Please help selecting an engine and forced induction for Backdraft Cobra

[AlmostThere]

Hi Guys,

I am very new to the site but hope to get some help from the veterans here. I am 28 and I'm looking to get a Backdraft Cobra. Because I'm not a purist like many of you might be, I was looking to turbocharge my Cobra. Jay at Vintage Motorsports has been extremely helpful is telling what I need for this project.

First I need you guys to give me the cons and pros on turbocharging an american V8 such as a 427...402 or a 351 engine. Jay mentioned that the compression ratio for a turbo needs to be 8:1 so most engines are out of the question as they all put out 10:1 ratios. If anyone thinks that I have wrong info please let me know. So please advise as to what engine would best pair up with a singe or twin turbo set up. I am leaning towards Garrett twin or single turbo systems.

Second...please advise if there will be much turbo lag with a V8 or should I just simply get a supercharger instead. I want the torque to be available at all times so If I'm going 65 I want to be able to shoot to 100 quickly.

Last thing..please let me know if you think the car will look good in a matte black satin finish. Its a rare combo I know but I have seen it on Lambos and such and it looks so cool. Wonder if it will look cool with PowderCoated side pipes...

This is where I got an inspiration for a turbocharged cobra...

http://www.hermanndesign.com/cb1project/cb1Cached.html

Anyway...please help as I am ready to order this insane car but the heart of the snake is still confusing to me. I would appreciate all comments good or bad and please let me know what you think

Thanks a lot guys,
Max

[stuartb]

Mine just went to paint and I test drove it a little bit. I have a 427 windsor and we were just guessing but well over a 100 from a stop in less than 1/4 mile while missing the shift to third. It has about 500hp and about the same tq at the flywheel. Lets just say it is scary fast. Don't really think that you would need a turbo or supercharger. But all that said its your ride do what you want.

[Three Peaks]

You're young enough that you probably grew up with 4 bangers in foreign cars that needed a turbo to get the power needed to feel like you have a fast car. My advice would be to get a ride in a Cobra with a plain old American V8 in it and see if you really think you need the extra power.
Besides not needing excessive power to make one of these cars ridiculously fast, the short wheelbase makes bad things happen in a blink, especially if you've never driven a car like a cobra before.

My advice would be to build/buy a standard V8 car first, then decide if you really need the extra push of the turbo or supercharger. I'm betting it will be quite awhile since you can easily get 450-500 hp out of a stroked 351W and it will have much better street manners.

[macloft]

Max
If you want power to go with your name break tradition (you are young enough) and go with an LS7 with a 6 speed from TCI with paddle shifter
Light powerful and if you get bored hot her up plenty of bits avaliable.
Plenty of scope nowadays with LS motors coming avaliable. Don't get angry guys. You must admit they are a bloody nice motor.
Bruce

[olddog]

You can build any engine to 8.0:1 compression ratio.

Forced induction can run higher compression if you have an intercooler, but a Cobra does not have a lot of room to put an air to air heat exchanger, nor does it have room under a standard hood for large parts.

The Bill Cosby car had (I think) twin paxton superchargers. I have seen quite a few supercharged SB fords in Cobras and one turbo charged buick V6.

It's not hard to build 600 hp N/A engines. Short of all out racing there is no need for forced induction, when starting with a blank sheet of paper. My opinion. You really need to go for a ride in such a car before you pull the trigger on your engine.

There is absolutely nothing wrong with a Chevy engine. However if you put one in a Cobra and then try to sell it, you will loose 80% of the potential buyers.

So how much hp are you looking to have? What was the Hp and weight of the fastest car you have driven? You really need to be thinking the ratio of weight to Hp. Most cars are over 3500 lb and have less than 350 HP or 10 lb/HP. A 2400 lb Cobra with 600 HP is only 4 lb/Hp. That is a huge differance!

By the way, these cars can get you killed with only 300 hp in them, if you do not keep your head on straight at all times. Your odds drop off rapidly, as the power goes up.

[olddog]

Just looked at your link. To only make 650 hp with 12 psi boost is pathetic in my opinion. That is only about a 375 hp engine without the turbos. You could likely get the same Hp N/A for about the same money. However the tubo engine will drive like a sowing machine around town, where the N/A engine will not have as good of manors below 2000 rpm.

