# Pontiac 400 Engine Recomendations



## GTO8686 (Jul 14, 2010)

Hello, 

I am wondering if anyone has some good suggestions for my Pontiac 400 Rebuild. I was given a block from 1975. I am rebuilding the entire motor and hope to be around 400HP. It will be attached to a 4speed manual. The car will be a street car, but I am wanting a very quick car. Does anyone have recommendations on good cams, cranks, carbs, intakes, heads, headers, etc....? I am willing to spend a little, but not thousands. 1-2K is my current budget. Let me know if you have any build ideas. 

Thanks.


----------



## tyler t (Aug 15, 2010)

doug thorly or hookers for headers and defanitly get the ram air 3 heads.. a 750 or 800 cfm carb edlebrock performer intake and a mild cam... that might be more than you wanna spend but it should get you some decent power


----------



## jetstang (Nov 5, 2008)

Buy Jim Hands book, "how to build a hi-performance Pontiac" for $20. I bought it, haven't read it yet, lol.. He is the master so I've heard. He is on PY years forum.


----------



## Rukee (Feb 8, 2007)

Stroker crank, bored .030" over with forged pistons, aluminum heads, Tri-Power with the 068 cam, HYPO RAM AIR III exhaust manifolds, MSD unit......400HP easy.

Substitute an Edelbrock intake and carb for the Tri-Power if out of price range.


----------



## dimitri (Feb 13, 2009)

jetstang said:


> Buy Jim Hands book, "how to build a hi-performance Pontiac" for $20. I bought it, haven't read it yet, lol.. He is the master so I've heard. He is on PY years forum.


Deffinately read this book before you make any plans or buy any parts. It's the Bible. 

Must have 0 deck highth, flat top pistons, Best Gasket rear main. Roller cam and lifters. Talk to Kaufmann at KRE before selecting a cam.


----------



## 66tempestGT (Nov 28, 2009)

you will want to learn a little more about pontiacs. 400 hp at 5800 rpms will get dusted by 500 ft-lb at 2800 rpm and 360hp. and will melt your tires.


----------



## BearGFR (Aug 25, 2008)

GTO8686, do I understand correctly that you only have the bare block at this point, no heads or rotating assembly?
I don't know where you're located, but I highly recommend that you contact Jim Lehart at Central Virginia Machine Services. He's on most of the Pontiac forums and usually goes by the name, "Mr. P-Body". He's also the guy who actually wrote the 'Building Your Short Block' chapter in Jim Hand's book. The first things he'll ask you are what you have, what you want to do with the car, and how much you want to spend. There's no one more qualified to help you design a combination that will be the best it can be and stay within all those limits.

I see folks are recommending stroker kits and other heads, but it's going to be very tough to do all that and stay within your $1-$2k budget, especially if all you have at this point is a bare block. 

66temptestgt's comment was dead on. 

There's an old saying, "Horsepower sells cars, torque wins races." That's especially true with Pontiacs because they're monster torque engines, and they make it all at lower RPM. That causes the horsepower numbers to be deceptively low because horsepower is actually a calculated number - it can't be directly measured. The formula for horsepower is (RPM times Torque) divided by 5252. So, if you have an engine that makes 500 lb.ft. of torque at 2000 rpm and another that makes 500 lb.fr. at 3000 rpm, the second one 'makes' (calculates to) more horsepower even though the actual amount of twisting force they produce is exactly the same. 

With your budget, I'd definitely go with mostly stock components including the rotating assembly. Find yourself a decent pair of factory cast iron heads that already have screw-in rocker studs and the larger valves - there are many out there to choose from. The later model 6x's have a larger combustion chamber so that will help you get the compression ratio down to where you need it to be for todays gas, and they also have the hardened exhaust valve seats - for the same reason. It's possible to use the earlier heads with the smaller chambers, but you'll want to either use dished pistons or have dishes cut into your existing pistons to get the compression down to where it needs to be. Choose a cam that will maximize torque around 2500-3000 rpm, since you've got the 4-speed. I'd go lower than that if it was an automatic car. The motor will have a smooth idle, make plenty of vacuum for power brakes, and will be happy on 93 octane as long as you can keep the static compression ratio down around 9.3:1 or even lower. Since it'll never even get close to 7000 rpm, and probably never even be 'north' of 5500 rpm, there's no need to waste money on a forged crank. Probably not even forged rods. Most crank failures that get blamed on weak cranks or rods are actually caused by detonation, not weak parts. Also, for the rpm range that this motor will see nothing can touch the factory iron intake and a well set up Qjet. (Get yourself a copy of "How to Build and Modify Rochester Quadrajet Carburetors" by Cliff Ruggles. You can find him on many of the Pontiac forums too, and he has a web site.) 
Pontacs aren't Chevy's, and it's a mistake to try to build them as if they were. With a motor like what we've been talking about and some extra investment in good suspension pieces to get the car to 'hook' so you can actually put that torque to use, you'll be embarrassing lots of folks who like to believe that horsepower is king.


