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post #1 of 10 (permalink) Old 01-31-2017, 11:53 PM Thread Starter
 
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Engine Build Expectations

Hey Guys, looking to build an engine for my 68 GTO vert.....I just received the year code block & crank....current motor is a (semi-built) 350 out of a LaMans.

I am leaning toward a Pro Touring type build for the car, but only drivetrain, suspension & wheels will be upgraded.

My question is....Is a streetable, sometime long distance 500 hp motor build possible with the 400 c.i. block without getting too crazy with add on mods...i.e. electric fuel pump, fuel injection, tall intake, etc

I'm sure to get there it would need to be stroked, new heads, etc....

Are my expectations for 500 hp too high or should I set the bar a tad lower?

Gear ratio I believe is 3.88.....so it doesn't jump out of the hole....and that's fine.....not looking to drag.

Any help, opinions or advice would be appreciated.
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post #2 of 10 (permalink) Old 02-01-2017, 08:44 AM
 
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I think you ahve a 2.88 rear, if it were 3.88 it would jump out oof the hole like a jack rabbit.

500 hp isn't hard to achieve. The easiest way is to use a stroker kit when rebuilding the engine to give you over 460 cubes. Cheaper than aluminum heads or ported iron heads and will give you that awesome Pontiac torque in a scary way. Remember, horsepower is torque x RPM so torque is very important in getting you there. Butler is probably your best source for a stroker kit and many other parts as is Ames Performance. Check them out.

http://butlerperformance.com/c-12348...495-cu-in.html

Ames Performance Engineering, Classic GTO Parts, Firebird Parts, and Full Size Pontiac restoration parts.

Luck!
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post #3 of 10 (permalink) Old 02-01-2017, 09:45 AM Thread Starter
 
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You are correct Sir.....Just checked PHS docs....3.36 gears.....but that may not be correct now.....In the 2 years I've had it I've found several things that weren't as advertised when I bought it.......but not complaining....got a good deal on her.

Thanks For The Input!
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post #4 of 10 (permalink) Old 02-01-2017, 12:55 PM
 
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a 4.21 or 4.25 stroke "stroker asm" used in a pump gas friendly build with a pair of stock flowing Dport heads isnt, in itself, going to break the 500hp mark. With stock flow original 455 HO or SD heads, its not going to happen with stock flow, either. All buying a near $2000 stroker asm does, is increase cubic inches by aprox 50 cubes. Add up the parts prices, + balancing job, & the stroker kits are truly a winner for the parts seller. A lot of guys recommend the 461 stroker route, but actual performance gained is not going to be measurably more than going with a .030 455, ESP one that's been upgraded with 6.8" steel rods & custom pistons. That can also be an option if one knows how to buy right & not fall into a trap of buying a stupidly priced complete pullout 455 engine just to come up with a buildable block & decent crank.

In either such build, where the needed power to make it above 500hp is in the heads, selected cam, carburetion, & exhaust. My experience is to make that level of power, a 461 or 462 is going to need heads with at least 260 cfm on the intake side, & the heads need velocity. Several years ago I supplied a forged rod, pro built 455 shortblock for a box stock flow 87cc Ehead "performer rpm" build. On the engine dyno with a tuned Holley 850, performer rpm, RARE 2.5" outlet manifolds, & 2.5" head pipes & turbo mufflers this alum headed 455 peaked at 434 hp & little over 500 ft lbs of torque. Unlike the touted figures from early articles (using Westech's "happy" engine dyno), the actual figures were not that impressive. Less than a year before, a low 9-1 compression 6X-8 headed 462 was initially tested as a baseline before headport work, & made 8 hp less on the same dyno with the same cam.

Desiring to take such a heavy car ('68-72 convert) into the low 12's, it's going to take many thoughtful actions. A set of of properly picked KRE Dports are a good selection & you'll knock some weight off the front of the '68. If you can afford it, stroke the 400 to 461, then its all about the right cyl head & cam package. Kaufmans or Butler are not that far from you, but I would ck with long time local Pontiac racers & quick street guys & see who they have been using locally for machinework & assembly. Also going to need to upgrade your fuel system, most likely your transmission, springs, shocks, tire selection, & I could type on for hours on what it takes to hold up @ the near 600 ft/lb torque level in a footbraked heavy GM A-body with various strengthened GM A-body posi rears, the stock gray iron 3.36 ratio Pontiac 8.2 is not worth throwing hard earned money at.

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post #5 of 10 (permalink) Old 02-01-2017, 06:55 PM
 
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Agree a lot with PH. 500HP for a street engine is probably going to be somewhat leaning towards a "race" engine and moving out of the street cruising engine.

