Bore x Stroke Ratio

[i l k e r]

ok, we're talking about the C1J here,

we get 1397 cc from 76x77mm with a bore/stroke ratio of 0.99

but what happens if we use the 72mm crank from the 1100cc engine and use it with std C1J pistons;

it would give us 1306cc with a bore/stroke ratio of 1.06

now what I'd like to know is do we actually gain anything by sacrificing 91cc for a better borexstroke ratio?

come on guys, let's talk :D

[Sparkie]

less torque, better for revs.
think you will have probs with the height of the turbo piston in the bore though?

[i l k e r]

good point Sparkster, we need to find out the piston deck heck height of the 1100cc engine. hmmm.

do you think it would help the spool-up times of the turbo being more rev happy or will it simply just rev higher??

[Adey aka Ewok]

higher reving means you can run a bigger turbo

[Andrew Cooke]

higher reving means you can run a bigger turbo

wrong, coz each rev pumps less air.

There is no advantage to short stroking a GTT.

[Adey aka Ewok]

awell im totaly missnformed then, reason was that the hondas rev so high they can run massive turbos? woulda thought even tho your shifting less air per strok you would make up for that by reving alot more thus shifting more air?

[Andrew Cooke]

awell im totaly missnformed then, reason was that the hondas rev so high they can run massive turbos? woulda thought even tho your shifting less air per strok you would make up for that by reving alot more thus shifting more air?

the reason for a short stroke is to limit the piston speed, so 2L 16V = 93mm stroke, you can rev that to about 8K, maybe a bit more, 1.8 16V, 83mm stroke, can rev it more, GTT 77mm, you should be able to rev that to 10K, can we, no, because the head won't let it breathe well enough, and the valve train won't like it. Hence there is nothing to gain from destroking a GTT.

F1 engine, ~38mm stroke and 20Krpm, double the stroke, halve the revs.

[Adey aka Ewok]

i see said the blind man :agree:

[Sparkie]

now that is good reading :)

[Matt Cole]

I wouldnt write the idea off. Gordini head with toughened pushrods and rockers. Maybe even roller rockers??:scratch:

[Andrew Cooke]

I wouldnt write the idea off. Gordini head with toughened pushrods and rockers. Maybe even roller rockers??:scratch:

They fitted a stroker crank to the Maxi...

[Mart]

I'm with Andy on this one. Can't think of any reason why you'd want to do that to the c1j, as there's certainly no (power) gains to be had.

Even if you worked the head so it flowed more efficiently, you're still gonna be limited by the rickity rockers and 'weak' pushrods.

Soz Ilkerski, this is one for the FAIL bin ;)

[gtmatt]

I'm with Andy on this one. Can't think of any reason why you'd want to do that to the c1j, as there's certainly no (power) gains to be had.

Even if you worked the head so it flowed more efficiently, you're still gonna be limited by the rickity rockers and 'weak' pushrods.

Soz Ilkerski, this is one for the FAIL bin ;)

but if money was no object , wouldnt you put in uprated pushrods etc:) uprated rockers just an idea:)

[Matt@CodeRedMotorsports]

but if money was no object , wouldnt you put in uprated pushrods etc:) uprated rockers just an idea:)

If money was no object.....would you still have a C1j...? I wouldn't!

[Scoff]

If money was no object.....would you still have a C1j...? I wouldn't!


oof, brave man.. I tried that comment once, but changed money for common sence, it didn't go down well :laugh:

[BriC]

oof, brave man.. I tried that comment once, but changed money for common sence, it didn't go down well :laugh:

Pfft, yeh, but what do you know!? ;)

[Mart]

:laugh:

Matt, you'd be wasting ya time & money mate. Sure, you can get uprated pushrods, but Sparkie aside, no-one here revs their c1j high enough to warrant having stronger items in situ, hence they haven't really been tested to see how durable they are. Sparkie usually has other mechanical issues to deal with, hence not the greatest of examples anyway ;) (just joking mate :D ).

