<VV> 145 Turbo

[Hugo Miller]

I am always wary of quoting compression ratios. The figures in 
themselves are meaningless unless you take cam timing into account. As a 
rule of thumb, the lower the CR, the more bottom end torque an engine 
will put out (I am talking about engines in general, not Corvairs 
specifically, about which I know very little). The reason for this is 
that if you have a low notional CR, it implies that the inlet cam is 
going to be closing early, and that in itself will give good torque. By 
contrast, some high performance engines have notional CR's up there with 
diesel engines. The only way they can tolerate this is by leaving the 
inlet valve open till very late in the cycle, which will give power at 
high rpm, but not so much lower down.
Another thing I like in an engine is a torque figure which is higher 
than the bhp figure.


On 2019-06-01 20:48, kevin nash via VirtualVairs wrote:
> I have a 63 Spyder with the orig 145CI motor that I'm rebuilding but
> everyone i communicate with try to talk me into converting to a 164ci
> instead, Why..?
>
> Thoughts on staying or converting
>
> Thx Flat6fan
>
> --
> Isn?t it funny how day by day nothing changes, but when you look back
> everything is different?
> C.S. Lewis
>
>
> Here's some reasons why you might leave your stroke alone and get
> "Torque" some other way.
> The stuff that has to be changed when going to the longer stroke:
> Late pistons, late cam, late crank
>  and HB and some work clearancing the short stroke case for the
> longer stroke crank. Not as easy as it sounds! Also, a major reason
> for the lack of torque that all corvair turbo's have (late or early)
> is timing and compression ratio. You can easily jump the compression
> on your stock heads, with a better cam you can and should bump it 
> more
> and if your heads have been worked on (better squish, turbulence and
> flow) you can go higher still. My heads are 8:1, and with the cam 
> that
> is in it now, (along with some other changes) I kind of which I had
> bumped the cr up to 8.2 or perhaps a bit more. The stock distributor
> timing for Corvair turbo's leaves a LOT to be desired... it is way 
> too
> conservative, and is really only kinda sorta close to right just
> before going into boost. The lack of vacuum advance and rpm advance
> until way too high of an rpm causes the engine to be way down on both
> torque and power, until the late advance hits and by then you've
> already lost the race!
> My ignition timing is programmable and the easy way to explain it is
> its like having a 140 distributor with a different vacuum advance
> curve with boost retard. I've had an opportunity to drive a stock 
> Late
> vs my little short stroke engine with more compression, timing and 
> air
> flow mods
> and I can tell you it is NOT down on torque enough to feel. When I
> hit the throttle, it feels way more healthy than the stock late car.
> As it should with more compression ratio, higher flowing heads better
> timing and a bit more than double the stock peak boost. Yup, 18 to 19
> in second gear!
>    Another reason to keep your short stroke crank, is that the late
> ones have been known to break, I haven't heard of a early spyder 
> crank
> breaking yet!
> One last thing, if you do want more torque via displacement, larger
> bores work extremely well with the short stroke crank.
> Kevin Nash
> 63 Turbo port injected daily driver,
> baddest cooling fan on the planet!
>
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