Cstraub69

to many of these on here and for you guys these combo's would be more street friendly and cfm friendly. Why are more of you guys not putting these together?

Belgian1979vette

Most have thing for the CI-rule.

Cstraub69

What is the CI Rule?

gerry72

There is no replacement for displacement.

Cstraub69

The shorter stroke with a 3.48 or 3.5 crank will give you less piston speed which puts less demand on the induction allowing for less camshaft and less intake volume. This kills 2 birds with one stone, gives you better idle characterics which seems to be important with the majority and the need for less intake which helps with hood clearance issues. You still get over 370CID.

cv67

Sure these guys would be interested in hearing good power combos that fit under the hood Chris go to it.

Cstraub69

Let bore make up your CID and slow piston speed, which swallows up induction and makes for bigger cam profiles, with a shorter stroke. This would give owners CID in excess of 370 CID and lesson the load on the induction system by slowing down the piston speed.

Les

The short stroke also allows for more RPMs if somebody wants to build a motor with that goal in mind. That's my kind of motor and if I was building one for fun I'd be considering that combo.

Little Mouse

Most today want to operate at lower revs everything from 1800,2000 rpm freeway speeds to very low rpm juice cams to just keeping there 3.08 rears. So if your going to stick to 372, 377 or 383. the longer stroke smaller bore is more of an advantage. Your not trying to turn any rpm 90 percent of the time therefore piston speeds are still kept low 90 percent of the time. So the longer leverage arm of the longer stroke is more helpfull then the bigger bore short stroke. Someone willing to run better gearing and higher revs then the bigger bore shorter stroke becomes the advantage.

Cstraub69

Most street cars on street tires can hold 450# ft of torque. A large bore, 4.125" x 3.48" stroke engine can make this amount of torque without breaking a sweat. The reduced piston speed equates to smaller cams needed with such heads like AFR/Brodix/Dart which gives the user a much friendlier powerband at the lower driving speeds.

v2racing

If you build a 377 with good heads, cams, compression, etc... all matched up well to build the power band you are looking for, a change in stroke to build a 406 (3.75) with the same compression will amount in a large gain in bottom end and mid range with a little gain in peak horsepower. It will act milder with the same cam as the 377, pull more vacuum, will make it's power at lower rpm's and won't have much of a piston speed increase because the rpm range is lower. I've played with different size engines with the same combination and only change stroke. This is what I have seen every time, and not just in Chevy's.

Cstraub69

It requires a cam change. The demands piston speed put on induction makes it a must to change camshaft. Larger stroke needs larger camshaft.

gerry72

Where does this notion come from? True, a shorter stroke does reduce piston speed. I'd like to see your data/research that lays the foundation for these principles tying piston speed as a critical component to camshaft and airflow in a street application. I'm not too old to learn something new.

gkull

This is the same old stupidity of using 3.00 and 3.25 stroker cranks.

The rule is: As cubic inches goes up the less RPM required to make the same amount of power. So that blows the less feet per minute of piston speed out of the water if you are comparing like power levels.

Also from a practical factor. It cost the same to build a forged 421 ci as a 370 ci

If your tires only handle 450 foot pounds........... Have you ever thought about installing 335 width sticky tires?

Cstraub69

Why wouldn't it? Greater piston speed puts more demand on the induction system as it creates a greater depression that needs to be filled. Take 502's and 496's. The 502 is greater in CID but needs less cam than the 496 when equally headed for same rpm. Piston speed puts more demand on induction therefore the valve needs to be held open longer.

Cstraub69

Smaller camshaft will allow more cylinder pressure on the shorter stroke. More cylinder pressure more power.

Would you say a 427 CID BBC on pump gas that makes 579# of torque makes nice torque for a street engine?

A 421CID with either a 3.875 or a 4" stroke requires a kickout style oil pan at the pan rail. These pans are not cheap.

gkull

I don't have all the scientific data to prove or disprove whether a short stroke motor of the same ci as a long stroke motor of the same ci with identicle heads and cam would create more power.

If I have a 50 cubic inch cylinder. It still is filling the same amount.

I do know that longer stroke motors are more fuel efficient for the same ci. The brake-specific fuel consumption (BSFC) is lower. emmissions are lower in a long stroke.

OH, I run a 434 ci small block in my Vette and it beats up on BBC Vettes on road race track.

Crepitus

Gkulls got it right here. Unless there is a class CID limit the long stroke wins. the 377 (destroked 400) bottom end can spin more rpm than a 383 with comparable parts. BUT a 383 3.75 stroke has a slight advantage in leverage the piston is pushing in a 1/4" longer arm. There is a bunch of friction and cyl filling data points that can be batted around but here is some real world application that makes the difference.
A 383 will turn 6500 with fairly cheep parts. Hydraulic cam will also turn 6500rpm.
A similar 377 bottom end can do nearly 7000 but then you will need a mechanical cam.
A 400 that turns 6500 is a nice little step up. Still uses a Hyd valve train unshrouds the in valve a bit and coughs up a extra 20cid read that 20-30hp
If you have a 4 1/8 bore it makes little sense not to take advantage if an additional 20cid with the 3 3/4 stroke

Cstraub69

The greater the piston speed the more demand (depression created) it put on the induction. That is a fact. Think of it as wheel and tire size. Car goes down the road 70MPH, a 14" tire has more wheel speed than a 17" tire.

Cstraub69

Why would you need a mechanical cam? I have BBC hyd rollers spinning 7300 rpm plus. The "internet myth" that a hyd roller won't spin rpm is just that, a myth.