Corvair DiagramCorvair Photo
Corvair Center
home forum corvairs calendar links Corvair Podcast
California Corvairs
Clarks Corvair
Clarks Corvair
“CORSA"



Chevy Corvair License Plate
Chevy Corvair Chrome Wheel
Corvair Center Forum :  Corvair Center Phorum The fastest message board... ever.
Corvair Center 
Pages: Previous123
Current Page: 3 of 3
Re: Turbo Cam
Posted by: nirvairna ()
Date: February 04, 2020 08:37AM

"I do have to drill and tap the end of the Corvair cam for a Allen style head screw to hold the degree wheel on a custom spacer"

sounds like a job for a neodymium magnet

Options: ReplyQuote
Re: Turbo Cam
Posted by: JimBrandberg ()
Date: February 04, 2020 02:01PM

Darrin wrote:

"Ok, finished fitting bearings and measured the brand-new-from-Clarks TB20 camshaft. I measured lift on both intake and exhaust in a thoroughly inexpert manner and got the following:

Intake: lift measured 0.302 (x1.57 = 0.474, x1.56 = 0.471)

Cam card on Clark’s site says 0.300 or x1.57 = 0.470

Exhaust: lift measured 0.286 (x1.57 = 0.449, x1.56 = 0.0446)

Cam card says 0.290 (1.57 = 0.455)

These strike me as being pretty darn close to the card.

------------------------------------------------------------------------------

Yes it does indeed look like a dual profile cam. Thanks.

Jim Brandberg
Isanti, MN
CorvairRepair.com



Options: ReplyQuote
Re: Turbo Cam
Posted by: dryenko ()
Date: February 04, 2020 08:10PM

Maybe a magnet might work, but the wheel has to be centered, and adjustable to within one degree of position.

Bob C aka Dryenko
Dobson, NC 27017

Options: ReplyQuote
Re: Turbo Cam
Posted by: Jonathan Knapp ()
Date: February 06, 2020 09:47PM

Quote
Kevin
Also, the rocker arm ratio's used on the Otto cam cards are "theoretical", if you measure the actual lobe lift it does correspond to the change in lift from stock. Using a 1.5 rocker ratio for a .3 lobe lift gives .450" lift, using 1.56 rocker ratio for the same .3 lobe lift gives .468" and a whopping .018" change from the rocker ratio difference wouldn't seem to make a hill of beans worth of difference, compared to using a E-flow turbo, water injection, and a huge carb and extra compression like Dick Griffin ran to go as fast as he did.
Here's more on why old school turbo cams are different than now, and what is important..

Thanks, Kevin, for that article on how cam selection has changed as turbos have evolved. I didn't realize that exhaust pressure was such a limiting factor with old turbos.

I didn't mean to imply that a trivial difference in valve lift projected by different cam manufacturers using different rocker arm ratios were responsible for Griffin's remarkable car. Clearly other factors were at play. I mentioned Griffin's car because I have run the 280 Isky in a normally aspirated engine and found it very streetable. Griffin also drove his car daily at the time he was campaigning it. It seems to me that even without the E-flow and the huge carb and the water injection and the other modifications that he made, it might be a good candidate for people who are looking to have a little better performance with their turbo engine.

I just thought it was revealing that the conversation was focusing exclusively around Otto TB-20 cams and no one was mentioning any other cams as potentially suited to turbo engines. The irony is that the 280 Isky pretty much does all of the things that the Hot Rod article says. And Griffin's car ran a stock exhaust housing. I wonder how he dealt with the exhaust pressure issue.

Jonathan Knapp
Wheeling, WV
'66 Corsa Autocrosser

Options: ReplyQuote
Re: Turbo Cam
Posted by: 63turbo ()
Date: February 07, 2020 06:48PM

>
> I just thought it was revealing that the conversation was focusing exclusively around Otto TB-20 cams and no one was mentioning any other cams as potentially suited to turbo engines. The irony is that the 280 Isky pretty much does all of the things that the Hot Rod article says. And Griffin's car ran a stock exhaust housing. I wonder how he dealt with the exhaust pressure issue.

