225 /6 at 250HP?
This is a very interesting discussion with lots of possibilities... and, with several different ways to go. but, since it's YOUR car, you make all the decisions; I will offer what I think might work for you. The fact that you are only looking for a modeate amount of power (250 HP?) will make this a lot cheaper than if you wanted 450.... and, I will try to enumerate some pertinent facts along the way.
First off, the turbocharged slant six has some unique personality quirks, not the least of which is the strange final drive ratio gearing it seems to like best. Two guys (both FABO members) have turbo slant sixes that make a little over 500 horsepower each, and extensive testing has shown that they both run quicker and faster in the quarter-mile, with 2.76:1 gears. My own car, another turbo slant six, proved to show the same results.
So, you won't need an overdrive. You'll already have one. And, that negates the necessity for two ratios, one for the hiway and one for the strip... which means, you can install a cheap, plentiful, 8.25" unit out of a Dart, Duster, or Aspen/Volare (to replace your 7.25" weak, one-legger and be done with it.) Forever.
The 8.25" rears are getting expensive... and are just not necessary for this car.
The Buick V-6 that powers the Grand National has virtually the same engine size as your 225, so, that factory-installed turbo is the perfect size and, you might be lucky enough to find one used, online, or in a local junkyard.
The two-barrel Super Six manifold can be used to mount a Holley 350 or 500 CFM carb, with blow-thru mods, saving the cost and hassle of EFI.
The Pishta turbo-mount/ exhaust setup (pictured) is a cheap, easy way to handle the header problem. He (Pishta) is a FABO memeber too, and has lots of good advice. Just ask...
A water-injection unit (Snowperformance.com makes a good one) will negate the necessity for an intercooler.
This should be a pump-gas motor.
A stock, electronic ignition distributor hooked to an MSD Blaster coil, with an MSD 6-AL module (usually available on eBay, used) will handle the ignition with probably no problems.
Your stock cam and valvetrain should work fine for this. It will still idle like a stock motor.
You can run a manual transmission OR a 904 automatic with this setup, but, the manual-transmission clutches seem to be problematic in trying to deal with the gobs of torque these boosted engines make. My advice would be to run an automatic because turbos seem to like them...
Iskenderiam (the cam guy) rents an O-Ring cutter so you can cut your own O-Ring receiver grooves in the block and it is FOOLPROOF... I know that because ~I~ did it... successfully. :)
At this point, I should tell you that the nicest thing you could do for yourself is, buy a wideband, data-logging oxygen sensor (Air-Fuel) meter. This is an absolutely CRITICAL part of this build and will save you time and money. You simply cannot do this build without one. That should be in all capital lettters. I just learned that, for the first time, somebody is selling these A/F meters with the capability of measuring the exhaust of vehicles running on leaded fuel... Lead would always kill the O2 sensor in there units, before. $91.00.... Ask me how I know...
The cylinder head needs bigger valves, but the ports are OK, untouched with 1.74"/1.5" valves... They are on eBay, too, I think.
A stock converter and stock tranny should work fine...
You WILL have to buy a wastegate and a blow-off valve, and I would recommend buying a boost controller from Racin' Jason Kramer in Utah. He has a website. About $50.00, but, worth it.
Keep your Air-Fuel ratio about 11.5:1 at full throttle under boost, and you limit your igniton timing to 18 degrees. You will have to run a vacuum diaphragm to get better gas mileage, but it quits creating spark advance when it comes under boost, because the vacuum goes away.
With those settings, you should be abot to avoid detonation, entirely, and 93 octane should work well in yhay motor.
Make your redline 5,000 rpm.
This, with 12 pounds of boost, should give you the 250 horsepower you are looking for, and maybe a ittle more.
Wallace calculatirs says that amount of power should generate quarter mile times of about 13.90 at 97+ mph, if you can get it hooked up. That's in a car with a total weight of 3,400 pounds, including driver.
It's not easy; tuning the carb for an 11.5:1 mixture under coost is the hardest part. The A/F mewter makes it a lot easier...
I forgot the fuel system...
Stock pump with a boost-referencing line running from a fitting the top of the pump. to the intake manifold. This will raise your fuel pressure at the carb to 5 or 6 pound more than whatever the boost is, guaranteeing a suficient supply of fuel under boost.
Below is a picture of the Pishta-designed J-pipe (you'll have to build it, yourself.) And, some picture of my junk.