To many people are more concerned about HP numbers when you would be better served to shoot for torque numbers. Assume 500HP is just some arbitrary number you selected. To get these numbers, the costs will be high and you can do it, but you are looking at aluminum heads, aluminum intake, roller cam, professional built/prepped Q-jet, better ignition, headers, etc.. And, as PH pointed out, expect to upgrade your entire driveline to match the extra torque and HP, so that will also become an added expense. My guess, if you have the 10-12k, or more, to invest, then go for it.

However, anyway you go, your parts must match. Get one wrong, and you will have a disappointing engine, or one in which you invested a large sum and don't get the full potential out of it. That said, you might want to nail down a better idea of what you want within a specific RPM range. Do you want a smooth bottom end to mid range, mid range to upper, or upper range RPM engine. Your cam is what determines where your power range will be. You have to give up one aspect of the engine to get the other. Think Ram Air engines. No true street manners at the bottom end, but mid to upper RPM's is where it came alive. That's why they needed the 3.90 & 4.33 gears and close ratio 4-speeds so that the RPM's were kept where the engine was designed for. You would not be cruising on the highway at 65 MPH with this combo.

Next are your head selections. CFM flow is important, because this can/will effect your engine's responsiveness. With small ports and higher velocity, you will have a great kick in the pants acceleration at lower & mid range RPM's, but HP will drop off due to the fact that they will not flow as well at upper RPM's. But this can be improved with porting & a good valve job. Buy a set of aluminum heads which flow more CFM's out of the box and you might experience that the bottom end RPM's are a little sluggish, but mid to upper RPM's are explosive. In all cases, the heads must be matched to the cam or either could be bad performers with the wrong cam. Again, you want to have an idea of where you want your power band to be, then match trans converter (if automatic), trans gearing, rear axle gears, and tire size to the engine RPM you want to get the most out of your engine.

Cubic inches rule, but not always. As an example, you could have a 400CI spinning 6500 RPM's with iron heads, or a 461CI running out of steam at 5500RPM's. The 400CI would be built for mid/upper RPM's while the 461CI would be built for lower/mid RPM's. The 461 would produce more torque and you might have traction problems keeping tires glued to the pavement. The 400CI might be a little slow on the bottom end, so you need a higher stall converter which means more slip/heat at lower speeds. It would really pull at mid/upper RPM's, but this means your engine has to run in mid/upper RPM's to run its best - and that means more wear at these upper RPM's. That said, my personal pick would be the 461 going for a realistic street engine that will hold its own, be driveable, have more than enough torque to fry tires, and cruise without breathing hard. 3.36 gears may actually be too much for the 461CI (which you could drop by going to taller tires) and you could opt for a set of 3.08's for a real highway cruiser and still have the torque to move right along. BUT, I love the high winding sound of any engine and a 6500RPM shifting 400CI is also appealing to me.

As you can see, not just a simple answer to your question because there are a lot of variables that go into selecting what you want your car/engine to do.
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post #6 of 10 (permalink) Old 02-01-2017, 10:12 PM
 
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My 461 is 550ft/lbs at the flywheel, I have a TH400 with 3.23 gears, I get about 8.26mpg (half city/half highway). I never go over 55mph tops on the freeway to save fuel, I just cruise in the slow lane, nothing to prove. I have to use premium.

You mentioned "sometimes long distance", just something to think about. Personally I wouldn't care if it got 6mpg if it made me happy. In November I drove 1,700 miles across part of the country to break my engine in, great fun. It's also my daily driver. I do about 800 miles a month. Have almost 5,000 on my new 461 now.

I have a very mild 461, cast iron heads, 750 carb, mechanical pump, I go old school.

http://www.TheFOAT.com/92GTA
1969 Pontiac Firebird w/BP 461ci stroker kit, 670 heads & XE274H cam. Primer black w/black interior.
1992 Pontiac Trans Am GTA w/SLP Performance Package. Dark Jade Grey Metallic, grey leather, T-Tops.
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post #7 of 10 (permalink) Old 02-02-2017, 10:48 AM Thread Starter
 
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Originally Posted by PontiacJim View Post
Agree a lot with PH. 500HP for a street engine is probably going to be somewhat leaning towards a "race" engine and moving out of the street cruising engine.

To many people are more concerned about HP numbers when you would be better served to shoot for torque numbers. Assume 500HP is just some arbitrary number you selected. To get these numbers, the costs will be high and you can do it, but you are looking at aluminum heads, aluminum intake, roller cam, professional built/prepped Q-jet, better ignition, headers, etc.. And, as PH pointed out, expect to upgrade your entire driveline to match the extra torque and HP, so that will also become an added expense. My guess, if you have the 10-12k, or more, to invest, then go for it.

