340 Cam Size

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gabe380

gabe380

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My father-in-law has a '68 340 with about 5k on it, that he'll sell me (only me) for $2K. I'm thinking about putting it in my '67 Dart, but not sure if it's really what I want. It is currently set-up with an M-1 intake, 2.02 X-heads (w/hardened valve seats), Milodon pan, and a 508 cam. Engine has about 5k mi on it. Sounds like a fun little motor, except my car is never going to see the track. If I bought it, I'd convert it to a stock pan, LD340 with my FiTech (currently on my 318) on top, and TTI headers, mated to my 904.

It would be fun to have the lumpy idle of the 508 cam, but I'm just wondering if it would be too aggressive for street only use (also, I need enough vac for brake booster). Honestly, I'm pretty happy with my 318 (w/stock 340 cam), and having a stock converter is nice for driving in traffic. The idea for this swap only came up because next month we're adding a/c and p/s, and converting to floor shift, so it makes sense that now would be the time to swap engines - if ever. Also, I decided to go with TTI headers, and TTI says that I need their special 273/318 headers because the 340/360 headers will leak on the 318 - so if I ever wanted to swap to a 340 later, I'd need to buy headers again $$. The engine is sitting on the stand, so it makes sense that now would be the time to swap cams. Would love to hear any/all thoughts and suggestions.

Gabe
 
508 is a very mild cam ran it in one of my engines years ago nothing to worry about(was never thrilled with the performance of it..
 
go ahead and stick it in- or run a compression check on the floor/ stand and let us know
you could use the 318 headers on the 340 heads just not vice verse without plates
motor has been rebuilt undoubtedly
what pistons and what compression now
do you have specs on 508 cam?
U can always change it later after you get some benchmarks
 
508 cam is a **** cam for daily driving.
I'd do as wymrider said with checking the compression.... but so that you can transfer your 340 cam and lifters into it without detonation issues...lol

508 is not a great low end cam, you'll want something with less than 270 degrees if you really wanna daily drive with an automatic transmission. 4 spd is a diff story...
 
MOPAROFFICIAL said:
508 cam is a **** cam for daily driving.
I'd do as wymrider said with checking the compression.... but so that you can transfer your 340 cam and lifters into it without detonation issues...lol

508 is not a great low end cam, you'll want something with less than 270 degrees if you really wanna daily drive with an automatic transmission. 4 spd is a diff story...
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The cam in my 318 is the MP Purple P4452782. I was told that this is essentially a stock 340 cam...429/440, 268/276. I suppose I can just buy another one of those and a set of lifters and drop them into the 340. Won't be too awful exciting, but should be a solid runner. Thoughts?
 
gabe380 said:
The cam in my 318 is the MP Purple P4452782. I was told that this is essentially a stock 340 cam...429/440, 268/276. I suppose I can just buy another one of those and a set of lifters and drop them into the 340. Won't be too awful exciting, but should be a solid runner. Thoughts?
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It'll pull harder than the 318 by mere cubic inch and the wayyyy better X heads.
 
gabe380 said:
The cam in my 318 is the MP Purple P4452782. Thoughts?
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This cam is the general hot rod cam. Betterin largercubic inchengines. It has 2* less than the typical aftermarket [email protected] cam. It works very well with well prepped heads. Porting not needed due to low lift. Just a good valve job a bracket racer would like, that is it. Most any dual plane intake up top is good. Larger port size a favorite..... HINT HINT....Purchase a die grinder and some bits, spend 30 minutes on the intake.
A 650 carb of your favorite flavor. Headers w/2-1/2 exhaust. Works well with up to a 3.91 gear. Which is a stretch for me. 3.55's would be excellent. Or 3.73's as a max for myself.
 
I ran that 292/508 cam for one summer with an HO 367,A833/3.55s and was glad to get rid of it. It really needed 4.xx gears with my 2.66low 4 speed. I was unwilling to do that. Otherwise from 5000 on it was a great cam. It just really sucked at take off,lol. Even with the 11.3Scr I was running. Not dissing the cam so much as the combo. She really flew once wound up., the problem was, 65mph was 5500 in second, just getting on the power. Course it spun the tires all the way there,lol. Was it overkill? Heckya!
In a 340 it's gonna want a lot of cylinder pressure or a hi-stall, and forget sub-4.xx gears, unless you have an overly-high for the street, convertor. This is a lotta fun for a week or three but the novelty wears off. A combo like this, seriously limits your "streetability"...... IMO.

EDIT; My booster ran fine with the 292/108. I think it came out of a either a 77F car or a 75 Dart. But I have manual trans and tend to blip the throttle on every downshift, which keeps the rpm up, and 11/1 compression is a lot of compression braking.
 
