'65 GMC 1500 project. From the Netherlands

[Prowbar]

Did a couple of things last weeks:

1. Made some better battery cables. The old ones were junk and made out of old welding wire and battery terminals we had laying around. One of the reasons for poor starter performance. Bought some 50 mm2 wire (equal to 1 AWG) cable with fine strands, very flexible stuff. Proper fitting battery terminals were soldered in and heavy-duty connectors were crimped and soldered. Heat shrink with glue protects from moisture and corrosion. I've added an accessory wire to the positive cable to supply the new relay-operated headlights with direct battery voltage. A connector will be added to easily connect/disconnect them in case of repairs.
The engine turns over much better now.

2. There is a picture of the added bronze bushings to the clutch pedal. I've mentioned this before but did not show a picture. As you can see a washer welded on the lower clutch rod. This prevents the clutch linkage from wearing in to the corner of the rod. The clutch linkage was made from hardened material, and couldn't use a regular drill, endmill, or reamer to cut the material. However, a carbide burr and some patience made a nice 1/2" hole, and the made up bronze bushings were pressed in with LocTite.

3. Made a new adapter for the Impco mixer to go on top of the carburetor. Hood clearance is minimal but present due to the higher raised manifold on the earlier 478s.

4. Welded up one of the downpipes, in this case, the right side. Still need to weld in the O2 sensor bung.

5. Started tearing apart the engine to remove the camshaft. Been studying the original grind and seeing how one could extract a little better performance from one. I've considered Pete Chronis' grind, but it is more of a higher RPM camshaft. Another issue is the lack of CNC camshaft grinders - all of the companies use a copy camshaft machine with existing cam profiles to regrind camshafts.

Some thoughts:
All durations are based on advertised numbers since this is what the GMC book gives.

- Stock cam LSA (Lobe Separation Angle) is 110 degrees. I would have liked to go lower, for example, 108 or 106, to improve low-end torque. However, not possible without welding up the cam I would think. Still open for discussion. Pete's specs keep a 110 LSA as well.

- Keep the stock 63-degree overlap between intake and exhaust. Pete's cam has a 32.6 crank degree overlap, which is much less. I believe the book also gives all cam duration in crank degrees since advertised duration numbers comparable.
- Stock intake closes 61 degrees after BDC. I would like to close the intake earlier, for example, 50 degrees ABDC for an increased dynamic compression ratio. Since the static compression ratio is low as is, one could extract a little more compression out of one. However, cylinder filling might become a problem. Pete's cam closes intake 46 ABDC, which is even earlier.

-A bit more cam lift would be nice to compensate for later intake closure. Still need to measure the stock camshaft lift.

-Keep the same intake duration of 268 degrees, if possible. However, reduce exhaust duration from 298 degrees to about 275-280 degrees.
Pete's cam has an intake duration of 236 degrees and an exhaust duration of 268 degrees.

Seems like Pete's cam really 'sacrifices' on intake filling by closing the valve early, having less intake duration, and less valve overlap.

Your thoughts on the camshaft?

[Prowbar]

As mentioned, I also converted the headlights to relay. I was given a universal relay conversion kit for headlights. I made my own harness, with the original colors. The box has relays and also 2 30 amp fuses to protect the circuit. It is nicely hidden.

Had to cut off the original connector from the OEM harness to supply the relay box. Not pictured, but I've also added the original clips to fix the harness to the grill. Power is supplied by the battery cable accessory wire.

This should take a huge load off of the headlight switch and the rest of the wiring while improving the headlights' brightness as well. From a fire hazard in the making to a win-win situation.

[Prowbar]

Been working on a cam design.

I've added Pete Chronis custom cam specs. Note these specs close the intake much later, to up the dynamic compression ratio. Note the shorter duration figures (advertised) These specs also have a little improved lift.

Stock lift figures as measured by me, with the current camshaft, without any valve lash, are .415" for both intake and exhaust.

I also added the cam I want to have ground for my build. I have to decide on the lift, but the rest is pretty much final. Unless you have groundbreaking suggestions

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It is a compromise between the stock camshaft and Pete's design.

Compared to stock, earlier valve intake closing to improve dynamic compression. A little less duration as a result. The exhaust is about the same as stock. I was concerned with cylinder filling at first, but don't think it matters as much due to the improved valve job and slight porting in the heads.

I've also decreased the valve overlap compared to stock, but not as much as Pete's design. The lobe separation angle comes out to 109 vs the stock cams 110.

Let me know what you think.

[James]

I have done some flow testing on a stock magnum head (reference the link). I didn't show it on the graph but the head continue to flow more air when there is more lift.


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Also I have measure the maximum lift for both valves (reference the link).


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Hope this will help in your planning on the cam lift profile.

[Prowbar]

Thanks, James. Forgot about those posts. Good job on the data.
Your cam lift measures a lot more than mine, didn't think mine was all that worn. Not sure now, maybe the cam lift was revised a couple of times. Have to measure my 305 now also to compare.

