Is my 340 stroked

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jim whelan

jim whelan

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My 1969 340 is 40 over, when I pulled the motor to freshen up the cylinders still had a fresh hone so I just did the heads over new gaskets painted and back in, but I did go with a new comp cam xe268h lifters rods and rockers. I just lined up the dots no dial in. Without taking the engine to far apart what is the easiest way to tell if the the crank was stroked and would that mean my cam needs to be dialed in differently. I have been fighting with timing, and carbs forever. It used to sit and spin and go sideways when it hit second now it’s just flat somewhere in the rpm range no matter what I do , plugs are always rich and I can’t ever get it to to much timing where it kicks back or is hard to start hot it just starts to drop vacuum and run worse. any direction would be great Ty guru’s
 
What carb? Need to list as much info as you can. Every piece of info about the car, transmission, rear gear.
 
i have used the XE268 cam in a warm 340. Comp say it is fine with a stock converter. I had 3.23:1 gears and 27 inch tires and found it was lazy at lo rpm. So a call to Sean at Dynamic and a new converter...problem solved. Fast forward to my current car and it is a stock 340 with a stock cam, fries the tires easily at lo rpm and pulls hard top well past highway speeds. lesson learned about cams in street driven cars. Now having said that from midrange up that 268
made unbelieveable power...where it was never used!
 
ir3333 said:
i have used the XE268 cam in a warm 340. Comp say it is fine with a stock converter. I had 3.23:1 gears and 27 inch tires and found it was lazy at lo rpm. So a call to Sean at Dynamic and a new converter...problem solved. Fast forward to my current car and it is a stock 340 with a stock cam, fries the tires easily at lo rpm and pulls hard top well past highway speeds. lesson learned about cams in street driven cars. Now having said that from midrange up that 268
made unbelieveable power...where it was never used!
Click to expand...
Agreed, and that’s part of the reason for the thread. Because if I’m giving up on this cam I want to verify a new cam is better suited to the mechanicals, do they run different cams for stroked engines? The cam I got it with was a Hughes seh2428AL-11
 
What were the specs on the original cam? i am running a stock converter and 25.8" tires. Big rear tires make a difference too. You may have some tuning issues but i had difficulty cleaning up the idle with that 268 cam, with 224
and 230 duration.
Stroking a 340 to 416 will make way too much lo end torque for the street unless burnouts are your thing. Having said that, the hobby is different for everybody.
I like lots of lo and midrange power, quiet exhaust, smooth idle and 20mpg. There, i said it!
 
well...stoke your 340 to 416, put in a high lift short duration cam and .410 gears! It'll be
like driving on ice!
 
jim whelan said:
My 1969 340 is 40 over, when I pulled the motor to freshen up the cylinders still had a fresh hone so I just did the heads over new gaskets painted and back in, but I did go with a new comp cam xe268h lifters rods and rockers. I just lined up the dots no dial in. Without taking the engine to far apart what is the easiest way to tell if the the crank was stroked and would that mean my cam needs to be dialed in differently. I have been fighting with timing, and carbs forever. It used to sit and spin and go sideways when it hit second now it’s just flat somewhere in the rpm range no matter what I do , plugs are always rich and I can’t ever get it to to much timing where it kicks back or is hard to start hot it just starts to drop vacuum and run worse. any direction would be great Ty guru’s
Click to expand...
Is it stroked? You will need to measure the stroke length. Stock stroke (from top dead center to bottom dead center) is 3.310". Most (most stroked small block Mopars have a 4" stroke.
 
toolmanmike said:
Is it stroked? You will need to measure the stroke length. Stock stroke (from top dead center to bottom dead center) is 3.310". Most (most stroked small block Mopars have a 4" stroke.
Click to expand...
Thank you, is this measurable thru the plug hole ? Possibly? And would that change the cam set up?
 
jim whelan said:
Thank you, is this measurable thru the plug hole ? Possibly? And would that change the cam set up?
Click to expand...
May be with a thin tape measure. It doesn't need to be exact but there is a difference between the two measurements. Starting at deck height would be the tricky part. I would bet it's a stock stroke. It would change the cam needs because of the increase in cubic inches. by 75+
 
So you have the engine out and somewhat disassembled and are still not going to degree the cam. Alrighty then.
 
