Engine performance upgrade

marty koirtyohann

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I hate to go down this path.
Here goes.
Milling the heads is useless without milling the deck and a piston change. Now you are into a complete build. Any pistons you are getting off the shelf that don't cost $800-$1000 a set are going to put you right back in crap compression ratio. Someone mentioned milling the heads to 90cc hear is what that gets you if you also deck the block to 0.0 and use stock cast type pistons.


View attachment 558805
Here is what you really get from the average mid70s 440 or 400 View attachment 558806
Now you could mill the heads and replace the pistons with some KB step head pistons and you might get to 9+:1 compression, but that's a good chunk of change, a lot of work and probably net you 25-30 horsepower and a mile or maybe 2 pet gallon fuel mileage.
Gear changes in the 9.25 rear in your car are a PITA, and with modern traffic all rolling at 70-80 mph, 2.9 gears is as low as I would go without a overdrive transmission. Sucks being in a cool old car and getting passed by a old lady in a Toyota, also sucks humming along at 3000+ rpm at 75mph with those flowdrones you have on there.
My suggestion is just stick with basic hot rodding tips.
Put a good aluminum intake on there, block your heat crossovers. Fix or change your carburetor. The TQ is a great carburetor, but yours is a lean burn. Not lean when you bury the pedal in the carpet but normal driving it is lean, you opening the exhaust and ditching the cat has made this worse. Woodruff's carburetor (sponsor here) can set your TQ up to run spot on, or you can switch to another aftermarket carb and go down that road, still will require tuning because you do not have a 350 Chevy.
Distributor could use tweaking (they all need it even dead stock). There is a crap pile of info on YouTube and Google on what and how to do this. Basically you need the advance curve to come in early (like early in low 2k rpm) to light that lazy compression ratio and make some pressure early in power stroke. I forgot to mention you need to set the timing for total timing @3500 rpm. Needs to be 36° BTDC, although 38-40 is not out of the question for one of these 7.5:1 low compression slugs. Your torque converter is most likely a low stall unit and they don't help anything, also a PITA to change without a lift. If your trans starts going away it may be something to consider.
Hope this helps.
well it will help verses the 8-1 pistons & heads combo or u can go out & do s full rebuild &high lift cam . now a low compression motor is perfect for a turbo/supper charger too but u r talking lots more $$$$$$$$$ too these came from the old direction racing book (it was written by the same folks that brought u the Ramchargers cars from the 1960's( its what the the super stock racing series guys still use today

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70bigblockdodge

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well it will help verses the 8-1 pistons & heads combo or u can go out & do s full rebuild &high lift cam . now a low compression motor is perfect for a turbo/supper charger too but u r talking lots more $$$$$$$$$ too these came from the old direction racing book (it was written by the same folks that brought u the Ramchargers cars from the 1960's( its what the the super stock racing series guys still use today

View attachment 558810

View attachment 558811

View attachment 558812
Not really, I have a set of 516 castings that have 1.74 exhaust, and a fair amount of porting and enough milled off them to yield a 73cc chamber(very small by big block standards), these on a 73 std bore 400 only yielded a 8.43:1 C.R. with fel-pro gaskets, a drop to steel shim would have gained approximately .1 in C.R.. While that sounds like a good increase it only made it completely intolerant of 87 octane gas. The cam, the heads, and headers, along with decent exhaust make it pull extremely strong from 4000 to over 6000 the bottom and mid range (what you need to move a big car) is really lacking. I could improve it by moving to a smaller cam. Not happening because I'm lazy and have better plans than a cam swap.
My car runs low 14s with a meh converter and 3.23 rear. Using drag strip calculators it averages out around 280-290 horsepower, compare that to the 220-230 a 73 HP engine with 7.5 ish compression and crappy 72 up HP exhaust manifolds that point in compression along with the other hot rod tricks and parts equals approximately 50-60 horsepower or roughly a 24-26% gain total. From past experiences I have to give the exhaust, intake, carb, cam, and head work at least 15-18%. That leaves about 8-10% increase from gaining almost a point in compression. Milling .100+ of a set of heads ain't that cheap for less than 20 horsepower.
IMO milling is not the answer.
 