As far as I know, Dick Griffin dealt with it by running custom free flowing headers, and a wrapped exhaust and a fairly large (numerically) A/R exhaust housing, meaning the stock F flow housing. It has a A/R ratio of .7, and this is supposedly nearly perfect for drag racing but does slow down the response a lot compared to a smaller A/R ratio of .63-.55. Those bigger A/R ratio exhaust's give more "leverage" to the exhaust turbine but spin it slower for any given engine speed and load, the smaller housings give more speed to the exhaust turbine but lose leverage, making the smaller housings more fun, faster boosting but down on peak power relative to the bigger housings. For drag racing, the old rule was to be hitting peak boost in third gear and part of the set-up to achieve that was to use a bigger exhaust A/R ratio and an actual bigger exhaust turbine if need be/if available. I do kind of wonder how long Dick Griffin's cams lasted! until recently, I had not appreciated how tough a life the exhaust lobes can have if they start opening the valve a little too soon with a little too much boost!
After reading that article, and the part about toasting exhaust lobes, my own cam failure from a few years ago made more sense, as it was a flattened exhaust lobe.

------------------------------------

Kevin Nash
Friday Harbor Washington
63 Spyder, Daily driver, EFI read about my project here: [corvaircenter.com]
first test start on EFI here:[www.youtube.com]
first official EFI boost test here:[www.youtube.com]
My new fan! [corvaircenter.com]
engine less 62 Spyder
Canadian 64 Monza Parts car



Options: ReplyQuote
Re: Turbo Cam
Posted by: Jonathan Knapp ()
Date: February 08, 2020 09:14PM

When I talked to Dick (probably in '72 or '73), he told me he used 110 HP exhaust manifolds that were bored out for the 140 heads' primary tubes. The idea was that the smaller volume of the 110 manifolds would speed up the exhaust flow toward the turbo. I don't think he used headers at all. I believe just the pipes (not the manifolds) were wrapped.

I don't remember talking about the A/R ratio of the exhaust housing specifically, but thought the only modification to the original turbo on the car was the Crown E-flow intake side.

I do remember him saying that the car started generating boost in first gear at around 2800 rpm. That 280 Isky definitely would have started opening the exhaust valve much earlier than the stock GM cam. We never discussed that he had to watch out for exhaust valve train wear or problems.

Jonathan Knapp
Wheeling, WV
'66 Corsa Autocrosser

Options: ReplyQuote
Re: Turbo Cam
Posted by: goatsnvairs ()
Date: February 13, 2020 05:13AM

I converted my 140 to a 180. The 140 was pretty fresh and had an Isky 270 and since it was a fresh rebuild I wanted to keep the case intact, plus didn't want the added expense of another cam and gear. I was worried about excess overlap but when I compared the data on the OT20 to the 270 it wasn't too big a difference so I kept the 270.
Now I'm running the 270, turbo heads with some material removed in the exhaust ports, wrapped exhaust, an early/late turbo, meth injection and a 45mm mikuni slide carb all with factory points ignition and it flies.

Options: ReplyQuote
Re: Turbo Cam
Posted by: Wagon Master ()
Date: February 13, 2020 05:31AM

With all the added exhaust temp that the A.I.R. system created, GM decided stainless steel exhaust stub stacks were needed. Did anyone ever put the 140 smog set-up on a turbo?

Options: ReplyQuote
Re: Turbo Cam
Posted by: zarfnober ()
Date: February 13, 2020 07:47AM

If I ever decide to put 140 heads on my stock turbo, I’d add the NOS stainless exhaust tubes that have been sitting in my parts box for at least 25 years, cause you never know when you’ll need them!

Rocco

Options: ReplyQuote
Re: Turbo Cam
Posted by: edconnolly ()
Date: February 13, 2020 09:07AM

110 manifolds bored to match 140 primary exhaust tubes for the reason you describe in such a turbo motor can crack at the interface with the tube gasket because the manifold material becomes too thin there .

Options: ReplyQuote
Re: Turbo Cam
Posted by: JimBrandberg ()
Date: February 17, 2020 06:19AM

At least with lift it looks like the current Otto TB-20 cam still has a dual pattern with more on the Intake side.
There was a comment that Corvair engines "always" need more on the exhaust side. I understand that to be true with normally aspirated.
I skimmed the Hot Rod cam article but didn't see much to help Corvair specifically. Maybe I'm just looking for easy answers.
I've got some time and I'm still not finding a frontrunner for a cam in a stock turbo 164 CI engine.
Blake was pretty good when designing Corvair cams back in the day. He must have had his reasons for putting more on the Intake side of turbo cams. He put more on the Exhaust side of normally aspirated.
If Otto TB cams are what they used to be are they a good choice today? Otherwise something fairly generic like Isky 260? How does a GM 304 compare? I should get out the Bob Helt book I suppose.
Given the stock nature of these two engines I'm wondering about TB-10. We've only had discussion of TB-20.

Jim Brandberg
Isanti, MN
CorvairRepair.com



Options: ReplyQuote
Pages: Previous123
Current Page: 3 of 3


Sorry, only registered users may post in this forum.
This forum powered by Phorum.