SBC Derby Build
12-15-2008, 07:27 PM
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SBC Derby Build hey guys im buildin a 305, stock internals with a stock of 350 heads for a derby car...i was wonderin if anyone had any tricks with these to make them real cool or give them a little extra power
12-15-2008, 09:05 PM
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ok; wanted to make sure, it's been a dozen years but was a total blast. You have not mentioned if you are on asphault or mud... Stuff I remember -
You want a 2bbl, not a 4bbl - for what you are doing the 4bbl will not make you any more competitive but will put a ton more heat into the motor. STAY 2bbl. If you must run a QJet then lockout the secondaries, the smaller primaries will make the car perform snappier. OK here is a major reliability secret, jet the carb to deliver a WOT AFR between 11.8:1 and 12.0:1, the richer that you run the motor (and it still performs well) the more internal combustion heat will be carried out of the motor by the raw unburned gasoline aka COOLING! You don't want a rich idle, so you can still start a flooded car. Your carb is critical, do not skimp here; I would say 1/4 of the guys will stall out because they got crappy carbs.
We made our own headers exiting through the hood; zoomies will work too, that way you can see the motor running. Also, much more exhaust heat was carried up out of the engine compartment and we ran the plug wires under the primary tubes and never again burned a wire. Burning spark plug wires is a common issue, prevent it. You can get a exhaust shop to weld you up some suitable headers if you take the car to them for cheap, you're looking for functional not pretty.
You want to construct the air cleaner assy so that it is drawing ducted fresh air from the passenger compartment - we would run aluminum flex duct from the air cleaner through the hole left in the firewall from the climate control box. The reason for this is that when the radiator is punctured you will have a ton of steam underhood and it will suffocate the motor, unless the carb is drawing in air from the passenger compartment or cowl area. ALSO, speaking of steam, silicone the distributor cap so you don't loose spark. We always swapped the HEI for a more reliable point distributor but YMMV.
Speaking of ignition - this is another area that puts 1/4 of the crowd against the logs. Run good high heat silicone wires (summit, $35) not 20+ year old wires! Run correct ignition timing and have a correct curve in the distributor, if your timing is too retarded or advanced you will generate LOTS of extra (unwanted) combustion chamber heat. ALSO, even moe important, you want the motor easy to start when hot, and ignition timing will be critical with this. Run the correct spark plugs, don't be one of those idiots who thinks switching to colder plugs makes the motor run cooler lol. Boots - we would actually silicone the plug boots to the distributor cap & plugs to assure that no steam (from ruptured radiator) would wet down the ignition, in hindsight this might have been overkill but just make sure the boots are VERY high quality so you do not get wet ignition when you finally loose the radiator.
STARTER is critical, we ran the starter cables into the passenger compartment to dual truck batteries wired in parallel; BUT, and this is the cheat! we had the battery cabling such that the driver could move a couple cables and quickly re-configure the batteries in series, that would give 24-volts to the starter and lemme tell you that will turn over any stubborn motor no matter how hot. Be careful not to cook the starter with 24-volts!
If you want snappy performance then work on final gearing (run 4.56s or steeper) and possibly different converter, maybe a 6-cylinder converter will stall higher for you??? Not sure but research the possibilities. Do not go wild with stall, because you don't want to boil the ATF but a little more stall will do wonders to deliver a good short-range "punch".
Weld the spider gears solid; we would spend HOURS doing this, you don't want it breaking! You DO want a solid spooled rear because when you loose one tire you'll still move.
Cooling - remove the clutch fan. Don't bother with electrical fan(s), you can't power them with battery alone and the ones you can get for cheap at the wrecking yard cannot move enough air to make a dent in the radiator's heat. Leave only the water pump pulley and crank pulley on the motor (remove ALL other accessories) and run a pair of tiny v-belts straight from the crank to the water pump; yeah it'll be a biatch getting it on there assign the job to the FNG in the group lol. Remove alternator, good charged batteries will last you all night. Definitely remove the power steering pump, because power steering is VIOLENTLY flammable, I'd rather be fighting a gasoline fire than a P/S fluid (ATF) fire. Remove ALL the fan shroud and ANYTHING even remotely close to the radiator, you don't want anything that can be "pushed" into the radiator and rupture it. We've had '69 New Yorkers where the front core support was moved back 6+ inches and the radiator still in tact!
Radiator hoses - use preferably flex/bendy hoses and wrap with at least 6-layers of duct tape for reinforcement from bursting; the issue is that as coolant goes past 230 the rubber will soften and want to give, wrapping with duct tape will keep it's integrity. At the local pick-n-pull, we would rob all the internal springs from all the lower radiator hoses, and pack like 3-4 springs inside both the upper and lower hoses to prevent them from collapse in the derby.