However, anyway you go, your parts must match. Get one wrong, and you will have a disappointing engine, or one in which you invested a large sum and don't get the full potential out of it. That said, you might want to nail down a better idea of what you want within a specific RPM range. Do you want a smooth bottom end to mid range, mid range to upper, or upper range RPM engine. Your cam is what determines where your power range will be. You have to give up one aspect of the engine to get the other. Think Ram Air engines. No true street manners at the bottom end, but mid to upper RPM's is where it came alive. That's why they needed the 3.90 & 4.33 gears and close ratio 4-speeds so that the RPM's were kept where the engine was designed for. You would not be cruising on the highway at 65 MPH with this combo.

Next are your head selections. CFM flow is important, because this can/will effect your engine's responsiveness. With small ports and higher velocity, you will have a great kick in the pants acceleration at lower & mid range RPM's, but HP will drop off due to the fact that they will not flow as well at upper RPM's. But this can be improved with porting & a good valve job. Buy a set of aluminum heads which flow more CFM's out of the box and you might experience that the bottom end RPM's are a little sluggish, but mid to upper RPM's are explosive. In all cases, the heads must be matched to the cam or either could be bad performers with the wrong cam. Again, you want to have an idea of where you want your power band to be, then match trans converter (if automatic), trans gearing, rear axle gears, and tire size to the engine RPM you want to get the most out of your engine.

Cubic inches rule, but not always. As an example, you could have a 400CI spinning 6500 RPM's with iron heads, or a 461CI running out of steam at 5500RPM's. The 400CI would be built for mid/upper RPM's while the 461CI would be built for lower/mid RPM's. The 461 would produce more torque and you might have traction problems keeping tires glued to the pavement. The 400CI might be a little slow on the bottom end, so you need a higher stall converter which means more slip/heat at lower speeds. It would really pull at mid/upper RPM's, but this means your engine has to run in mid/upper RPM's to run its best - and that means more wear at these upper RPM's. That said, my personal pick would be the 461 going for a realistic street engine that will hold its own, be driveable, have more than enough torque to fry tires, and cruise without breathing hard. 3.36 gears may actually be too much for the 461CI (which you could drop by going to taller tires) and you could opt for a set of 3.08's for a real highway cruiser and still have the torque to move right along. BUT, I love the high winding sound of any engine and a 6500RPM shifting 400CI is also appealing to me.

As you can see, not just a simple answer to your question because there are a lot of variables that go into selecting what you want your car/engine to do.
I am tending to agree more & more as advice seems to be trending this way Jim.......In reflection the 500 hp number was more of a "Pride" thing.....I just want to let them boys with their Mustangs & Camaros know that old school can hang......Stupid thought I know......I lost sight of what Pontiac engines are famous for.....Torque.

I am now thinking of backing it down a bit to say maybe the 400 + range with emphasis on torque range.........I am a true believer in keeping things as simple as possible for the goal I set.

All the HP in the world doesn't matter if you can't stick it to the road........While I will be modifying the suspension......modifying to keep 500 hp on the ground may be a deal breaker or bank breaker.

I truly appreciate the wise advice of people that know waaaay more than me on this subject........and why I sought your advice......The more I read the more I understand......Thank You!
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post #8 of 10 (permalink) Old 02-02-2017, 10:49 AM Thread Starter
 
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Originally Posted by anguilla1980 View Post
My 461 is 550ft/lbs at the flywheel, I have a TH400 with 3.23 gears, I get about 8.26mpg (half city/half highway). I never go over 55mph tops on the freeway to save fuel, I just cruise in the slow lane, nothing to prove. I have to use premium.

You mentioned "sometimes long distance", just something to think about. Personally I wouldn't care if it got 6mpg if it made me happy. In November I drove 1,700 miles across part of the country to break my engine in, great fun. It's also my daily driver. I do about 800 miles a month. Have almost 5,000 on my new 461 now.

I have a very mild 461, cast iron heads, 750 carb, mechanical pump, I go old school.
I like this set up.......
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post #9 of 10 (permalink) Old 02-03-2017, 08:20 PM
 
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Shoot for a realistic 400-425 or so HP and 500-525 ft lbs of torque. Iron heads will save money over aluminum heads and you can use some of the money saved to get your heads worked on to flow some good numbers. Or simply get a good port match to a set of RA IV intake gaskets and 3 angle valve job to improve flow numbers.

The Butler 461/467 kit is a good deal to get a nice torque engine. With the forged rods/Pistons you should have no problem hitting 6000 RPM's but I would build the engine to work in the 2000-5500 RPM range so you can have some low end drivability.
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Shoot for a realistic 400-425 or so HP and 500-525 ft lbs of torque. Iron heads will save money over aluminum heads and you can use some of the money saved to get your heads worked on to flow some good numbers. Or simply get a good port match to a set of RA IV intake gaskets and 3 angle valve job to improve flow numbers.

The Butler 461/467 kit is a good deal to get a nice torque engine. With the forged rods/Pistons you should have no problem hitting 6000 RPM's but I would build the engine to work in the 2000-5500 RPM range so you can have some low end drivability.
I think this is a realistic build......Great advice Jim!
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