SBB 350 Square Engine advantages.

I was looking up square engines, ie engines with same bore and stroke. I found buick 350 and Caddy 500. A 350 is basically a small 500 which is the king of low end torque even more than the mighty 455 because of its design it builds its max torque low in the rpm range 2400. Does anyone in the sbb forum take advantage of the square design and build for low rpm?

 

It isn't as simple as "long stroke = torque, short stroke = hp".
The induction controls it all, with limitations on torque due to cubes.

One of the issues with trying to get a peak torque well below the port's limiting airspeed is that you have to restrict it to do it.

Peak tq closely follows airspeed through the port. Peak hp happens just before the port chokes out, appx. 1500-2000 rpm higher.
When you try to lower the peak tq rpm via shorter cam events or restrictive intake/exhaust the hp drops, the VE suffers (cylinder fill%), the torque eventually suffers.
You can tilt the curve slightly lower with the cam, but you are still choking the cylinder.

You can try to squeeze it tighter (compression), enhance combustion via shorter rod (faster peak piston speed and more pull on the intake) and more mixture motion (swirl the port faster, releasing more energy from the burn), enhance VE in that range (longer intake runners-ram tuning and cam lending to higher airspeeds through slight restriction), but there's a limitation there.
The Buick already takes advantage of most of these.

You can build more torque than stock with surprisingly...faster flowing heads (ported and valve job tricks, enhance swirl), slightly more/faster cam profiles (more VE%), long tube headers (scavenging for higher VE% and cylinder pressure), etc.
Even if you think the slightly greater cam would push the peak rpm's upwards, a better VE and combustion will bring the bottom up as well, keeping in mind that the further up you push everything the more response you lose down low.

If the reason for wanting to push your peak torque rpm's low is mileage and towing, keep in mind that you can still make improvements by 'slightly' raising the powerband and running the engine in it's more efficient range.
Engine sees lees load = less throttle opening = higher manifold vacuum = less actual air mass inside the engine per rpm level.
Basically, there's less inside the engine but it releases more energy due to it's moving faster...make sense?

Being that the gasoline engine is fairly limited to cylinder pressure at low rpm's, diesels are most often looked at for their ability to handle cylinder pressure if the low rpm is a must.

This help?

 

The problem with what many people do when they build a Buick 350 is they add to large of a cam and they kill the low RPM torque.

Below is example of the cam I have used in a bunch of engines and it works great for low RPM torque and mid range power. I have used it with and without the turbos. Sure it gives up some high RPM HP but for a street car the TQ is needed more.

This is a desktop dyno but it is pretty darn accurate. Poston 114 cam:



And the larger cam see the loss in low RPM torque? Poston 111 cam:



And when my turbos were sized they were kept small to give super quick response to further enhance the low/mid RPM range.

I feel that the Buick 350 is an airflow challenged engine and until the get the alum heads then forced induction is the best way to make power with them. The bore is small, and a larger bore can help the cylinder heads flow more air into the engine, however if strength is a concern (as in a boosted application) then we need all the cylinder wall thickness we can get so I stay with stock or 30 thou overbore. Stroking the engine can raise the torque substantially, but a lot of custom custom work is needed to make it happen.

If I wanted to build a Buick 350 for low RPM torque engine it would be a stroked out version with a supercharger.

 

Excellent post, Tony.

Adding to it and putting actual parts to the picture, I have designs on such a beast using much of the aforementioned methods along with a Crower level 2 cam (or custom variation, haven't quite decided yet, but very similar), a large 2v carb (of course, and for reasons I've discussed before), high compression and merge pipe/manifolds along with some intake manifold/head/exhaust manifold porting/massaging techniques as well as getting it as close to 'blueprinted' specs as I can.

I could add in long small tube diameter headers for max effort in this regard, and may still, but the goal is to try and get as much as reasonably possible out of a very basic 350-2 combination just to see what it's capable of using these parts.

I've done this type of build before, but it was a long time ago and I want to implement some tricks I've learned along the way that weren't used back then.

The results then were impressive, and would only be improved.

Final componentry isn't chiseled into stone yet, so there may be some changes, but the basic premise remains the same.

