Drivetrain and Exhaust losses

[Tallguy]

I think my mind is made up on using a 428FE, non stroked for my Cobra project. I am going through drivetrain design, and want to get an idea of what losses I'll see from BHP to RWHP. I have searched a lot, and based on that and other internet searches I am estimating the following:

Driveline Losses
Manual Trans - 2%
Driveshaft/U-Joints - 1%
Rear End - 10%
Accessory Losses - 2%

Total Driveline and Acc losses = 15%

Sidepipe Losses - 45 HP (guess based on 50HP loss @ 500 HP)

So if I get a 428 motor with 450 BHP I lose:

68 HP in driveline
45 HP in exhaust

Total to wheels = 337 HP which is a 25% loss.

Does this seem right? Are the sidepipes usually that restrictive?? Seems like a lot, but that is what I have seen in the searches I did.

Another thing, on the 15%. It seems like the drivetrain losses should be somewhat constant whether you have 200 or 700 HP and not a %. Same HP to overcome the loss.

Thanks,
Mark

[RICK LAKE]

Tallguy Some of the cars have brakes that lightly drag on the rotors. Total power loss is about 22-24%. Exhaust side pipes are the biggest killer of all. If you go with a race muffler you will have less backpressure and make alot more noise. The power loss will be 5-10 HP instead of 20-50 HP depending on what muffler is used inside. My ERA pipes pass the noise police at racetracks and are a glasspack inside with good sound. After some racetime I get the ringing in the ears. I now wear ear plugs the the problem is stopped. I have racepipes and they are loud. It's all about backpressure. The idea number is about 1.5-2.0+ pressure in the system at WOT. Anything more and you are wasting power. The other thing is that if you are going to build an engine like your 428 add a stroker crank of 4.25. TORQUE is what moves your car, HP is what keeps it going at top speed. Unless you are racing and turning 7000 rpm, don't worry about how much HP you have. The correct gearing in the rearend and trans will offset a car with 30-50 HP more than you. I have a 452 motor 9.2-1 compression,501-533 hydro cam,5spd, 3.31 gears, the car runs 12.5 all day long at 108-109mph. I am easy on the jag rear, it is not a good drag racing rear. 368 rwhp and 458 tork rear wheels. Car idles at 700 rpm smoothly and pulls to 5,800 rpm hard, I don't like to spin motor over 6,000 rpm, it is out of power by this time. Stroke the motor with a set of BBC rods and 4.25 crank and find a nice cam in the .550-575" lift. hydro lifters are fine and are maintainance free on adjustments. Add a accusump system to your car and use it as a peroiler. 80% of engine wear is on startup. Have a little port work done to the heads and you will have a 400-450 rwhp car. This is a nice combo and still drivable. You car will be like most here, a work in process. Buy a good rocker setup like ERSON. FE shafts break, even the heavyduty ones. Rick L.

[Tallguy]

Rick,

Thanks for the reply and insight. Although I will be building the Cobra, I won't be building the engine myself. Just don't have the skills, so I will be shopping around to other sources.

I am trying to make sure that I do not put in a motor with too much torque for my very rookie driving skills. I am balancing (on paper) BHP of the motor with driveline losses, trans gearing, rear end gearing, and tire specs to see how much torque is available at the rear tires in various scenarios.

I do not plan to road race, but maybe a trip now and then to the local 1/4 mile strip. My overall goal is a streetable car that can break 4 seconds 0-60, but still be civilized. I also want to stay stock on the 428, as to me having a motor that is exactly 427 CI just seems a perfect fit.

I am leaning to a close ratio Top Loader (2.32 1st) with 3.31 or 3.54 rear end to get me to 60 mph at near 6000 RPM in 1st gear. Maybe 450-500 Ft lbs at the flywheel....

Mark

[496fe]

Just a coupla thoughts... The close-ratio toploader might not be such a good idea with the amount of torque you have. Usually, the more torque, the wider you want your gears. I had the close-ratio toploader in a previous Cobra and found that first gear was too high, plus I found myself skipping gears while street driving. A lot of 1-2-4 and 1-3-4 and sometimes even 2-4! The FE is quite literally a truck motor and you will get tired of using all the gears. Almost everybody is going with the TKO 600 because of it's wide ratios and unbelievable tall overdrive 5th gear.