Radiator - we would take 3 per night (one for each heat); use bailing wire (coat hanger wire) to hold them to the core support so that as the front of the car changes shape it will not rip the tanks apart. Still, after 15-mins we would eventually take enough damage to loose the radiator. We've run engines another 30-40 mins *after* loosing the radiator no prob. A lot of guys will tell you to not run a pressurized system, ignore them and put on a 20-lb cap (if you can find one) just know when that SOB blows it's gonna have a head of steam to it lol. Coolant, you may be limited by rules, some rules say 'water only' for environmental reasons but lets face it if you can keep the coolant from boiling over at 240-260 then it's worth considering.
Tranny - we would bolt a plastic 5-gal bucket with lid inside the pass compartment, fill it with ice/brine and fashion-up a poor-mans fluid-2-fluid ATF cooler, always worked a treat the ATF lines were always cold to the touch even when the motor was blistering hot.
IMO, it is worth the effort to keep the carb cool as possible to prevent vapor-lock; it'll be a real concern. I made an alternating alum/gasket sandwich stack to shed/insulate the base of the carb from the intake, I guess a phoenolic (wood) spacer will work well too. I also splurged and bought from Summit 6' of trick silicone/fiberglass insulation tube to insulate the upper fuel line atop the motor and the ignition wiring.
Engine Oil - synthetic 10-40; BUT if you take a motor that is 20+ years old and suddenly change from dino oil to synthetic the detergent in todays oil might wash 1/2" of sludge down into the oil pan & plug the filter solid. Replace the valve cover gaskets if there is ANY chance they are beyond their years, you do not want a crapped-out cork gasket hemorraging oil down the side of the head because you might get black-flagged for fire. Take the car to the car wash and with hood off spray motor with at least 2 cans of cheap oven cleaner (wait 5-mins) then spray off, you do not want any oil on the outside of the motor to catch fire.
If rules allow, use a 3/8" x 2"-wide strap, drill a 3/8" hole in one end and bolt to the intake manifold or front of head, then heat/twist/bend the strap to the frame rail and weld solidly; almost every car entered in the derby will have busted motor mounts including yours. This is a critical concern IMO. If rules do not allow welding to the frame "at all" then use 3/8" chain to secure motor to frame. Likewise I would chain around the transmission to the rear crossmember.
I'm running outta gas, that should be enough to jog your mellon and further your project. I miss demo derby, I built 38 cars in 2.5 years in northern CA, and I miss it.
Mr. P.
You want a 2bbl, not a 4bbl - for what you are doing the 4bbl will not make you any more competitive but will put a ton more heat into the motor. STAY 2bbl. If you must run a QJet then lockout the secondaries, the smaller primaries will make the car perform snappier. OK here is a major reliability secret, jet the carb to deliver a WOT AFR between 11.8:1 and 12.0:1, the richer that you run the motor (and it still performs well) the more internal combustion heat will be carried out of the motor by the raw unburned gasoline aka COOLING! You don't want a rich idle, so you can still start a flooded car. Your carb is critical, do not skimp here; I would say 1/4 of the guys will stall out because they got crappy carbs.
We made our own headers exiting through the hood; zoomies will work too, that way you can see the motor running. Also, much more exhaust heat was carried up out of the engine compartment and we ran the plug wires under the primary tubes and never again burned a wire. Burning spark plug wires is a common issue, prevent it. You can get a exhaust shop to weld you up some suitable headers if you take the car to them for cheap, you're looking for functional not pretty.
You want to construct the air cleaner assy so that it is drawing ducted fresh air from the passenger compartment - we would run aluminum flex duct from the air cleaner through the hole left in the firewall from the climate control box. The reason for this is that when the radiator is punctured you will have a ton of steam underhood and it will suffocate the motor, unless the carb is drawing in air from the passenger compartment or cowl area. ALSO, speaking of steam, silicone the distributor cap so you don't loose spark. We always swapped the HEI for a more reliable point distributor but YMMV.
Speaking of ignition - this is another area that puts 1/4 of the crowd against the logs. Run good high heat silicone wires (summit, $35) not 20+ year old wires! Run correct ignition timing and have a correct curve in the distributor, if your timing is too retarded or advanced you will generate LOTS of extra (unwanted) combustion chamber heat. ALSO, even moe important, you want the motor easy to start when hot, and ignition timing will be critical with this. Run the correct spark plugs, don't be one of those idiots who thinks switching to colder plugs makes the motor run cooler lol. Boots - we would actually silicone the plug boots to the distributor cap & plugs to assure that no steam (from ruptured radiator) would wet down the ignition, in hindsight this might have been overkill but just make sure the boots are VERY high quality so you do not get wet ignition when you finally loose the radiator.
