Craig
Thanks again
I had calculated the stroke:bore ratio however I never knew the Mercedes
link! I am going to pursue the 82mm stroker with the L14 rods, and with the
FIA head it should be fairly efficient at high revs.
The 82mm stroke with 88mm bore gives a 0.93 ratio, which could be a bit
high. The rod:stroke ratio however is 1.67 which keeps me happy.
Regards
Brad HALLETT
http://www.powerup.com.au/~bhallett
Proudly Endorsing:
...DATRATS...
http://203.33.35.34
Datsun Dedicated
For Nissan Motorsport Components
Professional Budget Priced competition equipment
Contact Errol SMITH
email: [EMAIL PROTECTED]
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]]On Behalf Of Craig Overend
Sent: Wednesday, November 01, 2000 5:12 PM
To: [EMAIL PROTECTED]
Subject: Re: Factory 87.8mm pistons
Brad,
The reason they used 87.8mm is because 78/87.8mm= .89!
Do the sums on the stock L16 and you get .89 aswell. On the old racing
BMW 3000 CSL, '92 V12 6.0L Merc 600SE/SL/SEL etc. No coincidence. The L
series was supposedly based on a Merc design that the japs modified.
Running a standard L18W crank stroke of 78mm with L14 136.7mm rods will
lower volumetric effeciency by about 1% depending on head but also move
the whole powerband upwards sacrificing a tiny amount of bottom end.
What basically happens is the average airspeed through the valve is
reduced and therefore requires more rpm to max the port out compared to
the shorter rods. You gain lighter pistons from lower pin height but
loose with longer(heavier) rods too. The engine would probably be
happier accelerating at mid to high engine speeds revvier i guess you'd
call it and be smoother. Piston sideload friction would also be reduced.
Craig.
"I'm not even going to bore you with my sleeping habits."
Brad HALLETT wrote:
>
> Craig,
> Thanks for your advice. I still haven't had a chance to calculate
anything
> because of work commitments so I am glad you did it for me (5hrs sleep
since
> Friday - things have gone nuts here.) I came up with the same conclusion
> that the Factory teams would have built strokers if they were permitted or
> if they were more efficient, my only thought was why did they use 87.8mm,
> and not 88mm?
>
> When I planned my engine I was unaware of the L14 rods, and they are now
> what I will use. Compression ht is no probs as I am ordering custom
forged
> slugs from Precision (when I save some $$$)
>
> I figure if I build the stroker and it's a slug I'll bolt in a std L18W
> crank with 32mm comp ht pistons/L14 rods and see if it works better.
>
> Regards
> Brad HALLETT
> http://www.powerup.com.au/~bhallett
>
> Proudly Endorsing:
> ...DATRATS...
> http://203.33.35.34
> Datsun Dedicated
> For Nissan Motorsport Components
> Professional Budget Priced competition equipment
> Contact Errol SMITH
> email: [EMAIL PROTECTED]
>
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED]]On Behalf Of Craig Overend
> Sent: Monday, October 30, 2000 10:43 AM
> To: [EMAIL PROTECTED]
> Subject: Re: Factory 87.8mm pistons
>
> Brad,
> I have looked into the factory engine and they are not 88.7mm but
> 87.8mm X 78mm for 1889cc. Here are some of my thoughts. I too was
> planning on an 88mm bore and 82mm stroke until I did some calculations
> and measured my L18W block. One problem is rod length. 133mm rods are a
> bit too short for ideal and this moves the whole torque curve down and
> also reduces volumetric efficiency(torque). Ideally ~135mm rods are the
> go for the 82mm stroke when combined with 44mm inlets, 40mm port at seat
> and a cam with about .510" of lift. For this reason I have been trying
> to track down whether there was an L20 6 Cylinder model that used 135mm
> rods. All my calculation says there is such a rod but so far I cant find
> reliable info or rods to support that. Near ideal stroke/bore ratio for
> the widest possible powerband comes from a ratio of about .88-.90
> varying depending on friction, rpm operating range and other factors.
> For this and reliability reasons to do with bore diameter, I assume
> these are the reasons they designed the factory L18W rally engines the
> way they did. Also instead of stroking the engines for more capacity
> they just ran more rpm to use the available flow through the heads.
> While the engines might not have been as torquey as they could have they
> would be good HP producers. Other factors may have included rulebook
> limits though. I'm sure that if they could reliably bore the block out
> further they would have and stroked them too and run bigger valves
> etc... Guess what I'm looking at doing. :)
>
> L14 rods being ~136.7 would be a better choice for an 88x82mm engine
> just depends on valve/ports/cam. You'd need ~30mm pin height.
> 136.7/82=1.67 ratio same as L18 for similar reliability. L14 rods use
> the same journal size as L16/L18. I'm sure Errol could tell you if he
> has bent any.
>
> The current factory VW Golf kit car that Simon Evan runs uses something
> near 90mm bore x 78.5, can't remember exactly. This is excellent for a
> 2L and one reason why it screams and goes so well.
>
> cheers,
> Craig.
>
> Brad HALLETT wrote:
> >
> > Gday everyone
> > There has a been a lot of talk about the factory rally cars using 88.7mm
> > pistons. Whilst I was planning to build a stroked L18W with 88mm bore,
I
> > have become more and more interested in the factory engine.
> >
> > I therefore have two questions:
> >
> > 1) The engine I am building is L18W block, 88mm bore, with the crank
> > stroked to 82mm, L18 conrods with forged flat tops at custom compression
> > heght to suit. This gives a swept volume of 1995cc to keep in the
> 1600-1800
> > class. Would it be more beneficial to not build this stroker but to
copy
> > the factory engine spec?
> >
> > 2) Are 88.7mm flattops still available?
> >
> > Whilst I personally can see no problems with the stroker in terms of
> > reliability I am interested to hear your opinions.
> >
> > Another question I must ask, whilst I have done no calcs or schematics
so
> > may be way off the mark, would L14 rods be worth looking at for the
> stroker?
> > I have had nothing to do with them so I don't know there strength,
weight,
> > or even journal size.
> >
> > Regards
> > Brad HALLETT
> > http://www.powerup.com.au/~bhallett
> >
> > Proudly Endorsing:
> > ...DATRATS...
> > http://203.33.35.34
> > Datsun Dedicated
> > For Nissan Motorsport Components
> > Professional Budget Priced competition equipment
> > Contact Errol SMITH
> > email: [EMAIL PROTECTED]
> >
>
--membersozdat-------------------------------------------------------
OZDAT Mailing List Please Note:-
Send (un)subscribe requests to [EMAIL PROTECTED]
Send submissions to [EMAIL PROTECTED]
No unauthorised redistribution of this email
http://www.ozdat.com/ozdatonline/index.htm
http://www.ozdat.com/ozdatonline/listindex.html
http://www.mail-archive.com/[email protected]/
---------------------------------------------------------------------
