Allpar Forums banner

1 - 19 of 19 Posts

·
Registered
Joined
·
3,313 Posts
Discussion Starter · #1 ·
Is a 1-3/4" exhaust pipe too small for a 225? What is a good size pipe to use? "Performance" isn't the main consideration, fuel mileage is.
 

·
Super Moderator
Joined
·
21,683 Posts
1 ¾" shouldn't cause any performance or economy issues in normal driving and may even help low-end torque. Fitting it to the inlet of a muffler may require an adapter unless you can come with a 1 ¾" inlet muffler.
 

·
Premium Member
Joined
·
20,158 Posts
If you are replacing the pipe, that is a good size, and if you are just wanting to make sure there is enough restriction and proper flow, remember the rule, the exhaust system is only as large as its smallest diameter/cross section of pipe. So, if the pipe itself that is on there, for example, is 2 inches, putting an adapter and muffler of 1 3/4 inch diameter will be the final overall flow of the exhaust system. It goes the other way, too, a larger 2 inch muffler and end pipe on a 1 3/4 inchhead pipe is not going to help at all.
 

·
Registered
Joined
·
3,042 Posts
Who would straddle a 440 with a smaller Twin exhaust than 2 inch?
2/ 225=450 cui....
 

·
Registered
Joined
·
3,313 Posts
Discussion Starter · #6 ·
If you are replacing the pipe, that is a good size, and if you are just wanting to make sure there is enough restriction and proper flow, remember the rule, the exhaust system is only as large as its smallest diameter/cross section of pipe. So, if the pipe itself that is on there, for example, is 2 inches, putting an adapter and muffler of 1 3/4 inch diameter will be the final overall flow of the exhaust system. It goes the other way, too, a larger 2 inch muffler and end pipe on a 1 3/4 inchhead pipe is not going to help at all.
I'm building from scratch. I've got plenty of 1-3/4" Harley exhaust pipes. The exhaust that was on the truck was cobbled together and the head pipe had a huge hammer ding in it to clear the oil pan rail. A "standard" slant 6 head pipe won't work because my truck has the low mount starter.
 

·
Registered
Joined
·
3,313 Posts
Discussion Starter · #7 ·
Another question. Will a gear reduction starter fit in place of the direct drive low mount starter?
 

·
Premium Member
Joined
·
20,158 Posts
Who would straddle a 440 with a smaller Twin exhaust than 2 inch?
2/ 225=450 cui....
Smaller valves, smaller lift on the cam, all around a 225 will never put out the exhaust capability of a 440, or half a 440. 1.75 inch will be large enough for a slant six all day long.
As far as I know, 2.25 was stock for 44os.
 

·
Registered
Joined
·
3,042 Posts

·
Registered
Joined
·
3,313 Posts
Discussion Starter · #10 ·
AC TC,
You do realize that anything slant 6 related that Doug Dutra has anything to do with is "high performance", right?
 

·
Registered
Joined
·
3,042 Posts
AC TC,
You do realize that anything slant 6 related that Doug Dutra has anything to do with is "high performance", right?

"Is a 1-3/4" exhaust pipe too small for a 225? What is a good size pipe to use? "Performance" isn't the main consideration, fuel mileage is. "

Ok dutra does build performance parts but sometimes its the same thing as fuel economy parts.
- but a 1 3/4 tube isnt even big on a 2 litre Engine let alone a 3.7 litre (225 cui) one.
Exhaust backpressure is always unwanted but dont confuse backpressure for the chock wave that a tuned
system uses, that is effectively a timed pressure wave. The "dead" backpressure of a restrictive exhaust only causes pumping losses for the Engine and thus it uses more fuel and runs hotter.
Id say that a 2 1/4 would be a good bet and use low restriction dampers.

Bob, the link you provided was ok but clearly made for industrial use.
 

·
What color are the clouds in your world?
Joined
·
30,506 Posts
Do you think the numbers change because this is for automotive? They dont.
 
  • Like
Reactions: Bob Lincoln

·
Super Moderator
Joined
·
13,931 Posts
Another question. Will a gear reduction starter fit in place of the direct drive low mount starter?
I see no reason why not. Needless to say: match up both starters very carefully; especially the nose dimensions as well as the number of teeth, etc. Why I say that is apparently some of the Canadian Slant Sixes used a different starter than our USA vehicles till about 1967, 'our' Slants used the same starter as the V8's. I know for a fact that a 1988-03 5.2L/5.9L ND Mopar starter bolts right up to a 1966 318 Poly.
 

·
Registered
Joined
·
749 Posts
IIRC the 1978 Aspen station wagon with 225 cid slant 6 and 2bbl Carter BBD carburetor that was in my family had 1.875-inch pipes.
 

·
Registered
Joined
·
3,042 Posts
The exhaust manifold outlet is only 1.980"dia., so 2"dia. pipe is the maximum that would possibly be of any benefit.
Its only partly true that the weakest part makes all the pressure, its actually the sum of all pressure fall that
ends up as backpressure. But you can never get lower values than the weakest part gives.
 

·
Premium Member
Joined
·
20,158 Posts
And with that, if is a single 1.75 tube without kinks or bends that restrict flow and remember, kink bending was and is very common, including the double walled pipes buckling and causing the the inner pipe to collapse and shrink the passages (hacksawed many an old pipe to see it), which is why mandrel bent pipes are better, and 1.75 is going to be slightly smaller than stock, if it is 2.00 inch stock (probably 1.875), it is going to breathe better than stock, but not to the point of being performance.
 
  • Like
Reactions: Bob Lincoln
1 - 19 of 19 Posts
Top