Big Block vs Small Block

George

CURRENTLY BANNED
Hello Guys

Me not being an engine builder or anything even close to one, I dont understand the relation between HP/Torque/RPMs etc.

To what I do know...

In a muscle car, that weighs alot, if its a purpose built circuit car, better of going small block as it weighs less and can make huge power.

On other hand big block has a flatter torque curve making it more fun on the street in a sense (But sacrifices handling due to weight)

Now in a GT40 which weighs nothing, big block or small block it still weighs nothing and the added weight of a BB might be favourable as it will give it some extra grip with that extra weight on rear wheels, however wanting a full alloy block etc, theres not gonna be much weight difference at all.

Now

Why would I option to go with a small block over a big block, in terms of... Small Block provides more RPMs than a big block...

Why would someone want more RPMS when I can get 600hp out of a big block...

Yes a small block will be a hotter motor to produce 600hp, but why go small block 600hp High rpms vs big block motor, 600 hp low rpms?

Would the small block have more top end speed due to being 'more race like built' or power is the thing that dertermines top end speed not RPMs...

Hope u kinda get what im trying to ask... im finding it hard to write up.
 

Doug S.

The protoplasm may be 72, but the spirit is 32!
Lifetime Supporter
General rule of thumb....torque is important for acceleration, horsepower is important for top speed.

If you're trying to be period correct, the rule would be for MKI and MKIII, small block, for MKII and MKIV, big block.

Other than that, it is a matter of personal preference. The small block will be more difficult to drive if it is configured in a high-horsepower, high RPM manner. You'll need to give it more RPM's to get it started from a standing stop, and the power band will be higher in general than a big block with equal horsepower.

Do you like the "snarl" of a well built, high compression, high RPM small block, and are you willing to sacrifice the drivability to enjoy that sort of engine? I do, so for me, given that my body choice would be a MKI, the choice is obvious.

Engine compartment room is important, too...while I suppose it's been done, an FE in a MKI might be a bit tight (understatement is only one of the many fine services I offer). Keep in mind the FE was a torque monster, so you're more likely to encounter power capacity/longevity issues regarding the transaxle, too, not to mention cost factors to get one built to handle the big-block's torque capacities.

"Mid-block" engines of the 351W and 351C variety are an option....better torque than the 289/302 series, higher horsepower potential, easier to fit than an FE. Still, you may have to give up "the look" if you want Webers or IR stack fuel injection, depending on how low you can get the engine/transaxle combo mounted.

Don't even dream about the Ford 385 series engines (429/460 CID), which is a shame IMHO, as they make cheap power and lots of it!!

Lots more factors to consider, too...front dress being one of them, availability of things like A/C if you want that in your car, yada, yada, yada.

Good topic...I'm sure you'll hear from many others, it's a timeless "my dog is better than your dog" issue among us Fordophiles!!

Cheers from Doug!!
 

Terry Oxandale

Skinny Man
I've gone the high-stressed 289, followed by the torque monster 383 (351W stroker). The intent of the 289 was a motor that I could twist fast, yet have sufficient torque to move a small car without spinning the tires all the way down the road. With the 289, it was set up for a 6700 RPM peak torque, which made for a fun ride in a 2300 lb car. And the sound of the 289 twisting to 8000+ was a blast! The lighter motor was another attribute.

Then I decided to try a new feel...of more torque, but less RPM potential. I went with the shortest "stroker" kit for the 351w. It had the best rod length to stroke ratio, and was very strong even at 7000 RPM. Peak torque was about 5880 RPM, Same size headers (1-3/4" tubes), but I used a Jeg's Torque Masters Competition winning spare camshaft. This change transformed the car into a monster that took some getting used to. Even with the 315s, it treated them like 225s. As it ended up, the 383 only weighed 60lbs more than the 289.

Long story short, torque is what you feel, and when I look at both engines, I'd have to say hands down, the torque motor won out as it related to overall "fun". Yes, the 383 had a lot of internals that allowed it to live at a 7000 RPM shift, but having a large percentage of the torque curve coming on at 2500 RPM was even better.
 
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Any Ford V8 has loads of torque compared to most high performance engines, particularly those from Europe (ferrari, lambo, maser, etc.). A SBF in basic form with decent induction provides tons of torque and power for a GT40 replica.

