# Pontiac 455 stroker question



## chdu2686 (Jun 12, 2013)

Hi, i have a 1968 pontiac lemans GTO clone with a 70's pontiac 350 in it. The engine has a bad camshaft and leaks oil all over the place so if it has to be fixed i want to replace it with a badass and larger displacement engine. I want my final engine to be 455 cid. I can buy a pontiac 400 on craigslist for 100$ or reuse my 350. I've done some research on the 400 stroker to 455 and i understand i must get a 455 crank with 3 inch main journals ( i have looked at one from butler for about 300$). I was wondering since the main journal size listed in my service manual for both the 350 and the 400 is 3 inches if i can use the 455 crank with the 3 inch main journal in the 350. however i have seen no material online for stroking the 350 to 455. Is it possible for me to use my 350 block and save the 100$ or do i have to buy the 400 to get my goal of 455 cid? Thank you for your advice i very much appreciate it. I hope to start this project this upcoming weekend.


----------



## Rukee (Feb 8, 2007)

I deleted your other thread and moved this one to the right section of the forums.


----------



## BearGFR (Aug 25, 2008)

The problem with trying to stroke a 350 will be the bore size and finding pistons. The cylinder walls in a 350 don't have enough material in them to allow boring them out to standard 455 (4.150) size. Starting with a 400 block is the right way to go. One of the most popular builds is actually a 461. That's a 400 block, bored +0.035 (to 4.155) and running a 4.25" stroke crank (455 is 4.21). These engines are stronger than an original 455 due to the smaller main journals which leaves more metal in the block main webs. Butler sells 461 kits too, so do others.
I built my 461 with parts and guidance from Jim Lehart at Central Virginia Machine. He was willing to spend time talking with me and sharing lots of information even before I spent any money with him.

Central Virginia Machine Service - Home of the ***** Engine!

I recommend talking with him. --- also going with the "long rod" version of the stoker kit with 6.800" rods instead of the factory stock 6.625 length.

Bear


----------



## chdu2686 (Jun 12, 2013)

awesome thank you guys for the help, (moving the thread, im new to the site and i appreaciate that help and the great information for the stroker). I have a tight budget for this build, are the longer 6.800 absolutely necessary and if so would used rods work? id like to save some money since im seeing that the new longer rods are almost 500$. will the shorter rods result in a longer overall length of stroke or will this combination be too weak to last? If an extra 500 will be the difference between a long lasting and well performing engine i can make room for them. I also plan on using some of the external parts from the 350 to keep costs down since ive seen a lot of information suggesting that the externals are interchangeable between the 350-400-455, but i will upgrade some parts such as the fuel pump, carb, intake manifold. any other suggested upgrades to squeeze more power from this bad boy? Thanks again guys your input is very valuable and i appreciate the help and tips.


----------



## BearGFR (Aug 25, 2008)

Don't even think about building a stroker motor with anything other than good forged rods. The factory rods were always the weakest link even in stock engines.

Building a stroker motor is already going to mean buying a new crank and pistons anyway - so adding a good set of rods (all purchased as a stroker kit) is a minor consideration. (or should be)

The reason for the longer rod is that it improves the "rod length to stroke length" ratio in the engine and helps reduce the extreme stress the rods and piston pin bosses "see" as the assemblies change directions at each end of the piston stroke. It also changes slightly the point in the stroke where the rod is at 90 degrees to the crank throw, making it occur "earlier" in the cycle (when there is more cylinder pressure acting on the piston crown) which does nice things for torque production.

(The topic of "long rod' engines is one of those that tends to devolve into sort of a religious war with people taking passionate stances on both sides. I happen to believe it's advantageous, but I'm not going to "argue" about it)

Bear


----------



## Instg8ter (Sep 28, 2010)

plan on having a budget of around 5,000 dollars if you want to stroke it. What heads do you have on the 350 (center exhaust stamp).


----------



## chdu2686 (Jun 12, 2013)

I can't see the stamp on the 350, its still in the car. However, i did pick up the 400 last weekend. It has 6X heads with the 4 ID so i researched and found they were the smaller of the 6X heads. Im guessing these are better than the ones i have on the 350 but i know know until i can get a better look at its heads. I cant find details on it in my 68 service manual. Im assuming thats because the engine is from 79. Do you know some specs on it? It also has a GM3 cast on it.


----------



## BearGFR (Aug 25, 2008)

6X-4's are a very good factory-style head to use on a big inch (455+) Pontiac. Google "Pontiac Engine Codes" should give you a good list of reference sites to use to "decode" what you have. Some of them even have photos that show where to look for the codes.

Before you get too deep into it, do call Jim at CVMS.

Bear


----------



## chdu2686 (Jun 12, 2013)

I did more research on the codes: My block is code 500557 and it was located on the top of the block in the rear, YZ was on the front of the block passenger side under what im guessing is the production number (0145429). Its actually from a 1976 f-body (i was told it was from a 79 firebird). Code J295 was near the distributor, that means it was made 10/29/1975. 

I noticed that late model 400's have much less advertised horsepower than its predecessors, is this because of the gas crises, or environmental regulations requiring modification of the engine? i am hoping to produce much more horsepower than that (400+), is it possible with this late model block?


----------



## leeklm (Mar 11, 2012)

There are a variety of reasons why HP went down such as lower compression, smaller cam profiles, carb restrictions, intake/exhuast restrictions, etc. The piece of iron holding it all together (the block) is fundamentally the same on a 350 factory HP motor or a 185 hp motor.

However, the blocks that carry your serial # from about 75 on up are not considered good cores for rebuilding due to less material in various areas of the block that make it strucually a little weaker. This does not mean you cannot rebuild it though. If you are on a strict budget, you could re-ring the current pistons, new bearings, etc, and an improved cam. 

My 66 had a low compression 400 when I purchased it with a 185hp factory rating. I installed a decent qjet and it had headers. Combined with a 4 spd and 3.36 gears, the performance was reasonble for what it was. Granted, nothing like my new 455, but we are comparing a $4,000 motor to a $400 motor...

Speed costs money, how fast do you want to go?

On edit... I see you mention 400+ HP. You "should" plan on spending a minimum of $4K for a reliable 400hp motor. You could save money with stock pistons & rods, but reliability could be a factor.


----------



## BearGFR (Aug 25, 2008)

chdu2686 said:


> I noticed that late model 400's have much less advertised horsepower than its predecessors, is this because of the gas crises, or environmental regulations requiring modification of the engine? i am hoping to produce much more horsepower than that (400+), is it possible with this late model block?



Good job on running down the codes. Wasn't that fun?

The "557" block isn't a good choice for building a serious race engine (550-600 HP and up) because of the thinner/weaker main webs. However, for the type build you're anticipating it'll be just fine. It'll be more important to build it with good rods than it'll be to worry any about the block strength.

About the reason for the horsepower rating drop: "all of the above", plus a change in how HP was reported (change from "gross" to "SAE net"). Making power is all about how much air you can move through an engine in a given amount of time, and that's all determined by the combination of cylinder heads, cam profile, intake/exhaust system, etc. It has very little to do with the block.

Bear


----------

