I've just begun rebuilding a 270 GMC for my roadster and wondering what could be done to improve the oil pan. Motor was pulled from a Deuce-and-a-half, so the stock pan was fine for rough ground and steep inclines, but what about hard driving at speed? I'm hoping the car will see action at drags, dirt track, and hill climbs. Thinking windage tray and gated baffles. Maybe an extra baffle or two closer to the pickup? Do I ditch that huge pickup screen or was that the secret to being able to handle inclines? It seems like back in the day it was common to run a dry sump, but I don't want to go to that expense. So wet sump it is.
Have you thought about adding a kick to the pan for added capacity? My dad used a 235 rocker cover (I haven't forgiven him for that) as a kick on his S.B.C. oval track race car.
I don't think it lacks capacity. If I was only racing on a dirt oval a kick on the RH side would be beneficial, not good if I want to steer in the opposite direction. Road racers use a diamond shape gated box around the pickup to trap oil no matter what direction. I'm wondering if that stock pickup serves a similar purpose? It looks like it would trap oil around the pump.
Older pic of my roadster. It has progressed a bit since then. I'll update when I can roll it outside again. DSCF2429 by Gofannon posted May 10, 2018 at 8:47 PM
Depending on what they came out of gmc made differerent pans and pickups for those pans. You might look at a 228 or 248 pan. They had differerent sumps and baffles
A 228-248 pan is easiest because it can be used stock. Adding hinge doors on the existing baffles which have factory holes near the bottom will hold the oil from forward movement at the end of a drag race where it wants into the timing cover. I pop rivet or machine screw them in from piano hinges. Welding a flat 3” long plate at the front side to side just clearing the rod is good also. 3/4” long stitch weld works fine for this. This is if your using the stock oil pump which is very good. From your photos you just need the floating oil pick up off a different stock pump and the piano hinges to keep the oil in the center section for drag racing. More work I’ve described if your going to turn right and/or left on a track. The civilian 302 and military 270-302 pans are the best to convert because the block rail is reinforced with a 1/8” strip over the stock rail. I’ve seen aftermarket BBC pan bottoms cutoff and welded to most of a GMC when using an external oil pump (which I do) or a dry sump. If you doing a right side kick out make sure you leave room for the starter. The pan doesn’t need to be any lower that the bell housing for the most part if your making one but using the stock oil pump can cause a clearance. There are at least 5 oil pump bottoms depending on the application but all the pump bodies are the same. My racing pan uses an external oil pump, belt driven, and full length kick outs on both sides. Panels with doors and oil catchers are on both side but no louvers or screens. I have photos somewhere. A single pick up near the back on the left side to feed the pump. Moroso oil pick up parts from Summit and some welding. Good luck.
Here's what I ended up doing. I started by thinking I could just sit a windage tray on top of the existing baffles, but found that would interfere with the crank. Measuring across the inside of the block was about 8 1/2", so I set the windage tray at 4 1/4" from the bottom of the block.. I added 2 extra baffles with trap doors closer to the pump. I decided to keep the original pump pick up as it adds shrouding from windage. Supposedly these pans hold 11.5 quarts, so I measured out 11.5 quarts into the pan and found the oil level is just above the stock baffles. This would mean the crank throws would dip into the oil. Measured the dip stick, Full is 4" below block, low 4 5/8". Now I'm wondering whether I should drop the oil level up to 1/2" lower to make sure the crank is clear? The pan holds a lot of oil, and I have much better control of it. How much would the oil level drop while the engine is running? I can see why dry sumps are popular for these engines. Also drilled and tapped the block for full flow filter, and an oil feed to the distributor gear.
Your idea for the trays are very good. When I used the 11-12 quart pan at Bonneville I ran 8 qts. However I used the floating oil pickup which was 3/8” off the pan bottom when the pan was empty and on a stand. When I changed to the pickup truck 228-248-270 shallower pan I just changed the oil pump bottom. I had one of the oil pickups you show but never used it. There are 3-4 different bottoms to the oil pumps for different depths of the pan that will accept the same floating pick up I believe they only had one of those. I’ll see if I can find them and take photos. As for a statement above I’ve raced GMC’s since 1975 at Bonneville on gas an fuel up to 216 mph in a roadster and ever had or used a dry sump.
@jimmy six I have a few more questions for you, or anyone else. I'm grateful for the power of the HAMB, so I can pick the brains of people with real world experience. Oil line to distributor gear - What size hole do I need in the fitting? Lifters - I have a steel cam, and bucket type lifters that my machinist says are good enough to resurface and use again. He can grind the correct radius. Would there be any advantage in switching to milk can type, and which are the correct ones for a steel cam? Crank gear - What's the difference between a GMC crank gear and a 235 Chevy one? Cam gears are the same? Rockers - I'm using sheet metal rockers. I've seen it mentioned that they benefit from a dab of weld to strengthen them. Where is the weak point that needs weld? Head has SBC valves +0.100", Buick 455 valve springs (similar spec to "Z28" springs), and Chevy 235 retainers. Rocker stands - I have steel or aluminium. Use aluminium and machine 0.100" off the height? Or is that not necessary with +0.100" valves? My valves are the same length as the OE GMC ones. Steel stands look stronger. I haven't talked to a cam grinder yet, but I'll probably base it around this Schneider grind.