Seems like more lift definitely helps.
Will talk with the cam grinder about how much I can safely improve the lift.
More seems better but I would have to probably change/modify the valve springs also.

The stock ones are lousy on seat pressure, maybe 50 pounds, maybe shim them for improved pressure or change them for another spring.
They are good are break-in springs, though.

I left the stock exhaust duration as is, the exhaust port on non-Magnum heads is pretty restricted, not much can be done about it I think.

[James]

Originally Posted by Prowbar

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The stock ones are lousy on seat pressure, maybe 50 pounds, maybe shim them for improved pressure or change them for another spring.
They are good are break-in springs, though.

Personally I would installed bronze valve guide sleeves first. Then I will be using valve springs from Comp Cams #972. I will also need to use spring seat cups Comp Cams #4704, guide will need to be machine to allow installation. While you are getting it machine I would also get machine for positive valve stem seals. And to top it off with Comp Cams retainers #743. The springs comes extremely close to the stock seat pressure base on the maintenance manual specs, I also double check a set just to be sure. The springs are good for .700" before coil bind.

Here is something I found on Motor Trend web site:


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Lobe Displacement Angle (LDA):
Although the installer can advance and retard the lobe centerlines, the displacement angle between the centerlines is ground into the cam at the time of manufacture and cannot be changed by the end-user. Narrow LDAs tend to increase midrange torque and result in faster revving engines, while wide LDAs result in wider power bands and more peak power at the price of somewhat lazier initial response.
A street engine with a wide LDA has higher vacuum and a smoother idle. On the street, LDA should be tailored to the induction system in use. According to Comp Cams, typical carbureted, dual-plane manifold applications like 110-112 LDAs, while fuel-injected combos want slightly wider 112- to 114-degree LDAs. Fuel-injection doesn’t require the signal during overlap that carburetors need to provide correct fuel atomization, and most computer controllers require the additional idle vacuum that results from decreased overlap.
Bracket racers with higher stall-speed converters, high compression, single-plane intakes, and large carbs usually want 106-110-degree LDAs.
Engines equipped with blowers or turbos, or used primarily with nitrous oxide, typically work best with wider 110- to 116-degree separations. Race engine speeds have increased over the years causing a corresponding upward creep in LDA and duration

Duration:
Duration has a marked effect on a cam’s power band and driveability. Higher durations increase the top-end at the expense of the low-end. A cam’s “advertised duration” has been a popular sales tool, but to compare two different cams using these numbers is dicey because there’s no set tappet rise for measuring advertised duration. Measuring duration at 0.050-inch tappet lift has become standard with most high-performance cams. Most engine builders feel that 0.050 duration is closely related to the rpm range where the engine makes its best power. Typical daily driven, under-10.25:1-compression ratio street machines with standard-size carbs, aftermarket intakes, headers, and recurved ignitions, like cams with 0.050-inch durations in the 215- to 230-degree range if using a hydraulic grind, or 230- to 240 degrees with a solid.
When comparing two different cams, if both profiles rate the advertised duration at the same lift, the cam with the shorter advertised duration in comparison to the 0.050 duration has more aggressive ramp. Providing it maintains stable valve motion, the aggressive profile yields better vacuum, increased responsiveness, a broader torque range, and other driveability improvements because it effectively has the opening and closing points of a smaller cam combined with the area under the lift curve of a larger cam.
Engines with significant airflow or compression restrictions like aggressive profiles. This is due to the increased signal that gets more of the charge through the restriction and/or the decreased seat timing that results in earlier intake closing and more cylinder pressure.

Big cams with more duration and overlap allow octane-limited engines to run higher compression without detonating in the low- to mid-range. Conversely, running too big a cam with too low a compression ratio leads to sluggish response below 3,000 rpm. Follow the cam grinder’s recommendations on proper cam profile-to-compression ratio match-up.

Lift:
Another method of improving cam performance is to increase the amount of lobe lift. Designing a cam profile with more lift results in increased duration in the high-lift regions where cylinder heads flow the most air. Short duration cams with relatively high valve lift can provide excellent responsiveness, great torque, and good power. But high lift cams are less dependable. You need the right valvesprings to handle the increased lift, and the heads must be set up to accommodate the extra lift. There are a few examples where increased lift won’t improve performance due to decreased velocity through the port; these typically occur in the race engine world (0.650-1.00-inch valve lift). Some late model engines with restrictive throttle-body, intake, cylinder head runner, and exhaust flow simply can’t flow enough air to support higher lift.
Besides grinding a lobe with more lift, you can increase the lift of an existing cam profile by going to a higher rocker arm ratio. For example, small-block Chevys where the cylinder head runners are not maxed out may benefit from moving up from the stock 1.5:1 ratio to 1.6:1 rockers. But going up more than one tenth in rocker ratio can lead to trouble; there’s a limit to how fast you can move and accelerate the valve before the valvespring can no longer control the system. If a profile was a good design with 1.6:1 rockers, it’ll probably be unstable with 1.8:1 rockers. The correct solution is to design the profile from the ground up for use with high-ratio rocker arms.

