Roush 427r only made 400whp :(

[ssqpolo]

Hey everyone. New member. Bought a new BDR cobra last month. Great looking car, and it definitely has a lot of character.
Specs are roush 427r crate motor with tko600 trans.

Crank hp is 550hp (546 exactly), but after break in miles, I strapped it to a dyno and it put down a measly 401whp. That is a HUGE drivetrain loss. I was expecting 15% loss, but this is near 27% unless Roush is over rating their motors.

Car was also running really rich in some areas, and lean in others... I will sort that out soon.

Any ideas if this is normal? If so, what are best ways to get more power without ruining streetability.

This is a mustang dyno which reads lower than dyno jets, and it is correctly calibrated. I have dynod many cars here, and it's a reputable shop.

I was expecting closer to the 450 whp number

[brettco]

Well im sure it's because no one has a great exhaust system for a cobra. I wonder if under car wouldn't be better.

[ssqpolo]

Honeslty, I don't expect an exhaust to make more than a 10whp difference, if that

[jhv48]

My Roush 427SR (rated at 515 hp from Roush) made 440/460 rear wheel hp/tq after I changed to a double pumper carb and 3" side pipes.

And, yes, the pipes can strangle that engine. Insert a small mirror into your side pipe and shine a light inside. Check out how big the internal pipe actually is. My spf side pipe measured 1 3/4" inside diameter and was choking my engine. Make sure your timing is spot on as well. Mine ran better at 36 degrees total advance.

[blykins]

Pretty typical for a Mustang dyno.

If the tune is right, you can probably sneak a few more out of it. If it's got a Street Avenger carb, you can gain a good bit more from a Quick Fuel carb swap.

[ssqpolo]

Thanks for the input. Do you have any before numbers to compare?

[ssqpolo]

Also, blykins, why would you choose quick fuel ocer prosystems

[mikeinatlanta]

If you want the power you will need to install a quality exhaust. I have yet to see a quality aftermarket cobra exhaust so I had one built. You also want to look at the air filter assy. Lots to lose there.

[blykins]

I suppose I'm a little biased as we custom assemble our own Quick Fuel carbs. Never tried a Pro Systems, but have heard good things about them. I have sent Quick Fuel carbs all over the world (literally) and have some good reviews from my customers. The carbs that come with the Roush engines are pretty sub-par...

As far as the dyno, a 25% loss through the driveline and exhaust isn't abnormal with the Mustang dynos.

[ssqpolo]

Okay. Could you send me an offer/suggestion for a QFT carb. It will probably be the 750 right? Also, what are your thoughts on the annular booster? Actually effective, or snake oil?

Also, if anyone has any exhaust suggestions, please post or PM me.

Prices for both are appreciated

[ssqpolo]

If you need specs for carb tuning, I live in south Florida. So, hot, humid, and sea level

[jhv48]

I actually have both of the aforementioned carbs. I have a Prosystems 850 on my Roush 427SR and a Quickfuel 850 on my Lykins Motorsports 427. Both are easily tuneable and will wake up that engine. The stock street avenger is the first thing I would replace. Cost is around $750.
The sidepipes are the second thing I would replace.
Full Throttle in Sparks Nevada will modify your pipes but they will be loud. Mine cost $1200. Basically, he sent me a pair that had already been modified and I sent him my used pipes plus $1200.
There are other side pipe manufacturers out there that will do a fine job of making a set of pipes for your car. Do a search and you'll find lots of recommendations.
Pipes and a dp carb will get the air in and out so you can use every horsepuppy your engine can churn out.

[ssqpolo]

Sounds like a plan

[blykins]

Yes, a Q-750 would run about $685.

Annular boosters have their places, I don't think a Cobra with a 5-speed is one of them though.

[DAVID GAGNARD]

[quoteCrank hp is 550hp (546 exactly), but after break in miles, I strapped it to a dyno and it put down a measly 401whp. That is a HUGE drivetrain loss. I was expecting 15% loss, but this is near 27% unless Roush is over rating their motors.
][/quote]

There has been documented cases here (not going to look for them,would take me all day and half the night) of 100hp loss just thru the side pipes alone,not counting restrictive air filter or "normal" driveline loss.......

not knowing what size/type/kind of side pipes/headers/air filter you are running, I could easily believe a 27% hp loss.......

easy way to tell,go back to the chasis dyno, and take off the air filter and disconnect the side pipes from the collectors and run "open" headers and then compare the numbers.......you will likely be surprised......

David

[twin turbo]

I agree with what others have said, certain sidepipes can literally strangle higher hp engines. I wouldn't worry about the carb until you look at this first.

[vatdevil]

Firefly Stainless Steel performance pipes have been designed

[750hp]

Did you put it on the chassis design because it wasn't performing to expectations or just to get the "in-car" tune dialled in? If it's performing fine, or if you haven't driven it to it's full potential already, don't fall into the trap of spending money to make a magical but entirely irrelevant number on a dyno...

[ssqpolo]

I put her on the dyno because I felt her breaking up in higher rpms, and in general just not running as smooth as I would prefer. I mainly wanted to check AFRs to make sure everything was safe.

Also, I like to put all my cars on the dyno just to see what they actually put down compared to numbers from the manufacturer.
I always tend to tinker with my cars, so it's nice to have a baseline for comparison.

[ssqpolo]

Thanks for posting the exhaust. $2700 is steep for an exhuast. I will definitely look into it though.