This engine would be an excellent candidate for the ST300 transmission that everyone seems to love to hate, and so the controversial combination would be complete with this entire package, including the big single exhaust in my G body Regal. lol

...only THIS time, it will see track time and recorded results instead of just a recollection of memories, the validity of which could be questioned.

I figure the 3.23 beefed up 7.5 Torsen rear (using the 'bulletproof' recipe among other tricks (including the 28 spline axles) I plan to implement) would hold up fairly well to the gentle persuasion of a 1.765:1 low gear...

The Buick 350 is renowned for its low-end grunt in stock form, even the later models with super low comp and tiny cams, so none of this should come as any real surprise.

What may come as a bit of a surprise, however, is just how much grunt you can get out of one using very simple stuff that most hotrodders would have chucked in the trash.

Doing more with less!

Some may ask why? To which I say: why not?

It certainly won't compete with dragsters or modern day muscle, but it would definitely be different and interesting and fun.

Who knows, maybe it'll start a trend. haha

Either that, or it'll be a total and complete flop and I'll go back to the drawing board.

I do strongly suspect, however, that quite the opposite will be highly likely.


Rather than hijack this thread, I'll start a new one when my plans become closer to fruition.

 

and then what would the numbers be at what rpms?

 

as author of this thread I hereby authorize you to hijack/augment it at will. thanks for your input! p.s. when will this engine be ready for testing as my residual youth and lifespan are limited?

 

Copied from the other thread...

RPM range? That's more of a function of the induction system.
It is true that there are very small % differences in mechanical leverage.
At the rpm's of street and mild race engines like we see on these forums, the limitations of bore/stroke aren't so much of an issue.
There are much greater gains to be had on the induction side of things, percentage wise it can easily overcome bore/stroke differences.
To the induction system, a longer stroke makes it act like there's more rpm, due to peak piston speeds being higher.
Are there similarities within the Buicks? I'd closely study the induction systems for similarities.

As a general comparison, a 454 BBC and B455 have similar bore/stroke.
For the most part, the 454's induction was designed for a higher rpm range.
Larger ports, valves, combustion chamber more suited towards mixture motion (swirl) for a higher rpm range.
The B455 has more swirl and slightly faster port speed (CSA), which works with a combustion chamber more suited to the slightly lower rpm range intended by the engineers.
The newer iterations of the 454 BBC used smaller ports and more Buick looking chambers to rival the torque and response below peak torque rpms.
Peak torque still being mostly controlled by a limiting speed through the port and how it mathematically correlates to "the size of the cylinder", not the bore/stroke ratio...even though things can be done to enhance output below peak torque.
Keep in mind when reading magazine articles, they weren't always using fully correct info or valid descriptions.

 

Right off idle it would make enough torque to break driveshafts, rear ends, and transmissions:

https://www.youtube.com/watch?v=zktYYQhCtqU

 

I built a 215 to optimize the torque curve and it was reasonably successful. I did it by adding an Eaton M-90 blower, which at WOT in the upper rpms exceeded 16psi of boost but that was only half of the story. It was not a max HP effort.

Now the 215 is not a square engine (2.8" stroke x 3.5" bore) but it does share the 350's general engine geometry and to some extent, it's limitations. My approach was to use an 8:1 SCR, intercool the blower output somewhat, and add efi and edis. The rest of the induction system was kept stock, for the reasons given above, and to limit max cylinder pressures at the top end. In fact I used the Olds heads which are claimed by some to be even a bit more restrictive than the Buick ones, and used a stock cam. (I wanted the extra row of head bolts, six per cylinder.)

For the most part the results were quite good. Boost began to build very quickly off idle, and by 1500 rpm was making considerable contributions to engine power. From that point on it built very quickly and I do not recall now at what speed the needle pegged but in the power band of the engine it was way up there. The engine speed was limited only by the valve springs and power continued to climb all the way to valve float. At the top end I am quite certain that intake side restrictions were the only thing that allowed the engine to survive. So what I had built was an engine that was overboosted, therefore boost came in early and heavy. Then the restrictions in the intake restricted the output of the blower and kept the engine from blowing itself apart. Yes, this hurt the efficiency of the blower, of course it did. But at that point, this was exactly the goal, and there was a means to help remove excess heat. The result was to maximize power under the torque curve. Realistically, horsepower output was probably in the 300+ range. I never dynoed it. In a 2400 lb car this was a lot of fun. However the low CR hurt it coming off idle. Well, not that you could say that combo was really hurt, but the off idle performance wasn't up to par with the overall engine performance so to a discerning driver it was noticeable. No bog or anything like that, just that letting the clutch out with no gas wasn't as easy as one might expect.

