1971 340

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twool

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i have a 1971 340 with orig. crank piston and rods.what build do I need to get 425 to 450 hp
 
Get CR up to a true 10. To 1, pocket port and good valve job on the heads, or good aftermarket heads, FT cam in the 550 lift and 248 to 252 @.050 range at maybe 108lsa. Air gap with 950HP holley, good headers. That should get you in the ballpark it will be a rascal of a engine. Might want to think about a stroker.
 
I think im at 10.5 to 1 now mill the heads should bring it up to 11 to 1
 
JMHO..... Look at head flows for the Edelbrock Performer RPM heads on their website; that is where you need to be in flow levels to have that HP level with a decently broad torque curve too. Get that flow in any head and get near to .525-550" lift and you will be there with standard stroke, with a pretty typical SBM cam profile, a good intake and exhaust, and modest sized carb. (I just reread El5Demon340's post.... looks very similar.)

The CR as suggested is good for general drivability. No need to go up to 11:1 at all IMO, and may be an issue for detonation unless you put in a longer duration cam...which in turn makes street driving suckier. I would stick with the 10.5 max for any street use, and look at some AL heads. But you have not said what you want to do with the car to see if that is needed...Is this purely for drag racing or street driving too? Any long cruising miles? That can make a big difference in the best plan of action.
 
how did you end up at 425 hp?
Stock 340 in an A body with a gear and a converter would run low 13's and that's only 275 hp.
a 450 hp 340 may not be the best street combination.
 
ir3333 said:
how did you end up at 425 hp?
Stock 340 in an A body with a gear and a converter would run low 13's and that's only 275 hp.
a 450 hp 340 may not be the best street combination.
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Works for me , just need good tires . Daily driver , idles 900 not a problem in traffic never overheats , as of yet , knock wood . Was @ 424 hp before I shaved the heads to make them closed chamber , went from 9.8 to 11.4 compression . Small cam with the 273 1.6 rockers , ede heads and Mahle forged pistons . 3:55 gears 26" tire and a gear vendors overdrive , fun on the street , highway and track . Around $10.00 in gas gets me to the city 48 miles @ 1.42 a litre , sometimes less depending on traffic and weight of foot .
 
there is a guy running around town in 1968 Camaro 327 with 400 to 425 hp very fast.i want shut him down
 
Throw the 340 under the work bench and save it. Buy a crap 360 and build a stroker. That 340 is worth saving. Not like they're makin anymore of them.
 
nm9stheham said:
JMHO..... Look at head flows for the Edelbrock Performer RPM heads on their website; that is where you need to be in flow levels to have that HP level with a decently broad torque curve too. Get that flow in any head and get near to .525-550" lift and you will be there with standard stroke, with a pretty typical SBM cam profile, a good intake and exhaust, and modest sized carb. (I just reread El5Demon340's post.... looks very similar.)

The CR as suggested is good for general drivability. No need to go up to 11:1 at all IMO, and may be an issue for detonation unless you put in a longer duration cam...which in turn makes street driving suckier. I would stick with the 10.5 max for any street use, and look at some AL heads. But you have not said what you want to do with the car to see if that is needed...Is this purely for drag racing or street driving too? Any long cruising miles? That can make a big difference in the best plan of action.
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how about 284 duration with 490 lift
 
RustyRatRod said:
Throw the 340 under the work bench and save it. Buy a crap 360 and build a stroker. That 340 is worth saving. Not like they're makin anymore of them.
Click to expand...

This. Smoke Chubbies & furds at will.( Sorry ,RRR..)
 
RustyRatRod said:
Throw the 340 under the work bench and save it. Buy a crap 360 and build a stroker. That 340 is worth saving. Not like they're makin anymore of them.
Click to expand...

This. Smoke Chubbies & furds at will.( Sorry ,RRR..)
 
Easy ways to make power:

-Lighter rotating assy
-Roller Camshaft (Hydraulic Roller is fine)
-lighter/lower friction vale train (beehive springs also help)
-stroker
-airflow
-complete combustion w/o detonation
-control oil

my engine has everything but the stroker. I didn't go stroker because I wanted the car to hook on the street (didn't need the extra torque). Turns out it made 400 lb-ft at 2800 rpm anyway. 455 lb-ft at 4000, and 470hp at 6000.

It rips. Pulls 3.23's like a champ and hooks well enough on the street. Pulled 13.5 in Hg with the 750 double pumper at 950 rpm. I was looking at my EFI log today and it now is running 58.5 kPa at idle which is over 17 in Hg at the same rpm, so yeah this thing is streetable.

We took a TON of rotating weight out of this thing with the pistons and K1 rods. Beehive springs and the hydraulic roller helped a lot. The heads are stock edelbrock other than the valve job (no porting). Box stock intake. You just plain can't throw it together with X or J heads, the old heavy TRW/FM pistons, flat tappet cam and expect it to make this much power.

Those LSX engines don't make all that power for no reason. The same tricks they applied work on these too.
 
Message blu340dart, he just got his stroker motor from Compuflow back in his car! He's running right at 11 flat, with 10's a sure bet!! Can you say Camaro killer?? And it lives easily on the street!!
 
thanks for all the info!. One more ?with stock pistons,crank and rods with magnum heads.What cam as far as lift and duration in one 1/8 mile
 
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