This is a very interesting discussion with lots of possibilities... and, with several different ways to go. but, since it's YOUR car, you make all the decisions; I will offer what I think might work for you. The fact that you are only looking for a modeate amount of power (250 HP?) will make this a lot cheaper than if you wanted 450.... and, I will try to enumerate some pertinent facts along the way.
First off, the turbocharged slant six has some unique personality quirks, not the least of which is the strange final drive ratio gearing it seems to like best. Two guys (both FABO members) have turbo slant sixes that make a little over 500 horsepower each, and extensive testing has shown that they both run quicker and faster in the quarter-mile, with 2.76:1 gears. My own car, another turbo slant six, proved to show the same results.
So, you won't need an overdrive. You'll already have one. And, that negates the necessity for two ratios, one for the hiway and one for the strip... which means, you can install a cheap, plentiful, 8.25" unit out of a Dart, Duster, or Aspen/Volare (to replace your 7.25" weak, one-legger and be done with it.) Forever.
The 8.25" rears are getting expensive... and are just not necessary for this car.
The Buick V-6 that powers the Grand National has virtually the same engine size as your 225, so, that factory-installed turbo is the perfect size and, you might be lucky enough to find one used, online, or in a local junkyard.
The two-barrel Super Six manifold can be used to mount a Holley 350 or 500 CFM carb, with blow-thru mods, saving the cost and hassle of EFI.
The Pishta turbo-mount/ exhaust setup (pictured) is a cheap, easy way to handle the header problem. He (Pishta) is a FABO memeber too, and has lots of good advice. Just ask...
A water-injection unit (Snowperformance.com makes a good one) will negate the necessity for an intercooler.
This should be a pump-gas motor.
A stock, electronic ignition distributor hooked to an MSD Blaster coil, with an MSD 6-AL module (usually available on eBay, used) will handle the ignition with probably no problems.
Your stock cam and valvetrain should work fine for this. It will still idle like a stock motor.
You can run a manual transmission OR a 904 automatic with this setup, but, the manual-transmission clutches seem to be problematic in trying to deal with the gobs of torque these boosted engines make. My advice would be to run an automatic because turbos seem to like them...
Iskenderiam (the cam guy) rents an O-Ring cutter so you can cut your own O-Ring receiver grooves in the block and it is FOOLPROOF... I know that because ~I~ did it... successfully. :)
At this point, I should tell you that the nicest thing you could do for yourself is, buy a wideband, data-logging oxygen sensor (Air-Fuel) meter. This is an absolutely CRITICAL part of this build and will save you time and money. You simply cannot do this build without one. That should be in all capital lettters. I just learned that, for the first time, somebody is selling these A/F meters with the capability of measuring the exhaust of vehicles running on leaded fuel... Lead would always kill the O2 sensor in there units, before. $91.00.... Ask me how I know...
The cylinder head needs bigger valves, but the ports are OK, untouched with 1.74"/1.5" valves... They are on eBay, too, I think.
A stock converter and stock tranny should work fine...
You WILL have to buy a wastegate and a blow-off valve, and I would recommend buying a boost controller from Racin' Jason Kramer in Utah. He has a website. About $50.00, but, worth it.
Keep your Air-Fuel ratio about 11.5:1 at full throttle under boost, and you limit your igniton timing to 18 degrees. You will have to run a vacuum diaphragm to get better gas mileage, but it quits creating spark advance when it comes under boost, because the vacuum goes away.
With those settings, you should be abot to avoid detonation, entirely, and 93 octane should work well in yhay motor.
Make your redline 5,000 rpm.
This, with 12 pounds of boost, should give you the 250 horsepower you are looking for, and maybe a ittle more.
Wallace calculatirs says that amount of power should generate quarter mile times of about 13.90 at 97+ mph, if you can get it hooked up. That's in a car with a total weight of 3,400 pounds, including driver.
It's not easy; tuning the carb for an 11.5:1 mixture under coost is the hardest part. The A/F mewter makes it a lot easier...
I forgot the fuel system...
Stock pump with a boost-referencing line running from a fitting the top of the pump. to the intake manifold. This will raise your fuel pressure at the carb to 5 or 6 pound more than whatever the boost is, guaranteeing a suficient supply of fuel under boost.
Below is a picture of the Pishta-designed J-pipe (you'll have to build it, yourself.) And, some picture of my junk.
