340 or 408?

[67_Slimer]

OK I know this is done to death and I apologize in advance. I'm a huge 340 fan and currently have a mildly build one in my 67 Dart now. 10.5/1 , Eddy heads solid flat 525 lift cam , 1.6 RR , Hooker headers , Eddy Victor intake , Quickfuel 750 race carb , 4 speed with 4.56's. Fun car. Motor is super strong but wanted to start slowly building a small block for down the road. I currently have a 360 block (1976) .030 over that I planned on building a 408 with but then I have a chance to buy a 340 (1970) block but has a sleeve for a decent price. I am looking for minimum 500 HP at the flywheel. I'm a huge 340 fan and leaning towards the 340 but My concerns are the following. Is 500 HP too much to ask from a standard stroke 340? I'd look at 11/1 compression , I'd port my current eddy heads and Victor intake and obviously go Roller cam with more lift and duration. Another concern I would have is if I go with the 408 , Would the 4.56 gears I have be too steep for that? I really don't feel like changing out my rear gear. It's a Dana. The car is driven locally , cruise nights , shows and to work etc. Looking to rip some gears and have fun , maybe take it to nostalgia day at the track. Never was or will be a daily. Just looking for realistic answers. Thank you in advance.

 

[famous bob]

OK I know this is done to death and I apologize in advance. I'm a huge 340 fan and currently have a mildly build one in my 67 Dart now. 10.5/1 , Eddy heads solid flat 525 lift cam , 1.6 RR , Hooker headers , Eddy Victor intake , Quickfuel 750 race carb , 4 speed with 4.56's. Fun car. Motor is super strong but wanted to start slowly building a small block for down the road. I currently have a 360 block (1976) .030 over that I planned on building a 406 with but then I have a chance to buy a 340 (1970) block but has a sleeve for a decent price. I am looking for minimum 500 HP at the flywheel. I'm a huge 340 fan and leaning towards the 340 but My concerns are the following. Is 500 HP too much to ask from a standard stroke 340? I'd look at 11/1 compression , I'd port my current eddy heads and Victor intake and obviously go Roller cam with more lift and duration. Another concern I would have is if I go with the 408 , Would the 4.56 gears I have be too steep for that? I really don't feel like changing out my rear gear. It's a Dana. The car is driven locally , cruise nights , shows and to work etc. Looking to rip some gears and have fun , maybe take it to nostalgia day at the track. Never was or will be a daily. Just looking for realistic answers. Thank you in advance.

Having built a 406sbc , I can say , I was truly impressed with it !!! I`d go for it , if I were wanting to build another engine ...

 

[Demonracer]

The 4.56 ratio will get tiring after a while, my suggestion would be a 3.55, 3.73 or possibly 3.91 ratio. The 4.56 will have you turning really high RPM's for just a cruiser type car. I've run 3.55 and 3.73 ratios on the street and they are a real kick in the pants.

 

[67_Slimer]

The 4.56 ratio will get tiring after a while, my suggestion would be a 3.55, 3.73 or possibly 3.91 ratio. The 4.56 will have you turning really high RPM's for just a cruiser type car. I've run 3.55 and 3.73 ratios on the street and they are a real kick in the pants.

Well I've had 4.56's in it for 25 years so I don't see myself changing anytime soon. lol

 

[Scott_ 69HemiDart]

~450hp from stock stroke 340?

Hey all, I’m starting my 340 build and I’m looking to get around 450 hp or possibly even more out of my stock stroke 340. This is mainly a street build so drivability is a must. Stock bottom end 72 340 (Keith black pistons), trick flow heads (Specs for them), 1.6 harland sharp roller rockers...

www.forabodiesonly.com

 

[furrystump]

So, I think you are asking it the 4:56 would hurt the longevity of the 408 more than the 340 you have been running. I have 60,000+ miles and 1000’s of passes on my 4” stroked 360. Went through it in 2016, bearings, rings, pistons(compression bump). Only needed a dingle ball hone. I spin mine to 6300-6400 to shift and 6800 at the stripe. 4:10 gear. In my opinion, there is ZERO difference in longevity between a 340 and a 4” stroked LA. I would go 408.