Light is fast no matter what the configuration. Lotus proved this in F1 back in the 70's and it's just as true today.

Personally, I think the sweet spot is an alloy block SBF with a modest stroke on it (331) and good internals, heads, and valve gear so that it can run up to 7K without imploding and put out peak hp/tq in the range of 425+/425+ on a nice progressive (and flat) torque curve. Frankly, that's more power than most non-pro drivers can handle safely!
 
I like Cliff's idea of an alumimum SBF at 331CI or even a 347. Good torque and rpm available throughout.
 
To Simplify this a bit...
1. It doesnt matter whether its a big or small block, once you get above ~7000 the valve train will become expensive & require more frequent maintainance.

2. Big Blocks with large cylinder diameters become somewhat sensitive to flame travel distance & octane rating especially when you start to push them hard at higher RPM for longer time/distance at Wide open throttle.

3. The transaxle thing is an issue, but a lot of the problems appear to be driver related, this is not a 'new' thing, reading a lot of the comments from guys like Bondurant etc shows that the better drivers [ or to be more correct the ones that had consistant success ] were those that had a high degree of mechanical sensitivity & were easy on gear changes & throttle application etc.
 

Seymour Snerd

Lifetime Supporter
George --

This discussion is getting kind of diffuse (and it usually does; it's old as the hills), so let me point out some possibly clarifying points:

  1. Horsepower is torque multiplied by rotational velocity (RPM) so strictly speaking in a mathematical sense they are inexorably tied to each other; if you know one you know the other. So common wisdom like "torque is for acceleration, HP is for speed" are incorrect, although they each have a grain of truth. You accelerate in proportion to the amount of torque the engine is putting out at that moment (that's one grain of truth).
  2. The word "torque" is precise in the scientific/engineering world and can't correctly be "opposed to" horsepower (see above). But in the automotive world it has a second meaning: an engine with "a lot of torque" usually means "makes relatively large amounts torque at low RPM vs what it makes overall". This is how it's used in most of the preceding posts. What people are really describing is the shape of the torque curve, not the amount of torque. But when you are looking at the torque curve from a dyno run, you need to think in terms of it's formal meaning: amount of rotational force.
  3. As Terry says, if you want to know how the engine is going to feel, look a the torque curve.
  4. Horsepower is a term of convenience to attempt to express in one number the total overall performance capability of an engine. However, it is really only useful when you have control over gearing. If you don't, it's easier to mentally evaluate the engine's behavior by thinking in terms of its torque curve.
  5. A relatively "high horsepower" or "highly tuned" engine usually does so at relatively high RPM, which means it's torque figure (all other things being equal) is relatively low. So with the same gearing it will have a higher top speed (the other grain of truth).
  6. Big block vs small block have nothing to do with large displacement vs small displacement except that the small block engines cannot be made as large in displacement as big blocks. So you don't want to confuse the two subjects. BB and SB are just historical design families of engines. Aside from history, the only profound difference is that BB's can have larger displacement than SBs because they are, well, bigger. But they are heavier (somewhat). And they have a whole bunch of other differences completely unrelated to size but that are important to understand.
  7. For a small-displacement engine to generate the same horsepower as a large displacement engine, the small one usually has to be configured to makes its horsepower at a higher speed. Thus it is thought to have "low torque" although what "low torque" usually means is "lower torque at low speeds than at high speeds." This is why small displacement engines (in our context) tend to be associated with higher RPM. But that's a side effect of the decision you make about the engine family (big block/small block) and the displacement you choose.
  8. There is a large amount of overlap in the displacement ranges available in each engine family. The Windsor family easily goes to 427 CI, the big block (FE) family goes as low as 332 CI.
  9. The upshot is, don't confuse
    1. "Torque vs Horsepower"
    2. Big vs Small block
    3. Large vs small displacement
    4. Highly vs Mildly tuned.
  10. My main point: All four concepts mean entirely different things and are essentially independent variables that (except for #1) you select from. You can have a small block engine of large displacement with a lot of torque. You can have a big block engine with low torque. You can have a small block engine making more horsepower than a big block engine.
Until you have all four concepts clear in your head none of this is going to make sense. To put a finer point on it, the first two things you said you "know" are completely false.
 
