9secRR
Well-Known Member
My butt dyno says i have a much larger cubic inch then 355” which is backed up by the 1.29 60’.
340 or 408?
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9secRR
Well-Known Member
11.4 comp
W2 heads, flow 286
Indy intake
264/268 @ .050 Hughes SFT
Ductile iron rockers
3.46” stroke
BME aluminum rods
904
5600 stall
4.86 gear
2700 lbs
ValiantRacing
Well-Known Member
How tall of a tire do you run?
9secRR
Well-Known Member
14/32
Newbomb Turk
Well-Known Member
Funny thing, these quarter mile calculators a lots seem to hold in high regard don't care about cid and torque, it's all about hp and weight. If torque played a significant role outside of hp these calculators would have to factor it in or they would be useless.
Newbomb Turk
Well-Known Member
Has anyone tested a 340 vs a 340 with nothing more than a 4" stroke. lol
I know which one I would pick to be the winner.
I know which one I would pick to be the winner.
.20 is probably average
There's a stock (4bbl & headers) magnum 360 vs 410 but they added almost 2 points of compression when they stroked it, it gain 29 hp, 305 hp vs 334 hp but obviously a chunk of it's from more cr.
There's also a more performance build 360 vs 410 using same parts think it was Edelbrock headed, and the 410 made less then 10 hp more.
Look at that 302 vs 327 vs 350 they were pretty much identical builds especially the 302 and 327 and made same hp. Plus the 400 hp magazine 318 & 360 builds all are fairly identical to each other.
In a car that's gonna see street duty, area under the curve matters. A lot.
Now...on a drag application, with appropriate stall etc, maybe it doesn't matter as much. But if you're going to operate over more than a 1000 rpm window, that area under the curve is everything.
I really don't understand how this is a debate.
Now...on a drag application, with appropriate stall etc, maybe it doesn't matter as much. But if you're going to operate over more than a 1000 rpm window, that area under the curve is everything.
I really don't understand how this is a debate.
Newbomb Turk
Well-Known Member
Here is what you aren’t getting. Since we are talking about are under the curve, you are talking about WOT.
What I’m saying is the numbers you see at WOT do not translate to part throttle mid load power.
You (and most others) assume or suppose is a better way to say it is that what you see at WOT is what you see at part throttle.
For example, at say 2500 at WOT you have 400 TQ and the smaller engine makes only 325 TQ.
Is there still a 75 TQ difference? No, there isn’t. Partial throttle openings reduce that difference.
This is easy to see on a dyno where you can control things.
And I know some will argue there is still a difference and the bigger engine will still be making more torque and that’s correct.
But…you still have to account for gearing. And not just the rear axle ratio either.
At some point, you end up with gearing most guys wouldn’t use and then the gap between the two engines performance gets wider.
Looking at WOT area under the curve and correlating that to part throttle area under the curve isn’t what happens.
And, as either engine starts making more power the tune up window gets smaller and you have less room for errors in tuning.
The engine with less stroke (or even the same stroke with different bore sizes like the 273/318/340) will have a smaller tune up window sooner.
They are certainly less forgiving once you start getting to 1.3 HP/CID.
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The problem is many things are being vaguely debated and interchangeably.
1. Can a 408 & a 340 make the same power curve basically stall to shift, I believe the answer is yes.
2. Is it gonna be some huge extra effort to do so, I believe generally no.
3. What about the extra torque of the 408, if geared right (take full advantage of the power curve) they should be putting similar torque to the ground.
4. What if they aren't geared right and run similar gears in most case it seems people under gear so it's generally gonna be to the advantage of the larger cid. Which is to me generally a good reason to build larger, build for the gearing your gonna use.
5. Should a similar hp/weight cars be able to produce similar performance eg.. 1/4 mile, I believe yes.
To me that's one side of the argument can these two engine have similar performance, I believe the answer is yes.
Now will they be streetable and that's a huge question cause it means many things to many people, some might find both not street friendly. It's really up to the individual, what will they find acceptable/perfered.
Will a 500-550 hp 408 be more streetable than a 340 I'd say yes, does that make 340 unstreetable ?
A 500+cid will be even be more streetable does that make a 408 a terrible build ?
Which would I probably do, I'd just add heads to what he's got and decide after, depending how that goes.
Plus when normal driving your only making the hp needed at that moment so at 2500 rpm one engine makes 400 tq vs 325 tq at full throttle so maximum tq available at that rpm , but you might only using/making 50 hp which is only 105 tq, but you have 190hp/400tq or 155hp/325tq in reserves, more than enough if you all a sudden need it, plus in that case you generally drop a gear.