Your young and may not care, but my ass can make better sounds, after a good meal of pinto beans, than a turbo car. Me, I love the sound of a narly V8 puking out fumes, while at an idle, with a big bump stick in it.

[RodKnock]

There's a friend nearby who's building a Hunter Cobra with a twin turbocharged 351 that will be putting out 800HP with about 8-9 lbs of boost and about 1,100 HP with around 20 lbs of boost. There's a lot of engineering and custom work involved, but it all could fit:

Its been a long time coming........

[twin turbo]

Oops, double post, see my post below.

[eschaider]

Originally Posted by AlmostThere

...please advise if there will be much turbo lag with a V8 or should I just simply get a supercharger instead. I want the torque to be available at all times so If I'm going 65 I want to be able to shoot to 100 quickly.

Max,

Turbos don't sound good, don't give you the kick in the keyster when you stand on the throttle and can be, lets say, surprising when the boost finally does come in. Lots of turbo guys do absolutely great at the drag strip and poor around town. If you ever track your car, turbos will add an additional dimension to the complexity of controlling one of these vehicles. A Cobra is basically a land based rocket that holds on to the terra-firma by the thinnest of threads.

Almost any Cobra can break the tires loose at the drop of a hat because of their light weight and high power to weight ratio. Turbos complicate this already tenuous relationship the car has with its driver. Once the boost does come in, the turbo lag quickly translates into a boatload of power you (and the car) are not ready for.

If you are looking for period correct nothing but nothing beats a 427 (or larger) FE engine. This is visually the way these cars were born so many years ago. The 289/302/351 small block based engines will absolutely astound you in terms of power production and they can easily be stretched to the magic 427 (and larger if you choose) cubic inch space.

In terms of absolute visual knockout points the high watermark is probably a 427 SOHC with webers. A totally uninformed non car type is still going to be flat blown away when you open your bonnet (hood). If the individual is a car nut I doubt there is anything that could possibly be more impressive.

If, as you say, you are not emotionally or psychologically tied to the period correct implementation restrictions then I would encourage you to look at a Terminator engine from a 2003/2004 Cobra. It not only comes from the right gene pool it produces staggering power. Put a twin screw on and two or three Ford GT fuel pumps and this will move a 3800# car, with driver, down the quarter mile in the high 9 second range at 140+ mph. Now take that same powerplant and put it in a car that weighs a half ton less and guess what happens.

For what it is worth, the Terminator engine idles at 800 rpm gets over 20 mpg (when you don't have your foot in it) and is as large as a 427 SOHC when you open the bonnet. It is almost as visually stunning as the 427 SOHC. By the way, at about 16 psi of manifold pressure this little thumper produces right at 600 ft/lbs of torque from 1800 rpm to redline! The torque curve is as flat as a pancake. Ask any big block owner what he likes most about the big block and he will tell you the instant blast when he touches the loud pedal. Ask a small block owner and he will tell you his car is much more nimble because of the lighter weight small block up front.

I have an aluminum block version of a '03 Terminator with a Whipple. the whole engine with blower comes in less than 420#s! The performance from one of these engines will blow your mind.

In the end this is your toy. Build it the way you want it! You can buy it the way someone else wanted it much cheaper than you can build it your way. As long as you are spending the big bucks get it your way - not someone elses.

Ed

<begin edit>
p.s. Forgot to mention, if large displacement rings your chimes the Terminator Engine probably will not. It is only 281 cubic inches. But if horsepower rings your chimes, you will be quite happy. You will easily put 650 HP to the ground, at the rear tire, with that Whipple based combo - and that is with Whipple's small 140AX blower. They have two larger compressors that will bend your brain.
<end edit>

[twin turbo]

I have to disagree with many of the comments in this thread. Lag is virtually nill with a properly set up turbo system. Turbo cars drive as well, if not better, around town than a NA type car that attempts to make anything close to the same hp/tq. Turbo cars do kick you in the keyster when you stand on the throttle. Turbocharging allows you to maintain great gas mileage, if you can keep your foot out of it. Turbo cars are much quieter, which to some is a good thing.
Regarding your questions, 8:1 comp is too low, IMO, for a street driven V8 turbo car. Most people run 8.5 to 9.5:1 for good off boost performance.
It's very important to size your turbo system to the engine you are going to use. If you run a giant turbo on a tiny engine, you will have lots of boost lag.
550 to 600 rwhp is the sweet spot for driving a turbo Cobra on the street, IMO, with good sticky tires. Much more than that is only good for the track or freeway. My car with a twin turbo 331 does 0-60 in 2.8 seconds (or less) on the street in that power range. The great thing about turbo cars is that you can adjust boost on the fly with an electronic boost controller, in case more power is called for.
Go to theturboforums.com for all the info you will need.

