CHP article
Thread Starter
Le Mans Master
Joined: Jun 2005
Posts: 5,037
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From: Texas
CHP article
I was flipping through August 2006 issue of Chevy High Performance and found an interesting side bar on page 83, "Bore vs. Stroke". I am planning out an engine for my (now) offroad C4. Currently, I was thinking of a standard 383 but now I am curious about something.
The Little "M" block supports a bore of up to 4.185" and a stroke of 3.875". After doing some math, I found that a 4.175" bore and a 3.5" stroke will get you 383.3 CID. Forgetting about part availability for the moment (I am not sure how many companies make a piston for a 4.175" bore short of custom making them and the only 3.5" crankshafts I can find are two piece rear mains), how would the bored out 383 compare to the standard, stroked 383? Pros/Cons of each setup?
Lets say the configuration is a 200cc head with Miniram intake (or a single plane intake). The camshaft I am unsure about since the RPM range might be different with the smaller stroked engine. I am not sure if the same profile camshaft would benefit each engine the same or if both engines would need a completely different camshaft profile to compliment it, so that is a wildcard.
Anyone running a large bore, small stroke engine V8?
The Little "M" block supports a bore of up to 4.185" and a stroke of 3.875". After doing some math, I found that a 4.175" bore and a 3.5" stroke will get you 383.3 CID. Forgetting about part availability for the moment (I am not sure how many companies make a piston for a 4.175" bore short of custom making them and the only 3.5" crankshafts I can find are two piece rear mains), how would the bored out 383 compare to the standard, stroked 383? Pros/Cons of each setup?
Lets say the configuration is a 200cc head with Miniram intake (or a single plane intake). The camshaft I am unsure about since the RPM range might be different with the smaller stroked engine. I am not sure if the same profile camshaft would benefit each engine the same or if both engines would need a completely different camshaft profile to compliment it, so that is a wildcard.
Anyone running a large bore, small stroke engine V8?
Burning Brakes
Joined: Feb 2005
Posts: 894
Likes: 91
Originally Posted by Performance nut
I was flipping through August 2006 issue of Chevy High Performance and found an interesting side bar on page 83, "Bore vs. Stroke". I am planning out an engine for my (now) offroad C4. Currently, I was thinking of a standard 383 but now I am curious about something.
The Little "M" block supports a bore of up to 4.185" and a stroke of 3.875". After doing some math, I found that a 4.175" bore and a 3.5" stroke will get you 383.3 CID. Forgetting about part availability for the moment (I am not sure how many companies make a piston for a 4.175" bore short of custom making them and the only 3.5" crankshafts I can find are two piece rear mains), how would the bored out 383 compare to the standard, stroked 383? Pros/Cons of each setup?
Lets say the configuration is a 200cc head with Miniram intake (or a single plane intake). The camshaft I am unsure about since the RPM range might be different with the smaller stroked engine. I am not sure if the same profile camshaft would benefit each engine the same or if both engines would need a completely different camshaft profile to compliment it, so that is a wildcard.
Anyone running a large bore, small stroke engine V8?
The Little "M" block supports a bore of up to 4.185" and a stroke of 3.875". After doing some math, I found that a 4.175" bore and a 3.5" stroke will get you 383.3 CID. Forgetting about part availability for the moment (I am not sure how many companies make a piston for a 4.175" bore short of custom making them and the only 3.5" crankshafts I can find are two piece rear mains), how would the bored out 383 compare to the standard, stroked 383? Pros/Cons of each setup?
Lets say the configuration is a 200cc head with Miniram intake (or a single plane intake). The camshaft I am unsure about since the RPM range might be different with the smaller stroked engine. I am not sure if the same profile camshaft would benefit each engine the same or if both engines would need a completely different camshaft profile to compliment it, so that is a wildcard.
Anyone running a large bore, small stroke engine V8?
