[6pack] Advancing or retarding the stock camshaft

Mon Dec 30 08:18:56 MST 2019

I modified a front cover once so that it had a removable plate that allowed access to the adjustable cam sprocket.  It never sealed 100% and I gave up after a couple of years.  More bother that It was worth to me.

Marty

Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------
From: Robert Lang via 6pack <6pack at autox.team.net>
Date: 12/30/19 8:48 AM (GMT-05:00)
To: TR6 <6pack at autox.team.net>, Robert Perry <rgperry at earthlink.net>
Subject: Re: [6pack] Advancing or retarding the stock camshaft

Hi,

I can say with authority that advancing the cam will help a bit, but it won't result in gobs of power. Note that you must have a proper cam gear to do this, some on the market are not drilled properly limiting the amount of "change" you can make. Adjustable cam gears give you more adjustability and hence allowing you to optimize the cam on the dyno. BUT accessing the gear on the dyno is pretty hard to do, so we tend to stick with what has worked in the past with various cams. All that said, you will likely find a few torques if you advance the cam up to about 4 degrees. Retarding the cam does NOTHING GOOD. Regarding tuning,  you want torque, not HP. Trust me on that. Side story: I had a late TR6 with really low power, the former owner spent scads of $$$ trying to get the car to run right. After I verified the basics, I was able to determine that the cam was retarded. A LOT. Intake was opening ATDC. I fixed that and got over more 30 HP to the wheels. Cam timing does make a difference!

I got around 100 HP to the wheels with stock late cam (advanced 4 degrees), header, mild porting and a free-flow exhaust. The biggest gain: ditch the crank-driven fan. 8 HP. You could probably get another one or two by underdriving the alternator, but I've never done that. This was an SCCA "Street Prepared" car with stock compression, pretty much no internal mods and balancing. If you want real power, you can only get there with higher compression or boosting. Period.

The 5 main idea is good, but we would also suggest / recommend nitriding the crank no matter what. Stock rods work great when properly prepared, but you can increase reliability by going to aftermarket rods that are lighter. Carillos are e$pen$ive but are also over 110 grams lighter than prepared stock rods. There are cheaper alternatives to Carillo, but they come with some risk. But over 100 grams: That's a LOT of both rotational and reciprocating mass and that will help for your killer harmonics. Note that 6300 is only one of them. The key is not staying at the killer RPMs - you need to not get there or go beyond them.

That's enough for now. ;-)

C ya,
Bob Lang

p.s. the chart below is backwards - advancing a cam opens it EARLIER than the published numbers (and retarding opens the valves later. For a stock late TR6 cam, try to open intake at around 22 BTDC. But the REAL number to go for is the lobe center, move that towards TDC to advance the cam. The stock cam lob center is around 110 ATDC, so make that less than 110 and your're good to go.

On Monday, December 30, 2019, 5:30:29 AM EST, Robert Perry via 6pack <6pack at autox.team.net> wrote:

Hello All,

Since there is talk about modifications of their vehicles, has anyone tried to advance or retard the stock camshaft? I know why bother just change it.

The camshaft tooth degree is 8.57 (360 /42 teeth) with half tooth being 4.28 degrees. So that would be
2.14 crankshaft degrees.  Therefore advancing the camshaft a half tooth in crankshaft degrees
would be the following;

10/50 50/10 becomes 7.86/47.86 47.86/7.86

18/58 58/18 becomes 15.86/55.86 55.86/15.86

35/65 65/35 becomes 32.86/62.86 62.86/32.86

 and if one retards the camshaft

10/50 50/10 becomes 12.14/52.14 52.14/12.14

18/58 58/18 becomes 20.14/60.14 60.14/20.14

35/65 65/35 becomes 37.14/62.86 62.86/37.14

Regards,

Robert

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