Dynoed my LT4 today (on a Mustang 1750 Dyno-conservative!)...figured it would be a good day since it was Friday the 13th...

New parts added: CNC Cylinder Heads Stage III package on my original LT4 castings (includes: cnc'ed intake/exhaust/combustion chambers, angle milled deck (55.6 cc) for a 11.2 to 1 compression ratio, REV SS valves, REV double springs, titanium retainers, 10 degree locks), and match ported LT4 intake. I also added a 7 quart Canton Roadracing oil pan, but doubt it added much other than durability.

This was added to my previous combination of stock shortblock, HOT cam, Corsa exhaust, and pretty much everything else stock (cast iron exhaust manifolds, cats, programing, etc)

Car peaked at 331 at 6000 rpm and 297 Torque at 4900 rpm.

That is a gain of 28 RWHP and 11 RWT from my HOT cam/Corsa combination on the same dyno, same operator, all corrected numbers.

Notes:

Glad it didn't blow at 6800 rpm (82,000 mile OEM original bottom end with 1 piston .022 in the hole more than the other 7-bent rod???)

Glad it made more hp for the amount of money. Also appears to have an insignificant, if any, loss of torque at lower rpms.

Unhappy because all 3 runs the engine peaked at 6000 rpm and took a sudden dive...not 6100 not 5900, but 6000. The curve was not peaked (good), but I have some other gremlin at work (bad).

Glad the air/fuel ratio was lean so I know more power will be made with that change...it spanned 13.1 to 13.8 during the run on machines wideband O2.

Interpolating the curve past 6000 rpm may result in 345 RWHP with the richer air/fuel mixture...just my uneducated guess:) I will try to post the dyno graph soon.

Please don't get wrapped around the LOW dyno numbers...I used a Mustang Dyno that uses a steady state 300 rpm per second acceleration just like an engine dyno...not the typical DynoJet Inertial setup. A conservative DynoJet WAG would be (13% adjustment)...374 RWHP By the way, each dyno run last nearly 20 seconds! Went from 1500 rpm to 6800 rpm...awesome sound:D

Any ideas on the drop at 6000 rpm?


[Modified by No Go, 12:13 AM 6/14/2003]

 

:thumbs: :cheers:

 

My CNC Cylinder Heads heads/cam LT1 seems to make the most horsepower in this range. When I leaned it out to this range, I gained 10 to 20 hp all the way up to peak.

 

I would expect 13.8 to be just too lean...my understanding that on the street/track, etc...more fuel is needed and you will be running lean/less power if you tune for absolute max power on dyno. But I think I see where you point is...maybe not much to be gained by richening my combination except safety margin.

I think I would prefer a 12.9 across the board...willing to give up some power for safety.

I will try to post the graph now too. :)




With just HOT cam and Corsa the combination peaked at 6200 rpm so I would expect adding ported heads would peak at 6200 or more likely even higher...:) but not until I figure out what is going on there.

Any guesses?



[Modified by No Go, 2:07 PM 6/14/2003]

 

On my best runs my A/F started at 14.7@2700 rpms and tapered down to 12.9@5900 rpms.

From everything that I have read the hot cam's horesepower peaks around 6100 rpms. I wouldn't think that ported heads would raise the peak HP rpms.

 

I'm not sure of the emissions laws in your state,but there is some serious power to be gained from full length headers,no cats,and reprogram.I'm kinda suprised you haven't done this already. :rolleyes: I've seen dyno charts showing 30hp gain on a stock LT1 with fl headers and exhaust.With your combo............WOW.....you should be fly'n.Good luck and keep us posted. :flag

 

Well, Nebraska has no emission laws...or should say they have no periodic checks. I know I'm giving up HP for the cast iron manifolds, but I really like the stock look. Besides if I can achieve my goal without headers, etc then that is preferred.

I was just basing my peak on my previous dyno run (HOT cam peaked at 6200) and the stereotypical ported heads making more power upstairs while loosing it on the lowend. I want the engine to have a 6800 shift point at least in the end, bigger cam will be necessary I suppose, so a higher peak is welcome.

:D

 

Probably the cast iron exhaust manifolds, cats. LT Headers should help the motor make peak power longer. And definitely look into a reprogram.

 

Here is the dyno graph of my LT4 before and after a Stage I porting by Trevor Johnson Cylinder Heads near Dallas. The some total of all the mod's is the the heads, K&N filter, and throttle body bypass. Pictures and more info is on my website (link in signature).

Since this was done on a Dynojet, the absolute numbers are higher than the Mustang but there is no drop off at 6000 rpm. I suspect something is causing this on your engine as my pulls very strong until the rev limiter. It could be a number of things, but since it a very sharp drop, I would check out the ignition system. I doubt the AFR, cat's and exhaust manifolds would not cause a sharp drop like you have.




[Modified by Mez, 12:14 AM 6/15/2003]

 

Hmm, wow. I guess fellow forum member JasonL has the strongest running stock LT4 on the board then. He only had cut off mufflers with a flipped filter lid/K&N filter. His car made 324rwhp with that setup on a Mustang Dyno...Hmm..But your numbers look good! :cheers:

 

Mez: Your curve is what I expect from the engine-different numbers, but same shape. This is the shape of my previous runs too although I stopped those at 6400 rpm, the OEM fuel cut.

I definitely agree there is something wrong...dyno operator/owner didn't think Optispark (have 9800 miles on it) or ignition related as the curve was very smooth (new plugs/wires)...it just hits 6000 and falls off...you can see I didn't let off until ~6300 rpm, but the engine already signed off. He said he could detect it by the sound too-but was very slight. He recommended switching to a 1/8 turn on the lash...currently it was 1/4...but otherwise was thinking valve float-hard to believe-you never know...

I will post my previous runs with just Corsa and HOT cam for comparison.

TIMSPEED: Sounds like your friend has a ringer...:)



Again above is Corsa/HOT cam compared to Corsa/HOT cam/CNC heads. Note < ~3700 rpm I had gotten on the gas too agressively and caused the car to cycle for and aft (I could feel it) and shows with all the peaks and valleys...> 3700 it smoothed out and gave good data-two other runs backed this up (with no cycling-this run was my highest though...:))

I figure the curve should peak and then slow drop off just like before... :confused:


[Modified by No Go, 2:39 PM 6/15/2003]