Bear


----------



## DukeB-120th (Oct 19, 2009)

BearGFR said:


> So, if you have an engine that makes 500 lb.ft. of torque at 2000 rpm and another that makes 500 lb.fr. at 3000 rpm, the second one 'makes' (calculates to) more horsepower even though the actual amount of twisting force they produce is exactly the same.
> Bear


Informally and intuitively speaking, you got it right Bear. We all know what how well those torquey Goats eat Camaros for lunch. :cheers 

As a mechanical engineer though, the mathematics of motion being my specialty, I just gotta get on my soapboax:

Note that the second engine _does_ indeed make more power. It's not a hand-waving funny math trick. If both engines are making 500 lb-ft of torque but one has revved to 3000 rpm, it *will* be accelerating the car better than the other doing it at 2000 rpm. If they both make 500 ft-lb, then what that higher power number signifies is an ability to apply that 500 pounds of force over a foot's distance more quickly.

We know that "torquey" engines rule though, because the poncho is getting that torque right away in the low end before the Chev can do anything with its better power.:cool


----------



## BearGFR (Aug 25, 2008)

DukeB-120th said:


> As a mechanical engineer though, the mathematics of motion being my specialty, I just gotta get on my soapboax:
> 
> Note that the second engine _does_ indeed make more power. It's not a hand-waving funny math trick. If both engines are making 500 lb-ft of torque but one has revved to 3000 rpm, it *will* be accelerating the car better than the other doing it at 2000 rpm.


Of course you're right, Duke, the definition of power being the rate at which work is done (I minored in physics). I'm just trying to caution folks against sacrificing torque to chase a high horsepower number - especially if it's only a peak number we're talking about. Since RPM is part of the equation, the shape of that torque curve matters a great deal. 

If an engine is really "peaky", meaning that it makes a ton of torque/power at a specific RPM but on either side of that RPM the torque is significantly less, then that engine will definitely get spanked, and badly, by one that has a much lower peak horsepower number but has a higher average torque value over a broader rpm range. - in a race, that first engine will be at the RPM where it's making that big horsepower number only for a very short time. The rest of the time it will be at a disadvantage to the engine with higher average torque production over a broader RPM range.
Horsepower and torque measurements both are much better yardsticks to use when you use their average values taken over the whole rpm operating range. Peak numbers are good for bragging but won't get you to the finish line first by themselves, unless you can gear the car such that it stays at peak horsepower rpm "all the time" - sort of like the nitro guys do with those multi-stage weighted clutch packs.

Fun stuff...

Bear


----------



## Rukee (Feb 8, 2007)

I might disagree here, if you shift at the right points for each motor, the engine making peak power at the lower RPM should be faster as you will be up-shifting into the next gears quicker, making the torque at the lower RPM and not rev'ing as high as the other motor, should be faster as you go through the gears faster, you could be in 4th with the lower RPM range as the other one is shifting into 3rd waiting for the RPMs...IMO anyway. Would like to see some side by side comparisons on the track.


----------



## jetstang (Nov 5, 2008)

:agree
But torque is relevant to HP, so the higher the R's with Torque, the more horse power it will make? Semi's are all in by 2700 RPMs with 700 HP, and 1200 Ft Lbs of torque. So, the 3000 RPM car will make more HP than the 2000 RPM car. Big HP cars need high stall converters to get out of the hole because they make no torque down bottom. But, they make huge numbers on both up top, less torque than HP. Long rods and stroke make torque, short crank and rods spin faster and make HP.


