455 Engine Math
 

Hello,

New to the Pontiac world; was a BBC guy before the LS came out. Picked up a 76 Firebird with a 400 that I am restoring. The previous owner had the engine rebuilt in 98 and then put the car into storage; but it turns out there is more to the story than that. Long story short, I have the opportunity to pickup a 455 block out of a 73 (I think). Also found a few early 70s 400 blocks local. I need to make a decision on the block asap. Not sure what I would do with it, but I am intrigued by Ohio Cranks $895 4.500 stroker crank. I think it may use BBC tall deck rods, no idea what piston. Anybody else running this setup?

if your gonna build it, with a stroker kit especially the 400 block is best...but id take a look at the 73 455 and make sure its nothing special...especially if the price is right....stockish rebuild...id say go with the 455


edit...when i said the 400....i meant the early ones

The 76 400 is not a good choice for building a stroker with since that block has reduced thickness main webs.
Go with the 455 especially since it has the motor mount holes where you need them to not have to possibly use frame adapters.

Stock heads on stroker motors of the cid size your looking at will HP peak at 5200 rpm so very ported iron heads or aftermarket heads will be a need also possibly.

What is your goal?How much HP do you actually want?Is it going to stay a street car or intend to race it?If I was starting to build a good street engine I would start with a good 400 block.3in main stroker cranks are avail from many suppliers.Usually 455 blocks go for a premium.Tom

i thought the 4.5 cranks weren't a great idea for street usage.

A stroker 400 /= a 455. While the cubic inches become nominally the same, the differences in bore size is enough that the two engines do make power a little differently.

A stroked 400 using the standard 4.25" stroke ends up being pretty under square with a nominal +0.030 overbore. On the other hand a 455 if using it's factory 4.21" stroke, starts to move towards square as the engine has over bore's done. A +0.060 bore 455 with the factory stroke becomes square. As a result the 455 may tend to make a bit more power, later in the rpm band vs a stroked 400.

The other thing to keep in mind about the differences are the main sizes. The 400 block will have a 3" main while the 455 carries a 3.25" main. The larger main in the 455 does carry load better than the smaller 3" main 400 blocks, but you have to contend with higher bearing speeds and subsequent oil heating and pressure requirements, as a result.

As mentioned already, you want to stay away from 400 blocks with the 577 end casting numbers.

My +0.040 455 makes peak torque at 4700 rpm and peak HP at 5800 rpm with a 240/248 on 112 cam. You can see it wants to make power a bit later than a typical 460+ inch Pontiac. It still makes over 500 ft lbs well below 3000 rpm though.

If you are just looking for a 500 HP street engine, 455 all day long. No crank to buy. Basic stuff will get you 500 HP with little effort. Aluminum heads would be the easy way to go. You can put a little money into iron heads and get there too but will need more cam.
No reason to stick a 4.5 crank in any stock block for a street engine. Asking for trouble. I know, people do it, just not me.
A 500-550 HP well built Pontiac engine will outlast a Chevy. They get it done at lower RPM is the big reason for that.
Welcome to the Pontiac world.

Regarding the 3” versus 3.25” main bearing speed, on a street engine and in many non-endurance race engines it’s pretty much a non-issue.

https://forums.maxperformanceinc.com...7&postcount=12

Smokey Yunick did turn the mains down to 3” from 3.25” to make the 421 SD engines live for NASCAR events. However for street engines it’s not worth worrying about.

There are guys here with 455 engines running deep into the 10s with 600 horsepower street cars driven to the track. I knew a fellow racer running a 455 with 1970 614 RAIV heads in a roadster running in the 8s, shifting it at 7500 and the 3.25” mains weren’t holding him back.

As far as 4.5” strokes are concerned there’s an issue with side loading the piston skirts and the inherently short cylinders in a Pontiac block. A 4.21” or 4.25” crank is a better choice from the standpoint of longevity.

This is true. I had thought to include this, but edited it out.

The only time I'd really be looking at this as a possible issue is if I was doin stuff like road racing or mile racing where significant time spent at high RPM's would occur.

Let me share a little more detail with you. The 76 block I have, I found out is a 77 block so its no longer a matching numbers car. A tab on the block is broken, and its cracked. The heads were installed dry and the bolts were rusty. A quick conversation with the previous owner leads me to believe it was assembled without measurement. Granted, I'm sloppy with my measurements on LS's but they are very forgiving. So, no plans to put any money into the "77" block. A guy locally has three 400 blocks 70-72, so that could be a good base. A guy not locally has a 455 block.

I have a set of Speedmaster 72cc aluminum heads.

My goal is to turn gasoline into noise and smoke. I'm not sure how much horsepower I need. I've got a 750whp CTS-V so it's never going to be fast, just need it to be fun.

I don't know the answer to this, that's why I asked. I would guess the piston sideloading and rotation at the bottom of the block probably wears the motor a little quicker, but its not a daily driver I am going to put 100K miles on so I don't think it matters all that much.

I guess nobody does though because nobody has chimed in with one. I may call Ohio Crank and see who they sell those to and what the intended purpose is. A standard 4.25 kit, or even a stock rotating assembly if i snag the 455 will probably be fine but the block is empty, so... why not a 4.5 ?

do a forum search on the 4.5 cranks and terms like scuffing, side loading, ring location, rod length, etc.

It isn’t that the 4.5” crank doesn’t work, there are even a few Pontiac’s with 4.75” cranks running around on the street. Overall the 4.5” and larger cranks work a lot better in aftermarket blocks with big 4.31” plus bores. More than 4.25” or 4.375” stroke the stock bore is getting out of square enough power gains are harder to find.

I have both 455s and 400 based strokers. We use to rev a 4.25” stroker in a 3.25” main combo (455 block) to 6700 at the end of the straight in a circle track race car. Tracks start out slick, the engine would start out around 6000 RPM then get higher as the night went on. The A feature was 25 laps on a 1/3 mile track, if the car had to go thru the B feature and the heats it was about 40 laps. Pretty much the same as what B-man said…As long as the engine was set up with proper oil clearances, we could never tell any difference between the 3” and 3.25” mains. A stock rod 455 is a pretty long rod compared to a 454.

I'm going to see about grabbing that 455 block. I really don't see any downsides to it. The mains are of zero concern to me, and the displacement is already there if I decide to refurb some stock parts.

After the block is in my possession I can look around for an affordable rotating assembly. I will drive it very fast, I will burn the tires, but it will never see a prepped surface or sticky tires, there appears to be (at first glance) some affordable options.

My previous car a few years back had a 454 bbc that was rebuilt with stock bottom, ported iron heads, and a cam that was probably a little too big. I mated it to a 4L60-E (yes E), and I used to turn it to 6500 from 1-2 regularly, to make up for the gap in gears; I never had an issue. Maybe it would of in the future. I really hope its new owner has nothing but issues with it (it was stolen).

Feel free to keep posting opinions, this has been an interesting read.

Thanks!

Smokey talked about this in his book: Best Damn Garage in Town.
He went to the foundry and bribed some workers into making 3" main 421 blocks with a case of whiskey. One of those blocks would be rare......

if your not racing it, the 455 wheel make more power than any street tire can hold. i wouldnt even waste the money on a forged crank....a cheap factory crank with good rods and pistons is all thats needed....even if you were gonna put a sticky tire on it at the track it would be plenty