Fundamentally speaking why is it

[tinweevil]

that a cossie 4 pot 2 ltr 16 valve engine can hold together 800+ bhp while sprint engine of the same outline spec can barely handle a quarter of that? Is there a fundamental design feature (flaw?) that holds it back? On the plus side 4 valves per with centre spark plug is the about the best arrangement there is. Its got the correct number of crank bearings too. The exhaust valve map is a pretty massive compromise but is it that important? Is it too oversquare? Do those angled head fixings fundamentally limit combustion chamber pressure?

Or is it just the sum of the whole - no significant factors. If you had the money to get components made to the standard that Darren uses could a whole hill more bhp be released? Somehow I doubt it or the F3 engines would have had a better time.

Step up to the mic Darren, Hans, Ken etc.

Tinweevil

[Lewis]

Fundamental similarities bear no use at all - the design, specification, tolerance and materials give the engines their extra strength and output, along with machining techniques used to make the components.

It's a bit of a washy answer but I'm off out, so I can't blabber on for long (probably for the best )

A Cosworth engine requires a lot of development work and finances to generate a reliable 800BHP+, which is worth bearing in mind - plus it's turbocharged which gives it an edge. No doubt the flow rate through the head is much higher, the combustion chamber better shaped, the bottom end stronger and more resistant to fatigue and so on.

I'll elaborate later when I get back, if others haven't come up with better or longer posts by then

[Carl]

I thought that the biggest limiting factor for a Sprint was the timing chain/sprockets/jackshaft. As I understood it, getting a Sprint engine to rev reliably past 7500rpm was a major engineering challenge (he says, frantically trying to find his Broadspeed spec. sheets).

[Jon Tilson]

is vaguely on the money...

The Sprint crank has a harnmonic balance issue at high rpm. Rpm isnt all though...
The pistons and rings need to stand a much higher effective compression ratio too so need to be stronger, withstand higher combustion temps and seal better. Bore tloerances and oil supply also come in. The we have the big fat turbo and all the induction and exhaust issues.

The cossie block is obviously very strong. I'm not sure how many miles it will do giving out 800hp.

I'm quite happy with my 130k miles at 140 ish...

Jonners

[tinweevil]

With all the QI sirens and alarms ringing - turbocharging is precisely what I don't mean! The point is Darrens engine holds together when producing that. I'm sure there's plenty of companies that advertise in Max Muppet Magazine that could calculate and fit the turbo & nitrous combination to get that out of a stock sprint. But we all know lots of things would let go before you got halfway up the first rolling road run. Flow can be improved within the limits of the basic design, but does the basic design prevent significant throughput?

Specification, tolerance and material differences I can understand but I have no experience on which to quantify those. Design is the word I'm hoping to better understand. For example; there are ideal formulae banded about for things like inlet to exhaust curtain ratio. Is there one for stroke vs bearing surface (two utterly plucked from thin air parameters so forgive me if they are unrelated) that Triumph didn't observe that dooms the sprint crank to terminal resonance?

Timing gear, now there's a huge difference between our engines and current technology. Are belts that massively superior?

[xvivalve]

Not sure of the provenance of the statement but I read somewhere that the single cam design, whilst very innovative, did actually limit what could be done to the engine power wise because of the absolute connection between what was happening to inlet and exhaust valves...?

Isn't it BMW that have reverted back to the far superior chain technology?

[Mad Mart]

Have a chain on my S2000

[HolgerS]

.....Isn't it BMW that have reverted back to the far superior chain technology?

Yes my V10 monster has chains in it but BMW use dynamic valve timings to overcome the general issue.

[SprintV8]

Doesn't the BMW engine have problems with the Vaneos Timing gear.

Mercedes are all chain's even the 55/65 AMG's

And my new engine the TVR AJPV8 is chain driven.

[DavePoth]

AFAIK the problem with getting obscene power out of the sprint engine isn't the top end, which was always designed with performance in mind. Bear in mind that the sprint engine in Jigsaw racing's TR7 makes around 240bhp, which is pretty damn good for a NA engine, even today. (about the same as the S2000, in fact)

Now that is not a reliable 240+bhp, and I think it's very telling that the first thing Saab did when they modified the slant-4 engine was to considerably beef up the bottom end. (main bearings out to 58mm, 56mm big ends on the con rods, and some other stuff I can't find data on) And they did this with forced induction in mind. But even then the highest output I can find from a Saab 99 or 900 is around 300-350bhp.

[ALGIK]

The ports on a dolly sprint head are bigger than a cossys
but you would have to change off the top of my head
EVERYTHING
The cosworth block material is far superior
Has anyone ever tried picking a 200 motorsport block up
Also mine has had nicasil liners put in it
They have oil cooling jets as standard for the pistons
Some of the freeze plugs are deleted in the 200 block
The rod bearings are huge compared to a sprint as is the crank bearings
The sprint rods are also puney
Also i dont know of any decent head gaskets for the sprint engine
and the method in which the head is bolted down is somewhat .
The cos valves are 2 piece friction welded sodium filled
The valve guides are bigger
I dont think the sprint water cooling system esp the block water jackets would cope with the elevated temp of forced induction,
My exaust wheel in the turbo runs at 1100 deg c and that has a water jacket to cool it
Im not saying you could not do it
but it would be more about look i have turboed a sprint engine
Also the sprint crank would be thrown straight out of the block
Its not the power as such its the torque which would kill it
The money you would spend doing it properly aint worth the hasle
I toyed with the idea years ago

[SprintV8]

May as well then buy a 360bhp engine to start with then

[2F45T4U]

but isn't that an engine close to the top of the tuning to the extent of makin it unreliable peak?

[Jon Tilson]

engines are all dohc too IIRC...on the old 900 that is.
The Rover 800 Mi16 was dohc and meant to go on a TR7 engine IIRC.
The sohc but 16 v design is I think a bit limiting. Nobody esle does it that way.

Ive done a head job on a T plate 9-3....bore almost no resemblance to
anything Ive seen under a dolly bonnet...sideways and vertical...dohc with single chain and external spriing tensioner.

The Cossie engine is some sort of summit. Even VW dont go that high with the 5 valve turbo engine they do in the TT etc.

Basically all the normally asprirated induction tricks like valves, cams and variable timing etc are worth what? 70-80 bhp? Its the forced induction and compression ratio that does the damage...and mandates the cooling, lubrication and metalurgy to do the job.

which is what Daz is saying I think.

Seems to me that 800 bhp form 2 litres means stress whatever way you look at it....probably explains why most engine makers who want those kind of numbers go for V12's

Given the price of 750 beemers and old XJ-S's....hmmm no...too big and heavy to fit a dolly..

Jonners

[Lewis]

in Jigsaw racing's TR7 makes around 240bhp

I'd like to see it on a rolling road. I remember that being disputed a bit.