To my knowledge no-one produces/supplies uprated rockers, and by the time you've flaffed around fitting rollers, if that's at all possible, you might as well cut ya losses & stick the Gordini head on, as the o.e head still won't be anywhere near as efficient.

And even at that point, it still comes back to the fact that you've now got less air per rev, as Andy mentioned, due to the now smaller displacement, so fine, you start running more revs to make up for that, which then puts you back on an even playing field...except you're then putting untold amount of high rpm stress on the rods, so they'd have to be replaced with forged items, and then there's the worry of is there enough lubrication getting to the bottom-end bearings, and it's etc etc ad nauseum worries for still no real gain.

If you want power, you either do what Andy's done with his engine, or rip the c1j out altogether, and do what Scoff or Matt C (to name 2) have done.

[Matt@CodeRedMotorsports]

Seriously....If I had a bottomless pit of money, I don't think I would stick with a C1J........ Is that wrong? As there are loads of people on this site that have changed from C1J power to something else.....with less money than a bottomless pit.

[gtmatt]

thanks mart i totally understand :)well this was a good topic to read ,the limits of the c1j have been found by alot of members on here i know you can get a bigger a better engine ever 1 knows that, but some people do chuck alot of money at things ,and sometimes people make it work ,at the end of the day its a c1j ,but people researched it alot ,should give the engine some credit,:) oh cant forget the carb:rolleyes:

[Rob@Backyardracing]

Agree its a FAIL... Also Id say that the GT has reasched its power limit with the C1J head in place anway, Yet to see a lightening EFI/C1J head break the 120trap unless ive missed out on something as that would be good to see to what power the heads good for with the carb in the bin where it belongs....

Blah just get a D16....... someones got to keep Scoff on his toes ;)

[Mart]

Don't forget Stuart Clark has posted a ~125mph trap speed with an o.e head (albeit worked) & carb in situ.

Maybe that's starting to get near to the limits of the c1j, but for sure no-one can truly say they've reached the optimum of what's achieveable/obtainable.

Regardless, in this instance, and going back on-topic, there's no gains to be had from de-stroking the c1j. Period.

[Scoff]

stuart is an interesting case. he has reached the limit of what his particular engine will do because adding nitrous made no extra power at all. imagine that, it's like he's literally maxed it out post chamber. if he had larger exhaust valves, a better manifold and a bigger turbine then maybe it would be a different story.

agreed, you would not want to loose stroke on the c1j. it is just about right for the best cylinder heads we have seen so far. like andy says, improve the cylinder head (read cross-flow, maxi and so on) then you would want to go longer still else you will need a lot of rpm to reach the limit of the new cylinder head.

[Andrew Cooke]

stuart is an interesting case. he has reached the limit of what his particular engine will do because adding nitrous made no extra power at all. imagine that, it's like he's literally maxed it out post chamber. if he had larger exhaust valves, a better manifold and a bigger turbine then maybe it would be a different story.

agreed, you would not want to loose stroke on the c1j. it is just about right for the best cylinder heads we have seen so far. like andy says, improve the cylinder head (read cross-flow, maxi and so on) then you would want to go longer still else you will need a lot of rpm to reach the limit of the new cylinder head.

I don't think even my head will stretch a long stroke engine, as it stands I think the valves and ports are good for maybe 8500rpm, and as you up the stroke you up the capacity which will drop the optimum revs for the head. I think it needs a 16V head to max out the rpm potential of the bottom end. Maybe I'm wrong.:scratch:

[Big Jim]

Guess it's all been said really but I do like to have my penn'orth! Good to think around the norm but this is a blind alley. You'd just make a less powerful engine. In the turbo F1 days BMW initially based their unit on a de-stroked existing race engine. They got better results when they reduced the bore size and increased the stroke. Playing with bore/stroke ratio's and stroke/rod length etc is really for getting the most from a given capacity.

If money was no object you'd re-insert the head for the biggest valves that would fit, stagger bore the block for the biggest bore custom liners and get a stroker crank made... Reckon you'd get about 1800cc, loads of power and bugger-all reliability.

