Type: Mustang 250 in 300 rpm/sec rate from 2000-7200 rpm range.
Combination: 28,000 mile 381 cu in LT4, 11.9 CR, GM 847 camshaft (.575/.595, 296/304), CNCed LT4 heads/intake, 26918 Beehive springs, AFR Hydrarev Kit, 58 mm TB, K+N Filter, 31.6 Delphi injectors, AC Rapidfire #12 plugs, OEM Optispark, OEM PCM with LT1 Edit, Corsa exhaust, and OEM ZF/3.45 axle.
Details:
• First visit occurred during 85 degree day with passing weather front and nearly negative density altitude. Second visit was with 90-94 degree temps and > 1400 ft DA.
• Initial run resulted in a 50 WTQ increase, but with 11 to 1 AFR…this was the coolest run of the 6 made. Last and best run was with worst air-I say this as my previous dyno data used an operator that standardized the numbers compared to my current location where that is not done.
• All runs were with a heat soaked intake and no effort was made to cool the engine other than the 20 minutes it took to download data and reprogram the factory PCM. Typically the runs started with digital reading of 180 degrees and ended at 205.
• Also note peaks appeared to move around quite a bit between the pre and post runs…probably due to the very flat curves rather than significant curve displacements, etc.
Fine print: this is a Mustang 250 Dyno…a conservative, but highly accurate tool that replicates an engine dyno vs strictly an inertia type dyno as a Dynojet system.
Bottomline: although this wasn’t as apples to apples test as my previous comparisons, I think safe to say that the headers bumped power significantly. Whether this is worth the ~$1700+ to upgrade…I am running out of areas to find hidden power so…
I will post the dyno sheet tomorrow.
Final dyno sheet:
Comparison between pre and post header install (punched data into Excel):
The sheets wil be interesting to see. Yes that Mustang dyno is very nice i enjoy tuning on them almost as much as an engine dyno.. It would be interesting to see the difference in the area under the curve change as opposed to just peaks to see if areas were traded off or better everywhere.
Dave
I am wondering what the gains were in relation to the stock emissions controls being removed, what gains were made by axing the cats and how much were the exhaust manifolds costing you
Area under the curve: yup...it would be interesting, but didn't get those calculations from the dyno shop. I suppose I could hand jam them in...
Emissions system: The OEM exhaust manifolds flowed into OEM cats pre install...post install is headers into the Random Tech cats. No emissions were removed.
Exotic Muscle quotes single digit HP loss for the RT cats...I recall Lingenfelter believed the OEM cats are similar-I do know the OEM cats are nearly twice as round as the RT 'bullet' cats. I tried non cat connector pipes and found the car incredibly loud...almost open headered loud. Thus more expense doing it a second time with the RT cat equipped pipes...expensive trial and error.
OEM manifolds exhibited an easy .25 inch blockage with my CNC ported heads...that along with the lack of tuned layout a tubular header allows...show the difference.
Folks may note the plateau below 3000 rpm...unsure why. I'm certain it is a tuning issue. I did pull timing and the car picked up, but not like would be expected with the rest of the curve (this checked with part throttle pinging I got on the street after the install).
I've not had great experience with headers in my past. Exhaust leaks, poor fit, lack of durability kept me from install them on this car (owned for 9 years) as durability was slightly more important than outright power. So I agree this was an interesting comparison with a part that most people jump on first...in this case it was the last modification I did!
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1996 LT4
404 WHP 381 CI
12.447 and 116 MPH
184 MPH Home Page
Yeah most definately, the power under the curve is what really will make that car faster. Alot of guys may see a few peak hp on the dyno but not gain anything at the track. Its the mid range power increases that make the car fast. I picked up 30lbft thru the mid range, and 10-15hp or so in the mid upper range to peak on a dyno tune and gained 2-3 mph at the track.
Corvette Store
Header vs OEM Manifolds Results on Healthy 381
Thats some pretty big #s for just header swap.
416rwhp/375rwtq (SAE) - NA Stock Bottom End 
People who don't have first hand experience most definatley.
Take no prisoners!