Hope this is not too much information ("Information Overload"). I just want you to make the best choice with the information you know.

Good luck.

[Prowbar]

Not a problem at all. I used cast iron guides for the exhaust, with the positive valve stem seals. Bronze would have been better, couldn't find any in the size I wanted. The engine is assembled, last thing is the cam, because I had some issues with it.

I've read a lot about cam design in general. Tried to stay very mild on the cam, to increase torque and drivability, and get as much out of the engine as possible. No need to try high hp/high rpm tricks if the engine doesn't turn past 3200 rpm.

Those Comp springs are pretty stiff I think but could work. I would prefer 85 pounds of seat pressure. Pete Chronis talked about Ford FE390 springs. For a low RPM engine, this should be sufficient in my opinion. A 5.9 Cummins uses about the seat pressure.

I'd like to increase lift but it has to be doable.

One way to increase lift is to reduce base circle size, there is indeed a possibility of running into geometry trouble.

I am going to discuss with the cam grinder if they can weld up the lobe to increase the lift and accommodate the new profile.

Different rocker arms are also possible. But would need to be custom-made.

Hope it makes sense.

[lizziemeister'sV6]

Was wondering what changes you are thinking about that differ from Pete's grind specs. I run a Pete spec ground cam - it sounds nice which was one of mine goals and seems to do good at highway cruzin' speed. My truck clocks at 60 mph about 2600 rpm. I think this is about where the power band comes in due to the cam grind. My truck sees mostly highway speeds and most generally pulls a car trailer lightly loaded. You can relate my truck's usage to that of 379 Peterbilt pulling a chrome reefer - gets the job done with a little flair. Sure there's better builds and combos but hey - it's a little different that any run-of-the truck - and it gets more looks that any 2023 decked out $100,000 truck when you pull up to gas pump.
I guess it's all in what you want - but the truth is anything you do to a 60 yr. old GMC V6 motor will never be equal to what a truck engine of today's manufactured engineered marvels can do in performance. BUT when we raise our hoods we CAN see a motor and are ABLE to work on it. This is just my thoughts - give me and other GMC V6 caretakers your inputs - for now I think I go out and crank-up the 1960's Diamond T "Cat" powered road tractor and blow some smoke while dreaming about a V12 powered "Crackerbox". Have a good day!

[Prowbar]

Originally Posted by lizziemeister'sV6

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Was wondering what changes you are thinking about that differ from Pete's grind specs. I run a Pete spec ground cam - it sounds nice which was one of mine goals and seems to do good at highway cruzin' speed. My truck clocks at 60 mph about 2600 rpm. I think this is about where the power band comes in due to the cam grind. My truck sees mostly highway speeds and most generally pulls a car trailer lightly loaded. You can relate my truck's usage to that of 379 Peterbilt pulling a chrome reefer - gets the job done with a little flair. Sure there's better builds and combos but hey - it's a little different that any run-of-the truck - and it gets more looks that any 2023 decked out $100,000 truck when you pull up to gas pump.
I guess it's all in what you want - but the truth is anything you do to a 60 yr. old GMC V6 motor will never be equal to what a truck engine of today's manufactured engineered marvels can do in performance. BUT when we raise our hoods we CAN see a motor and are ABLE to work on it. This is just my thoughts - give me and other GMC V6 caretakers your inputs - for now I think I go out and crank-up the 1960's Diamond T "Cat" powered road tractor and blow some smoke while dreaming about a V12 powered "Crackerbox". Have a good day!

The reason for the changes is a comprimise between the stock cam and Pete's cam. A powerband of 2600 is a bit high for a 3200 rpm engine in my opinion. I like the low end torque and want to retain this. So a powerband around 1600-2000 or so. I hope to achieve this with the modified design.

Figured I added some info where I explain my reasons:
Most people agree that there are two key events in a camshaft: intake valve closing point and valve overlap. The others are important too, but not as much.
Generally speaking, intake valve closing determines the place where in the rpm range the torque is generated. Valve overlap has about the same effect. The intake can be timed later for higher rpm power. Valve overlap can be extended for higher rpm power.

Intake valve closing point:
The stock cam: 61-70 degrees ABDC, depending on the year.
Pete's cam: 46 degrees ABDC (After Bottom Dead Center)
Modifed design: 50 degrees ABDC - I agree with closing the valve earlier to up dynamic compression as much as possible.

Valve overlap:
Stock: 63 degrees, might vary with the year.
Pete: 33 degrees
Modified: 45 degrees - Searched the middle ground, as a compromise between the two.

I am thinking Pete's cam has a sweet spot at about 2600 rpm where the pulses act to charge the cylinders better. According to the 'books,' it should behave as a lower RPM cam.

Not trying to build a race monster, but hope to improve the usable power as much as possible.

[Prowbar]

By the way, Lizziemeister, do you have any videos of your V6 running? Would love to hear what it sounds like.