[twin turbo]

http://www.youtube.com/watch?v=TlsJUMTxrpk
Here is a short video I made with my car a couple months ago.

[olddog]

Twin Turbo - after my smart ass comment earlier, I feel compelled to say I like the sound of your Cobra. I think you did it right. Your engine will make respectable power without the turbo. That allows you to not have to go to such high boost that gets you into all the other issues.

Most of the time you hear a turbo on a 4 or 6 cylinder import. I respect them, but don't like the sound.

I agree that boost no matter how you get it will make power. I also agree that designed right the turbo lag is small and manageable. The few I drove, the lag was perceptable, but not that bad. You only notice it, when you first stand on it at lower rpms.

I agree that if you take a mild engine and turbo it, it drives like a family car, but still has power. Much more civil, but not my personal cup of tea for a Cobra. I do feel that 600 Hp in a Cobra is too much for the street, and you don't need forced induction to get there. I know 600 is streetable in the hands of the right person, but not all that many are the right person.

Anyway I didn't intend to toss rocks at anyone elses car. I was just being a smart ass. Sorry if I offended you or anyone else.

[mln385]

Max,
If you are in the New England area, the Kit car nationals at Carlisle PA. are coming up soon. If you can get down there attend the event,you will get many ideas as well as maybe see a great deal.

This economy has the buyer in the drivers seat.


Good Luck ;
Marc

[fkemmerer]

Originally Posted by AlmostThere

Hi Guys,

I am very new to the site but hope to get some help from the veterans here. I am 28 and I'm looking to get a Backdraft Cobra. Because I'm not a purist like many of you might be, I was looking to turbocharge my Cobra. Jay at Vintage Motorsports has been extremely helpful is telling what I need for this project.

First I need you guys to give me the cons and pros on turbocharging an american V8 such as a 427...402 or a 351 engine. Jay mentioned that the compression ratio for a turbo needs to be 8:1 so most engines are out of the question as they all put out 10:1 ratios. If anyone thinks that I have wrong info please let me know. So please advise as to what engine would best pair up with a singe or twin turbo set up. I am leaning towards Garrett twin or single turbo systems.

Second...please advise if there will be much turbo lag with a V8 or should I just simply get a supercharger instead. I want the torque to be available at all times so If I'm going 65 I want to be able to shoot to 100 quickly.

Last thing..please let me know if you think the car will look good in a matte black satin finish. Its a rare combo I know but I have seen it on Lambos and such and it looks so cool. Wonder if it will look cool with PowderCoated side pipes...

This is where I got an inspiration for a turbocharged cobra...

http://www.hermanndesign.com/cb1project/cb1Cached.html

Anyway...please help as I am ready to order this insane car but the heart of the snake is still confusing to me. I would appreciate all comments good or bad and please let me know what you think

Thanks a lot guys,
Max

Max,

The two biggest issues that you're going to face if you go the turbo route is exhaust routing (especially if you want to run sidepipes) and underhood heat. You might want to consider a centrifical supercharger. This approach would eliminate both of these issues and would produce instant torque when you apply the throttle. This is also a bit more original setup as some of the 60's era HP fords used a similar setup based upon Paxton Centrifical Supercharges. This is would be a greate way to go with a 351 or perhaps a stroked 351. You would easily get in the range of torque output that would be equivalend to a naturally aspirated BBF.

On the subject of compression ratios, its not always best to go with really low compresson on a street motor. I'm running a 6-71 roots supercharge with 9 lbs of boost with 9.2:1 static CR on pump gas. This kind of setup results in better low-end torque and drivability. The low compression setup with optimize high RPM horsepower better. The key to this sort of combination is selecting the proper camshaft to keep the cylinder pressures under control. A set up aluminum which are free flowing is also a good idea as the reduced intake pressures will result in less heading from the turbocharger or supercharger. If you're going to do a project like this, its best to work with someone with considerable forced induction experience as such a builder will have tested many combinations and will know what works.