Oh, and in my humble opinion, no-one has come close to c1j limits:)

[THE MASTER]

has any one tryed exploring the valves and more so valves springs . we all know about valve timming and how important it is to get valve timming correct , wot happens if your boost pressure is opening your valves before there suposed to open

a weak valve spring is not going to keep the valve closed with high boost
:confused:
same goes for the exhaust valve
the more boost that is dialed in the more you gotta drive the turbo, hence more pressure will be in the zorst mani and the zorst valve will have trouble shutting

ps im using twin valve springs on the inlet but std on the zorst and in gonna put twin on the zorst aswell cos ive had no probs using two springs on the inlet :p

[Sparkie]

ps im using twin valve springs on the inlet but std on the zorst and in gonna put twin on the zorst aswell cos ive had no probs using two springs on the inlet :p

i had twin springs on both, and wore the cam follower and cam lobes out, so much so the cam follower mushroomed and the pushrod was poking through the hole and running directly on the cam....

[i l k e r]

thanks for all the input guys :agree:

this goes straight in the Fail bin as Mart says then :cry:

well, I've got something else in mind I'd like to discuss but that belongs to another thread....

so see you all soon :wasntme:

[rs250nut]

Throw the engine and carb in the bin and find something lighter, maybe an all alloy engine with sixteen valves

[Scoff]

Throw the engine and carb in the bin and find something lighter, maybe an all alloy engine with sixteen valves


who would do a thing like that :cool:

[Mart]

thanks for all the input guys :agree:

this goes straight in the Fail bin as Mart says then :cry:

well, I've got something else in mind I'd like to discuss but that belongs to another thread....

so see you all soon :wasntme:

We need more tech' discussion threads on here mate, so fire away :agree: :)

[Rob@Backyardracing]

We need more tech' discussion threads on here mate, so fire away :agree: :)


Agree... RTOC sucks ************ at mo :coffee:

[Sparkie]

summat to chew on...

http://keops-racing.skyrock.com/18.html

http://keops-racing.skyrock.com/10.html

http://keos-racing.skyrock.com/23.html

[Big Jim]

Ummm, what was I saying... Just need someone with the will (ie the cash!) to do it and anything is possible.

[i l k e r]

has any one tryed exploring the valves and more so valves springs . we all know about valve timming and how important it is to get valve timming correct , wot happens if your boost pressure is opening your valves before there suposed to open

a weak valve spring is not going to keep the valve closed with high boost



this is right to a certain extend but when the inlet valve(s) are closed piston is on it's way up in the bore which creates pressure into the combustion chamber helping the valve spring to keep it shut.

am I right?

[Big Jim]

Forget about boost and/or cylinder pressures affecting valve motion.

[Andrew Cooke]

Forget about boost and/or cylinder pressures affecting valve motion.

is that the same as saying "it's back pressure you need to worry about"?

[Big Jim]

is that the same as saying "it's back pressure you need to worry about"?

que?

[Andrew Cooke]

que?

during the induction stroke there may be more pressure in the exhaust manifold than the cylinder; seat load is about 45lb, exhaust valve area- lets call it 1", anytime there is more than 45psi in the exhaust than the cylinder the valve will leak, add in the pulsing and things get a bit unclear.

So when you say not to worry about boost, or cylinder pressure are you saying to worry about backpressure? Or don't worry about backpressure either?

[Big Jim]

It's all about context. Reading this thread some seem to have the impression that gas pressures are going to cause valves to be blown open prematurely. If springs are that weak that this is happening then you are going to be suffering from horrible valve bounce that will be affecting your performance to a far greater extent than a bit of leakage.

The situation you describe is feasible, of course, but what affect would a slight leak have under these conditions? If the exhaust manifold pressure is massively higher than boost pressure, which with a well sized turbine/housing won't be the case, then the residual cylinder pressure at inlet opening will cause a lot of charge contamination, a tiny bit more from a leaking exhaust valve won't change much.