P 350 for towing
 

OK, I'm building a P 350 to go in my 84 Chevy Truck because the crate stroker 383 is junk. I'm going to use either the 46 heads that came with it or some 670's I have that are already built. ( I know about the notches in the block). The question i have is cam choice. I'm thinking about Summit 2800 204-214. I want this motor to be smooth, quiet and super torque output for towing. Looking for about 320-350 HP.

Steve

If you want great torque from off-idle to highway cruising, then forget about HP. Look at the International Harverster V-8's, used in school buses and dump trucks. HP is blah, but they can pull HEAVY loads from a dead stop with no problem. They used reversed split, exhaust about 10 degrees smaller than the intake duration. Something like the old Comp 260 would probably work very well for what you are talking about.

Regarding heads i would drop the 670's on the block first with checker springs to see max lift before a valve hits the edge of the bore its a limitation on other large valve 4bbl heads

The 2800 wont be a bad choice but to help low end torque dont skimp on compression not saying push the limits

To get 320-350hp you'll need the CR the 670's will provide.

BUT, as mentioned, you don't need hp for towing. You need low end torque, AND gearing.

I had several one ton tow trucks, which I used to pull one & sometimes 2 cars to the track. Most of these had wimpy low CR 350 sbc engines. Some had 300ci inline six Ford engines. But, they all had 2 things in common: a 4-speed manual trans with granny low, and at least 4.10 rear gears. All these trucks made good tow trucks & got us safely to & from lots of races.

Also drove 2 ton milk trucks with these same type wimpy sbc engines, and a couple of 292 inline six engines. These trucks hauled 20,000# & more, most every day. They got their power from gearing, supplied by the manual 4 & 5 speed trans & 2-speed rear ends. Guessing that the high speed gear ratio was well into the 5's, if not closer to 6.00. When loaded heavy, and pulling a steep hill, we'd either downshift the trans or the rear end.

SO, IF you got enuff gearing from your trans & rear end, you can get by with a low CR P350, using the #46 heads. I would make sure you have screw-in studs. I've read that the early '73 model #46 heads had press-in studs. But, they can obviously be converted, for a couple of hundred bucks or so. I've read that all Pontiac heads built after about mid May of '73 had screw-in studs. So, most late '73 & 'all '74 #46 heads should have 'em.

I suppose that many will say the press-in studs are just fine for the small cam you'll be running. But, I experienced a pulled stud on one of those wimpy 350 2-ton truck motors. Just pinned it, in the truck, & kept on running it.

If you run the low CR #46 heads, you can use the small 250 Voodoo cam. It will increase cyl pressure and power. Probably make more power than the 2800 Summit.

http://www.lunatipower.com/Product.aspx?id=1773&gid=287

https://www.summitracing.com/parts/s...xoCnDwQAvD_BwE

If you have press-in studs & don't wanna switch, it might be a good idea to go with one of the low lift factory clones, like the 066. I think the Melling SPC-4 might be one of these.

https://www.ebay.com/p/Melling-SPC4-....c100005.m1851

I believe the Sealed Power CS-641 is also one of these.

https://shop.advanceautoparts.com/p/...E&gclsrc=aw.ds

https://www.summitracing.com/parts/s...w/make/pontiac

Butler also shows that the Melling SPC-5 is one of these low lift clone cams--maybe the 067 ?.

https://butlerperformance.com/i-2445...tegory:1234841

https://www.amazon.com/Melling-SPC-5.../dp/B000C4KLDK

https://www.ebay.com/itm/Engine-Cams...4383.l4275.c10

If you wanted to use mostly stock parts, this cam or the voodoo 250 with the 46 heads should work. It looks like a healthier version of the stock 350 cam.

http://www.lunatipower.com/Product.aspx?id=1757&gid=258

Butler performance make a stroker kit to take that up 388 cid and that's where I would start!

Me and a buddy were thinking the same thing. A Pontiac 350 in a chevy truck for "truck duty`s". A better working engine than the sbc. Stronger block, more space between bores, [better cooling than the 400 or 455], stronger crank, longer stroke, longer rods, longer runners in the intake, and a high velocity head. All on 354 cubes. Torque with decent mileage. :cool: Even an auto trans with a 2.78 to 3.42 gear would get most jobs done.

I see nothing wrong with your plan. I've used the 2800 on a 350, and had no complaints when used as designed. Gobs of vacuum at idle. And the 2800 will go with everything else, like press in studs, etc.

Tough call on which heads to use. 46's are small valve, so you would have less shrouding. If it were me, I'd use the 46's, but would still be curious how 670's would perform on a 350.

