1.6 Crank - Better Than We All Think?

[Batfink 201]

On my daily internet trawl for all things peugeot I can across this advert

205 rally car

 

nice bit of kit, but two things stood out; the 9000rpm limit and the fact its on a lightened and balanced crank.

 

So is the 1.6 crank a lot better at coping with high rpm due to its smaller stroke and longer rods than the 1.9, putting far less strain on the drivetrain? Still saying that thats a lot more revs - 30% more than standard limit. There will always be a margin of safety as standard but can balancing really help that much. Sounds far fetched to me but without knowing more I'll pass on judgement. Shame we don't push the limits of the 1.6 before moving to bigger capacities.

I bet Longmans fit all steel cranks to their Group A cars..

 

We need Vibration Free to sign up to this site lol

[McPikie 0]

Without a doubt that will be a steel item

[DrSarty 90 1 Cars]

Without a doubt that will be a steel item

 

Is that your wildest bedroom dreams now shattered Kev? You 1700cc freak you!

 

[Batfink 201]

lol nope. I wouldnt run 9000rpm on a standard crank.In fact I would wonder if the car does really rev that high lol. But my theory is if the standard crank is good for 6800rpm (incidently a car should be able to run all day there without blowing up - if cooling is adequate) so there should be a margin of error (maybe 10% would be fair) so with it balanced as best it can and running lighter rods; I think 7500rpm should be aok, which puts it into the revs i need it to cope with. My lightweight clutch and flywheel will lower stresses on the crank too

[SimonJ 2]

The 198.7 bhp was quoted by someone on a thread about a car build here recently, think his username was renault17 so is probably his car. The crank issue was discussed but don't remember the conclusion.

[ifcho 0]

So a standard bottom end shoudl be fine for 7k use?

[pee vee 1]

We need Vibration Free to sign up to this site lol

 

 

wouldnt be a bad thing!

he is the man that knows!!

[pee vee 1]

ps: would that be built to a 'super 1600' spec car? if so the engines have a life of 1000km...

 

as there is no way pug ever put a 205 into group A.... is there :s

[Batfink 201]

The 198.7 bhp was quoted by someone on a thread about a car build here recently, think his username was renault17 so is probably his car. The crank issue was discussed but don't remember the conclusion.

 

Renualt17 built a 1.6 mi16 so its not his. I think he was revving to 8000rpm with a standard balanced crank. I think he is one of the few people who has pushed the standard crank to extremes (who is actually on the forum)

 

So a standard bottom end shoudl be fine for 7k use?

 

dunno really but you dont set the rev limit to a car at the point where it will blow up so there must be a margin of safety built in. Its a case of guessing those tolerances and taking a gamble really.

[PUGugly 0]

Used to run my 1600 to 7k very reg (almost every time it was used!), never had any trouble until the head gasket went.

 

Got a Mazda Xedos (same family V6 as MX6, 626 and Ford Probe. Redlines at 7k and while I've been digging around on specs and info ready for a transplant into a Sierra found that it was run by Mazda at 9800RPM continuos in testing without failure. I certainly have reved it to 8,200 plenty and no problems yet..... touching wood!!

[Tom Fenton 1,542]

In my experience standard crankshafts are a whole lot stronger than people give them credit for. When did you last see a broken XU crankshaft? I never have. What are the more usual failures? Rod bolts perhaps, which can be uprated.

 

I have run a Mini crankshaft, fully worked but standard material, to 9200rpm regularly for a year. It hasn't broken yet, even with only 3 main bearings.

[ginjaspeed 0]

i used to rev my standard old 309 GR 1600 to 7500 regularly, never had and issue with that car . No rev limit on a standard carb engine

Edited January 27, 2008 by ginjaspeed

[Miles 331 1 Cars]

As said my completly std Mi engine on bodies the crank stood 8500 until a std big end bolt went and wrecked it all so they are pretty good for a std crank

[DrSarty 90 1 Cars]

No rev limit on a standard carb engine

 

Well that's not entirely true. There IS a limit; it's just a mechanical 'go bang' limit, rather than an electrical one imposed by the ECU stopping things breaking.

Edited January 27, 2008 by DrSarty

[Batfink 201]

As said my completly std Mi engine on bodies the crank stood 8500 until a std big end bolt went and wrecked it all so they are pretty good for a std crank

 

it was my understanding that the bolts are not able to cope with the extreme high revs so should be upgraded??

[saveloy 8]

Going beyond 7500 rpm puts one into the realms of associated issues. The crank isn't the weakest link. Rods and caps will take alot of stress and running a rubber timing belt (rather than a geared) system means that the bigger tolerance between piston and valve will result in kissing, and possibly something more amorous.

[Miles 331 1 Cars]

It was a quick build on basic Reground Kent cam's and made paek power from 7500 > 8000rpm and tailed off at 8500, Was never built to go that far but it did and I think lasted quite well with the spec it had

[Batfink 201]

Going beyond 7500 rpm puts one into the realms of associated issues. The crank isn't the weakest link. Rods and caps will take alot of stress and running a rubber timing belt (rather than a geared) system means that the bigger tolerance between piston and valve will result in kissing, and possibly something more amorous.

 

Thats where the longer rods and shorter stroke I plan to do will come into its own, theres a lot less stress on the pistons as its a more gentle movement

[James_R 3]

I'll let you know how a XU7 bottom end fairs up to 8500 shortly

 

On a side note, std Redtop cranks are good to over 10krpm (balanced though)

[Batfink 201]

i would hazard a guess and say the redtop cranks are more like the 16v cranks rather than the 8v's - with more counterbalancing

[DrSarty 90 1 Cars]

it was my understanding that the bolts are not able to cope with the extreme high revs so should be upgraded??

 

I'm not sure if this is correct, but isn't this what ARP (?) bolts is all about?

 

I asked Matt if I needed them and I seem to remember him saying - probably quite correctly - that for my engine it would be an unnecessary expense, as it won't be going to silly revs. I also seem to remember these ARP bolts being called 'red top' or something like that too.

 

If this is the case Kev, it would seem silly for you NOT to fit them. Belt and braces and all that!

[Batfink 201]

Matt uses a different brand to ARP which he reckons are superior though i forgot the name the moment he told me lol

[Miles 331 1 Cars]

After seeing the quality of the metal of a std bolt I would never use one again on any uprated engine, but it really is luck of the draw

[VisaGTi16v 1]

A friend that tarmac rallies a Lotus Sunbeam used to rally a Grp A spec 205 back in the day, it was a B reg 1.6 (one of the first?). Just queried him and his response for his spec was 8k limit, standard crank and rods, cosworth pistons etc and never had an engine issue and was revved high all the time and on gravel back then when you are constantly wheel spinning so average revs higher than on tarmac. Asked his opinion on 9k

Edited January 28, 2008 by VisaGTi16v

[Batfink 201]

well its good to know my plans are not completely barking