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Cam for heavy truck?
https://slantsix.org/forum/viewtopic.php?t=59685		 Page 1 of 2
Author:  Rick Covalt [ Wed May 25, 2016 6:15 am ]
Post subject:  Cam for heavy truck?
Cam recommendation?

I am putting together another engine for Andrew Shank who races with us. He is buying one of Ryan's fleet. It is a 85 4X4 with a Slant 6, granny gear 4 speed, and 3.23 gears, and running 31 x 10.50 tires.The truck cut through an oil pump gear, so we are putting together a new engine.

Truck has Dutra duels, and an offy 4 barrel and 500 carb. Head will get Engine builder valves and be planed to match the needs of the cam / engine. So what cam should I have re-ground for this type of build. This truck is not going to be driven all that much, and gas mileage is not a big consideration.

I have the 819 in my 2WD truck and like it, but it is not too big at all for my tastes even with the stock automatic. But would this be a good choice for a heavier truck with a manual transmission?

Thanks for your help!

Rick
Author:  Dart270 [ Wed May 25, 2016 7:20 am ]
Post subject: 
Since it's a stick, I would go a bit bigger. Does he want to use pump premium or 87 octane?

I design all my motors for premium since it is usually not much more and I don't drive my cars 20,000+ miles every year. Limited usage, so fuel cost difference will be tiny, even if gas prices go up.

Here's my initial thought:

OREGON lobe 1947-INT lobe 819 - EXH
dur I E dur@0.050 I E LSA lift I lift E overlap overlap @0.050"
270 248 224 219 105-106 0.47 0.437 47 9.5

Then mill for high 8s or low 9s static comp. 9.0 target? Install centerline at 100 deg.

Lou
Author:  Rick Covalt [ Wed May 25, 2016 9:34 am ]
Post subject: 
I am checking, but I doubt that he will care if it needs premium. If he cared much about fuel costs he would not be buying a 4X4 shaped like a brick! :lol: :lol:
Author:  Joshie225 [ Wed May 25, 2016 9:44 am ]
Post subject: 
3.23s and 31" tires makes for 2100 RPM at 60 MPH. That's not spinning very fast at all for a small motor pushing a small barn. I would keep the cam rather conservative unless a gear change is planned.
Author:  Rick Covalt [ Wed May 25, 2016 10:00 am ]
Post subject: 
Quote:
small motor pushing a small barn.
:lol:

No gear change happening. Running local he has 3rd gear, and on the highway, speeds will be closer to 65-70 I would guess.
Author:  Joshie225 [ Wed May 25, 2016 10:16 am ]
Post subject: 
It's not around town that it's going to be a problem. It's rolling hills and the huge gap between the 1.66:1 3rd gear and 1:1 high gear. I'm assuming this is the NP435 trans since you mention the granny gear. Too bad it's not the NP445. That has a 1.31 3rd gear which would help a lot, but it also has a 4.56 1st gear rather than 6.68.
Author:  SlantSixDan [ Wed May 25, 2016 10:56 am ]
Post subject: 
Quote:
3.23s and 31" tires makes for 2100 RPM at 60 MPH. That's not spinning very fast at all for a small motor pushing a small barn.
I agree, and in my mind all that math also adds up to "Might wanna rethink that carburetor several sizes smaller".
Author:  Dart270 [ Wed May 25, 2016 11:24 am ]
Post subject: 
It will be a matter of taste, of course. Personally, I am not shy about downshifting and I like more power. I do not consider 224/219 duration to be a large step above stock, especially if you have good compression (8.5 true static, or higher). Degreeing at 100 will give good low end and likely best overall power.

If it were my truck, with a stick, I definitely wouldn't mess around with a cam that small, but I have learned that most others like to run at low RPMs and so I recommend a more conservative cam with a street-type vehicle.

Really, head flow and compression will have more effect than cam anyway, and it is probably better to go on the smaller side (like 224/219).

Lou
Author:  Rick Covalt [ Wed May 25, 2016 11:28 am ]
Post subject: 
Quote:
Too bad it's not the NP445.
I believe I have a line on one of these with low miles.

It has a 500 carb on it, plus unhooking the secondaries if needed is a piece of cake.

thanks for the help.

Rick
Author:  ryandcovalt [ Fri May 27, 2016 9:20 pm ]
Post subject: 
To make it even worse. The truck actually has 33x12.50 tires on it so the gear ratio is even worse. 2 years ago I ran the truck to Clay City on 35" tires with the intentions to drag race it. (Broke the u Joint on my first time run.) But I did learn on that trip that no stock engine slant six should ever have 35" tires. The spread between gears was very very bad, and climbing mountains was almost dangerous.

I think the 4 speed without granny will help a lot.... as would smaller tires. There was a significant improvement when I put the 33" tires on it. I'd like to think that with the larger cam, big valves/porting the head and higher compression would make it much better to drive. I know Andrew would like as much power as possible and wouldn't mind shifting to keep within the power range. But I know he would like better than stock torque too.

I always chose to run huge cams and just run high RPMs. Andrew is much more conservative than me when it comes to these things so I think your cam selections would suit him better.

Are there any long term problems with running only the primaries on the edelbrock 500?
Author:  Rick Covalt [ Sat May 28, 2016 4:57 am ]
Post subject: 
Quote:
The truck actually has 33x12.50 tires on it
Sorry, my bad! :lol:
Author:  Dart270 [ Sat May 28, 2016 7:15 am ]
Post subject: 
Running only primaries is a good idea, at least until things are tuned in very well. With the cam I recommend and head/comp, it will definitely have more torque than stock, at any RPM.

If an engine is tuned well and has matched comp to the cam, my experience is that even big cams can make more torque than stock. I believe that folks feel the higher power at higher RPM with a cammed up engine and expect to get that much oomph at lower RPM too. They still have more than a stock engine, but it feels like less due to the comparison.

Lou
Author:  Rick Covalt [ Sat May 28, 2016 1:13 pm ]
Post subject: 
Here is how i view it. Ryan ran it stock with 100 HP. We are going to add about 50 -60 HP so it has got to be much better, me thinks!! :lol: :lol:

Rick
Author:  Jase [ Mon Aug 06, 2018 7:21 am ]
Post subject:  Re: Cam for heavy truck?
What cam did you end up using, and has it performed as expected?

I am slowly exploring ideas for an engine build for an M37.
One that will support a 5500 pound empty weight 3/4 ton 4x4, with a cruising engine speed around 2700-3500 RPM The engine does not need to spin past 4K, but it would be really nice if it was efficient right up to that point.

As it is geared right now 55MPH comes in at 3200RPM and overdrive is not really an option, so some engine efficiency at what would be considered a fairly high cruising RPM would be rather nice.

The truck will be used locally, and not so much for long trips, but it would be wonderful if a well build engine combo would allow for a 50mile round trip with out the trip being a chore..

Any thoughts and perspective are welcome.
Author:  Rick Covalt [ Mon Aug 06, 2018 1:55 pm ]
Post subject:  Re: Cam for heavy truck?
The cam I put in is Oregom 791 -Intake , 230 @.050, .489 lift
and 1947 - Exhaust, 224 @.050, .470 lift
102 Centerline installed at 100, 106 LSA.

Yes it runs nice. It is not too big at all with the manual transmission. I just drove it again last week. Still will need the 3rd gear on the big hills, but that is what gears are for.

9.77 Compression ratio, 8.5 Dynamic
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