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what engine is lightest and wich engine can be mounted the lowest etc when you want say around 500 NA/hp
also which type needs the lowest attention (reliable)
I guess when you drive a "new" replica on old plates you need also an "old" engine...
so sadly no modern reliable engines can beinstalled then I guess...or are there ways.
 

3. The transaxle thing is an issue, but a lot of the problems appear to be driver related, this is not a 'new' thing, reading a lot of the comments from guys like Bondurant etc shows that the better drivers [ or to be more correct the ones that had consistant success ] were those that had a high degree of mechanical sensitivity & were easy on gear changes & throttle application etc.

This is probably where you should start. I think this has been Howard's mantra from day one. Figure ot what transaxle you will be using, and many of your options are settled. Big block FE have been fitted into MkI replicas, with interesting results:

1966 CAV GT40 - 640 HP For Sale | GT40 ArchivesGT40 Archives

With a BBF, transaxle choice really becomes the main issue, even if driven calmly. The sheer amount of low end torque (or, more appropriately, the sheer amount of torque over a broad range) that you get from a well built BB is going to need something stout. Ford/Shelby realized this when racing the MkIIs and MkIVs. The ZFs did not hold up, so the Kar Kraft T44 was used. So, perhaps a highly modified ZF or Porsche G50, G50/50, or 930 4 speed may work, the reality is, you are going to spend big bucks to properly harness a built BB for any kind of driving other than Sunday light foot cruising. Recalling earlier posts/queries you (G-man) made, I do not think this is an option for you.

You are going to be much better served and happier with a 302 or 351W based stroker, mated to a well sorted ZF, ZFQ or Porsche transaxle with suitable gearing.

Ian
 

George

CURRENTLY BANNED
Hi

Thanks for all the feedback

Half of that I dont understand as its technical...

Can we simplify it to this

A hot built Small Block (351-400ci) (race cam etc etc etc) to produce 600hp and whatever torque it would have, I assume around 500-550ft/lbs

Vs a Mild built street big block with 500ci producing 600hp and 600-650ft/lbs torque.

Which 1 would be the 'faster' car around a track and in acceleration 0-100km/h etc.

THe race built SB or the Street built BB which has 100 flbs of torque 'more'.

In that sense, the race built motor has MORE RPMs but the BB dont need the RPMS, that might help me understand a little easier what Im trying to work out.
 

Seymour Snerd

Lifetime Supporter
Half of that I dont understand as its technical...

Can we simplify it to this...

No, George, you can't simplify it to that. It can't be made simpler and it can't be made not-technical.

What's the title of the forum?

"GT40 Tech"

...help me understand a little easier what Im trying to work out.<!-- google_ad_section_end -->

You're asking basic automotive questions that you could answer for yourself if you would just put some effort into it, like read a book or some wikipedia articles. This is not a "basic automotive" forum nor is it a "Make life easy for George" forum.
 
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George,
A mild 302 will give you heaps of fun in a GT40. Look at the XR8 220kw 302ci based engine or the 347ci engine in TE50 or TS50 Falcons they go hard in 2tonne cars. In a GT40 they would lightup very nicely. good enough to loose your licence...
Cheers, Gus.
 

Jim Rosenthal

Supporter
It sounds to me like 1) you REALLY ought to do some reading, George, and also 2) invest in a driving course before you buy a car. A few hours behind the wheel with good instructors will teach you things you will never learn sitting behind the wheel of a PC.

And for some practical advice, if you ever DO buy a GT40 replica, start with a robust transaxle, like a ZF, and a SBF in the range of 350hp or so, with a rev limit of about 6000 and a relatively mild cam. That will be good for all the thrills you can handle. And maybe serve to keep you from killing yourself and your car until your driving skills catch up to your ambitions. Then you can get a bigger engine- either in cubic inches, or tuning level, once you can handle it.

There's a good article in SCM a few months ago about the level of performance of modern sports cars, written by Mike Sheehan. It's about Ferraris, but it applies to all of us. Most of us on this forum own cars whose performance potential is scary. Most of us are older, and experienced, and so far only one Forum member has been killed in a GT40.

That was, IMHO, one Forum member too many.

So watch your appetites, George, and get some experience under supervision in someone else's car.
 
Geez, people need their grumpy pills today...


G-man-
Torque is a measurement of a twisting force.
Power is work that can be done with that torque i.e. torque x revs. You just need to think about that a bit.
I recommend you read about force, torque and power on howstuffworks.

