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]
>
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