Big bore questions round II

Okay Lets try this again.

I have a 2001 VFR.
According to Honda's website for dealers and most of the web media
the stock bore and stroke of the motor is
72 X 48.

All the literature on the 870cc upgrade lists the change in bore as
74mm, Including Dynamo Humm. After checking with a JE piston supplier
at work it was speculated that the actual bore change was 74.5mm
if there is no stroke change and the dimensions are 74.5 x 48 the
engine only goes up to 837cc. Which a couple of sites list as their
only upgrade for the VFR800.

But I kept hearing from the list that the DH 870 kit was just a big
bore kit nothing more. Which means that something just doesn't match up.
So I threw together a little spread sheet to sort out where the info
is wrong, it turns out there are two ways to arrive at the desired 870cc.
One would be to increase the bore to a whopping 76mm. This is too
much for the factory cylinders to withstand and would require a set
of sleeves, but it lands on the 870cc mark. Since I don't see that
mentioned in any of the 870 kit literature I must assume that it is
not the method used in their kit

Second method is to bore to 74.5mm and then increase the stroke by
2mm to 50.mm. That drops us in on the magic 870cc mark. Offset
grinding the crank to get the additional 1mm of radius on the journal
bearing center is still a reasonably safe thing as well as the longer
stroke tending to make more torque. No sleeving of the block would
be required to get to this displacement.

I ask this here before I move onto other sources, does anyone know
the dimensions of the JE pistons used and/or the center to center
length of the rods?



JohnS
A Dragon Ascending
"Forging my body in the Fires of my Will"

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vfr@xxxxxx
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Here is the actual form E-mail that I sent to TTS Performance in the UK
(makers/source of the pistons that DynamoHumm uses) and their reply - Joe.
________________________________________
It fits both but gives 837cc as its 74mm bore (should say 2mm o/s on the
800, sorry) I can go 870 with this engine at no extra cost (3mm o/s).
piston kit is £350 (approx $665) you will need to get your bores bored out
to 75mm by Millenium Tech in the USA. regards Richard

----- Original Message -----
From: "Joe Cargal"
To:
Sent: Friday, September 08, 2006 5:55 PM
Subject: Enquiry from TTS Performance Parts Ltd


> tts-performance.co.uk Online Enquiry:
>
> Name: Mr Joe Cargal
> Company:
> Position:
> Customer Type: Private Individual
> Vehicle Type: Honda
> Model: VFR800FiY
> Year: 2000
>
> Request:
> In referencing the overbore piston kit at the following page on your
> website:
>
> http://www.tts-performance.com/catal...cPath=46_103&p
> roducts_id=472&PHPSESSID=6f4bcd565f6128959c4939fa574aa378
>
> ...it is stated that they overbore is 4mm and will result in 837cc.
> It is also stated that the kit is for a VFR800. A 4mm overbore on a
> 94-97 VFR750 will result in 837cc, but a 4mm overbore on a 98-06
> VFR800 will result in 870cc. Is the kit for a VFR750 or a VFR800?
> Thanks, Joe.
>
> Add to Mailing List:
>
> ------------- end of email -------------

-----Original Message-----
From: vfr-bounces@xxxxxx [mailto:vfr-bounces@xxxxxx] On Behalf Of
JES_VFR
Sent: Tuesday, October 31, 2006 12:00 AM
To: vfr@xxxxxx
Subject: Big bore questions round II

Okay Lets try this again.

I have a 2001 VFR.
According to Honda's website for dealers and most of the web media
the stock bore and stroke of the motor is
72 X 48.

All the literature on the 870cc upgrade lists the change in bore as
74mm, Including Dynamo Humm. After checking with a JE piston supplier
at work it was speculated that the actual bore change was 74.5mm
if there is no stroke change and the dimensions are 74.5 x 48 the
engine only goes up to 837cc. Which a couple of sites list as their
only upgrade for the VFR800.

But I kept hearing from the list that the DH 870 kit was just a big
bore kit nothing more. Which means that something just doesn't match up.
So I threw together a little spread sheet to sort out where the info
is wrong, it turns out there are two ways to arrive at the desired 870cc.
One would be to increase the bore to a whopping 76mm. This is too
much for the factory cylinders to withstand and would require a set
of sleeves, but it lands on the 870cc mark. Since I don't see that
mentioned in any of the 870 kit literature I must assume that it is
not the method used in their kit

Second method is to bore to 74.5mm and then increase the stroke by
2mm to 50.mm. That drops us in on the magic 870cc mark. Offset
grinding the crank to get the additional 1mm of radius on the journal
bearing center is still a reasonably safe thing as well as the longer
stroke tending to make more torque. No sleeving of the block would
be required to get to this displacement.

I ask this here before I move onto other sources, does anyone know
the dimensions of the JE pistons used and/or the center to center
length of the rods?



JohnS
A Dragon Ascending
"Forging my body in the Fires of my Will"

_______________________________________________
vfr mailing list
vfr@xxxxxx
For subscription and delivery options:
https://lists.cs.wisc.edu/mailman/listinfo/vfr


_______________________________________________
vfr mailing list
vfr@xxxxxx
For subscription and delivery options:
https://lists.cs.wisc.edu/mailman/listinfo/vfr