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marty koirtyohann

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Not really, I have a set of 516 castings that have 1.74 exhaust, and a fair amount of porting and enough milled off them to yield a 73cc chamber(very small by big block standards), these on a 73 std bore 400 only yielded a 8.43:1 C.R. with fel-pro gaskets, a drop to steel shim would have gained approximately .1 in C.R.. While that sounds like a good increase it only made it completely intolerant of 87 octane gas. The cam, the heads, and headers, along with decent exhaust make it pull extremely strong from 4000 to over 6000 the bottom and mid range (what you need to move a big car) is really lacking. I could improve it by moving to a smaller cam. Not happening because I'm lazy and have better plans than a cam swap.
My car runs low 14s with a meh converter and 3.23 rear. Using drag strip calculators it averages out around 280-290 horsepower, compare that to the 220-230 a 73 HP engine with 7.5 ish compression and crappy 72 up HP exhaust manifolds that point in compression along with the other hot rod tricks and parts equals approximately 50-60 horsepower or roughly a 24-26% gain total. From past experiences I have to give the exhaust, intake, carb, cam, and head work at least 15-18%. That leaves about 8-10% increase from gaining almost a point in compression. Milling .100+ of a set of heads ain't that cheap for less than 20 horsepower.
IMO milling is not the answer.
well i used tge same heads on a 73 400 in a polara but i used a 13.5 dc cam it hada 68 degree over lap it ran a 16.5 @ 115 in 2nd gear with 2.71 gear in thr rear , now some say thart no way a 400 would run thst hard i shifted @ 6000 rpm i ran 95+ lbs of oil pressure all i know it ran very well i toped it out @ thee chrysler proving ground(back n the early 1980's on their top end track @ 142 mph! & i wasnt @ my shif point yey i had to lift as it wouldnt steer (floating really bad). i dont know what the hp of the motor eas but i twisted 2 carrer tube out of 2 81/4 rear ends with possie /sure grip . after that i ran opennwth the sam grears . u should be making more hp that i was .
 

70bigblockdodge

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well i used tge same heads on a 73 400 in a polara but i used a 13.5 dc cam it hada 68 degree over lap it ran a 16.5 @ 115 in 2nd gear with 2.71 gear in thr rear , now some say thart no way a 400 would run thst hard i shifted @ 6000 rpm i ran 95+ lbs of oil pressure all i know it ran very well i toped it out @ thee chrysler proving ground(back n the early 1980's on their top end track @ 142 mph! & i wasnt @ my shif point yey i had to lift as it wouldnt steer (floating really bad). i dont know what the hp of the motor eas but i twisted 2 carrer tube out of 2 81/4 rear ends with possie /sure grip . after that i ran opennwth the sam grears . u should be making more hp that i was .
I should be making more, the 284/.484 cam kills it. The dynamic CR is probably crap. Cam was already bought and paid for so in it went.
My point was milling heads is IMO not worth the effort. OP will be farther ahead with carb correction and timing, also heat crossovers block off.
 

marty koirtyohann

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I should be making more, the 284/.484 cam kills it. The dynamic CR is probably crap. Cam was already bought and paid for so in it went.
My point was milling heads is IMO not worth the effort. OP will be farther ahead with carb correction and timing, also heat crossovers block off.
blocking off the heat cross over will make it very cold nature . i didnt do that as i was driving it yr round . what carb r i running . i had a non egr b/rb thermoquad , it flat flowed the gas , i thing a;ll other thermoquads r a egr carb it was a 1 yr only (72) in 73 they was all egr carbs i no longer have it . some guy bought it to put on a 1974 340 car . im afraid he will drownd the poor 340 . with my set up i would almost pull the frount tires on launch i had to drop the pipes (I had ball flanges & they dumped right under the drivers door i had high flow manifolds
 
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