340 build .30 over

[RustyRatRod]

You will be fine. I have a 10.2:1 J headed 340 w mp .284/.484 cam runs just fine on 89-91

Two completely different animals. Your camshaft has a much later intake valve closing event, which causes the cylinder to start building pressure later in the compression stroke, resulting in less cylinder pressure.

His camshaft is specifically ground to maximize cylinder pressure and has a much earlier intake closing event, which results in pressure being built much earlier in the compression stroke for more cylinder pressure. I think he will have trouble on pump swill or be right on the edge.

 

[swinger340]

Two completely different animals. Your camshaft has a much later intake valve closing event, which causes the cylinder to start building pressure later in the compression stroke, resulting in less cylinder pressure.

His camshaft is specifically ground to maximize cylinder pressure and has a much earlier intake closing event, which results in pressure being built much earlier in the compression stroke for more cylinder pressure. I think he will have trouble on pump swill or be right on the edge.

True... I installed my cam @ 104* 4* advanced for that reason. Running 160 cylinder pressure.

 

[elevensies]

looks a nice build, have you had it dyno'd yet? would like to see the figures

 

[19scamp72]

Not yet ill let you guys know how it gos, right now i just ran into a rocker issue the roller is not 100% sitting center on the lash cap here is a pic with valve open. Will i be ok to run it like this? I know it will wear in time but how much time?

pc screen shot

Next option run my stock 318 rockers how muchloss of power will i loose?

 

[EL5DEMON340]

You wont notice the power loss, maybe 5hp, the stock rockers will be much more reliable

 

[swinger340]

Personally Id use 273 rockers over the pro comps. Thats just me.

 

[replicaracer43]

You really should go ask your engine builder, you said your not worried because hes built tons of them.... I personally don't like lashcaps, I would get some decent rockers, and figure out the proper pushrod length..... Do it right, and do it once...... Just trying to help!

 

[19scamp72]

This is getting build by a professional machine shop well known place. The guy who has giving me.information is not the one building the motor. He just gave me good advise on what to buy.. but anyways i am using the procomp rockers ill take my chances will give me a good reason to build a stroker one day. And yes i may need to run a octane booster. Maybe not, only time will tell. Ill shoot out dyno results in a few weeks.

 

[19scamp72]

You really should go ask your engine builder, you said your not worried because hes built tons of them.... I personally don't like lashcaps, I would get some decent rockers, and figure out the proper pushrod length..... Do it right, and do it once...... Just trying to help!

From what i got from shop. in order to make my rockers sit correct on the cap i would need to change my valves and possible head work around the valve seat.. heads are already together. I dont think it will be a problem if im not reving it like a nascar..wish me luck.

 

[EL5DEMON340]

Those rockers might not last the dyno pull! Do a google search.

 

[RustyRatRod]

From what i got from shop. in order to make my rockers sit correct on the cap i would need to change my valves and possible head work around the valve seat.. heads are already together. I dont think it will be a problem if im not reving it like a nascar..wish me luck.

Good luck. Yer gonna need it.

 

[swinger340]

Same rockers caused my buddy to have to rebuild his 410 after only 500 mi. . 2 broken adjusters and aluminum shaving all through the engine. real impressive. I wouldn't chance ruining the complete engine, but not my call. Best of luck.

 

[swinger340]

From what i got from shop. in order to make my rockers sit correct on the cap i would need to change my valves and possible head work around the valve seat.. heads are already together. I dont think it will be a problem if im not reving it like a nascar..wish me luck.

Why would anyone do all that head work when a simple rocker change would fix the geometry, and cost less? Im confused that a shop would even recommend doing so.

 

[RustyRatRod]

Why would anyone do all that head work when a simple rocker change would fix the geometry, and cost less? Im confused that a shop would even recommend doing so.

I'm not confused one bit. That "shop" clearly doesn't know WTF they're doing.

 

[replicaracer43]

I'm not confused one bit. That "shop" clearly doesn't know WTF they're doing.

I think that is becoming really clear.......

 

[19scamp72]

I'm not confused one bit. That "shop" clearly doesn't know WTF they're doing.

The shop is told me the issues they never said that would be my better route, You guys have me conviced better safe than sorry. I will be calling them in morning, hope they have not ordered my pushrods, once again thank you. I did my research on procomp a little more and your right. I have a set off my 318 ill be using.

 

[19scamp72]

Not the shop problem its mine. Im no engine specialist thats why im asking questions even if they are sometimes stupid. But im learning.

 

[EL5DEMON340]

The shop is told me the issues they never said that would be my better route, You guys have me conviced better safe than sorry. I will be calling them in morning, hope they have not ordered my pushrods, once again thank you. I did my research on procomp a little more and your right. I have a set off my 318 ill be using.

Thank me with a big long burnout!

 

[K.O. SWINGER]

you can shim up the rocker shafts at the pedestals to move your rocker tip back

 

[19scamp72]

Will do! Ill be doing a few of those thats for sure

 

[DFX 340 Duster]

Personally Id use 273 rockers over the pro comps. Thats just me.

A buddy of mine who races a 1971 Demon 340 in Stock classes recommended just that for my 340 build with the 484 cam and big valve J heads.

 

[19scamp72]

Yes i have a set of 318 already, whats the pros and cons of the 273 rockers, I heard they are heavier than the 318 rockers, but adustable, what gains will i get from a 273 rocker rather than a 318.

 

[swinger340]

Yes i have a set of 318 already, whats the pros and cons of the 273 rockers, I heard they are heavier than the 318 rockers, but adustable, what gains will i get from a 273 rocker rather than a 318.

They are relatively cheap rugged as heck and are adjustable. I have used them in many diff 340s. Actually have them in my current 340. I hate to see a rocker break and ruin your otherwise awesome looking build. My buddy had a ton of money in his 410 and pretty near ruined it w the pro comp rockers. Luckily he shut it rite down and it was saved w a good cleaning, new bearings, and gasket set. Could have been much worse.

 

[RustyRatRod]

We're not hatin on you man. We're just trying to help.

 

[K.O. SWINGER]

Yes i have a set of 318 already, whats the pros and cons of the 273 rockers, I heard they are heavier than the 318 rockers, but adustable, what gains will i get from a 273 rocker rather than a 318.

durability. there just about bullet proof ..but yes they are heavier