"hey grumpy I built what I thought would be the ideal small block engine for my 1968 nova,
IT LOOKS A GREAT DEAL LIKE THIS PICTURE I FOUND POSTED ELSEWHERE
the idea was to build a torque monster that I could use as a daily driver, but still kick some ass on the street to street racing scene, its got a 4.11:1 rear gear a TH350 with a 2800 stall converter, and 27" tall tires, the engine is basically a 406 sbc with some dart 180cc port heads and this cam
http://store.summitracing.com/parts/drt-127221
the engines got 9.5:1 compression, a edelbrock 600 cfm carb, an edelbrock intake and headman headers, and 1.6:1 erson roller rockers
http://store.summitracing.com/parts/cmb ... dia/images
it runs decent up to about 5500rpm and has decent torque but its basically running out of breath above 6000rpm and gets about 10 mpg IF I DRIVE IT EVEN MODERATELY HARD ITS MILEAGE DROPS OFF TO ABOUT 7MPG.
any ideas on how to get better mileage without killing performance even further"?
YOUR HARDLY ALONE HERE IN WISHING YOU GOT BETTER MILEAGE WITH AN OLDER MUSCLE CAR, THERES LOTS OF OPTIONS BUT MOST ARE RATHER EXPENSIVE, (LIKE SWAPPING TO MULTI PORT ELECTRONIC FUEL INJECTION,, SO LETS LOOK AT SOMETHING YOU SHOULD BE ABLE TO DO IF YOU SHOP CAREFULLY AT A LOCAL SALVAGE YARD, AND THATS LOOKING INTO AN OVER DRIVE TRANSMISSION.
THE FIRST THING I SEE IS THAT THE ENGINES DESIGNED TO PRODUCE POWER IN THE 2600 RPM-5300 RPM POWER RANGE.
IF you want to get good mileage you need to operate the engine in the lower 1/3rd or its effective rpm range most of the time, and that will require an over drive transmission.
So your describing an engine thats not going to operate well much above 5500 rpm, due to small ports and a mild cam, on a fairly large displacement, as youve found thru experience and with that 4.11:1 rear gear your spinning well above 3600 rpm on any high way
the first thing ID think about is swapping to a 200R4 over drive transmission, that change alone would drop your cruise rpms by about 1000 rpm to about 2650 rpm, that alone should result in about a 25% increase in mileage you see. YOUR LUCKY IN THAT THE 200R4 OVER DRIVE TRANSMISSION IS NOT ALL THAT DIFFICULT TO SWAP FOR A TH350, obviously the engines state of tune would effect your results and Id like to see a compression check, your intake plenum vacuum and exhaust back pressure reading at 5000 rpm or so and pictures of your spark plugs would be helpful as would knowing your ignition advance curve, fuel pressure and anything else you can tell me
. the object being to increase efficiency and reduce the average operational rpm range to more effectively use the power band the engines designed to run in plus reduce the average rpms in use, remember as the average rpms are reduced youll be using less fuel and air mix , effectively increasing your mileage, for the distance traveled. just simple tuning issues like the wrong timing , the wrong carb jets, the wrong ignition advance curve or a restrictive exhaust or too much fuel pressure or a restrictive air filter ,not enough air in the tires , bad alignment, or a dozen other factors can each reduce your mileage so a tune-up and checking numerous other factors should also increase your mileage
related info
viewtopic.php?f=55&t=109
http://www.rowand.net/Shop/Tech/Automat ... onSwap.htm
http://www.maliburacing.com/transmission_swaps.html
http://www.ckperformance.com/resources/ ... TALOG.html
http://www.transmissionpartsusa.com/
viewtopic.php?f=71&t=741
IT LOOKS A GREAT DEAL LIKE THIS PICTURE I FOUND POSTED ELSEWHERE
the idea was to build a torque monster that I could use as a daily driver, but still kick some ass on the street to street racing scene, its got a 4.11:1 rear gear a TH350 with a 2800 stall converter, and 27" tall tires, the engine is basically a 406 sbc with some dart 180cc port heads and this cam
http://store.summitracing.com/parts/drt-127221
the engines got 9.5:1 compression, a edelbrock 600 cfm carb, an edelbrock intake and headman headers, and 1.6:1 erson roller rockers
http://store.summitracing.com/parts/cmb ... dia/images
it runs decent up to about 5500rpm and has decent torque but its basically running out of breath above 6000rpm and gets about 10 mpg IF I DRIVE IT EVEN MODERATELY HARD ITS MILEAGE DROPS OFF TO ABOUT 7MPG.
any ideas on how to get better mileage without killing performance even further"?
YOUR HARDLY ALONE HERE IN WISHING YOU GOT BETTER MILEAGE WITH AN OLDER MUSCLE CAR, THERES LOTS OF OPTIONS BUT MOST ARE RATHER EXPENSIVE, (LIKE SWAPPING TO MULTI PORT ELECTRONIC FUEL INJECTION,, SO LETS LOOK AT SOMETHING YOU SHOULD BE ABLE TO DO IF YOU SHOP CAREFULLY AT A LOCAL SALVAGE YARD, AND THATS LOOKING INTO AN OVER DRIVE TRANSMISSION.
THE FIRST THING I SEE IS THAT THE ENGINES DESIGNED TO PRODUCE POWER IN THE 2600 RPM-5300 RPM POWER RANGE.
IF you want to get good mileage you need to operate the engine in the lower 1/3rd or its effective rpm range most of the time, and that will require an over drive transmission.
So your describing an engine thats not going to operate well much above 5500 rpm, due to small ports and a mild cam, on a fairly large displacement, as youve found thru experience and with that 4.11:1 rear gear your spinning well above 3600 rpm on any high way
the first thing ID think about is swapping to a 200R4 over drive transmission, that change alone would drop your cruise rpms by about 1000 rpm to about 2650 rpm, that alone should result in about a 25% increase in mileage you see. YOUR LUCKY IN THAT THE 200R4 OVER DRIVE TRANSMISSION IS NOT ALL THAT DIFFICULT TO SWAP FOR A TH350, obviously the engines state of tune would effect your results and Id like to see a compression check, your intake plenum vacuum and exhaust back pressure reading at 5000 rpm or so and pictures of your spark plugs would be helpful as would knowing your ignition advance curve, fuel pressure and anything else you can tell me
. the object being to increase efficiency and reduce the average operational rpm range to more effectively use the power band the engines designed to run in plus reduce the average rpms in use, remember as the average rpms are reduced youll be using less fuel and air mix , effectively increasing your mileage, for the distance traveled. just simple tuning issues like the wrong timing , the wrong carb jets, the wrong ignition advance curve or a restrictive exhaust or too much fuel pressure or a restrictive air filter ,not enough air in the tires , bad alignment, or a dozen other factors can each reduce your mileage so a tune-up and checking numerous other factors should also increase your mileage
related info
viewtopic.php?f=55&t=109
http://www.rowand.net/Shop/Tech/Automat ... onSwap.htm
http://www.maliburacing.com/transmission_swaps.html
http://www.ckperformance.com/resources/ ... TALOG.html
http://www.transmissionpartsusa.com/
viewtopic.php?f=71&t=741