Hope this helps,

- Fred

[RICK LAKE]

AlmostThere Max there are good and bad issues with both supercharging and turbos. In the last 2 years the turbo lag has become a thing of the past. If you get the correct housings and turbo pinwheels, you can have almost no lag at all. I agree with compression of the motor in the 9.0-9.2 area. Street gas in the 6-8 pounds of boost. Race gas with the correct FI system. 15 limit. Make sure you have a min of two bypass valves, 4 small ones are better with 2 opening at 6 psi and the others opening at 8 psi. This also pervents turbo surging and damaging impellor. Snow makes a good water injection system that works like a fogger. They are adjustable. IMO works as good as an intercooler and uses less room. Just have to remember to fill the tank. They only turn on when you are running boost.
Superchargers IMO are easier on the motor with how boost is built. The only issue I had with my setup was running clog belts and banging the supercharger. The belt would belly and pop off, Vee belts work better and also limit the amount of boost you want to run. They slip around 10-12 psi and do the same after a WOT and you go to idle quick because the blower can't whine down that fast. Are you going carb or FI system for your car? Either way, 1/2" fuel line to the motor and return of 5/16" back. For every pound of boost you want a 2 psi of pressure added to a carb setup. I ran a 3-1 ratio with my FI system. My injectors where oversized for my setup.
Heat like Fred said is another issue under that hood, You need cool air coming in and removal of all the hot air or heat shields, coatings of the metal and small fans to help remove the hot air. A large radiator is also needed with a good 2,500 min cfm fan and fan shroud to move the air. Over build the drive train too. Build what every you want, but understand that a cobra with this kind of power, short wheel base, primitive controls will be a hand full. 400 rwhp is a hand full you are looking in the 500-650rwhp. This car don't have traction control, ABS, PS( some now do like mine) and "G" meters. You might want to build a motor, NA and then go for broke with another motor.
Are you looking for a ford or a GM motor? This will also help in your info hunting. Rick L.

[greg schroeder]

Do it. That's probably what I'll do with my next Cobra. In the link you supplied it shows 650 HP out of a twin turbo. That displacement could hit really hard, it's not like it's a two liter rice mobile or something. I'd go for some boost control and learn the computer stuff and have 850 on tap for rolling punches with drag radials. The nice thing is those turbos will quiet down the car too.

Keep it pointing in a straight line.

[Dinobyte]

[AlmostThere]

Thanks guys for all the good info. Everyone has been really great about the details and I appreciate the opinions. I keep hearing cons and pros about both turbos and superchargers although the Edlebrock E Force has caught my interest lately.

Check out the stats and let us know what you all think. I'm curious how many f you will like it and how many can recommend something else. By the way I am going to be running an EFI engine and not a Carb....given the daily driver issue I would prefer the EFI or CARB.

http://www.edelbrock.com/automotive_...injected.shtml


Thanks

[olddog]

I thought you was going for a 351W stroker.

I started out thinking of putting a 4.6 engine in a cobra. Several companies offer kits ready to slide one in. Several people have them. I like the 4.6 engine. In many ways, it is far more advanced than the push rod engines. I think 1995 was the last year for the 5.0 and I'm not sure when the 351W was dropped. Wow that was 14 years ago for the 5.0 engine. Time flies.

Well after you have a 4.6 on an engine stand and set it beside any pushrod engine, you understand just how huge the physical size is for a lousy 280ish cubic inches. When you tear one down, you get a feel for how demanding they are to put together correctly. The timing chains are not easy to time up the cams. Not all that bad on a stand, but it will not happen in a Cobra. Well maybe some can do it, but my fat ass with bad back couldn't.

I still like the 4.6 and would not toss rocks at one in a Cobra, but I have to say the older pushrod engines are easier to do. The performance parts are well sorted out and known. Also a pushrod engine looks more period correct. The further you get from a FE engine, the less accepted an engine is from many parts of the public. In the end, it is your choice.

[Cashburn]

Max,
Going back to budget guidelines... forget any SCs for now. That said a 4.6 3V would afford you the convenience of fuel injection now at a price in line with your budget AND down the road it is ready for the supercharger.

The Roushcharged 4.6 3V engine package in the BDR is quoted at $18k as a reference.