IRS vs live

[Selo]

After much research just made arrangements to purchase a Mk IV Roadster. Very excited, only reservation is no IRS. Does anyone care to comment, or is this seen as flogging a dead horse?

[Ron61]

It has been discussed a lot but no problem with asking. I have had both types of rear end suspension and raced them. The IRS does give a little better traction when cornering but the straight axle is just fine, especially if you aren't going to race it. Tell us a little bit more about your new toy and post some pictures. And don't let the no IRS bother you at all.

Ron

[Selo]

Thanks for the input! I'm purchasing from an aerospace engineer in Florida who built the car a couple years ago. It's a FFR unit with a small block making slightly north of 300 hp that favors driveability over intense hp. It has numerous thoughtful touches and modern conveniences that I believe will make it a great driver as well as a showpiece.
It's not in my possession yet, but as soon as I have it I'll post pics.
By the way, the rear suspension has a Panhard bar - not just a live axel, not sure if that's standard fare or not.

[jhv48]

My first FFR had the live rear axle. My current SPF has the IRS.
The solid axle rode a bit harsher until I massaged the springs and shocks to suit my taste. Seemed to handle better too.
You’ll have no problem with the solid axle. If the car comes with Bilstein shocks (they were used up until a few years ago when they began to fail and were replaced with adjustable Koni’s) replace them with adjustable shocks and you’ll notice a very drastic improvement in ride comfort.
Don’t sweat not having IRS. It's definitely a more comfortable ride, but not enough to worry about.
Enjoy the FFR.

[patrickt]

Originally Posted by jhv48

MDon’t sweat not having IRS. It's definitely a more comfortable ride, but not enough to worry about.
Enjoy the FFR.

I agree. An IRS is better on bumpy streets, but I wouldn't skip a nice car that I really wanted just because it didn't have it. Now, having an LSD will help you a bit. Probably the most dangerous condition you can encounter in these cars is the unexpected "snap oversteer" condition on hard acceleration. Even just 300HP can get you in to trouble real, real fast with these cars.

[saki302]

If it has a panhard bar it's probably the 3-link setup.

Street ride will be rougher, but they handle well with the Konis. I added swaybars to my old car, it handled (and rode) like a go kart ��

[undy]

Not that it applies to the OP, but a sturdy live axle will survive high HP/TQ applications better than an IRS setup will.

[Selo]

I haven't driven the vehicle - buying sight unseen. Seller assures me car will break tires loose in 1st and 2nd gear for sure. If I do want to add hp, what is the easiest way?

[olddog]

The easiest way to add Hp, is a bottle of laughing gas. It works. It can be hard on an engine if too much or not done right. I wouldn't recommend it, but it is easy.

[Selo]

Originally Posted by olddog

The easiest way to add Hp, is a bottle of laughing gas. It works. It can be hard on an engine if too much or not done right. I wouldn't recommend it, but it is easy.

What's the next easiest, and hopefully safer way to add horsepower?

[patrickt]

Originally Posted by Selo

What's the next easiest, and hopefully safer way to add horsepower?

Not knowing what you have under the hood, I would vote for a different camshaft and head work.

[olddog]

Originally Posted by Selo

What's the next easiest, and hopefully safer way to add horsepower?

How to get more intoxicating Hp. Man started this quest before Henry built the Model T. Assuming correct air fuel mixture (AFR) and timing, to make more power you need to burn more fuel per unit of time.

An AFR, timing side note. ~14.7:1 AFR is the correct ratio to completely burn all the fuel and have no oxygen left over. Around 12.5:1 makes the most power but leaves un-burned fuel in the exhaust, as it ran out of air. The reason is that the fuel is expanding into a high pressure gas making more pressure even though it is not burned. That high pressure un-burned fuel actually lowers the temp of combustion. WOT at 14.7 AFR will melt engine parts. Here is the important part. Ford engineers target 10:1 AFR at WOT. Why. It saves engines (cooler combustion). They understand they are giving up about 10 Hp by burning too much fuel, but since they cannot control what grade of fuel is put in and how someone drives, it saves them money. Timing is also retarded to assure that the crappiest fuel sold will not go into detonation and destroy the engine. Again they are giving up 10-20 Hp but it saves them from replacing engines. I am assuming from what you said that this is a factory EFI set up. So if you put the highest grade fuel you can get, reliably, into your car and have in tuned on a chassis dyno, a good tunner will be able to get you another 20-30 Hp. All the factory safety factor will be gone, and it is up to you to never dump in a lower grade fuel. If you hear pinging get off the throttle, especially when the engine is hot (running hard).