----------



## BearGFR (Aug 25, 2008)

You've got it pretty close, Jetstang. One of the main variables is the cam shaft. Keep in mind that everything about an engine is in constantly changing motion. It's tempting to think about intake flow and exhaust flow as 'contants' at first blush but that's not what's going on. Every time a valve opens and closes, the air flow associated with it has to start and stop. Air/fuel mixture and exhaust gasses both have mass, therefore they have inertia, and therefore they neither start nor stop instantaneously. It takes time for that gas to get moving so it can either flow into a cylinder or out of it. As engine rpm increases, the length of time that those valves are open gets shorter and shorter, giving the gas less and less time to get moving. That's even true in an artifically aspirated engine. So, to optimize volumetric efficiency you have to get that cylinder as full of air/fuel mixture as you can get it. As rpm goes up, the only way to do that is to open the intake valve earlier in the cycle and keep it open longer so you can fill the cylinders, and open the exhaust valve earlier and hold it open longer so you can empty them. It's possible to optimize for more than 100% VE at a given camshaft's peak torque range by taking advantage of the intertia of the moving intake flow. Just like it doesn't want to start instantaneously, it doesn't want to stop instantaneously either so if you can get that flow velocity up you can actually 'cram' more into the cylinder before that valve shuts. On the exhaust side, getting the flow velocity up helps you do a better job of emptying the cylinders. A common mistake the people make is putting on headers that have "too big" primary tubes for the amount of exhaust flow their engine really needs. The bigger cross-sectional area means you've got more volume of gas to 'get moving' and if the engine's exhaust 'blow down' can't move that much volume then the engine has to work (pump) to push it out (instead of taking advantage of flow velocity) and you loose energy that could have otherwise gone into making torque out the crankshaft. It just so happens that peak torque production usually occurs at or very near peak volumetric efficiency (VE) because that's where you're doing the best job of filling and emptying the cylinders, so there's more potential energy in there to release through combustion. So why does it usually work out that peak horsepower and peak torque occur at different RPM? It's because rpm, being a relatively large number (3000 to 6000 or so in our case) has more effect on the horsepower formula (HP = (torque * rpm)/5252) than does torque (around 300 to around 500 or so). RPM is almost always going up faster than torque is coming down - up to a point - and that shows up in the calculation.

But... (you knew there'd be a 'but' right?) here's the down side. Unless we're talking about a modern engine that has some sort of "variable valve timing -VVT" technology, that camshaft profile is going to be fixed - the valves are going to open/close at the same points, regardless of RPM. If we time the valve events such that we move peak VE (and peak torque) higher in the rpm range so we get more horsepower, the down-side of that is the engine becomes less and less efficient at low rpm, so it makes less and less torque at low rpm. That "nasty" cam sound at idle that we all know and love? What's really going on there is the engine is stumbling all over itself just trying to keep running. We're holding the valves open so long that during the overlap period (when both valves are open and that we love so much at higher rpm to get above 100% VE) we're allowing the gas flow through the engine to actually stop and reverse, sucking exhaust back into the cylinders and polluting the intake charge. We associate that nasty idle with a powerful engine, but in reality when it's running like that it's anything but.

The real purpose of a 'loose' torque converter is to allow the engine to quickly spin up to an rpm where it's "on the cam" and running efficiently. That's also why launch technique for a manual trans involves spinning the engine up and sidestepping the clutch.

That's what I meant way back in my original post where I said Pontiacs aren't Chevys and it's a mistake to treat them as if they were. Small block Chevys, even with low rpm street cams, just don't make a whole lot of torque - period - so to get power out of them you have to move what torque they have way up in the rpm range. They respond to that pretty well, but to take advantage of it you then have to resort to shorter gears and loose converters to let the engines get "up there" at launch - and those are the kinds of changes that make a car pretty unpleasant for street driving. Pontiacs, on the other hand, make mountains of torque and they make it down low. For example, the 400 stroker (461) I've built for my 69 GTO "only" makes 492 peak horsepower at 5800 rpm, and it's all done by 6500 or sooner. However, it also makes 543 lb. ft. of torque at only 3100 rpm (!) and it stays above 500 lb.ft. all the way through 5100 rpm. This is a 9.46:1, 93 octane pump gas motor with a moderate solid roller cam, iron heads, factory iron intake, and a 455 SD Qjet. I'm running 3.50 rear gears and a 3200 stall converter, both of which are very streetable even for the occasional road trip, but if I can get it to hook (which will be a challenge with that much torque) it should also run mid 11 second quarter mile et's - maybe low 11's with slicks. If I put a 'bigger' cam in it to move VE higher in the rpm range, it will be mostly because I want to take some low end torque OUT of it even though I do have the crank/rods/rotating assembly that ought to be plenty safe to 7000. Small block Chevy guys should be turning green with envy right about now...