1. I use a brass 90* fitting fill with solder, drill at angle towards the front parallel to the 90* to aim better at gear, .060” hole, steel cam needs a brass gear, Mallory, 2. GMC lifters from the military engine with the steel cam, 1939 Chevrolets chilled iron, I’ve only used the milk can style to have shorter push rods. Keep seat spring pressure in the mid 80’s so everything will live. If I knew your expectations I might adjust that. 3. Nothing I have found or heard. All have been the same from 1937 to the end of 1962. The 153-292, Pontiac Iron Duke straight cut, Etc will work. There even ones for line bored engines and different key ways for advancing and retarding. Cloyes 4. Ran stock ones since 1974. Never welded any. Oil needs the trough in both directions. At one time #130 springs and .520” lift. Didn’t hurt anything but backed off on the springs to #100 when found I didn’t need the pressure. All spring seats out to accept 1.550 diameter springs. 5. Never used steel rocker stands, only aluminum. Studs only, never a bolt. Always used 10* keepers with lash caps for correcting geometry. Used very few valve spring shims. Bought keepers with different height inner rings. I am the only one who ever assembled my engines including the cylinder head. I had shops do the machining. blocks, cranks, balancing, valves and seats. NEVER any assembly. I did all my own rod, piston, and ring work. In the head I set every spring height and install all seals..I am extremely picky. Even the 311” in my sons 40 Chevrolet was assembled the same way. Mike Kirby did his head but I checked the work. That head has 1.94 and 1.50 valves and a Howard 298 regrind cam on a cast stocker and #75 springs. Lift is approx .410” with 10.1 Ross pistons it’s a great street engine. A point to ponder: The rocker arm ratio is closer to 1.4 than 1.5. The higher the lift the more side force from the rocker tips prematurely wearing out guides.
View attachment 5383255 View attachment 5383256 [/QUOTE] nice work Mike ! But be careful, if you keep showing glimpses of your fine craftsmanship, HAMB members might start asking for a build thread…………
Thanks @jimmy six I have a bunch of milk can lifters from various Chevy engines, but I was of the understanding they are not all chilled iron. They are all from engines with cast iron cams, so I'll stick to the buckets. Rock Auto lists the Sealed Power AT887 milk can for '39 Chevys and GMCs, but also for any Chevy 6 with mechanical lifters including those with iron cams. Do chilled iron lifters also work with iron cams? Buick springs are Comp Cams #249-910-1. I can't remember what the installed height ended up at, but it was slightly taller than the spec for a Buick. Seat load is #94 at 1.850". The spring rate is quite high so it will be around #200 to #220 open with 0.474 lift. I knew about the Iron Duke gears, but they are long out of production. I think they needed a spacer or some machining to work? A lot of extra time and money for a noisy gear train that's not needed, but the sound would be cool. It's like the guy that runs a gear drive on a SBC just for the sound. I don't have high expectations. I'm not going for any records. I don't intend to drive long distances. I want a strong street/strip engine that can dust off a few flatheads, run at vintage drags, hill climbs, and a few laps of a dirt track. If it will make 250 hp out of 283 cu in (3 7/8" bore) I'll be ecstatic. What could I expect? Pistons are on order from Ross. I might be pushing it a bit at 10.5:1 CR. We have 100 octane (RON) at the pumps here in NZ now, I can always add a booster.
nice work Mike ! But be careful, if you keep showing glimpses of your fine craftsmanship, HAMB members might start asking for a build thread…………[/QUOTE] You know what my work space is like. I can't stand back far enough to get a decent pic.
I supposed they could but I follow Howard’s recommendation from the 70’s when using steel or cast iron. Spring pressure looks good on the seat and maybe slightly light on open but it will never hurt for sure. The bigger valves kill a little low end for the street but 4500 up will like them. Your head looks great flattened but not cut too much. I can see looking in the water holes near the exhaust valves the brass deflectors don’t seem to be there. Not a major problem but please install a water line on the top of the head last 1/2” pipe fitting up to the thermostat housing. Smaller GMC’s didn’t use it but all the military and big trucks did. A stock 270 made 140 hp and you are being realistic. With 10-1 and the cam you described and a good intake your # of 250 is right on to me. It would be great to see the torque line from 2500 to 5000 on a chart.
I forgot about those deflectors. I'll have to check if my small port head has them. I was going to fit the water line on the top of the head, but run it via a manifold heat plate. I'm struggling to find NPT fittings in NZ. One of the curses of being an old British colony, all BSP in these parts.
Back in the day Herb Adams (of Trans-Am fame) used an oil reservoir with an internal pressurized bladder, when the pump had oil the lubrication system worked as usual, if the pump was starved of oil, the pressurized bladder would push the oil in the reservoir to the bearings. If I remember right it was used in racing classes that wouldn't allow dry sump systems.
There was a certain NHRA Pro Stock owner/driver/engine builder that had a oil pressure tank in the lifter valley and a miniature AC compressor clutch on his dry sump oil pump. Seems he could deactivate the clutch and stop using the oil pump gaining HP after leaving the line. As I remember he was hard to beat in his day….
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