Roush 427r only made 400whp :( - Page 2

twin turbo · #1 (**permalink**) 02-28-2015, 06:52 PM

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.

NZCOBRA · #2 (**permalink**) 05-06-2015, 03:48 AM

I had my car on the dyno the other day , Hub dyno 408w and only got 420 at the wheels , with a dip in the torque curve , I thought it might be the mufflers , so we removed the center core (spirals) and picked up 62hp !. Cheers .

Gaz64 · #3 (**permalink**) 05-10-2015, 01:33 AM

Knowing your crank hp and rear wheel horsepower shows what is typical for driveline loss.

25-30% would be considered normal.

To get your 450 rwhp, you'll need about 600 flywheel.

Also shows how many dynos lie.

Compression pressure is related to compression ratio AND cam timing.

Does your mechanic know what cam you have before stating it should have "xyz" compression pressure?

Ace23 · #4 (**permalink**) 05-10-2015, 09:05 AM

Quote:

Originally Posted by Gaz64

Knowing your crank hp and rear wheel horsepower shows what is typical for driveline loss.

25-30% would be considered normal.

To get your 450 rwhp, you'll need about 600 flywheel.

Also shows how many dynos lie.

Compression pressure is related to compression ratio AND cam timing.

Does your mechanic know what cam you have before stating it should have "xyz" compression pressure?

All I'm going off of is what the engine builders dyno showed which off the top of my head let's say 591 hp. I'm not to judge whether that is a legitimate number or not but that's what the dyno sheet says so that's what we are going off of. I have the engine build sheet and the tuner has the cam size....we also spoke to the engine builder which stated it should have 175-180lb per cylinder and we got readings of 150-160lb. This motor has 11k miles on it and it was running insanely rich so both the tuner and builder diagnosed it with the cylinders been washed down. The tuners just said it didn't have the seat of the pants pull it should have and when it go to the WOT pulls it just wasn't in the ballpark of where similar setups have been. I'm going to keep a close eye on the oil level and enjoy it the rest of the season. When I'm ready we will pull the motor and do what's necessary. Atleast now it's tuned correctly and is running much better

vatdevil · #5 (**permalink**) 03-01-2015, 03:57 AM

Firefly Stainless Steel performance pipes have been designed

750hp · #6 (**permalink**) 03-01-2015, 04:41 AM

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 · #7 (**permalink**) 03-01-2015, 07:02 AM

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 · #8 (**permalink**) 03-01-2015, 07:06 AM

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

Ron61 · #9 (**permalink**) 03-01-2015, 07:20 AM

I gained nearly 20 horsepower when I changed the exhaust pipes on my old cobra. Also you haven't taken into account any of the parasitic loss in the movement of engine parts and I don't know if you have air conditioning or not, but the water pump alone takes some power as does anything attached to the engine. Remember, when they run them on an engine dyno, it is with open headers, no water pimps or anything else and the only loss is what is in the engine itself. On mine my flywheel horsepower was 530 and the RWHP was 390.

Ron

Dominik · #10 (**permalink**) 05-06-2015, 06:05 AM

Quote:

Originally Posted by Ron61

On mine my flywheel horsepower was 530 and the RWHP was 390.

Ron

had a similar "loss": 500/680hp...

Ace23 · #11 (**permalink**) 05-07-2015, 07:41 PM

Let me add a little Mayhem to the mix. Just got off the chassis dyno my car has a Keith Craft 427 with a motor dyno sheet showing 589hp give or take a few hp. Car went from a Holley 770 street avenger to a Quickfuel750......on the Mustang dyno it made 375rwhp and I will have to get the torque number as I have already forgotten. Pretty disappointing but if it runs better thats all that matters. We even did a compression test as the tuner was a bit alarmed and felt like the car should have been in the 420hp range on his dyno as other 427's have been......and before anyone ask the airfilter was taken off and that only made a 4hp increase. The sidepipes are not stock SPF pipes they are the Firefly brand with 2.5" diameter.

Dwight · #12 (**permalink**) 03-01-2015, 07:32 AM

what size are the header tubes?

a motor is a air pump, cubic feet of air in and same cubic feet of air out.
When you try to make max hp/tq you need to look at your carb, air cleaner, intake, heads, headers and sidepipes. All must work together.
Everything could be matched but the air cleaner and you will lose hp/tq.

Take a look at Classic Chamber Classic Chambered Exhaust Inc. - Cobra

I bought a pair of 3" i.s. pipes that were 4" longer than the ones I have. More hp and quieter.

I have a 354 c.i. motor in my Cobra with 401 rwhp / 416 rwtq.

A 155 hp lost is a lot.

Keith Craft told me that he typical saw a 20% lost in a Cobra from engine dyno to chassis dyno for the same motor.

Part of the fun is looking for 10 more hp.

Dwight

when they dyno motor they use air horns, largest headers, no mufflers, no alternator, electrican water pumps and other tricks to make max hp for the motors they sell.
the chassis dyno is the real story.

CobraDan · #13 (**permalink**) 03-01-2015, 07:52 AM

Classic Chambered Exhaust Inc. - Cobra

ssqpolo · #14 (**permalink**) 03-01-2015, 10:13 AM

Edited

ssqpolo · #15 (**permalink**) 03-01-2015, 10:43 AM

Great replies so far. looking into exhaust options.

Basically, I'll start with exhaust, move to air cleaner (any suggestions?),and finish off with the carb if needed. Hopefully I'll get her up to full potential. I'll document along the way

CobraDan · #16 (**permalink**) 03-01-2015, 10:55 AM

Side Pipes : Acton Custom Enterprises, Custom Metal for Cobras

twin turbo · #17 (**permalink**) 03-01-2015, 11:42 AM

If it was breaking up you likely have something else going on.

ssqpolo · #18 (**permalink**) 03-01-2015, 12:54 PM

That was a small concern which I have addressed. Like I said earlier, it was running very Rich in some parts, and very lean in others, so I have been adjusting. Since it was on the dyno, I just wanted to get an idea of real whp... And frankly I was disappointed. So now, I am seeing what I can do to make more power

MaSnaka · #19 (**permalink**) 03-01-2015, 03:13 PM

ssqpolo I would suggest since you are in Fl that you select a carb body without the choke horn. I found with my car the air cleaner was practically resting on top of the choke horn causing an air flow restriction. Also as others have said certain muffflers can be restrictive, I picked up 80 hp by switching mine out to Classic Chambered 2 1/2" bore and also a better intake manifold.

itstock · #20 (**permalink**) 03-01-2015, 05:06 PM

Check to make sure the throttle is opening all the way. Some backdrafts had a problem with the gas pedal bracket bending and there was no amount of adjustment that would make the carb go WOT. My car dynoed 383rwhp before fixing the pedal assembly so that it wouldn't bend when you push the pedal, and it now makes 482rwhp. It was running rich and the a/f was very bumpy.

Also, was this with or without an air filter, and which air filter? My little K&N ate up something like 30rwhp (EDIT: It was 21rwhp).