A car is more than just a motor. You have to consider how you're going to drive it, what you're going to do with it, and then choose/build the entire drive train so it's optimized for that. The reality is that there's no such thing as a 'one size fits all' car. A competitive and class legal NHRA Stocker or Super Stocker would be miserable to downright impossible to drive on the street for more than a couple of miles at a time, especially in traffic, and you can't build a street car that will run those kinds of e.t.'s without going *way* outside what would be class legal, and also hideously expensive.

It's the thinking and the planning what you want to do, then making it all come together that makes all this such fun stuff. arty:

Even more so when you do it with something other than a bow-tie....

Bear


----------



## MichaelG (Sep 19, 2010)

Hey Bear can you come over and rebuild my motor???

Fantastic thread.


----------



## jetstang (Nov 5, 2008)

BearGFR said:


> You've got it pretty close, Jetstang. One of the main variables is the cam shaft. Keep in mind that everything about an engine is in constantly changing motion. It's tempting to think about intake flow and exhaust flow as 'contants' at first blush but that's not what's going on. Every time a valve opens and closes, the air flow associated with it has to start and stop. Air/fuel mixture and exhaust gasses both have mass, therefore they have inertia, and therefore they neither start nor stop instantaneously. It takes time for that gas to get moving so it can either flow into a cylinder or out of it. As engine rpm increases, the length of time that those valves are open gets shorter and shorter, giving the gas less and less time to get moving. That's even true in an artifically aspirated engine. So, to optimize volumetric efficiency you have to get that cylinder as full of air/fuel mixture as you can get it. As rpm goes up, the only way to do that is to open the intake valve earlier in the cycle and keep it open longer so you can fill the cylinders, and open the exhaust valve earlier and hold it open longer so you can empty them. It's possible to optimize for more than 100% VE at a given camshaft's peak torque range by taking advantage of the intertia of the moving intake flow. Just like it doesn't want to start instantaneously, it doesn't want to stop instantaneously either so if you can get that flow velocity up you can actually 'cram' more into the cylinder before that valve shuts. On the exhaust side, getting the flow velocity up helps you do a better job of emptying the cylinders. A common mistake the people make is putting on headers that have "too big" primary tubes for the amount of exhaust flow their engine really needs. The bigger cross-sectional area means you've got more volume of gas to 'get moving' and if the engine's exhaust 'blow down' can't move that much volume then the engine has to work (pump) to push it out (instead of taking advantage of flow velocity) and you loose energy that could have otherwise gone into making torque out the crankshaft. It just so happens that peak torque production usually occurs at or very near peak volumetric efficiency (VE) because that's where you're doing the best job of filling and emptying the cylinders, so there's more potential energy in there to release through combustion. So why does it usually work out that peak horsepower and peak torque occur at different RPM? It's because rpm, being a relatively large number (3000 to 6000 or so in our case) has more effect on the horsepower formula (HP = (torque * rpm)/5252) than does torque (around 300 to around 500 or so). RPM is almost always going up faster than torque is coming down - up to a point - and that shows up in the calculation.
> 
> But... (you knew there'd be a 'but' right?) here's the down side. Unless we're talking about a modern engine that has some sort of "variable valve timing -VVT" technology, that camshaft profile is going to be fixed - the valves are going to open/close at the same points, regardless of RPM. If we time the valve events such that we move peak VE (and peak torque) higher in the rpm range so we get more horsepower, the down-side of that is the engine becomes less and less efficient at low rpm, so it makes less and less torque at low rpm. That "nasty" cam sound at idle that we all know and love? What's really going on there is the engine is stumbling all over itself just trying to keep running. We're holding the valves open so long that during the overlap period (when both valves are open and that we love so much at higher rpm to get above 100% VE) we're allowing the gas flow through the engine to actually stop and reverse, sucking exhaust back into the cylinders and polluting the intake charge. We associate that nasty idle with a powerful engine, but in reality when it's running like that it's anything but.
> 
> ...


That's what I said.. You just have to read between the lines.
OK, so why is a small base circle motor, 3.0 stroked 400 better than a 3.5 455? Long stroke, small bore beats out an even motor like the 455. But the 3.0 to 3.5, does the 3.0 oil better or what is the perk, why isn't bigger better and stronger?


