340 For street duty

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71Duster

71Duster

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So I've decided to start fresh with my 340.

Its the original number smatching block with x heads. The engine will end up at .040 over the original forged crank may or may not be good anymore its .010 under already and bubba weleded the mallory weights on in his backyard badly so its to be decided by the engine shop.

Now what I'm looking for out of the build is a good STREET engine. Things it must work with are a 2800rpm stall, 3.55 gears, an edelbrock rpm intake and FBO ignition and run on 91 octane.

I want a simple build. Nothing too wild or exotic. I plan to keep the x heads freshen them up an dmaybe have it gasket matched?

I want to run stock rocker arms as well. I was thinkign about re-useing the stock rods and useign arp bolts on them. Pro's or Con's?

Also a stock 340 oil pan and hi-volume pump good bad bigger pan?

I need to find a shop to build the long block and obviously they have their own ideas but just looking to see what some guys are building to see if they are close.

I want to build just under 400hp 360-380 range I thin k is easily do-able without any adverse idle problems etc.

Unknowens are the cam and carb mostly. For a carb I was thinking a Holley with vacum secondaries?
 
if the crank is bad build a mild stroker engine. to keep it streetable you may need dish pistons with the X heads, but as long as you have a good block and heads to start with you can really make some serious torque and power with a 416 cubic inch small block.

If the crank is good then you will have to be a bit more radical with the engine, but a .040 over can certainly be bulit to that level.

Bob
 
If the crank is usable,turn it and run it. .020 under is nothing, and to be rebalanced (piston choice) you will be drilling on itany way. Grind off the welds and have them redone if you have to. If the crank is bad, buy a 360 and go that route with a rebuild. A very mild 408 is much more street friendly and not much shorter life span wise than a 340. And you dont put the numbers matching engine at risk. Not to mention costs. A 340 with a cam and modern parts, with modern machining will make 375hp pretty easy on pump fuel. Just watch static ratio and cam choice for the "pump fuel" part. Get that wrong, and you'll be pinging. A 408 will make 400hp easy, and beyond 480tq..which is really what you want anyway.
 
I'm currently running a 340 w/ an old Torker intake, older holley 650 DP and 292/.508 hydraulic MP cam. It's plenty streetable and has just enough idle lope to it. I'd say my combo is good for about 350-375hp.

I have a new in the box Comp Magnum 270/470 cam (part#20-214-14) & lifters & rebuilt 650 double pumper that'd go well w/ your 2800stall and 3.55's. PM me if your interested. Bought it from an FABO member but have decided to stick with my cam. I'd let the cam/lifters go for $115 and carb for $100, that's what I paid.
 
My 340 is built as follows:

early style high compression pistons (CR about 9.5:1)
stock x heads
Comp XE 268H cam
RPM Air Gap intake
Summit racing headers
Holley Street Avenger carb
electonic ignition
and everything else stock

I had it on the chassis dyno about a month ago and the numbers calculated out to be 340 hp at the engine. This was without the ignition timing tuned in and a stock out of the box carb. So there is more to gain from tuning it in. With it all tuned in, I'd expect it to put out about 350-375 hp at the engine
 
Your 2 unknowns will be;

Compresion, pump freindly @ or under 9.5-1 with an iron head. 9.0-1 will do fine.

Cam;

I can see one as mello as 218 intake duraton on a split duration cam, (1800 -5500 or so rpm range) as much as 230 intake duration on a split duration cam. Possibly slightly more, not much for the way I like the car to run.

You'll need to finialize this one with some reading. Good ideas have been made. The mentioned stall and gears tend to narrow it down abit. seems more like an inflexable dimention added on to the task.

Go to crane cams.com or compcams.com and read through there suggestions
 
Well I should re-phrase now that I remember theres an excellent tranny shop here who custom builds convertors has the machine to weld them back up etc and builds there own race convertor I see guys run at the local track I could re-work my current one but the gears I dont want to mess with.

Remaining questions are oil pan - stock or aftermarket deep sump?
high volume oil pump or stock
 
I would go with a high volumn pump and stock pan, I used a milodon pan and am not happy with it, it leaks. Only downside to the stock pan is that it is no baffled.

I run my 340 on the street all the time it's:

stock x-heads
speed pro forged pistons
xe-268 cam
650 holley DP
Eddie perf rpm intake
tti headers
msd 6al box and dist.

runs great, no problems.
 
If your turning more than 6,000 rpms for a second or so, I'd do a deep pan and hi-vol. pump. Otherwise, a stock set up will do well.
 
Stock pan, stock pump, stock bearings, MP high pressure relief spring.
 
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