 

[roccodart440]

Take some of the money you planned to spend on the new engine and install a Gear Vendors Overdrive. You won't be disappointed. Your engine will be happy and those 4.56's will be just fine with your stoker build down the road.

 

[Newbomb Turk]

If you ask the questions you are asking, you don’t need to build a 340.

I don’t mind 4.56 gears. In fact IMO it’s the best street/strip gear. I went to taller tires so I’m using 4.88’s now. I’ll see how that goes next year but I don’t think it’s an issue.

Getting 500 at the crank with 340 inches isn’t hard, but you need a plan. And then you have to live with your plan.

If you’ve never driven with 4.56’s then you should at least drive a car with that gearing before you build something.

If you think 6800-7000 rpm is spinning the guts out of an engine then build a stroker.

Be honest with yourself about who you are. If the above stuff is out of your wheelhouse then build the bigger engine.

 

[67_Slimer]

If you ask the questions you are asking, you don’t need to build a 340.

I don’t mind 4.56 gears. In fact IMO it’s the best street/strip gear. I went to taller tires so I’m using 4.88’s now. I’ll see how that goes next year but I don’t think it’s an issue.

Getting 500 at the crank with 340 inches isn’t hard, but you need a plan. And then you have to live with your plan.

If you’ve never driven with 4.56’s then you should at least drive a car with that gearing before you build something.

If you think 6800-7000 rpm is spinning the guts out of an engine then build a stroker.

Be honest with yourself about who you are. If the above stuff is out of your wheelhouse then build the bigger engine.

I currently have 4.56s and absolutely love them , that's why I'm asking if that would be too much gear for a 408? I've been told they don't rev as much as my current 340.

 

[Heywodja]

I would sell the 340 and use the funds to build a 360 magnum stroker. You'll be financially ahead of the curve.

 

[67_Slimer]

I would sell the 340 and use the funds to build a 360 magnum stroker. You'll be financially ahead of the curve.

I don't want to sell my 340 that's in the car now but to keep costs down I want to use the top end that's currently on my 340 so that's why I want to use an LA style 360 if I plan on doing the 408.

 

[roccodart440]

I currently have 4.56s and absolutely love them , that's why I'm asking if that would be too much gear for a 408? I've been told they don't rev as much as my current 340.

Depends on how much HP the 408 makes, and where it makes it.

i.e. when I made somewhere between 467-500hp range at high 5k RPM range or so RPM. 4.56 gears were perfect. I'd run it out the back door of the 1/4 around 6000-6200RPM in 3rd. In the 1/8th mile i'd run 6200 through the traps in 2nd gear + OD.

When I went to my new engine, Which makes 602hp @ 5900, I couldn't get through the traps unless I shifted into OD and it would fall on it's face and be low 5's through the traps. I switched to 4.10 gears and now trap properly in 3rd gear.

 

[furrystump]

or, put a 4” crank in your current or the newly bought 340 and at that point it still says 340 on the side of the block. Then you will have a healthy 340 AND a stroked 340. A rotating kit for a 4” crank is $3300ish from Molnar? Page 2 or 3 of engine parts for sale.

 

[Newbomb Turk]

I currently have 4.56s and absolutely love them , that's why I'm asking if that would be too much gear for a 408? I've been told they don't rev as much as my current 340.

Like post 12 lays out, gearing is based on power, rpm and tire diameter.

4.56’s will work with a 408 or whatever IF it will make power at that rpm range.

 

[Heywodja]

I don't want to sell my 340 that's in the car now but to keep costs down I want to use the top end that's currently on my 340 so that's why I want to use an LA style 360 if I plan on doing the 408.

If you can locate an early magnum block, they oil through the heads just like the LA motors. I would look for an 85-90 block if memory serves me right.

