Dynoed my 427so Cobra today.... interesting to say the least!

SL · #1 (**permalink**) 07-20-2007, 02:15 AM

nice numbers, is that a chassis or engine dyno

RACER X #99 · #2 (**permalink**) 07-20-2007, 06:21 AM

Not bad numbers makes almost as much as my Dart small block 408 built by the same engine builder, Dennis Hoffman. I alway knew I could kick Freddy's ass.

neverwouldof · #3 (**permalink**) 07-20-2007, 07:01 AM

Those are chassis dyno #'s.... It's a 23 year old in ground dyno which he didn't sound so sure how it was running anymore. He did say he was searching for new one but guess it doesn't matter as long as he gets A/F right. He left it just tad rich to keep on safe side. At what RPM do you think HP would have peaked?

Dwight · #4 (**permalink**) 07-20-2007, 08:22 AM

I had my Cobra dyno'ed in Memphis, Tn. at Dyno Speed Racing, they do a "lot" of Mustangs. Joe told me most stock 05-07 Mustangs dyno at 280-290 rwhp. He said that would be 330 flywheel range. Ford was sued for their advertised HP on the 03 or 04 Cobra Mustang. I think they now advertise a HP rate they know will pass on any dyno.

Dwight

ByronRACE · #5 (**permalink**) 07-20-2007, 09:24 AM

Your engine has not even reached peak torque by that RPM! What is the cam duration on intake and exhaust? If you want to see what this engine is really capable of, you're going to have to spin it at least another 1500 rpm; maybe more. Your peak power will occur somewhere about 1000-1500rpm beyond peak torque. It'll break 450 at the tires...probably 470.

The dip in the 4000rpm range could quite likely be detonation. Why? Your air fuel shows choppy readings, torque drops, then as piston speed increases, it recovers. It may need a little less spark in that range. Read the plugs...see if they are speckled. Listen critically in that rpm range for ping.

Air/Fuel looks quite good. It probably won't get much better with a carb, but if you have some magic way of leaning it out 1/4 to 1/2 a point up high, it'll help your power numbers. If not, we're only talking about 15hp probably.

neverwouldof · #6 (**permalink**) 07-20-2007, 02:45 PM

Byronrace, ya the dip he said was when the vacuum secondaries kicked in. This is two 1968 Holley 735's on a 1968 tunnel port and he said he could lean it out a bit and get 10-15 more HP but i said if a bit rich is safer then stick with that. It's still NOS 1968 std bore block and i don't want anything bad happening !!! And i later found out that the matched carbs were built for the 427FE as well which is nice to learn... think they were listed for a dragster. I'll probably take it to a local dyno shop to get a 7200rpm run and i'll post that up. Oh byron, I have the iridium plugs by the way and it does have large gap of .44 or .45 if my memory is correct. Oh and i switched to the cast aluminum valve covers which fixed the oil splashing into breathers. Had the chrome pent roof i believe they are called.

ByronRACE · #7 (**permalink**) 07-20-2007, 03:49 PM

OK, vacuum secondaries. I'll buy that.

The engine is running great; and you have a point...if you're happy with how it goes down the road, there's not much to gain (except risk) by increasing your RPM limit. I'm certain you have enough power/torque to scare yourself, so take the next suggestion with a grain of salt.

If you're not comfortable running the engine up to where it's currently making the power, consider a cam change. By shortening the duration of the cam, you will increase the area under the torque curve in the region you are comfortable running it, while at the same time creating a "natural" rpm limit. The engine will peak lower and make more torque, the power will go peak and flat sooner, and you won't be as tempted to keep your foot buried as the engine soars into the rpm range you're not wanting to run in. Right now you have a 7000-7500rpm engine and I'm sure it's pulling like a freight train right up to where you abruptly bump the limiter, leaving you with the feeling that there's a ton more up there if it were allowed. If that's not what you want, a cam change will give you a 6000rpm engine and a more natural feeling as you approach the rpm limit. Less duration will smooth out your idle as well. Depending on your taste, this may not be desirable. Part of a cobras personality is the idle note/beat.

There's nothing wrong with running it just like it is. You probably can't connect more torque anyway...so its pretty much academic, take it for what it is. I don't think there's a thing wrong with the way your engine behaves. I bet it's a blast.