Generally you don't spend much time at low rpms at full throttle during normal driving even with a /6 so obviously most these engines make more than enough low speed power when just driving.
Again....
For anything that's gonna see street duty or any application other than straight line drag racing, the area under the curve will reign supreme.
Think of it this way. with these "apples to apples" comparisons where they only change displacement. What are they *really changing*?
The answer to that is the mass flow rate of air flow --- and in turn the amount of fuel burned --- and in turn the amount of energy output --- for a given cycle is going up as the displacement goes up.
These power curve overlays are really just illustrating the airflow limitations of the combo. Hence they all make about the same peak horsepower.
What they are also showing --- and this is crucial --- is that the larger combinations are taking greater advantage of the flow processing capabilities of the engine, over a much larger rpm sweep.
For anything that's gonna see street duty or any application other than straight line drag racing, the area under the curve will reign supreme.
Think of it this way. with these "apples to apples" comparisons where they only change displacement. What are they *really changing*?
The answer to that is the mass flow rate of air flow --- and in turn the amount of fuel burned --- and in turn the amount of energy output --- for a given cycle is going up as the displacement goes up.
These power curve overlays are really just illustrating the airflow limitations of the combo. Hence they all make about the same peak horsepower.
What they are also showing --- and this is crucial --- is that the larger combinations are taking greater advantage of the flow processing capabilities of the engine, over a much larger rpm sweep.
I think another thing that is missing from this conversation is mechanical efficiencies of the system as we go up in RPM. These are just generalities but the harder you push a mechanical system the less efficient it tends to become. You make more heat, greater friction losses, etc.
Maybe this is one of the "little things" but I'd imagine that there's a Goldilocks zone of displacement and rpm where the rest of the combo exhibits the best overall efficiency.
Maybe this is one of the "little things" but I'd imagine that there's a Goldilocks zone of displacement and rpm where the rest of the combo exhibits the best overall efficiency.
Newbomb Turk
Well-Known Member
You just aren’t paying attention.
So gave you built a 500 hp small block and a 500 hp 408 and compared them driving around?
I can say this until my teeth wear out. A stoker will cover a bunch of errors that a 340 won’t take.
The tune up window gets smaller and smaller as the power goes up regardless of displacement. The smaller engine will always have a smaller tune up window.
If you can’t tune then build the biggest engine you can and live with it.
Will it drive better than a correctly tuned smaller engine? No if you can tune. Yes if you can’t.
And one of the major tune up issues is timing. If you think locked timing is a good thing, or the all in by 2500 curve then build a bigger engine.
What I’m saying is 90% of drivability is piss poor parts selection and crap tuning.
Newbomb Turk
Well-Known Member
Displacement creates more friction than rpm. This is basic ****.
Look at Pro Mod and Pro Stock.
For the displacements the PM should be far quicker and faster than PS but they are not.
That is friction.
Street car guys, 500 horsepower guys, simplicity guys, get a damn grip.
These guy's need to make up their mind.
Is the 340 the big block killer as claimed.
If so surely shouldn't have a problem with a 340 with a 4" stroke all else being the same.
I wish you fellas would make up your minds. lol
These guy's need to make up their mind.
Is the 340 the big block killer as claimed.
If so surely shouldn't have a problem with a 340 with a 4" stroke all else being the same.
It just goes on and on and on. Start a post of their own and have at it with every chart, graft, YouTube videos, calculations, formulas, etc. but it’s never on a post they start.
Newbomb Turk
Well-Known Member
These guy's need to make up their mind.
Is the 340 the big block killer as claimed.
If so surely shouldn't have a problem with a 340 with a 4" stroke all else being the same.
I get tired of the small block guys claiming if you build a street engine and don’t use a 4 inch arm it won’t drive.
If that’s the case they should just build a big block. And they would shove a long arm in that and do the same thing it.
I start post for types of conversations.
I don't have any vested interest what the OP builds, whatever he feels best suits him, for better or worse, best we can do is lay out realistic pros and cons and then it's up to him which way to go, then try to help him get the best out of whatever choices he makes.
He doesn't seem to have any interest in what my next move would be if I was him and I'm fine with that, still gonna try to help with whatever I can if that is to call out this idea you need to do like a Nascar level build to make 500+ hp out of a 340 that's what I'll do.
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