Need advice on exhaust diameter

[bigmal 225]

Hi Guys, I am running a 351C 4V in my 69 with original iron manifolds. I would like to go extractors but not a simple task with a right hand drive conversion so stuck with iron for now.

The current exhaust is a hotch potch of diameters as follows:

2 1/2" from manifold to just prior to muffler then steps down to 2 1/4" entering muffler. 2 1/2" out of muffler and over rear axle then steps down to 2". The twin chrome tips are 1 3/4".

I am running a 650 Holley and am not aware of any other mods to the engine. It seems a little under powered for a 351C. Has a traction lock diff and won't spin 245/60 T/As which I thought it would so I am suspecting the exhaust won't be helping.

Could I have some advice on the best pipe size for my setup. I think I'm better starting from scratch.

Thanks.

[barnett468 418]

Your exhaust is no likely preventing it from spinning the tires off the line, however having it narrow down to only 1 1/2" at the exhaust tips is your biggest issue that you have mentioned.

What mufflers do you have?

What is your diff ratio?

What is your trans?

What is your compression? 

[bigmal 225]

3 minutes ago, barnett468 said:

Your exhaust is no likely preventing it from spinning the tires off the line, however having it narrow down to only 1 1/2" at the exhaust tips is your biggest issue that you have mentioned

What mufflers do you have?

What is your diff ratio?

What is your trans?

What is your compression? 

Hi Barnett, I bought the car out of the US last year and don't have a lot of info on it. Has an FMX transmission and a single muffler each side. Don't know the diff ratio (doesn't seem too tall) or compression. The plate on the door is no help as it has been remade to show the new colour/trim/diff.

[barnett468 418]

6 minutes ago, bigmal said:

Hi Barnett, I bought the car out of the US last year and don't have a lot of info on it. Has an FMX transmission and a single muffler each side. Don't know the diff ratio (doesn't seem too tall) or compression. The plate on the door is no help as it has been remade to show the new colour/trim/diff.

 

That info would  be helpful . Also, your ignition timing may also be less than optimal which can have a fairly large effect on power . In in my experience, a stock 4V Cleveland will have a difficult time spinning 245/60 tires with a posi if the ratio is numerically lower than 3.25 . Even with 3.25, it wont roast the bejesus out of them . A higher stall converter will help as well if yours is stock.

Te very first mod I would do is get rid of those wimpy exhaust tips but some others might not.

.

[bigmal 225]

Thanks for that. With what we know about the set up what pipe diameter would you suggest?

[bigmal 225]

Other than rotating the wheels and calculating against the tail shaft rotations is there another method of determining diff ratio? No tag fitted.

[barnett468 418]

52 minutes ago, bigmal said:

Other than rotating the wheels and calculating against the tail shaft rotations is there another method of determining diff ratio? No tag fitted.

 

yes, you need a cell phone gps program and drive a measured mile then do some calculations

[bigmal 225]

3 hours ago, barnett468 said:

 

yes, you need a cell phone gps program and drive a measured mile then do some calculations

Thanks for that

[Mike65 476]

 

Here is a way to get close to the ratio I found by doing a google search. http://www.how-to-build-hotrods.com/gear-ratio.html

[stangnet33 88]

There's the Tremec Tool Box app