Ironically, the best 0-60 times seem to be obtained by "driving out" in first and short-shifting into second.

Driveline losses are a combination of percentage losses (exhaust), which are related to HP, and absolute changes (rear end) that are not functions of HP. My 608 HP at the flywheel turned into 474 HP at the rear wheel, just for comparison sake.

Brian

[CobraEd]

Kind of a personal issue here, but I always felt that with my 4" od 3" id glasspack sidepipe mufflers, I would have minimal exhast loss. Can't imagine that a straight thru 3" id muffler would restrict anything.

What do you guys think?

.

[Tallguy]

Originally Posted by 496fe

Just a coupla thoughts... The close-ratio toploader might not be such a good idea with the amount of torque you have. Usually, the more torque, the wider you want your gears. I had the close-ratio toploader in a previous Cobra and found that first gear was too high, plus I found myself skipping gears while street driving. A lot of 1-2-4 and 1-3-4 and sometimes even 2-4! The FE is quite literally a truck motor and you will get tired of using all the gears. Almost everybody is going with the TKO 600 because of it's wide ratios and unbelievable tall overdrive 5th gear.

Ironically, the best 0-60 times seem to be obtained by "driving out" in first and short-shifting into second.

Driveline losses are a combination of percentage losses (exhaust), which are related to HP, and absolute changes (rear end) that are not functions of HP. My 608 HP at the flywheel turned into 474 HP at the rear wheel, just for comparison sake.

Brian

Good stuff Brian. Thanks. It makes sense, as it would be much easier to "tune" by changing the rear gears if you wanted, and still have the versatility of the 5 speed with the lower 1st and OD.

Mark

[Anthony]

Originally Posted by 496fe

Just a coupla thoughts... The close-ratio toploader might not be such a good idea with the amount of torque you have. Usually, the more torque, the wider you want your gears. I had the close-ratio toploader in a previous Cobra and found that first gear was too high, plus I found myself skipping gears while street driving. A lot of 1-2-4 and 1-3-4 and sometimes even 2-4! The FE is quite literally a truck motor and you will get tired of using all the gears. Almost everybody is going with the TKO 600 because of it's wide ratios and unbelievable tall overdrive 5th gear

Its all a matter of personal preference. Personally, I prefer the close ratio toploader over the WR toploader or TKO tranny's. I've changed from a WR toploader to a CR in fact.

Yes, the gears are closely spaced, and you can skip gears while street driving, but that's not what the CR was developed for. I think it was developed mainly for drag racing. The true street tranny's offered by Ford were the 3 speeds, WR toploaders, and overdrive toploaders.

For street driving, the TKO and/or WR toploader is a better tranny, wider spaced gears, and the ability to get greater economy with cruising. But, when you're on the track, either drag or road racing, I think the CR toploader is clearly superior.

I just don;t see the BIG PROBLEM everybody is having with the ability to have optimal cruising, to save a few hundred rpms. I would say most cobra owners don't drive their vehicles daily, and saving a mile or 2 per gallon to me is taking away from the performance the cobra was meant to have.

I have a drag pack mustang, CR toploader, 3.91 rears, and it's fine for cruising down the freeway, several times a year, or even several times a month. No problem. With the cobra, a lighter car, you can run 3.54 rears and it would be even better.

For me, it's a CR toploader, or any other tranny with similar ratio's. No more WR tranny's for me.

Originally Posted by 496fe

Ironically, the best 0-60 times seem to be obtained by "driving out" in first and short-shifting into second.

That's because in most cases the tranny-rear ratio's are not optimally matched, and you have to short shift because of the short comings of the tranny-rear combination. No short shifts for me.

The TKO's are fine tranny's, and great for the street, actually, about any tranny would be fine for the street, because you usually don;t take the car to the limit while street driving.

It's all personal preference.

Tallguy, you have to decide what's right for you.