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I have been swinging both ways on this debate. I am trying to decide if I should run the 2" rams horns that I have and are original to the car or buy the Dorman repo 2.5" manifolds. They can be bought for less than $150 for the pair. I think I would like the 2.5 and have 2.5 exhaust all the way back. The engine is a 327 .30 over with cast flat tops and 1.94 Double Hump Heads. It will have a Comp Cams 268H cam and a dual plane intake. My thoughts are that the motor is similar to the 300HP 327 that came with 2.5" from the factory on corvettes and some passenger cars. So what do you all think, is it worth the money for the 2.5" manifolds?
 

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You will see an improvement. Especially with the pipe size carried at least through the muffler.

3/4 or full length headers would be even better.

Nice thing is it's extra power without a negative side effect other than the initial cost.
 

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That is what I was thinking. I don't want to run headers because I want to keep it stock looking. I wanted to make sure that the larger manifolds would be worth the investment.
 

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I just bought these 2 1/2"s and was pretty impressed with the way the castings look.



 

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Stock steering box clearance.

If the car is a stock trifive, be advised, depending on which manufacture 2.5" manifold you acquire, the driver's side might touch the steering box. Ours did. We made adjustments to the side motor mounts to correct.
 

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These are 2 1/2" ramshorn with a CPP 500 box in my 55

 

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I have 2 1/2" rams horns on my 55 350 and the driver side lightly touches and knocks on the manual steering box at low idle. How can I adjust my mounts to shift the engine a little to give more clearance? Engine is in stock position.
 

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I've been wrestling with this very question...until now. This discussion settled it for me. I've got a nice set of 2" manifolds, but wanted a little better performance. Headers are such an incredible PITA there was no way I was going down that road one more time. Since the 2 1/2" manifolds clear the CPP box (seeing is believing - thanks once again Pops), my choice is clear.
JR
 

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I've been wrestling with this very question...until now. This discussion settled it for me. I've got a nice set of 2" manifolds, but wanted a little better performance. Headers are such an incredible PITA there was no way I was going down that road one more time. Since the 2 1/2" manifolds clear the CPP box (seeing is believing - thanks once again Pops), my choice is clear.....JR
JR....What heads do you have?....I found that the rams horns had a clearance problem on my AFR heads.
 

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I've been wrestling with this very question...until now. This discussion settled it for me. I've got a nice set of 2" manifolds, but wanted a little better performance. Headers are such an incredible PITA there was no way I was going down that road one more time. Since the 2 1/2" manifolds clear the CPP box (seeing is believing - thanks once again Pops), my choice is clear.
JR
There have been a few people that had issues with the 2 1/2" rams horns hitting the steering box likely due to slightly differences in the factory frame build/engine location.
 

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I have 2 1/2" rams horns on my 55 350 and the driver side lightly touches and knocks on the manual steering box at low idle. How can I adjust my mounts to shift the engine a little to give more clearance? Engine is in stock position.
Just a thought, Put a washer between the block,and engine mount on each bolt on both sides.It should raise the engine which may be enough to clear the box.Another thought would be grind some material off the manifold at that spot.Might even remove a small amount off the edge of the box.
 

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JR....What heads do you have?....I found that the rams horns had a clearance problem on my AFR heads.
I'll be using generic GM iron heads, but can't say much more off hand. I'm headed out for an evening in the shop, and have the engine on a stand so will look for the casting number if it's of interest. Also mentioned was the engine 3/4" forward or not... I'm using Earle Williams' mounts, forward position, and will have a little side shift available if it becomes necessary for the box. Where is your clearance issue on those heads, Pops...? something a little grinding can cure?
JR
 

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You will have no problem with stock type cast iron heads JR...And having the Earle Williams mounts will be an advantage as well.
 
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