This way you can save the 340, it will be of little value after you stroke it. just sayin..

The photo below shows a magnum block with the oil LA style oil holes..

 

[RustyRatRod]

Not too much to ask, but you'll get there easier and at lower RPM with the stroker.

 

[PRH]

I look at it this way……..

It’s unlikely 4.56’s would be the “right gear” for a 500hp combo that’s running a 4” stroke in a Dart.

*Unless it was primarily a race car and had suitably sized rear tires to make the overall gearing work out.

 

[Demonx2]

I have both a 340 Demon and the avatar 408 Demon. The 408 will put a smile on your face every time you hit the loud pedal. If your 340 does that now, the 408 will only serve to widen the smile.

 

[273]

Do you plan on running the quarter mile ?

If not proper gearing become more what you like, you probably want the 408 turn the rpms your now 340 can at least with 4.56.

My guess is your probably around 450 hp, with porting heads and intake possibly more cam (never gave full specs) you should reach your goals but the powerband (peak tq & hp) will moved up around 500 rpms and depending on cam low speed might have to suffer more, how streetable is it now ? If you find it on the edge of streetability you might not like moving the powerband higher if you find it fine then might not be a problem for you.

As for 408, take the rpm powerband you have now and add power across the entire range is what a 408 is basically gonna do if you get enough air flow.

 

[33IMP]

Buy the 340 block with the sleeve, and put a 4" crank in that.

 

[67_Slimer]

Do you plan on running the quarter mile ?

If not proper gearing become more what you like, you probably want the 408 turn the rpms your now 340 can at least with 4.56.

My guess is your probably around 450 hp, with porting heads and intake possibly more cam (never gave full specs) you should reach your goals but the powerband (peak tq & hp) will moved up around 500 rpms and depending on cam low speed might have to suffer more, how streetable is it now ? If you find it on the edge of streetability you might not like moving the powerband higher if you find it fine then might not be a problem for you.

As for 408, take the rpm powerband you have now and add power across the entire range is what a 408 is basically gonna do if you get enough air fIow.

I probably wont run anymore but if I do it will be 1/4 mile. I'm just looking to street drive it and have fun like my current set up but faster. I'm just asking if 500 hp out of a 340 is fairly realistic. I don't care about cam size because its a 4 speed or if I go with the 408 will it be straining with my 4.56s beacause I'm told 408 are more of a lower revving motor.

 

[33IMP]

500 hp out of a 414/416/408 is a lot easier, and probably a lot easier to live with, than a 500 hp 340.
The extra stroke doesn't mean it can't rev as high as a 340 stroke, it just means the power might drop off a little sooner, and you won't NEED to rev it as high.
Imo, revability is determined by head flow, and valvetrain, not stroke length.

 

[67_Slimer]

500 hp out of a 414/416/408 is a lot easier, and probably a lot easier to live with, than a 500 hp 340.
The extra stroke doesn't mean it can't rev as high as a 340 stroke, it just means the power might drop off a little sooner, and you won't NEED to rev it as high.
Imo, revability is determined by head flow, and valvetrain, not stroke length.

So if I go 408 from a 360 , would my top end work if the right cam was selected? (edelbrock heads and Victor intake) I would port them as well.

 

[pittsburghracer]

I probably wont run anymore but if I do it will be 1/4 mile. I'm just looking to street drive it and have fun like my current set up but faster. I'm just asking if 500 hp out of a 340 is fairly realistic. I don't care about cam size because its a 4 speed or if I go with the 408 will it be straining with my 4.56s beacause I'm told 408 are more of a lower revving motor.

I baby my 408 and 422 shifting them at 6800 but they would handle more.

 

[33IMP]

So if I go 408 from a 360 , would my top end work if the right cam was selected? (edelbrock heads and Victor intake) I would port them as well.

Same heads and intake, appropriate cam for intended use, yeah, it'll rev just like your 340, with more power. (My opinion only).