So I agree with Sean that a blower is the way to go to get torque, and heads are the way to go to get horsepower. But I also feel that raising the CR above 8:1 in a blower app needs to be looked at closely. Usually it will mean lowering the max boost but I think that's a fair tradeoff if torque is your goal.

Jim

 

thats a great vid but it doesnt show the low rpm specs.

 

Being that there's some difficulty of a superflow dyno obtaining a good low rpm measurement, maybe someone in your area has a Clayton or Taylor large diameter diesel dyno?
You would be pushing the rpm limits of the dyno at peak hp, but you wouldn't need to run it that high.
It would be a good opportunity to test your Buick in the range you are looking for.
If you are mechanically inclined and think you could operate it safely...maybe pick up a surplus unit?

More importantly, (and less destructive to the engine) would be to come up with a testing procedure that uses transient response or part throttle.
My suspicions are that, you'll not find an easy time getting either low rpm or part throttle-step up torque tests on a sbb 350.
If you are going to look at dyno sheets in the 2200rpm range and lower (converter?) you'll have to take that with a grain of salt, as the run is just stabilizing.

 

So we need a diesel truck dyno to test the buick 350 at low rpm? Something like this one?

 

I just dont get why the dyno is limited to only higher revs? Wouldnt a dyno that can handle all rpms be more versatile?

 

This is something I've been giving some thought to lately.

 

An engineer with no funding paints a sad picture.

 

I'm not a dyno guru by any stretch of the imagination, but I suspect there are physical limitations coupled with the target audience/market that dictates where a dyno will function best, whether it be by physical limitations or practical application or both?

 

Dynos and their ease of use, training, data aquisition, etc. still have to be affordable to the shops, and be useful for the majority of their customer's engines.
Large diameter water brakes can test down low, but it's kind of like a propeller in the water...your boat can idle in gear without much load to the engine.

Gary's post #17 hits it on the head.

I wasn't suggesting a chassis dyno.
A large diameter water brake engine dyno is what they use...they can barely push 4000 rpm though.

More importantly...what are your goals and reasons for wanting the low rpm rests?
Low rpm full throttle is really tough on parts, they blow head gaskets and run into detonation concerns from accelerating the engine at such a low sweep rate (300-600 rpm/second).
Also, the inertia calcs used by the water brake dynos might not be accurate for the sbb 350.
Very few test cells take the load measurement in a manner negating the inertia calcs. It gets more complicated for the dyno testers.

One should consider that running at load below the converter speed would be a wasted test.
A flat torque curve at the bottom of the range still indicates it's strength below that yet.
Another thing to consider is that because of the sweep rate being different, the tune wouldn't be fully optimized for the vehicle.
It still needs to be able to duplicate accel at a rate similar to each gear's, ie. 1st gear and top gear being very different.
Current hot rod style dyno testing is as affordable as it is because of the simplicity to the shop.
(double negatives?)

 

Thanks! trying to say when something will be ready is an effort in futility at this point. Overthinking is my greatest downfall, and tends to cripple me in more ways than just here. Trying to work on that, and yes I know we're not getting any younger.

I would say be patient, but it's more like 'don't hold your breath' because something's liable to change. Ah well.

 

I would not get caught up in the low rpm torque numbers from a dyno.

Simply build the best engine you can and do dyno testing to optimize the tune up, then run it at the track to quantify the performance. Then you can calculate the Hp and TQ from the MPH. Getting the Hp from the MPH is the most accurate vs dynos..

But does it really matter if your car makes 400 ft it tq or 395?

If you have an engine that makes let's just say 400 foot pounds of torque at 3000 rpm and it pulls cleanly from idle then who cares what the actual torque number is at let's just say 1500 RPM?