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Discussion Starter #1 (Edited)
Hi Guys,
coming from the camaro forum (with less performance orientated guys) i wanted to give it a try here (as well as at YB):

i am currently in the process of gettin a new engine installed.
  • Before it was a 396 with stock 781 heads and flat tappet 224°@.050 .510 lift (both Int.&Ex.) --> Tq/Hp estimate is about 425Lbft / 400hp gross.
  • I will change to a 496 with dyno shown 675LbFt/670Hp // track shown below 10s in a prepped chassis.
Now i have the situation that both my carb and exhaust system are too small for the new engine.
  • Edelbrock Performer 750
  • 2.5" true dual exhaust (With 2" into 3.5" headers and 2x 2.5" straight through mufflers)
For now i will stay those, but i will upgrade to:
  • AED 850 Carb (With supposedly almost 900 cfm, according to an AED technician)
  • 3.5 open header 18" extension (with electric cutouts - side-attached to that i will use the existing 2.5" dual system)
Now my question - out of curiosity - for the experienced guys among this forum:

What is your experienced/educated guess of hp-gain, regarding each of those changes?

____


Here is what carb cfm-calculators say for a 496 with 6500 rpm limit:

Efficiency / cfm
1.00 = 933 cfm
0.95 = 886 cfm
0.90 = 840 cfm
0.85 = 793 cfm
0.80 = 746 cfm

And here is the recommendation from dynomax regarding exhaust size:
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Exhaust probably killing 60-70 HP, maybe even a bit more, with the carb another 25-30....I'd say together they are costing you 100HP if not a little more....depends on how bad the 2.5" mufflers are.

I've seem what most would consider a "good" 3" system chop 40 Hp off a 650 HP engine.

As far as Edelbrock carbs, I heard this blurb the other day, made me chuckle...."Edelbrock carbs, where horsepower goes to die" LOL
 

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Discussion Starter #3
Exhaust probably killing 60-70 HP, maybe even a bit more, with the carb another 25-30....I'd say together they are costing you 100HP if not a little more....depends on how bad the 2.5" mufflers are.

I've seem what most would consider a "good" 3" system chop 40 Hp off a 650 HP engine.

As far as Edelbrock carbs, I heard this blurb the other day, made me chuckle...."Edelbrock carbs, where horsepower goes to die" LOL
Thanks for the feedback. Numbers being worse than i expected. But thats ok.
The mufflers at least are straight through design mufflers.

At least now i have something to look forward to when changing the carb and exhaust.

I wonder where this idea of Edelbrock kllling hp comes from?
Another saying i heard is that Edelbrocks tend to save fuel compared to holleys (really the last thing i think about).
Isnt cfm = cfm ?
750 edelbrock cfm = 750 Holley cfm ?
At least regarding measured cfm, cause we all know proclaimed numbers differ from real world flow.
 

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Discussion Starter #4
I´ve done a little "research" regarding exhaust. Found out, my question was answered in Enginemaster Season 1 Episode 9. Its on youtube.


600hp engine, tested back to back with following combinations and following results:
  • 2.5" dual exhaust (straight through mufflers) --- Peak: 601.2 hp --- Avg. (5k-6.8k): ~ 565 hp (my exhaust setup)
  • 3.0" dual exhaust (straight through mufflers) --- Peak: 614.2 hp --- Avg. (5k-6.8k): ~ 585 hp (+ ~20hp)
  • 3.0" open headers 18" extensions___________ --- Peak: 618.5 hp --- Avg. (5k-6.8k): ~ 595 hp (+ ~30hp = about 5% --> my answer)
Peak difference i marked yellow. See how on the way there from 5000 rpm up, the difference is sometimes double that, like about 40 hp.
Makes it interesting, since average power is more different than peak power would indicate.

But please:
Average power is only measured via ruler on display.
Measured mm on left side (600hp-500hp) and set that relation to mm distance between lines.
Calculated the ratio between those lines and came up with numbers above.
Absolut level may be higher/lower, its a about the relative distance to other lines.
So please everybody interpret this graph as he wishes.

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Whether you can directly apply what info is from that video to your application fully depends on whether you have very many bends in your system, if they are crush bent instead of mandrel bent, and exactly how good a muffler core you have.....they are testing on straight pipe with minimal mandrel bends and two of the top flowing mufflers in each size class in that vid. They did mention that they would expect the test to be more of a dramatic difference if a lesser grade of muffler was used than the Magnaflow they tested with.

If you've got typical muffler shop bends and a lesser muffler, expect it to be worse. Also factor in you're application are putting another 50 cubic inches of displacement (496 vs 454)and another 70 hp through the system.

In you first post you said 2.5" straight through mufflers, I interpreted that to be typical glass packs or cheap straight through welded case mufflers, which would be worst case scenario.

What is your current muffler??
 

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Discussion Starter #6 (Edited)
Whether you can directly apply what info is from that video to your application fully depends on whether you have very many bends in your system, if they are crush bent instead of mandrel bent, and exactly how good a muffler core you have.....they are testing on straight pipe with minimal mandrel bends and two of the top flowing mufflers in each size class in that vid. They did mention that they would expect the test to be more of a dramatic difference if a lesser grade of muffler was used than the Magnaflow they tested with.

If you've got typical muffler shop bends and a lesser muffler, expect it to be worse. Also factor in you're application are putting another 50 cubic inches of displacement (496 vs 454)and another 70 hp through the system.

In you first post you said 2.5" straight through mufflers, I interpreted that to be typical glass packs or cheap straight through welded case mufflers, which would be worst case scenario.

What is your current muffler??
i think thats very correct way of thinking based on the info you have, but you must know too is, that i do have mandrel bent pipes and straight through mufflers just like in the test. The system just is a little longer with a bow across the rear axle.
Thats the only reason why i consider that test as relevant enough for me.
 
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