Deleted my explanation when I realized howstuffworks did it better... :)

Get that and what it means well understood, why gearing is important will become clear, then throw in weight etc and you'll be able to answer your own questions. :)


What's with the grumpy crap?
People ask for advice or to be taught by people they think can help and they get condescending answers that border on abuse... Great... Ffs, this used to be such a great forum...

Tim.
 
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George

CURRENTLY BANNED
Thanks Tim.

The time I asked on here was when I couldnt find anything after searching and searching AND searching, I didnt just "hey lets ask on here to make life easy". I read things like Torque vs Horsepower, Torque vs RPM, and so on so forth but none of that told me why build a race engine small block over a street version big block when both would have same power but the BB would have MORE torque than the race engine due to the CI capacity + be more economical on the road aswell.

I was just wanting to know why go SB with power, when that engine becomes not very street friendly due to being hotted up, and not economical at all, and yet a BB would have the same power and MORE torque while still being a totaly street friendly engine WITH some what economy in comparison.

From the asking around engine builders here, they said

"If both engines a 351ci Race engine and a 511ci street engine produced 600HP, the 511ci would eat the Small block for breakfast because it would have over 100ft/lbs of torque MORE than the Small block. They also said HP = top speed, not RPM. So it doesnt matter that the small block can rev up to 8000rpm and is 'race like', it still wont go any faster top end than the BB would at 6000rpm (if the BB is geared for top speed) and the BB would get the torque coming on sooner, making it pull away from the SB."

So in the end if thats the short version of the whole thing... then BB is better, its more economical for street use, accelerates faster, and has same top speed and would last much longer than the Small Block.

This is why I asked "Whats the point to getting a SB RACE engine", was something in there that Im missing?

1 other engine builder said "The Small Block would be MORE responsive than the BB and he would for circuit application pick a race small block due to that"

I asked "what do u mean by More responsive?" He said "More lively" So I said thanks for ur time and left it, realised im not getting anywhere with that.

O and I just shrug when I read stuff like 'bla bla bla' as if I did something wrong.
 
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I highly recommend that you really get your head around what all this means. As said previously, although the basics are relatively simple the real life choice you have presented is quite complicated.

You've edited since I responded. To be honest I disagree with a lot of what is said in your edited post but I'll just repeat what I said at the beginning of this post - spend a bit of time getting your head around this subject.

I'm not sure why but people never seem to quite get the concept of torque, and seem to misunderstand what power is.
I have had someone tell me that their understanding is that torque is bottom end power and power is top end power - this seems to be quite a common misunderstanding. I could not shake him of this view.
You need to get back to basics and really understand what it means.

Please reread Alan's post #7, it is very good.



Tim.
 
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Keith

Moderator
Well George, the Americans have always said "There is no substitute for cubic inches" and in a sense they are right. At the other end of the scale you will find engineers such as Colin Chapman who felt that the lighter you build a race car (including the motor) the faster it will go and the kinder to tyres etc etc.

In Europe now, they are developing massive engines because in a sense it is cheap and lazy horsepower which will never get stressed in a non race situation so I do suppose the American cubic inch prinicple is now accepted practice.

Personally, I prefer the sound and performance of a 'screamer' A low capacity but highly tuned motor in a light chassis. I have raced all sorts but much prefer the feel of a lightweight high revving thoroughbred but that's just me.

It isn't something you have to dwell on now, but as has been said previously, it is the torque that can kill your transaxle, shred tyres, and generally strain your drivetrain. Which is quicker? Depends on the driver but it has always been said that on most racing circuits, there are more bends than straights, so a nimble lightweight chassis with a lightweight high revving engine will possibly give you more of an edge.

But, there is no definitive answer. Everyone is right and everyone is wrong. The engine is NOT the most important component in a high performance car, but it is one of them. Brakes, suspension, gearing, aerodynamics and driver skill all play a vital part in overall performance and all fun to work out and develop in their own way.

Remember George, the journey in developing a unique car is sometimes far more interesting than reaching the finish line:)
 
I am also in the car is more than an engine camp, as well as the fast is more than just straightline acceleration and top speed camp.

Chapman was a f.....g genius, Shelby just a hot rodder. That's my opinion and you're stuck with it. ;)

Tim.
 
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