1.-Large(r) bore x short(er) stroke=low torque/high RPM HP
2.-Small(er) bore x long(er) stroke=high torque/low RPM HP.
It really takes a whole bunch much more defining, but that equation has been the "rule-of-thumb" since gasoline units have been around.
This is the reason very few units, both SB's and BB's, are using "short" strokes today. The basic SB is on the 383" unit based on the 4.000" bore platform and the basic BB is on the 540" unit based on the 4.500" bore platform. Thanks Gary in N.Y.
P.S. If you choose a "short" stroke unit you'd best have "light-weight" vehicle to place it in. Short stroke, light vehicle, vs. long stroke, heavy vehicle, it's kinda' been the "standard" for years now!
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by GOSFAST
This issue could involve an extremely long reply, but let me keep it as simple as possible here.
1.-Large(r) bore x short(er) stroke=low torque/high RPM HP
2.-Small(er) bore x long(er) stroke=high torque/low RPM HP
1.-Large(r) bore x short(er) stroke=low torque/high RPM HP
2.-Small(er) bore x long(er) stroke=high torque/low RPM HP
The HRM article showed that the bias's attributed to "big bore/short stroke" vs "small bore/long stroke" engines isn't as viable as once believed (at least by me). There is no doubt that piston speed and it's attending friction is less at any given rpm level, with a shorter stroke.
The old rule of "there is no substitute for cubic inches", still reigns. Unless you HAVE to have a 383 to meet some class rules, take the bigger bore block and stuff the longest arm you can afford into that sucker.
I have a Chevy Bow Tie block that I have left at a 4.125" bore, for strength and future clean ups, and put a 4.00" crank into for 427 CID.
RACE ON!!!
Thread Starter
Le Mans Master
Joined: Jun 2005
Posts: 5,037
Likes: 520
From: Texas
Thanks guys. No, this bored out 383 doesnt exist. Since I read that sidebar, I though I would ask about it. The last sentence "However, there are some exceptions to the rule and you have to look at the entire engine package as a complete system" left me wondering. Thanks.
I must say, the 427 sounds mighty tempting though!
I must say, the 427 sounds mighty tempting though!
Racer
Joined: Oct 2000
Posts: 491
Likes: 12
From: Los Altos Hills, CA
Performance nut:
The big bore, small stroke SBC is actually a popular combo and a "class" size motor for the circle track guys. Typically known as a 377 (4.155 bore x 3.48" stroke), you will find performance suppliers have all the parts to support this motor. The old school way to build this motor was to take a 400 block and get oversized bearings to allow the 400 journals to fit a 350 crank. (The bearings are off the shelf stuff.) With aftermarket blocks, you buy the small (350) journal Dart, Motown, or Bowtie block and directly drop in a 3.48" crank, well actually a 3.5" crank cause that's what the aftermarket crank grinders support. You will then find lots of catalog pistons to support this motor at a 1.25" pin height that mate up with a 6" rod and a 9" deck height.
This is typically used as a high RPM motor. For a street motor I'd go for the cubes. I am going to try a 374 (4.125" bore x 3.5" stroke) for autocrossing.
The big bore, small stroke SBC is actually a popular combo and a "class" size motor for the circle track guys. Typically known as a 377 (4.155 bore x 3.48" stroke), you will find performance suppliers have all the parts to support this motor. The old school way to build this motor was to take a 400 block and get oversized bearings to allow the 400 journals to fit a 350 crank. (The bearings are off the shelf stuff.) With aftermarket blocks, you buy the small (350) journal Dart, Motown, or Bowtie block and directly drop in a 3.48" crank, well actually a 3.5" crank cause that's what the aftermarket crank grinders support. You will then find lots of catalog pistons to support this motor at a 1.25" pin height that mate up with a 6" rod and a 9" deck height.
This is typically used as a high RPM motor. For a street motor I'd go for the cubes. I am going to try a 374 (4.125" bore x 3.5" stroke) for autocrossing.