RustyRatRod said:
That wasn't my point. I was trying to point out how important it is to do.
Click to expand...
Ok yes, I got that now I should have measured the stroke as well. I’m just another example of why you shouldn’t rush, live and learn, it runs and cruises just feels bogged down like I’m pulling a boat and when I tune for better bottom end it falls apart at the top cruising off load slight popping out exhaust sometimes
 
That comp cam xe268h you have needs more converter. I know they say 2500 but it will be lazy on the bottom and you will never have any usable low end. At least 3000 stall. I've been down that road. Really a GOOD 3500 stall and a cooler. Then you can tune it. You will have to work on the ignition timing as well. Base timing will most likely be around 16. Lock out the mechanical advance to a total of about 36. Some will say no vacuum advance, try it both ways. Myself I use it on a street car. That 650 will feed it just fine. That should get it the ball park.
 
1970 Mopar Hustle magazine suggested 3310/780 Holley, LD-340 manifold, Hooker under chassis headers as the first upgrade.
Maybe a bigger carb, won't help bottom end, but you'll feel it in the top end.
Good luck .
 
you could try to use a thin metal rod measure it's length from the spark plug hole at both tdc bdc try to contact same area of the piston.
 
jim whelan said:
Ok yes, I got that now I should have measured the stroke as well. I’m just another example of why you shouldn’t rush, live and learn, it runs and cruises just feels bogged down like I’m pulling a boat and when I tune for better bottom end it falls apart at the top cruising off load slight popping out exhaust sometimes
Click to expand...
If you have it out I would surely put the degree wheel on it.
 
Jus' sayin but you are not gonna measure stroke with an angled anything stuffed into the plug hole. I thought you had it torn down?? Is the pan off? Is the intake off? You could mount a reference "jig" and measure the stroke off a rod bolt cap or nut/ bolt end.
 
67Dart273 said:
Jus' sayin but you are not gonna measure stroke with an angled anything stuffed into the plug hole. I thought you had it torn down?? Is the pan off? Is the intake off? You could mount a reference "jig" and measure the stroke off a rod bolt cap or nut/ bolt end.
Click to expand...

Welding rod works pretty good. Put the engine at TDC, slide the welding rod into the plug hole and set it in a valve relief if you can (so it stays roughly in the same spot). Put a sharpie mark on the welding rod at the plug hole. Turn the engine over and put that cylinder at BDC, put another mark on the welding rod. Measure between the marks.

Will be it the exact stroke measurement? Of course not! But you don’t need to be all that accurate to know if it’s a 3.31” stroke or a 4” stroke now do you? Heck even if it was a 3.58” you should still be able to tell pretty easily.

I wanna know how the OP doesn’t know it’s a stroker. Because usually if it is and you bought it from someone else they’d have told you at least a dozen times the engine was stroked. 3rd hand blind auction or something?
 
ir3333 said:
i have used the XE268 cam in a warm 340. Comp say it is fine with a stock converter. I had 3.23:1 gears and 27 inch tires and found it was lazy at lo rpm. So a call to Sean at Dynamic and a new converter...problem solved. Fast forward to my current car and it is a stock 340 with a stock cam, fries the tires easily at lo rpm and pulls hard top well past highway speeds. lesson learned about cams in street driven cars. Now having said that from midrange up that 268
made unbelieveable power...where it was never used!
Click to expand...
Thumbs up with Sean @ Dynamic
 
ir3333 said:
well...stoke your 340 to 416, put in a high lift short duration cam and .410 gears! It'll be
like driving on ice!
Click to expand...
I have never understood this. You described my car almost exactly except it is on a 6” tire. Engine makes a ton of torque? Don’t push so hard on the “go” pedal. If you are driving it in the rain all the time Ok. A “fun” car? Build it for all the power you can afford comfortably.
 
The degreeing the cam thing is important. I mention it not to beat you up, but because a good number of guys don’t and the problem is exactly what you are facing. Put it together and something is off. You can only guess at this point. If it’s off, you’re pulling the front of the motor off. I will do it every time. I leave cams to the smart people, but that carb is pretty user friendly. You need to find out where it is going fat, then it will point to why. Borrowing or buying an AFR gauge will help. You can buy a $20 two wire Chevy truck 02 sensor and connect a digital volt meter. You can find conversion table online for afr to volts. Accurate? Not really, shows when it goes pig fat? Yep. I run an 800 thunder avs. Becareful with the air door spring. Don’t over tighten them. They break.
 
Those carbs are very close out of the box. What type of ignition are you using? A weak spark will make it look like the carb is rich.
 
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