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Discussion Starter #1
Ok, so I need this issue resolved unfortunately. I purchased what I thought was a 428 motor that had been stroked to 455. I have identified the block is indeed a 1970 428, now how can I tell if the engine has been stroked.


I do have a comp cams XE 262 in there, how would the car idle/perform with this cam in a 455 vs 428? This may be one way we can figure it out, right now the cam seems very mild with a very smooth idle. I am sure its pretty mild either way, but there should be a difference right?


Any help on this topic would be appreciated, and obviously easier methods are preferred.


Thanks again, and heres to hoping I didn't get ripped off. I am an honest guy and good money was paid to ensure I got a 455, I just hope I have it. Either way, both are great motors, but I hope its not an unnecessary trick, just so the builder could save some labor.
 

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i do not belevive there is anyway to tell if it is stroked while still being together. you would need to know rod length and crank stroke. also over bore but that is usally adds only 5cc total
 

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Well if there is no way to tell why do people get one over the other? Shouldn't there be some driving characteristics at certain RPMS with my cam that signify which motor it is?
 

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Well if there is no way to tell why do people get one over the other? Shouldn't there be some driving characteristics at certain RPMS with my cam that signify which motor it is?
you MIGHT try dyno testing ... the 455 should put out significantly more torque. Other than that, I don't know of any way to tell without either some very sophisticated test equipment or a teardown of some sorts.

OR

Perhaps you could pull one spark plug and hand crank the motor till that piston is TDC, then measure the travel to bottom and see how that compares to a stock 428 or 455 stroke. You could use a straw or something like it that is stiff but won't scratch anything.
 

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Teardown and measuring the crank pins, bore diameter, etc. will tell you the answer. If it were me, (and I've been at it a long time) I would leave it alone and drive it and enjoy it. Sounds like you have a good running engine. Cams will perform differently in different engines: a wild, lopey cam in a 350 or 400 will be much more mile in a 455. Stop worrying about it and drive!!! :)
 

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Discussion Starter #7
I know you are right, but I would like to know whether the motor I paid for is as advertised. Can anyone who has driven both in stock form tell me the difference in how they perform. At RPMS like 1000 how does a 428 pull vs a 455 (obviously the 455 should have more low end torque) How much low end does a stock 455 have? My engine makes nasty low end I can start it in 3rd gear from a stop, but I can hear the motor bog a bit.

Again I know we are working with perceptions and not facts, but anything that could help me is much appreciated.


What about sound?
 

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Pull the pan and look at the casting #s on the crank is the only way I know to be sure.
Goatman455, I know you're looking for an easy way to tell if it's been stroked, there isn't one. If you must know, I can relate I'm anal about this stuff myself, roll up your sleeves and do what Rukee recommends.

Teardown and measuring the crank pins, bore diameter, etc. will tell you the answer. If it were me, (and I've been at it a long time) I would leave it alone and drive it and enjoy it. Sounds like you have a good running engine. Cams will perform differently in different engines: a wild, lopey cam in a 350 or 400 will be much more mile in a 455. Stop worrying about it and drive!!! :)
It's a done deal, you already paid for it. All you're going to do is get pissed off and rifle wrenches around the shop if you find out it wasn't stroked. Run it, enjoy it and tell yourself it IS a 455. You'll feel much better...:)
 

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Goatman, you will NEVER BE ABLE TO TELL BY THE IDLE QUALITY BETWEEN THE TWO. They're just TOO CLOSE in displacement. You're picking flyspecks out of pepper here. It looks to me like you're going to have to pull the motor, pull the heads, and pull the crankshaft to verify if the crank has been worked or changed, and what your actual stroke is. Figure on about 20 hours of hard labor and about $300 in gaskets and materials. But you just gotta do it.....if you don't, you'll never sleep again!!!
 

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did you see if the block says 455? what is the casting number of the block? our little 389 makes 425hp. we can start in 4th gear. had too when detent plate in trans was stuck on the gear fork. it pulls harder than any 455 i ever had. they were all stock 455's though. i have had alot of 400 as well and this is the best running pontiac engine i ever had. it does have 670 heads on it, balanced and blueprinted, edelbrock intake and holley.
 

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If Pontiac is like Chevy, 427/454, bore is the same, 427 just has shorter stroke. Shorter stroke motors rev quicker and can go to higher RPMs. Depending on your application, light car, bigger gear, a short stroke motor will be faster. If you a pulling stumps with a truck or hauling heavy loads, then you want the big torque of a stroker motor. Cam, compression and head combination will dictate if you have a lot of torque. Big cams, high flow heads and big compression will not be 800 RPM torque motors, as they don't make power until 3,000 RPMs or so, that is why you run a high stall converter.
 

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Bore is not the same on a Pontiac. The Bore on a 428 is 4.12", and the stroke is 4", same as a 421's stroke. (The 421 had a 4.09" bore). The 455 has a 4.15 bore and a 4.21" stroke.....so it's the only Big-Journal Pontiac with more than a 4" stroke stock. You MIGHT be able to pull a sparkplug, stick a brass rod down the cyl with the piston at the bottom of its stroke, and very carefully turn the engine by hand and measure with a dial indicator guage the amount of travel of the rod from bottom of stroke to TDC (Top of stroke). I would use a piece of plastic or a brass rod or tube....something that won't get stuck in the engine or mar the cylinder wall.... You'll be looking for less than a quarter of an inch of difference between a 4 inch and a 4.21" inch stroke, so look sharp.
 

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Discussion Starter #16
Well the block is a 428, but it is supposed to be. I was told it was a 428 stroked to 455. I bought it from a professional, I double checked everything, but I haven't pulled the motor apart to see.

It feels strong, I dropped my drive shaft and shattered the yoke (that's a lot of torque!). It doesn't seem to like to rev very well and has a lot of torque off idle but of course the cam as I showed you is very stock (xe 262).
 

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I agree, Rukee. I have a '69 428 block in search of a crank....I pulled it out of my '65 in 1987 after I "upgraded" it to a Blue Journal crank!!! (Didn't like 7000 RPM on a Saturday morning long distance commute). 455 cranks are waaaay more common. Me, I'd rather have the 428 with the stock crank.
 

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Discussion Starter #19
The 428 crank is worth a bit more then a stock 455 crank, I bet the builder had no problem stroking it to a 455. ;)

Well this is certainly good news.


What happens if you just put the 455 crank in the 428? What about the bore? Can you just put the crank in but not bore it?
 

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Its possible to do, but your engine would run like complete crap. You have 2 options, either live with the engine (if it aint broke, dont fix it), or have someone tear it apart to check if its what the guy says it is.

I for one am kinda getting tired of this thread. I shall repeat in massive letters in red type what you can do.


THE ONLY WAY TO FIND OUT WHAT BORE YOU HAVE IS TO TEAR IT APART AND MEASURE IT.

Hope that helps! :cheers

(Disclaimer: Im not tryin to be an ass here, but we've said many times that that is what you've got to do.)

Oh, and if you need any help with anything else feel free to ask!
 
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