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Anatidaephobic
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2,370 Posts
Discussion Starter #1 (Edited)
ive tried my best to accurately est. the fly hp of my 302 using Dyno2000 ver. 3.06 program. and with it set up as stock exhaust manifolds w/ mufflers it was showing me making 268hp at 5500 rpm then changing it to small tube header w/ mufflers it was showing me making 315hp at 5500rpm. does that sound crazy or does it make that much of a difference 47hp? i am planning on installing tri-y headers so i figure they would be small tube.
 

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Anatidaephobic
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2,370 Posts
Discussion Starter #2
another question about the est. is with the combustion chamber at 54.58cc it has the compression ratio at 12.50 sound right?
 

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Anatidaephobic
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2,370 Posts
Discussion Starter #4
i dont think headers will give that much extra hp,and that comp. cant be right?
ive looked and ive heard other people say they have had 35hp jumps in power over manifolds. and as for the comp if i set it for 10.5 it est. the combustion chamber at 63cc and i am pretty sure i have the 54cc head 289s
 

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Anatidaephobic
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2,370 Posts
Discussion Starter #6
what piston are you running?
just stock and thats how i have it set up on the program. 302 w/ .030 bore 306ci i went through and input all the flow specs for the 289 heads. then it asks for compression ratio and at 12.5 it est. a 54 cc chamber which i believe i have and if i lower it to 11 or 10 i can't remember it est. 64 cc chamber.
 

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1,379 Posts
on performance counts dyno,try y over stock gave us 26 extra hp,with short stroke and stock pistons i we are comeing up with 1105 at .030 over.
 

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Anatidaephobic
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2,370 Posts
Discussion Starter #10
hmmm... i wonder what is a better est. then. 54cc (which i have) @ 12.5comp = 315hp or 64cc @ 10.5comp= 297hp
 

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Anatidaephobic
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2,370 Posts
Discussion Starter #11
alright i keep playing with the program and found i have my valves at the wrong diameter and i calculated the comp wrong. now with it set at 10.85 comp i am making 267hp @ 5500rpm on manifolds. with small tube headers i am making 316hp @ 5500rpm. still jumping like crazy but if that happens for real i won't mind :) but, i think ive got it pretty much 100% dialed in except exact cam specs but i feel im close on those numbers
 

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Premium Member
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2,247 Posts
See if this helps any. We use hedman headders. Fit alot better than tri y's and are only 149.00 and the Coated ones are 279.00 in summit. and fit and look great.
stock set up is 9.5:1 with the 54 cc heads. at 12.5 93 octane gas almost works
 

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most people on here dont like headmans.i have been useing them for 30 years and love them.i do a lot of the shortys on the mid 80s and up.easy fit and good power adder.
 

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Anatidaephobic
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2,370 Posts
Discussion Starter #14 (Edited)
whats the reasoning that people don't like them? and is it better to go with collector diameter for you exhaust match? IE those headers have a 3 inch collector so would 3 inch exhaust be the optimal fit?
 

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I Love Hedman headders. They fit with out dinging and have greater flow than tri y's.

The last 2 sets of tri y's we had to ding both sides at the back of the shock towers
 

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Anatidaephobic
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2,370 Posts
Discussion Starter #17
I Love Hedman headders. They fit with out dinging and have greater flow than tri y's.

The last 2 sets of tri y's we had to ding both sides at the back of the shock towers
have you tried to put a set on a 64-66 mustang or just your 68? because the 68s have larger engine bays
 

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I have put 2 sets on 1965 and 1 set on a 1966. Fit great Look good. Love the price.

My Neon Green 1965 have them and my 1965 GT Conv have them. And Intalled them on a Customers 1966 coupe with 4 Speed. Had zero problems.
 

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put the headmans on 65/66 with 2 1/2 inch to flowmasters and out the back.you cant go wrong.
 

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I've never had issues with the Tri-Y's. This is mu 2nd Mustang with them. I did get ceramic coated one this time. The rest of the exhaust is 2.5" all the way out the back with H-Pipe & 40 Series Flows. As for the Try-Y's having smaller tubes, it's called more torque, which IMO win's races.
 
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