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The 508 is a decent cam......IN ITS ELEMENT. It's true that it is a no cylinder pressure makin ****. lol BUT, with the right static compression, (a lot) and other matched components, it can and will scream. For an everyday street car, there are much better camshafts out there. But the 508 has its place.
 
RustyRatRod said:
The 508 is a decent cam......IN ITS ELEMENT. It's true that it is a no cylinder pressure makin ****. lol BUT, with the right static compression, (a lot) and other matched components, it can and will scream. For an everyday street car, there are much better camshafts out there. But the 508 has its place.
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It sounds like I'll be changing cams in the 340 if I decide to do the swap. Any recommendations on a good streetable cam that's a step up from stock?
 
gabe380 said:
It sounds like I'll be changing cams in the 340 if I decide to do the swap. Any recommendations on a good streetable cam that's a step up from stock?
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Something simple like the Comp 275DEH would be a nice choice. Old school ramps won't beat the valve train to death and it will sound good and give good power on the street.
 
See, here's the problem with asking for a cam recommendation on a forum like this........especially one this size. Everybody's got an opinion and they're ready to step up and say somebody else's is wrong, OR say they have a better recommendation. Which may or may not be true. Here's why that doesn't matter. You're not lookin for every ounce of power. Only something for the street. Not a points race car or bracket racer or any of the above. You simply want something that runs good, sounds good and will last. I answered that question. Wait till in the morning. You'll have so many people tellin you somethin different that your head will be spinnin. That's why I try to keep it simple. On a street car, driven everyday, or multiple times a week, you don't need lobe ramps so fast they pound the valves open and slam them shut. That's not the definition of a street cam. You want something easy on the valve train that will run for tens of thousands of miles reliably, be quiet doing it and be fun to drive. That 275DEH will do it. OR if you're afraid that's a little big, back down to the 265DEH, but I think you would like the 275.

Here's the 275DEH in a small block.......Chevy. Yeah, I know. LOL

 
If your engine was compression optimized for the 292cam, it could be very difficult to run a smaller cam without getting into detonation. So the first thing I would do is a compression test to get a handle on where it's at.
 
AJ/FormS said:
If your engine was compression optimized for the 292cam, it could be very difficult to run a smaller cam without getting into detonation. So the first thing I would do is a compression test to get a handle on where it's at.
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That make's sense, but would require pulling the heads to measure everything. That is more work than I honestly have time for right now, so I'll probably just pass on this motor.
 
do the cranking compression test
that 292 does have enough meat to have the intake reground shorter
or both
 
Wyrmrider said:
do the cranking compression test
that 292 does have enough meat to have the intake reground shorter
or both
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I've always been taught that there is ZERO correlation between cylinder compression (tested with a gauge in the spark plug hole) and compression ratio. In fact, changing cams (and nothing else) can result in a different reading on the pressure gauge.
 
gabe380 said:
That make's sense, but would require pulling the heads to measure everything. That is more work than I honestly have time for right now, so I'll probably just pass on this motor.
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Just run a compression test and report back with numbers.
 
gabe380 said:
I've always been taught that there is ZERO correlation between cylinder compression (tested with a gauge in the spark plug hole) and compression ratio. In fact, changing cams (and nothing else) can result in a different reading on the pressure gauge.
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That's true. However, it can tell us for instance if it has 180 PSI now, no way will a "smaller" cam work on pump gas. If it has say 120 now, then you have some "room" for a "smaller" cam.
 
[/QUOTE]
gabe380 said:
I've always been taught that there is ZERO correlation between cylinder compression (tested with a gauge in the spark plug hole) and compression ratio. In fact, changing cams (and nothing else) can result in a different reading on the pressure gauge.
Click to expand...


only partly true; it's a jumping off point.
If your gauge is accurate, and you know what elevation you are at, and what cam is in it,Then you can back-calculate the Scr within a tenth or two.
But to be accurate,you do need all three; psi, elevation, and Ica. And your results are only as accurate as your inputs.
If you don't have all three, or don't have a good calculator; then it is absolutely true.
An error in Ica maths to about just over 1psi per degree.
An error in the elevation can be 5psi per 1000 ft
An error in the gauge, well that can kill the whole deal; garbage in/garbage out.
 
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On top of ALL the other input-

-my friend put a FI TECH throttle body injection on his 355.

Before the cam was very lumpy, idle was less than desirable,
Afterthe FI Tech installation, that same camshaft idled in a very mild manner.

To it me it seemed like a 360 swallowing a moderately radical 318 camshaft.
 
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