Vintage Mustang Forums banner
  • Hey everyone! Enter your ride HERE to be a part September's Ride of the Month Challenge!
1 - 20 of 45 Posts

·
Registered
Joined
·
38 Posts
Discussion Starter · #1 · (Edited)
Hey guys.

Just curious how much this exhaust is robbing HP from my 408W. I have Hooker LT headers and the 2 1/4" pipes are crimped bent over the axles and mufflers down to about 2" in several places. Ive just picked up a Magnaflow 2 1/2" kit that will be fitted next month.

My last dyno run was a tad disappointing @ 352 HP, with AFR heads, custom cam and Performer RPM manifold I would have expected better numbers. The only component that I can see lacking is the exhaust.

Any guesses on what kind of HP gains I might expect to see with the new system?

Cheers!
[/URL][/IMG]
[/URL][/IMG]
 

·
NOT Canadian (Really!)
Joined
·
2,456 Posts
Do you have any sort of crossover piping in place. Like an H or X? Have to admit, some of those bends do look pretty restrictive. But adding a crossover might help more than nicer bends would. Either way, might be a good time for a new set of pipes.
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #3 ·
Do you have any sort of crossover piping in place. Like an H or X? Have to admit, some of those bends do look pretty restrictive. But adding a crossover might help more than nicer bends would. Either way, might be a good time for a new set of pipes.
It has an H pipe now. The new kit has the X pipe.
 

·
Registered
Joined
·
1,007 Posts
How high do you you spin it? At what rpm did it make its peak horsepower and peak torque? Do you have an automatic transmission or manual? If automatic, how loose is your converter?

These are all relevant questions on which to base an answer to your question.
 

·
Registered
Joined
·
693 Posts
A couple Q's (starting at the top):

What carb are you using?
Which AFRs?
Is the "custom" cam matched to your heads/intake? If it is a 7000rpm cam your intake side may need adjustment.

Assuming these numbers are on a chassis dyno, but what type (Superdyne or Mustang)?

What transmission are you using?

You should pick up some HP with a 2.5/3.0 inch exhaust but I wouldn't expect a 50 hp gain.
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #6 ·
Its a 69 Mach, currently running and FMX with a 3000 stall, an AOD is being built to replace that. AFR 225's and a Holley 770 The cam was matched to the set up.
 

·
Registered
Joined
·
5,674 Posts
This empirical data shows the effect of some restriction is not the +75Hp some claim by bolting on a set of headers or exhaust....:smile2:


 

·
NOT Canadian (Really!)
Joined
·
2,456 Posts
I have to admit I'm surprised by that number to be honest and can understand why you would be disappointed. You aren't going to find the difference in exhaust I don't think personally. There has to be something else farther upstream not quite working. Maybe time to start looking at timing curves and jetting? It doesn't sound like any of your "hard" parts are the bottle neck. Unless you have some sort of mismatch where you have unusually low compression or something else funky going on. It could also just be a heartbreaker dyno, some of em' just read that way.

Just thinking out loud. The exhaust certainly isn't helping, but I don;t think it's the silver bullet here either.
 

·
Registered
Joined
·
1,007 Posts
A 3000 rpm stall will show less hp and tq than a manual transmission, so some of your power on paper disappeared there. If your setup is optimized though, it will reappear at the track.

I'm still curious, what rpm's were your hp and tq peaks at?
 

·
Registered
Joined
·
655 Posts
Just bolt some tube and a straight glass pak muffler ending before the differential. Go take a few pulls on the chassis dyno.

You will find out if it's in the motor (carb, timing, etc.), and it will be a cheap way to find out where to start.
 
G

·
I'm glad you will have it Dyno'd again to see the results. Not many have ventured a guess :) Here's my thoughts . . . on a Dyno your WOT hp is going to go up by 18hp-22hp. I think that amount will be fairly consistent from about 2500 RPMs up. Can't wait to see the results.
 

·
NOT Canadian (Really!)
Joined
·
2,456 Posts
This empirical data shows the effect of some restriction is not the +75Hp some claim by bolting on a set of headers or exhaust....:smile2:


https://www.youtube.com/watch?v=azPKIjxmmdU
This exact video came to mind for me as well. I wonder if restrictions downstream are actually worse than in the headers as they have less velocity to push the gases through.
 

·
Registered
Joined
·
21,562 Posts
This should be interesting. I wonder how much is lost on the outlet of the muffler having the tail pipe slip inside? You have that sharp transition. I'd like to have it slip over the muffler's exit. On bang Shift, one member is a retired Chrysler exhaust engineer. He said the rolled lip common on today's tail pipe tips cost a few HP too.

On the dyno, was it a load bearing or inertia? Load bearing will show lower reading. A few years ago Hot Rod did a article on chassis dynos. They took 1 car and went to a half dozen different places in one day. What they found was everyone had did different results and the more runs you did on anyone dyno, the HP would climb each run with everything being the same
 

·
Registered
1970 Mustang Mach 1
Joined
·
1,317 Posts
No doubt the exhaust is a restriction. Not knowing the compression and cam, the following are my thoughts. AFR225 are big, I have AFR205's on a 418W. I suggest a Holly 950. The performer RPM is restricting. I ported and flow balanced mine and it made a big difference. Alan



Hey guys.

Just curious how much this exhaust is robbing HP from my 408W. I have Hooker LT headers and the 2 1/4" pipes are crimped bent over the axles and mufflers down to about 2" in several places. Ive just picked up a Magnaflow 2 1/2" kit that will be fitted next month.

My last dyno run was a tad disappointing @ 352 HP, with AFR heads, custom cam and Performer RPM manifold I would have expected better numbers. The only component that I can see lacking is the exhaust.

Any guesses on what kind of HP gains I might expect to see with the new system?

Cheers!
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #16 ·
No doubt the exhaust is a restriction. Not knowing the compression and cam, the following are my thoughts. AFR225 are big, I have AFR205's on a 418W. I suggest a Holly 950. The performer RPM is restricting. I ported and flow balanced mine and it made a big difference. Alan
Sorry, my mistake. They are 205`s.
 

·
Registered
Joined
·
1,143 Posts
Hi guys for reference me and OP live in the same city.

My milder 408w with a Z303 cam and eddy 170cc head put down 365rwhp on the same dyno which is a loading dynapac dyno through a AOD with a 3000 stall.
 

·
Registered
Joined
·
3,947 Posts
I had a similar exhaust setup on my old 306 combo. I replaced the front half with 2 1/2 pipes and free flowing mufflers and even with the crimped up 2 1/4 tailpipes there was a noticeable increase in power. About 3/10ths quicker at the track in the 1/4 mile and a couple mph. I agree the exhaust,intake and carb are all holding you back some. Track mph would be a better gauge though like was mentioned earlier. I have a buddy who's mustang dyno'd at around 390hp on a chassis dyno but was more like 600hp at the flywheel.
 

·
Registered
Joined
·
706 Posts
I agree with above poster....have a hard look at the timing curve(you at least have lighter advance springs,right?) and the jetting. Could make a BIG difference.
6sally6
 
1 - 20 of 45 Posts
Top