Hi List,
I received this from a PDLJMPR reader and thought it would make a great
discussion topic for us. Please correct anything I have wrong in my
response and cc to Terry (I don't believe he is on the list yet).
>Hi, My names Terry and I own a '66 Sprite. I am going to be rebuilding and
>hopping up a 1275 engine this winter. In the spring I'll remove and carefully
>store the original 1098. I would appreciate any tips on engine modifications
>(my target is about 80 horsepower with decent low end torque for the street).
>I am also looking for information on a five speed transmisssion swap for the
>Sprite. I read about it on a web page somewhere, and it involves a japanese
>five speed, and apparently someone supplies a kit for this swap. If anyone
>knows of this please let me know.
>Thanks, and a great web site.
>TMHEFFRON@AOL.COM
Hi Terry,
This would be a great topic for the Spridget mailing list. Have you joined
it yet? If not, send e-mail to majordomo@autox.team.net with the following
in the body of the message (nothing else):
subscribe spridgets
Then follow the confirmation routine in subsequent mail from majordomo
(automated - happens in a few minutes).
As for your question, an early 1275 with the right cam and header should get
you 80 HP (the stock 1275 in the Mini Cooper S made 76HP, the major
difference being the cam and bigger valves). As far as low-end torque,
these engines like to rev to make power - I'm not sure what you expect!
Torque values usually stay pretty much constant for a given compression
ratio, bore size, and stroke - the primary function of most performance cams
is to move the peak torque value to a higher rpm and since horsepower is a
function of torque and rpm, it gives more horsepower, but at a higher rpm.
By moving the torque curve higher, low RPM torque is less and the engine
usually makes less horsepower down low.
Further gains can be made by increasing volumetric efficiency (more complete
filling of the cylinder with fuel/air mixture) within the power band.
Different carbs, headers, intakes, cams, and head mods are all designed to
increase volumetric efficiency but these all must be properly matched to the
camshaft choice or the anticipated gains won't be realized. By the way,
supercharging and turbocharging works purely on increasing volumetric
efficiency to over 100% - the more fuel-air mixture you can get in the
cylinder, the more power you make.
It is possible to jack up torque across the board by 1) increased piston
stroke 2) higher compression 3) increasing volumetric efficiency
In my opinion, the best way to hop up an engine is to select the camshaft
you want to use and build the rest of the engine around it. Most cam
manufacturers have tested their grinds and know what other mods work best.
A little research with the cam manufacturers could prove enlightening.
By the way, I didn't do this when I put a cam in my 1275 - so who am I to
talk! But it feels good to try to exercise the gray matter once in a while.
There are lots of people out there that know about 5-speed conversions - but
I am not one of them - sorry.
Regards,
Les Myer
lmyer@qtm.net
67 Sprite
77 Midget
PDLJMPR Web Magazine
http://www.probe.net/~lmyer
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