603S Engine

[Kevin H]

Originally Posted by will7262

The question is how do I uprate the engine to say 300HP and will the gearbox propshaft, differential take it?

Assuming the gearbox propshaft and differential are the same as those that went before it (411/412) and those that after, Beaufighter, Brigand etc, then there will be no problem coping with 300HP.

As for how to get 300HP, it's an eminently tunable engine, with heaps of information and after market parts available. But what does the engine put out now? have you had it on a dyno?

[will7262]

Kevin

I have no reason to think she has been modified so assume all the running gear is standard.

My researches seem to indicate that with a 4BBL carter carb and an 8.4 compression she will have something like 225 HP. This may well be an American SAE figure so probably more like 200HP DIN. Not a lot for a car of this sort of weight.

[Kevin H]

Will,
I guess it goes without saying that an increase of 200HP to 300HP isn't going to be achieved with a couple of bolt on goodies, other than perhaps a turbocharger!

The good news is that the engine can produce a hell of a lot more power than 300HP, so it's just a matter of how you achieve it. Where do you stop? What gives the biggest "bang for buck"?

To my mind you want more torque and power within the same rev range, then you don't have to worry about the crankshaft and things like roller cams. What you consider doing to the engine depends on what condition it is in. The bottom end doesn't need much doing to it at all as the stock crankshafts were very strong to begin with.

Improved breathing is a must. A decent increase in power and torque could be achieved with some mild porting of the heads, bigger valves, a better intake manifold, and a modern carby with tuned jetting. Ideally you should also install some different pistons to increase the CR and a higher performance cam shaft to take full advantage of better breathing.

I'd also go for an electric fuel pump with pressure regulator, it could also be worth replacing the original water pump with an electric one.

There are a few books on the specific topic of tuning Chrysler "A" Series Smallblock engines.

OR you could just buy one of these Crate Engine - Chrysler 360 Engine

[Kevin H]

Just to clarify, what I mean when I say "The bottom end doesn't need much doing to it at all ", is that other than making sure the all the bottom end bearings and crank bearing surfaces are in good condition, it doesn't need any modification to cope with 300HP in the normal rev range.

[Kevin H]

Sorry, one more thing!

When I say "A" Series engine, it's technically the "LA" Series, but they are often referred to as the "A" Series, which can cause some confusion, because the old 313/318 used in the Bristol 407-410 were in fact the original "A" Series, but most Mopar enthusiasts seem to have forgotten about them!

[will7262]

I have to say the crate motor approach looks very attarctive but shipping costs from the states to UK and then import duty and no doubt VAT might tip the balance to rebuilding the original lump.

I wonder if anyone has fitted some sort of header or a better cast exhaust manifold to a 603 and later car. All about clearing the chassis I guess.

[Kevin H]

Originally Posted by will7262

I wonder if anyone has fitted some sort of header or a better cast exhaust manifold to a 603 and later car. All about clearing the chassis I guess.

According to the experts, Chrysler's original cast iron manifolds were quite efficient and able to handle "street" performance upgrades. 300HP certainly fits into this category.

The cost of getting custom headers made would probably not be warranted in terms of performance increase and may create problems by increasing the engine bay temps.

I am assuming that Bristol used the stock Chrysler exhaust manifolds, as they did on the 411.