small bore, high revving 6, anyone running one now? Options

[DanT]

I have the chance to acquire an 2.0L 6 case and have thought about building a small bore 2.0-2.5L high revving 6.
Anyone out there running such a combination right now?

This would be a street/AX motor. Prefer to do single plug.
Most likely use Webers, since MFI parts are getting hard to come by .
What combinations of Pistons/cams are you folks using?

Pictures of motor builds would be appreciated.

Just sliding in a 2.7L CSI motor is also a consideration if the small bore motor becomes too much of a pain. (IMG:style_emoticons/default/biggrin.gif)

[jjackson]

I have the chance to acquire an 2.0L 6 case and have thought about building a small bore 2.0-2.5L high revving 6.
Anyone out there running such a combination right now?

This would be a street/AX motor. Prefer to do single plug.
Most likely use Webers, since MFI parts are getting hard to come by .
What combinations of Pistons/cams are you folks using?

Pictures of motor builds would be appreciated.

Just sliding in a 2.7L CSI motor is also a consideration if the small bore motor becomes too much of a pain. (IMG:style_emoticons/default/biggrin.gif)

We ran a 2.4L 10.5/1 single plug motor for a while.Built on a 5r case (strongest small bore case) with carbs.We only turned up to 7200 rpm.To run more RPM than that, you need aftermarket rods in my opinion.Made 220 + HP on S cams.Motor was rock solid.J

[messix]

are you sure you want small bore?

a small bore will not make an engine a high rever.

how ever a short stroke engine will.

the short stroke has a slower piston speed compaired to a longer stroke engine per rpm. [distance the piston travels for each revolution, hence stoke]. this puts less stress on the crank and allows for higher rpm.

so for a long stroke 2.5= long stroke x small bore

short stroke 2.5 = short stroke x large bore

[ME733]

The ..2.0 six...had a short stroke...66mm.(same as a carrera 4 cam)., most also did NOT have a counterbalanced crankshaft....using a counterbalanced crank is essental for hi revs with reliability....titanium rods were used in the race engines, but carrello has excellant rods also...In my opinion the 911-S- cams are way too "peaky", and a better engine can be made with with other cams...get the bruce anderson book... "Porsche 911 performance handbook".read it, study it, then you can make some informed choises.

[campbellcj]

IMO you would not want a peaky small six for street or autox. Depending on the build specs and tune you might only make decent power between 4500-7000rpm's or so and regardless the peak torque would be modest compared to a larger displacement.

I have significant (18 years) experience driving 2.2 sixes and while they are gems and sound glorious, it can be challenging to keep them moving at a good clip. Short gears help.

[campbellcj]

IMO you would not want a peaky small six for street or autox. Depending on the build specs and tune you might only make decent power between 4500-7000rpm's or so and regardless the peak torque would be modest compared to a larger displacement.

I have significant (18 years) experience driving 2.2 sixes and while they are gems and sound glorious, it can be challenging to keep them moving at a good clip. Short gears help.

[J P Stein]

My old 2.7L would pull 7300 with all Porsche parts.....you want more, bring money.

[sww914]

They say the last 800 to get to 8000 will cost you $8000.00
That said, Henry Schmidt, a common sight on the Pelican board and a 911 engine builder for many years with much success says that the 2.5 short stroke is the best engine that Porsche never built.
That's a 66mm 2.0 bottom end with 2.7 90mm pistons & cylinders. You can't really use the 2.7 CIS pistons because the dome shape is designed for the CIS swirl, it gets in the way of the valves if you run a good cam and their compression is too low. You have to use some JE or other A/M pistons to build that engine. It would probably respond really well to twin plugging as well.

[brant]

I put 100 racing hours onto a 2.0/6 with an aluminum case
it was all S spec, real 67S heads, cams, Counter balanced crank, pistons-cylinders, stock 2.0S rods
it was great and only 9.8 compression (factory)
147hp to the wheels at 5000ft of altitude on a 104F day is not anything to sneeze at for a stock motor

We would usually shift between 7200-7500 and loved it
the quick revs (5lb tilton clutch and flywheel) are awesome
I really like the small bore stuff and its so "right" sounding

new motor is a small spigot 7R case
(these are kinda hard to find, but slightly stronger than the 5R cases)

I haven't driven it yet, but can't wait
66 counter balanced crank, big valves, 81mm pistons of just under 11:1 compression, twin plug, Pauter rods, lots and lots of head work with race cams
shooting for a little over 200hp and probably will shift at 7500rpm
(although the safe zone is somewhere around 8,500 rpm)

builder said that rpm is only dependent on how long you want it to last

I'm a huge fans of the small bore motors
used to have an SC 3.0, and the motors are nothing alike..
really love the small bores.

[GeorgeRud]

The 66mm crank with the 90 mm piston bore does make a great sounding, high revving engine, but it will cost money to do correctly. They were popular in the early 70s as it could be used in the under 2.5 liter racing class.

Though they're usually maligned, the 2.7 does give nice grunt and revs quite well compared to the later, larger engines.

In an autocross engine, I think that high torque should be the primary objective. That is achieved most easily with a larger displacement engine.

[Mark Henry]

If you're rebuilding all sixes work out about the same price in the end.
Even if you get a cheap core it's a pay it now or pay it later type of deal.

[MikeSpraggi]

Haven't driven it yet, but I've had a 2.2L six built for my track car I plan to run in vintage racing. Built on a 7R case, 84mm JE 11.3:1 pistons, Solex cams and reworked Zenith carbs. Oh yea, a little porting on the stock heads. Using a 2.0l non-counter weighted crank. Elected not to go with a lightened flywheel since the consensus was that I would not really see any gains.

I'll let you know how it turns out, say in April!

[d914]

I had a 2.5 liter short stroke six... loved it for the track,,, I even had fun on the street... auto cross not so much.. 220 at crank with 138 ft lbs.. The only thing that made it go was revs!!!! and lots of them... get caught low in a gear and your dead meat...

[Cap'n Krusty]

Ahem! I have an aluminum case, a long block, and a core motor. All are for sale. The core comes with a good regrindable counterweighted 2.0 crank. Bring money. I'm probably gonna use Cunningham rods in my 2.5.

The Cap'n

[J P Stein]

Ahem! I have an aluminum case, a long block, and a core motor. All are for sale. The core comes with a good regrindable counterweighted 2.0 crank. Bring money. I'm probably gonna use Cunningham rods in my 2.5.

The Cap'n

Hay Cap'n, have you priced U/S rod & main bearings lately? Bring money indeed.

[jfort]

Have a 2.5 short striker with E cam and short gears. Quick and the sound is glorious

[Mark Henry]

There's a set undersize rod bearings on the bird classifieds right now and I know of another set at a good price. First under size on some of the rods isn't that big of a price, the mains are a different story.
$1200 for set of SC first under mains...cheaper just to find a standard crank.

[koozy]

(IMG:style_emoticons/default/shades.gif) Hmmmmmm..... Whatcha doooooin??? (IMG:style_emoticons/default/idea.gif)

[Eric_Shea]

I have Greg's 2.5 now. It will be twin plugged soon. That said; autocross motor? I would find something with torque.

[DanT]

Mike,
I have always wanted to try a high revving 6 with the proper gearing to keep the motor up on the cam, plus they sound marvelous...
Just dreaming a bit... (IMG:style_emoticons/default/biggrin.gif) Ken has some interesting combinations he has used over the years.
need to check my source and see what he wants for the pieces (IMG:style_emoticons/default/sad.gif)