To me once your over 400 cid it's basically a big block now anyways just looks like a small block.
340 or 408?
- Thread starter 67_Slimer
- Start date
-
ValiantRacing
Well-Known Member
10 pages and still going strong. 
10 pages and still going strong.
Tomorrow we are getting into “warp speed” calculations of a stock 340 compared to a stroker
Well, no, it was a 4" stroke. This is the Small Block LS7, not the old BBC 427. That's why I mentioned the fuel cut-off speed of 7200 rpm. You are correct the old BBC 427 had the shorter stroke. The Small Block bore spacing did not allow for that old BBC bore size!
Newbomb Turk
Well-Known Member
Yep. And the head on that engine is probably as good or close to it as a 990 BBC head.
Put lesser head on it and see what it is.
@Newbomb Turk mentioned it in an earlier post. Longer strokes increase motoring friction. The increased stroke will breathe deeper at lower rpm and thus make more indicated power. So long as the airflow is higher by enough to keep the indicated power high enough to overcome the increased motoring torque (friction torque), the engine will make more brake power (output). At some point, the frictional increase MAY get high enough to overcome the additional airflow and the power will be either equal or less (ie. the power noses over earlier). Obviously this is describing only the same engine with a different stroke.
You can also see the opposite effect. Some will DEstroke the engine and the motoring torque (friction) will go down. Then you spin the engine fast enough to breathe more air and with the lower friction, you can make equal/more power at some higher rpm. It's all just simple physics actually. It also shows why the stroked engine generally makes peak power at a lower rpm and is normally higher, just not as much of an increase as the torque increase.
You can also see the opposite effect. Some will DEstroke the engine and the motoring torque (friction) will go down. Then you spin the engine fast enough to breathe more air and with the lower friction, you can make equal/more power at some higher rpm. It's all just simple physics actually. It also shows why the stroked engine generally makes peak power at a lower rpm and is normally higher, just not as much of an increase as the torque increase.
Last edited:
Glad you appreciate that LS7 head/airflow! Lol...
Moparmonster
Well-Known Member
I'd like to get Edelbrock aluminum heads for my 340, and they're not that expensive, about the price of my Holley Sniper setup.if just those two choices i think i'd go with a 408. seems guys make 500HP by accident with them. i think it would be less high strung then the 340 at those hp levels too..
what about a 416 from a stroked 340? that should be easy to get 500 hp from too..
That said, I have plenty of other things to spend that money on right now. I want Moon valve covers but will stick with my stamped steel cheap chrome valve covers for the moment.
John S
Member
They are 2 completely different animals that will have different characteristics. I have raced a stock warmed over 340 that ran 12.67/ 107. It was a dog below 3000 RPM but screamed like a banshee above 3000. I turned that into a 416 that I street drive now. It produces 530/ 524 TQ with 400 Ft/Lbs at 2000 RPM. The 2 combinations are worlds apart. I can leave in 2nd and floor it and your stomach will rise. The torque produced by the 416 is big. Cam is sized for max power at 5900. If you want to have a car that will pull like a beast without having to hammer it, build a 416, but never let anybody drive it without installing a Rev limiter that you can set with a hidden switch. I lock mine at 4000 RPM before I hand it over to someone that is helping me. There will be no street tires that will hold this and the rear will come around so quick, you better be ready for it.
What was the gears and stall for each ?
John S
Member
67_Slimer
Real Hot Rods don't shift themselves.
What have I done?!?!10 pages and still going strong.
Newbomb Turk
Well-Known Member
What have I done?!?!
You asked a question.
Thank God this isn’t school where you can’t discuss anything outside of what the teacher wants
67_Slimer
Real Hot Rods don't shift themselves.
I honestly appreciate everyone's comments and input. I go look at that block tonight and see if it's worth it.
You asked a group of Mopar guys which CID combo was better. Nothing gets people here more heated than that lol.What have I done?!?!
Only thing that would've gotten more people involved is if you were comparing a 318 to 408.... heaven forbid
Like I said before I love a 340, 360, or 408 type of build for the horsepower range he’s looking for. (500). For a drag race application like I build I prefer a 4 inch stroker build. It’s easier for me to build a 9 second engine than it would be a 12 second engine anymore. And again like I’ve said before we are so blessed to have the parts available to us today that we didn’t have 40 years ago. Build it, beat on it, and have fun.
9secRR
Well-Known Member
there is so many ways to achieve 500-550 hp builds with the parts today.
for years i had 4'' and 4.125'' strokers. then i switched to smaller cubic inch engines. no real reason other then i buy most stuff used. i now have a 3.875'' stroke W8 engine that will be ready for next year. again i bought it all used, only way i can afford this expensive obsession.
for years i had 4'' and 4.125'' strokers. then i switched to smaller cubic inch engines. no real reason other then i buy most stuff used. i now have a 3.875'' stroke W8 engine that will be ready for next year. again i bought it all used, only way i can afford this expensive obsession.
Dusterdan340
Member
I am another big fan of the 340. It is an amazing engine, well designed and very adaptable to upgrades. The 1970 340 should have a steel crank and rods. I believe you can stretch 2HP per C.I. if you really want to get extreme. The 275 HP rating is net HP and not gross so you are already around 350 HP with a stock 340, so pushing it to 500 HP is very doable. I would caution about going to much higher on the compression as 340s tend to blow through head gaskets. I picked up a set of T/A heads and a six pack years ago for my 70 Duster with 4:11 and a 4 speed, headers and a decent cam it made a formidable little street machine. The ford and Chevy guys hated getting smoked by a 340! Later I got the W-2 heads, a bigger cam and went back to a 4 barrel and ran her at the strip for a while with decent results with a 5:13 gear that I didnt really like that much. I am currently building a semi mild 440 for a 68 Dart but next year I want to get the Duster out of storage and bring her back to life. Stock 340 heads flow pretty good, the T/A and W-2s use mechanical tappets that are offset to allow more porting. Sounds like a great project you have there, keep us posted and HAVE FUN !
Well you talked me into it, I'm building another 451, gotta make use of this turned down 440 forged crank I kept for a spare.
No way man. That stock stroke 400 is where it's at. That's a real rev happy combo there.
67_Slimer
Real Hot Rods don't shift themselves.
Read an article years ago , not sure how true it is , but it said the 340 A bodies would have crippled the 383 Road Runner sales if they advertised the 340 at the actual 320 HP it produced. It's always been my favorite motor and especially in an A body. I look at it like the fox body of yester year. Small car , small engine that responds great to modifications street ripper.
I got no problem with that either.No way man. That stock stroke 400 is where it's at. That's a real rev happy combo there.
Newbomb Turk
Well-Known Member
The Hemi with a decent tune (talking race Hemi here) a set of race plugs and a timing change made well north of 525 hp.
That’s STILL a shorter stroke than a 408.
Yep, but with a much bigger bore. 7500 rpm is nothing for a 451. lol
-