----------



## DukeB-120th (Oct 19, 2009)

Well said Bear!!! You really know your stuff my friend! All the calculations are whizzing through my mind and you're speaking sweet music to the fluid mechanics and vehicle controls/dynamics they filled my head with at school.


----------



## BearGFR (Aug 25, 2008)

jetstang said:


> That's what I said.. You just have to read between the lines.
> OK, so why is a small base circle motor, 3.0 stroked 400 better than a 3.5 455? Long stroke, small bore beats out an even motor like the 455. But the 3.0 to 3.5, does the 3.0 oil better or what is the perk, why isn't bigger better and stronger?


Wasn't trying to argue with you at all, jetstang - you had it right. I just love talking about this stuff is all.

The issues with the 3.5" main (421/428/455) have to do with oiling (the larger diameter tries "harder" to strip the oil film away from the crank and sling it out through the clearance due to the higher surface speed and centripetal force), and also the bigger main bore leaves less material in the block main webs, so they're not as strong as a 3" main block. None of that matters much at all for street motors that spend their whole lives at 5500 and below, horsepower levels around 500 to 600. 455's make great street motors. Pontiac hit it out of the park with the 455 SD. It can become an issue for max-effort race motors that have to live at much higher rpm and power levels. More Pontiac cranks get killed by detonation than anything else. The factory cast cranks are plenty strong for street use. I'm running an Eagle CAST crank in my 461. My engine 'mentor', Jim Lehart at Central Virginia Machine  is who clued me into the better strength of the 3" main blocks and helped me plan out my 461. If you'd like to see the dyno sheet, it's here. (I remembered it wrong earlier, max power was at 5400, not 5800). The air that day was horrible - 95% humidity in the dyno room - I couldn't keep it from going pig rich above 5100 because of all the moisture in the air.

Michael G, you ought to contact him on your build. You won't be disappointed.

Jim's a great guy who knows TONS about building fast Pontiacs and sorting through all the considerable hype that's out there. He's even got guys overseas buying engines from him. He knows how to build Pontiac street engines that will make 500 to 600 horses all day long on pump gas and live forever doing it. Did you realize that the Pontiac, with it's tighter bore spacing, has a shorter crank than the BBC? That shorter length translates to more rigidity and less flex, which is why Pontiac cast cranks will live just fine thankyouverymuch under loads that will eat a cast BBC crank alive. 



Fun stuff...:cheers


Bear


----------



## 66tempestGT (Nov 28, 2009)

WOW! very technical stuff. my only point (that i didnt expand on) is that you can get more bang for your money by building an engine that does what they do best. you can build a cheap torque motor that will work well with the stock converter, rear gear and so on. and it will melt more tires than you can afford to replace. or you can get more exotic and spend a bunch of money looking for a dyno# then you have to buy the expensive components to compliment it or else it wont get out of its own way. i did learn a little though. :lol:


----------



## BearGFR (Aug 25, 2008)

66tempestGT said:


> WOW! very technical stuff. my only point (that i didnt expand on) is that you can get more bang for your money by building an engine that does what they do best. you can build a cheap torque motor that will work well with the stock converter, rear gear and so on. and it will melt more tires than you can afford to replace. or you can get more exotic and spend a bunch of money looking for a dyno# then you have to buy the expensive components to compliment it or else it wont get out of its own way.


Man is that ever the honest truth! I've learned on my GTO that once you start modifying things, you wind up also having to modify everything those things are connected to --- it cascades on you. Putting in that stroker crank caused me to have to use a different windage tray which needed different mounts which still needed some rework to clear the crank which forced a different lower dipstick tube which forced me to drill and tap a main cap to mount it. Using an SFI-rated balancer forced a different set of crank pulleys for the a/c which didn't line up with the original water pump which forced a new water pump which then didn't line up with the accessory drives which forced me to modify all the mounts to move the alternator and power steering pump forward 1/2". I had to modify my fuel tank to prevent the pickup from 'sucking air' under hard acceleration. I had to put in 1/2" fuel line to be able to keep up with the engine's fuel needs. I'm going to have to modify my muffler hangers at the rear to clear the aftermarket sway bar end links. I had to modify the mount for the brake differential pressure warning switch to get header clearance (and may still wind up moving it completely). Brakes.... I don't even want to talk about the brakes...

There's a reason it's called 'car building' and not 'car assembling'. 

Bear


----------