I agree with Steve. 350 cubes is not really enough cubes....I'm very aware of the stroke/bore advantage of a Pontiac over a Chevy, but it still doesn't make up for the grunt needed you are looking for.
One of the biggest problems with Pontiac 350's is getting the compression ratio to a respectable number to help the power production, BUT you don't want to go too far in a towing situation, with the engine being under a constant load situation. 9:1 would likely be the max for your deal...
A stock low compression 400 would get you to where you want without much added expense....

Any truck chassis that was designed to work with half the torque and HP of a moderatly prepped P350 should shine with the extra power of a P350

I agree. We used to have a `66 Chevy pickup. It had the "High Torque 250" decal on the valve cover. Hardly a big engine.

Back in the day, I`ve seen the Chevy C60 series 2 ton trucks powered by 2bbl chevy 350`s. Big ole truck with 350 cubes. A Pontiac 350 could have done what those engines did in those trucks.

In other words, one doesn`t HAVE to throw away any Pontiac 350 or automatically stroke them. They have a place for use if you have one.

Wonder what stroke most 383 sbc`s are? 6 inch rod [vs 5.7] with a 3.75 stroke? Hmmm.

which version of the 46 heads are these? 69 or 73/74. if they are 69, i would install harden seats on the exhaust and go with the small valve head. The 69 version have smaller chambers, around 72cc. I would run something like a SPC-5 cam (066).

Keep it simple and use the 066 cam, used in the '68 320 HP 350 HO auto trans applications.

Here's the perfect time to clear this up.

I assume that the Melling SPC-4 is an 066 clone, and that the Melling SPC-5 is an 067 clone. If this is NOT the case, will somebody please post the correct info.

Also, please list all brands & part numbers for 066 & 067 clones, and links to this info.

Thanks !

Butler shows some specs for the SPC-5, but don't say what it's a clone for.

https://butlerperformance.com/i-2445...tegory:1234841

This list on the Wallace site shows some specs for factory cams.

http://www.wallaceracing.com/camcode1.htm

Here's some more specs. As always, not all online info agrees.

http://ronspontiacpage.com/reference...ckcamspecs.htm

http://www.pontiacpower.org/PontiacCams.htm

http://www.classicalpontiac.com/restoration/cams.html

http://ronspontiacpage.com/reference-pages/crane.htm

Paul Spotts says this cam is "...factory blue printed 9779067 - 066...". Don't see how that can be possible in one cam, since the two are SLIGHTLY different. :confused:

https://www.ebay.com/itm/Pontiac-sto...sAAOSw0e9UwqDI

Also says "...Made by same company that supplies Melling, and others - US made!..." So, I assume it is exactly the same cam as either the SPC-4 or SPC-5.

Here are the Melling specs. Pontiac cams are near the bottom of the page. SPC-4 & SPC-5 are similar, but different.

https://www.melling.com/wp-content/u...ck-294-304.pdf

The 2800 has slightly less seat timing and slightly more off the seat duration and more lift than either 066 or 067 cams and having actually experience with it in a 350 it basically acts like a entry level 4bbl camshaft torque coming in not long after idle and it doesn't feel like it runs out of breath on the top end also it wont stress valve train much as its not a far departure from bone stock cams its hard to beat in a 9.2-9.6 compression P350

I have a stock 350 1977 Chevy 3/4 ton truck with a 4.11 rear, I may be doing the same thing soon myself.

Sounds like a cool project to me. Good use of a P350.


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Good point. I forgot that the 73/74 heads might be a possibility. I just assumed it had the heads from 69 swapped on. Those would make for a low compression engine. A bonus would be if they were screw in stud versions.

I would stash away the 670's. Or sell them to fund the project. If the 46's were the 70's heads, mill them for a compression bump. If the 69 400 heads, then use as is. Cast pistons, 2800 cam, and get on it. This is for a towing rig, and sounds like a "build with what's in the garage" thing. It doesn't sound like an all out performance effort, so I think it's ok to not go after every bit of ideal compression.

My 16 year old son wants a pre-87 GM truck, or possibly a 70's Nova. I told him that he has his choice of a few 350P's to drop in. One of them currently has a 2800 cam.

You’re talking about the 549. The block alone weighs nearly as much as a complete Pontiac engine. Not overly powerful, either. IH never had one that was rated over 250hp. Parts are difficult to find on a good day.

Truck has a crate 383. Same stroke as the P350.

I'd be curious about engine specs on the 383 (HP & TQ curves, CR, etc.,) and what is junk about it. Need to know exactly why it's not getting the job done.

Less cubes with the same stroke sounds like a step in the wrong direction.

The stated HP goals is gonna take a lot of compression to get the idle quality and off idle power the OP is looking for. IMO that compression requirement will be all wrong for an engine with 2~3 times the cruise load a car would have. That will make for a bunch of heat which is a problem with higher CR's.

Need to hear more about this truck and what kind of load it's got to tote...transmission rear gears and the like.

Clay

In addition to the above, this may be one of those ideal combos for an SP2P intake.