Thread Starter
Le Mans Master
Joined: Jun 2005
Posts: 5,037
Likes: 520
From: Texas
Originally Posted by chuntington101
american speed build a 685bhp motor for he Ultima GTR that is a 377. with the GTR oinly weighinut 2200lbs and using a porsche box that is rated at about 650lbsft its the ideal engine foe the car 
Chris.
Chris.
And for $22.5k, they can keep it. Besides, that is most likely a stroked 377 (4" bore with a 3.75" stroke).Still, 1.8HP per cubic inch is pretty impressive. Wonder what octane fuel it requires?
Racer
Joined: Oct 2000
Posts: 491
Likes: 12
From: Los Altos Hills, CA
The American Speed 377 is a big bore small stroke motor. It truiy is amazing the amount of HP they coax out of (relatively) low compression motors. The high-doller motor you are talking about is the full-on deal with dry sump. They would be happy to build a low-buck version of the 377 for a lot less than 10K. I have been to their shop in Illinois because my in-laws live there. I would have no hesitation having them build a motor.
They also have close ties to AFR. If you check out AFR's website, American Speed has built several of their dyno-tested samples.
They also have close ties to AFR. If you check out AFR's website, American Speed has built several of their dyno-tested samples.
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Thread Starter
Le Mans Master
Joined: Jun 2005
Posts: 5,037
Likes: 520
From: Texas
Originally Posted by Cris
The American Speed 377 is a big bore small stroke motor. It truiy is amazing the amount of HP they coax out of (relatively) low compression motors. The high-doller motor you are talking about is the full-on deal with dry sump. They would be happy to build a low-buck version of the 377 for a lot less than 10K. I have been to their shop in Illinois because my in-laws live there. I would have no hesitation having them build a motor.
They also have close ties to AFR. If you check out AFR's website, American Speed has built several of their dyno-tested samples.
They also have close ties to AFR. If you check out AFR's website, American Speed has built several of their dyno-tested samples.
Drifting
Joined: Jul 2001
Posts: 1,897
Likes: 0
From: La Fontaine Indiana
I remember about two years ago one of the auto rags had a article about this it may have been CHP. They built a 377 and run it on the dyno then put it in a old nova and run it at the drag strip After that they built it into a 406 using all the same components. Their was a slight difference in what rpm made max torque and power but the bottom line was the 406 made more torque and power and it was quicker at the strip when installed in the same car. Unless you are going to run in a class where you are restricted to a particular size it would be foolish so spend more money just to make the motor smaller.
While it is illegal a lot of us from time to time are guilty of street racing and in that case no class you run what you brung and you better hope you brung enough.
While it is illegal a lot of us from time to time are guilty of street racing and in that case no class you run what you brung and you better hope you brung enough.
Instructor
Joined: Dec 2004
Posts: 119
Likes: 0
From: Vancouver British Columbia
Originally Posted by Performance nut
Thanks guys. No, this bored out 383 doesnt exist. Since I read that sidebar, I though I would ask about it. The last sentence "However, there are some exceptions to the rule and you have to look at the entire engine package as a complete system" left me wondering. Thanks.
I must say, the 427 sounds mighty tempting though!
I must say, the 427 sounds mighty tempting though!
Le Mans Master
Joined: Apr 2003
Posts: 7,154
Likes: 1
From: I blame my Dyslexia MD
As far as finding pistons, you can probably have some made in the range of $1000-1500. I am currently starting a piston design for a person project and most quote for my 4 high dome alfa romeo pistons come to $550-650, not inc. rings, pins, ect. Now you might say you don't want to have to design a piston for your engine, but really, talk to Ross or Combustion Technologies or anyone else in the market, and they would just make a regular small block piston bigger for you.
I like the idea of having a big bore small stroke high rev engine, but then again I am selling my vette and going for something completely different.
MAtt
I like the idea of having a big bore small stroke high rev engine, but then again I am selling my vette and going for something completely different.
MAtt