STARTER is critical, we ran the starter cables into the passenger compartment to dual truck batteries wired in parallel; BUT, and this is the cheat! we had the battery cabling such that the driver could move a couple cables and quickly re-configure the batteries in series, that would give 24-volts to the starter and lemme tell you that will turn over any stubborn motor no matter how hot. Be careful not to cook the starter with 24-volts!
If you want snappy performance then work on final gearing (run 4.56s or steeper) and possibly different converter, maybe a 6-cylinder converter will stall higher for you??? Not sure but research the possibilities. Do not go wild with stall, because you don't want to boil the ATF but a little more stall will do wonders to deliver a good short-range "punch".
Weld the spider gears solid; we would spend HOURS doing this, you don't want it breaking! You DO want a solid spooled rear because when you loose one tire you'll still move.
Cooling - remove the clutch fan. Don't bother with electrical fan(s), you can't power them with battery alone and the ones you can get for cheap at the wrecking yard cannot move enough air to make a dent in the radiator's heat. Leave only the water pump pulley and crank pulley on the motor (remove ALL other accessories) and run a pair of tiny v-belts straight from the crank to the water pump; yeah it'll be a biatch getting it on there assign the job to the FNG in the group lol. Remove alternator, good charged batteries will last you all night. Definitely remove the power steering pump, because power steering is VIOLENTLY flammable, I'd rather be fighting a gasoline fire than a P/S fluid (ATF) fire. Remove ALL the fan shroud and ANYTHING even remotely close to the radiator, you don't want anything that can be "pushed" into the radiator and rupture it. We've had '69 New Yorkers where the front core support was moved back 6+ inches and the radiator still in tact!
Radiator hoses - use preferably flex/bendy hoses and wrap with at least 6-layers of duct tape for reinforcement from bursting; the issue is that as coolant goes past 230 the rubber will soften and want to give, wrapping with duct tape will keep it's integrity. At the local pick-n-pull, we would rob all the internal springs from all the lower radiator hoses, and pack like 3-4 springs inside both the upper and lower hoses to prevent them from collapse in the derby.
Radiator - we would take 3 per night (one for each heat); use bailing wire (coat hanger wire) to hold them to the core support so that as the front of the car changes shape it will not rip the tanks apart. Still, after 15-mins we would eventually take enough damage to loose the radiator. We've run engines another 30-40 mins *after* loosing the radiator no prob. A lot of guys will tell you to not run a pressurized system, ignore them and put on a 20-lb cap (if you can find one) just know when that SOB blows it's gonna have a head of steam to it lol. Coolant, you may be limited by rules, some rules say 'water only' for environmental reasons but lets face it if you can keep the coolant from boiling over at 240-260 then it's worth considering.
Tranny - we would bolt a plastic 5-gal bucket with lid inside the pass compartment, fill it with ice/brine and fashion-up a poor-mans fluid-2-fluid ATF cooler, always worked a treat the ATF lines were always cold to the touch even when the motor was blistering hot.
IMO, it is worth the effort to keep the carb cool as possible to prevent vapor-lock; it'll be a real concern. I made an alternating alum/gasket sandwich stack to shed/insulate the base of the carb from the intake, I guess a phoenolic (wood) spacer will work well too. I also splurged and bought from Summit 6' of trick silicone/fiberglass insulation tube to insulate the upper fuel line atop the motor and the ignition wiring.
Engine Oil - synthetic 10-40; BUT if you take a motor that is 20+ years old and suddenly change from dino oil to synthetic the detergent in todays oil might wash 1/2" of sludge down into the oil pan & plug the filter solid. Replace the valve cover gaskets if there is ANY chance they are beyond their years, you do not want a crapped-out cork gasket hemorraging oil down the side of the head because you might get black-flagged for fire. Take the car to the car wash and with hood off spray motor with at least 2 cans of cheap oven cleaner (wait 5-mins) then spray off, you do not want any oil on the outside of the motor to catch fire.
If rules allow, use a 3/8" x 2"-wide strap, drill a 3/8" hole in one end and bolt to the intake manifold or front of head, then heat/twist/bend the strap to the frame rail and weld solidly; almost every car entered in the derby will have busted motor mounts including yours. This is a critical concern IMO. If rules do not allow welding to the frame "at all" then use 3/8" chain to secure motor to frame. Likewise I would chain around the transmission to the rear crossmember.
I'm running outta gas, that should be enough to jog your mellon and further your project. I miss demo derby, I built 38 cars in 2.5 years in northern CA, and I miss it.
Mr. P.
Last edited by Mr. P.; 12-15-2008 at 09:37 PM.
