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Don Potter Racing Cam?

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Anecdote: When Don was alive he was found by many to be somewhat...uh "Abrasive"... In fact in the old Z Car Magazine he had a column which was proudly "Curmudgeon" or something...

I approached him at MSA back in the 90's as well, as someone pointed to him and said "he can recurve your distributor"... I went up and introduced myself and said so and so said you can recurve my distributor, what are we looking at for pricing and lead time? 

"$476, and when I get to it, you'll get it." And back he went to his conversation. "OK, fair enough" thought I... Poking back into the conversation I merely added "Do you have a card or something so I can call you later and make arrangements?" He seemed a bit shocked, but handed me a card and went back to his conversation paying me no more mind.

So I called him two weeks later, told him who I was...we started talking about the build, what I wanted, yadda yadda yadda and somewhere in there I mentioned "I kick myself in the ass for ever selling my SUN Distributor Machine, for what I would have paid to ship it I could just do this myself and not wait..." 

Don asked quickly "You had your own Sun Machine? Why?" I explained we had one when I trained back in Michigan, that I got a deal on a surplus unit at a military disposal auction but sold it, a Sioux Valve Grinding Machine, and one of those old Sit on the Block Top Boring Bars back to another fellow bidder with a shop because I was hopelessly overweight on household baggage and was maximizing my weight on Datsun Parts and not machine tools which I convinced myself were plentiful in the USA... "So much for that stupid decision."

Ended up talking to Don for about two hours and in the end he says "What did I tell you for the distributor recurve?" I said "$476" He just started laughing..."well, I was right again!" He apologized saying he gets approached all the time at car shows from guys with grand ideas but who just want everything for free. He says "I got a set of weights here, should be just what you need, give me your address and I can get them in the mail tomorrow." 

$20! Came in a heavy business envelope with three stamps on it. "DPE, Milpitas" was the return address. 

And he was right, they were spot on what I wanted them to do.

In so many ways I watch this exact same scenario play out on internet boards to this day and think "Man, if I acted like these guys today, I'd have lost hours of free advice and discussion with a veritable L-Engine Genius!" I mean, once he determined your bonafides, he opened up quite a bit especially if you were not a competitior and understood his side of the business and people always ripping him off (which I understood all too well!)

When we took over a distributor there in Milpitas and they made me interim service manager I was almost jumping out of my skin to go...all after work was 'see if I can get over to Don's' just to talk about nothing in particular. Just hang and hope for osmosis to kick in. 

It was a sad day when he passed on, we are all less without him.

Edited by Tony D
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Steve is a decent guy, I was trying to decide on a cam and i was stuck between the DP cam, Rebello 63D cam, and the ISKY L490. I used a very simple program called Desktop Dyno to try to simulate the vehicle behavior. After some discussion with Steve he shared the specs. He didn't have a dyno sheet to do a comparison but he did find the numbers to be lower than expected. There is a lot of assumptions in the model and the port flow is simply based on measurements a member has posted on facebook. Either way it should work well to compare cam to cam. So here is a comparison between the DP 535 cam(L28F) and the isky L490. This is "crank torque" and the assumptions are 87mm bore 79mm stroke; 44/35mm in/ex valves. 10.5  static C/R. 3 deg cam advance on both cams, free flow exhaust, induction flow = 1500 cfm @ 1.5 inHg.

 

image.thumb.png.d3a154e153c7b37af1f6aaa4466527ed.png

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1 hour ago, madkaw said:

I thought the DP cam had a shorter duration which in turn would not be making power later than the Isky- but I’m guessing here. 

So the higher lift is killing the low end?

 

I would think the only downside with higher lift is it harder to build. More thought need to put into drivetrain stability and piston to valve.

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yeah both of those cams are well suited for higher revving engines. Which is the only thing holding me back from the Don Potter cam. My pistons are still cast so my engine won't see much action above 7200 rpm. The clearance issues that Steve mentions are to the pistons. A higher peak lift will not affect valve to piston clearance as much an earlier and later closing valve. 

The higher lift will still require custom springs and valve seals. 

Personally i am leaning towards the 63DE (.487 lift, 279 duration)cam from rebello, it won't make as much peak power as the DP cam but  much higher torque until  5200 rpm. Peak power will be around 6500. 

 

image.thumb.png.1e4734e3e28bd08c37b9b4db0e171490.png

 

 

Plot shows both cams with 3 degrees advance. I would probably retard the 63DE which increases top end power. Retarding the DP cam really kills low end torque and the peak HP only slightly increases.

