would sound and idle like a factory 340 but be more modern.
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yea just have them custom grind it to the specs you want
 
toolmanmike said:
That will teach me to trust specs I learned from Moparts! lol
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I looked it up in the '68 Plymouth Service Manual.


I have two original 340 cars, one '68 and one '71, both auto. I recognized those numbers as the auto cam.


I've always wanted to get a hold of an original 68 4 speed cam just to see how much different it runs from the auto cam. They say it isn't good for power brakes due to low manifold vacuum. One of my cars does have manual brakes....


Someone should contact Moparts and let them know that they have some wrong information so they can correct it.
 
krazykuda said:
Someone should contact Moparts and let them know that they have some wrong information so they can correct it.
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Yeah, like that rear end width abortion in their tech archives I've complained to the owner about for almost 10 years. They'll get right on it!
 
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