Personally, my butt cannot feel much less than 25 Hp change. I would save the tunning until after I slipped a cam in or added better heads or both.

Back to burning more fuel per unit of time. Since the AFR has to be correct, you have to pump more air through the engine to burn more fuel. Hence the old adage, there is no replacement for displacement. The more cid the more air you pump. There is an alternative to displacement, Forced Induction. Turbo charger, centrifugal blower, lobed blower, screw compressor, these will all push more air into the engine. If you bring the intake manifold up to 14.7 psig you will have double atmospheric pressure (at sea level). You can then burn twice the fuel and make twice the power, minus whatever power was consumed to power the air pump used.

High boost levels has many issues that has to be done right or the engine is easily destroyed. Lot's of heat is added to the air that if not delt with, will auto ignite the fuel before the plug fires. Ford has mastered this with the turbo charged ecoboost engines. Today the standard tiny 4 cylinder engine in the Mustang makes more Hp than the GT with the old 5.0 or 4.6 modular.

There are many forced induction options that will bolt on to your 5.0, but fitting them into a Cobra can be a challenge. A mild 5-8 psi boost would get you well above the factory 225 Hp. North of 300 fairly easy. Getting to 400 hp without changing internal engine components is not very realistic. Well it would run for a while and then you could replace what is left of the engine.

Someone else mentioned stroking the engine to 347 cid (which includes 0.030" over bore). You cannot go wrong there. No replacement for displacement. Good heads make the engine. Factory heads are a huge bottle neck in the power making department.

Understand that your engine likely has 19 Lb/hr injectors. To burn more fuel you will need bigger injectors somewhere north of 300 Hp. Not too much north of that you will need bigger fuel rails and a bigger fuel pump. Your fuel lines may be too small too.

Also understand that if you stroke the engine and put good heads on it, the existing intake manifold and throttle body will be too small. If you go forced induction they can stay.

The biggest point I can make is that if you start adding a piece at a time to make a little more power here and there, start with an end goal in mind. The best heads for a 302 is not the best for a 347. Someone may recommend a great head for your 302 but if you are going to stroke it to 347 better to buy those heads, unless you can toss $2000 to a set of heads you are only going to run for a while and the toss another $2000 again later.

Food for thought anyway.

[Selo]

How expensive is it to pull out the Fox 302 and out in a nice small block/hipo crate motor?

[patrickt]

Originally Posted by Selo

How expensive is it to pull out the Fox 302 and out in a nice small block/hipo crate motor?

Call up Brent Lykins, a member here, chat with him for about an hour first, and then he'll give you a quote that will be quite competitive and the engine will be as solid as a rock. You can pull your own engine out, and swap a new one in, in your own driveway with a little help from a strong son or buddy.

[120mm]

If you have a 302, the easiest way to get more power is to drop a 347 in there, or have the 302 stroked to 347.

A well set up 347 should give you 400 crank HP easy and still be driveable. It will also bolt right in without changing anything.

The next easiest is to go with a 351W or a stroker based on it, such as 408W. Running this requires new headers at a minimum.

[patrickt]

But, to be honest with you, unless you've owned one of these cars before, I wouldn't do anything until you've driven it for a year. There's a decent learning curve involved....

[Selo]

I'm not planning on doing anything for awhile. Just a little concerned as we do lose some power at high altitude - supposedly about 3% for every 1000ft above sea level. We're at about 5000 ft, so theoretically starting at a 15% deficit. Just need to see how it feels, and how the EZ fast injection system works up here.

[Selo]

Need some quick advice:. Side pipes are stainless without heatshields. Should I put on ceramic or chrome heatshields, neither of which will be a perfect match?

[patrickt]

Originally Posted by Selo

Need some quick advice:. Side pipes are stainless without heatshields. Should I put on ceramic or chrome heatshields, neither of which will be a perfect match?

Neither. Stepping over the hot pipes is part of the learning curve.

[Selo]

Originally Posted by patrickt

Neither. Stepping over the hot pipes is part of the learning curve.

That's just not gonna fly with my wife. One pink leg on my kid and the car's gone I'm afraid!