 

Rebello also has a very attractive price for the cam, lash caps and springs (outer only required) as a kit. 

 

 

 

Edited by theczechone
damn grammar

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My 490 ISKY pulls hard to 7000, but I can’t be specific about the cam timing . My head is shaved over 50 thou without using shims and have my cam advanced 8 degrees. I didn’t degree after the last 20 thou shave , but with 30 thou cut the cam almost cam in too late . The other factor was I went from triples to n42 injection ( Megasquirt) . 

If that graph was accurate then it would seem that it wouldn’t be as user friendly on the street at low rpms. My ISKY just puts along at 1500 rom in fourth around town without a jug

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On 26/02/2017 at 11:58 PM, ryant67 said:

The Isky L6 grind is 270 duration and .540 lift.  I suspect the Potter cam has a little more duration and steeper ramps, meaning more duration at .050 lift.  It's more money, but potentially a bit more performance too.  

The Isky is $140 for the regrind, but that doesn't include the cost of your own supplied core and shipping both ways for those who aren't local to Isky.  

 

@theczechone The Isky cam I mentioned earlier in the discussion would be a good alternative.  Less duration, so it keeps the powerband lower, but more lift.  If you haven't already, I'd maybe give Isky a call after 2:30pm PST and speak with Ron Iskenderian.  Really knowledge and helpful guy.

Edited by ryant67

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Here is my 3.0 liter dyno with Isky 490 cam and SU carbs.  I have a later dyno that I can’t locate where I had the timing and carbs tuned much better.  It looks pretty much the same but peaked 13hp more. post-11707-023618100%201318743869_thumb.jpg

 

 

And for Sh!ts and giggles my new LS1/T56 combo on the same dyno.F23B86D7-84F8-4008-B2EA-24C7C2E85234.thumb.jpeg.4b25a681b1a044adc654fa8f35a142d0.jpeg

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On ‎2‎/‎26‎/‎2017 at 8:44 PM, TimZ said:

Well that sounds better.

FYI, Having had a Z with his one of his mild cams, I can tell you that virtually all of his cams provided a very smooth power band.  They were definitely worth the price.  I think the only issue now is that a cam is one part and an engine needs to have the right porting work to really match the cam as well as the rest of the components.  I am sure that if those really are Don's cam they have the potential to be way better than any other cam on the market.  One note his very high lift cam more used for 3.2 liter high HP engines worked great but he had issues finding a valve spring that could last; if he lived a bit longer he would likely have solved that but it did not work out that way. 

 

It is sad to see his great work was not being passed on as he definitely created engines with way more horsepower than others like Rebello and Don's engines were bullet proof.  I have drove cars with Rebello 3 liters and Don's 2.8's were way faster.  Andy Hengesteg in Oregon has one of Don's 2.8 engines that will blow the doors off V8's and he did learn Don's porting work but he does not have the machinery or knowledge to do the bottom end.  If you really want to recreate one of Don's engines I would have Andy build the head with the full porting work he learned from Don and have him advise you on which cam and then you need to figure out how to do the bottom end.  Andy might have some input on that as well?

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@ryant67 I sent Isky an email describing my engine plans and asked for his suggestions for selecting a cam i got a reply that said.

 

"I believe the 718148 is your best bet.  See import catalog enclosed.

Regards, Isky Cams""
 
The suggested cam is the L480 which falls quite short of the rebello cam. either way i ordered the cam from Rebello as i have heard good reviews and from my "calculations" it looks like what i want. No i just need to figure out if my core is good enough or source a spare to send to Dave.
 
@30 ounce Your peak torque is in about the same place as my plot predicts but your torque drops off faster in the higher RPM. I wonder if the SUs were limiting you a bit in airflow. After all you were running 20% higher displacement than what those carbs were originally specified for. 

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Wow... Desktop Dyno... I haven't played with that in ages. It worked out well when choosing cams for my Autocross/ Hillclimb 355ci SBC. I think my latest version is Desktop Dyno 2000. I'll   have to see if I can load it up on my Windows 7 machine.  

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On 2/20/2018 at 8:40 PM, madkaw said:

I thought the DP cam had a shorter duration which in turn would not be making power later than the Isky- but I’m guessing here. 

So the higher lift is killing the low end?

How is anything on that dyno chart 'killing' anything? It's above the L490 at every point of the curve.

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