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post #1 of 12 (permalink) Old 12-28-2013, 12:12 PM Thread Starter
 
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After sending emails out to alot of engine builders i seen referanced on this site, got to talk to a few on the phone, I decided to build my 428 with a stroker kit to a 489. We have to local shops, both come highly recommended. And both told me that with the Torque and HP that a 489 will put out that i run a risk of wiping out my M20. Three questions, 1st is this the case? can the muncie not handle it? 2nd Is it a wise choice to build up a 428 or should i just buy a new block and build from there? and lastly what are the draw backs to this engine. If you need specifics of the build i have most of the information just dont know what you need to answer the questions.
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post #2 of 12 (permalink) Old 12-28-2013, 12:21 PM
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The M20 will not handle your 489 unless you drive it very gently. They are marginal with a 389-400 if abused. Strong for the day, but not up handling 500+ ft pounds of torque. The weak point of a 428 (or 421 or 455) is the big crank journal size. The block is weaker than a 400 size block. Also, due to physics, the bearing size being what it is causes oiling issues at higher rpm. These engines do not like to be ran at over 3000 rpm for extended periods of time due to this. Used as planned, they are a rugged, torquey, low rpm powerhouse. I used to run a 428 in my '65. I'm happier with a 389. 428's and 455's are built up into great performing engines all the time. If you already have it and want to use it, go for it. You will need to upgrade the trans and the rear end of the car, too, to handle the power. Personally, I like a 389-400 based stroker engine more, though, due to it's better strength and tolerance for rpm due to having a better bearing size.
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post #3 of 12 (permalink) Old 12-28-2013, 01:46 PM Thread Starter
 
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I already changed the rear end, i have a 12 bolt welded tubes, 33 spline axles, c-clip eliminator, eaton 3.55 tru trac. Hopefully thats good enough there. So if the M20 wont handle it, whats a good alternative to it?
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post #4 of 12 (permalink) Old 12-28-2013, 04:13 PM
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At minimum, an M-22. After that, if you still want to go manual, it's aftermarket stuff, like Jerico, Keisler, etc. Big $$$$$. For automatic, a built TH400 will easily handle the power increase. Depends on how much of a race car you are making it.
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post #5 of 12 (permalink) Old 12-30-2013, 01:42 PM
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I already changed the rear end, i have a 12 bolt welded tubes, 33 spline axles, c-clip eliminator, eaton 3.55 tru trac. Hopefully thats good enough there. So if the M20 wont handle it, whats a good alternative to it?
Depending on how you plan to drive the car and how tall you're tires are, that's a lot of gear. At 70 mph you're going to be in the neighborhood of 3300 rpm (refer to GeeTee's previous comments about large journal engines not "enjoying" extended operation above 3000 rpm). Getting to 489 CID starting with a 428 means you're probably running with a +0.040 over bore and a 4.500" stroke - am I close? That's a lot of stroke - 0.029 more than a stock 455 (a full 1/2 inch more than a stock 428) in an engine that already doesn't "like" to live in the RPM stratosphere.

Also, you don't NEED that much gear. This ain't no chevy - your main problem with this engine is going to be having so much low end torque that it's going to be very difficult if not impossible to "hook" it, especially with a manual transmission. With as much torque as you're going to have on tap with this monster (please tell us more about your cam, heads, fuel system, etc.) I guar-ron-tee you're going to find every weak link in that drive train and quick. Make sure you've got control arm mount braces and good ones, a strong drive shaft, drive shaft loop, 1350 U-joints, and a transmission that's up to the task (that M-20 doesn't stand a chance).

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post #6 of 12 (permalink) Old 12-30-2013, 08:05 PM Thread Starter
 
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87cc rpm performer heads will be put on, Cam is going to be a custom grind, i dont have the numbers for that. I am pretty sure he said we would be using a cast eagle crack with a 4.25 stroke but i could have been mistaken. I had him go over a rebuild and then an up grade. And i havent pulled the triger on this yet because well, i do have my reservations and i want to make the best choice possible. I have a holly blue electric fuel pump. New drive shaft with billet aluminum yokes. And Bear you referred to my problem with this. I am concerned with taking a car that doesnt like RPM's and building to run high RPM's and yes at 75 i am turning 3500. At the moment i have 24" firestones indy 500s 15x10. I am looking at putting 26" I currently use the car as a daily driver although it doesnt like it. It helps me learning how to work on it since it breaks down once a week on adverage. My application for the car is 95% street, just basically trips that are 10 miles or less thats what i use it for now. But i would like to start to take it to the strip more and i am thinking of using it more for a strip / weekend warrior type car.
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post #7 of 12 (permalink) Old 12-31-2013, 09:37 AM
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Sounds like you need to put a 5 speed with OD in it.

Honestly though, I ran an M-20 behind my BLOWN BIG BLOCK CHEVY and put down over 750 Rear Wheel HP on a chassis dyno through this same transmission. How? By not powershifting, and no hard launches on sticky tires. Was I lucky? Probably, and I knew that any minute it could break but I didn't care because I had a couple of spares because M-20's can be had cheap.

OP, maybe consider finding a good 400 small journal block to build your next engine and keep the 428 intact for a spare.
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post #8 of 12 (permalink) Old 12-31-2013, 09:41 AM
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This ain't no chevy
Bear


True, but you could put a Chevy in it...........
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post #9 of 12 (permalink) Old 12-31-2013, 02:08 PM
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maktope, what Alky said. The way you are using the car, and the way you are planning to use the car, a 5 speed conversion will pay off huge dividends in performance and fuel mileage. That is the next logical step that will net the most bang for your buck.
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post #10 of 12 (permalink) Old 12-31-2013, 05:28 PM Thread Starter
 
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And that is why i turn to you guys. Ive fixed a few things that led to other problems. With this i am looking at spending a good chunk of money and want to do it right, and eliminate the chain reaction of problems i've been having. Even with rebuilding and upgrading the motor not liking over 3k scares me alot. I gotta really think this one out. Upgrading transmission i am ok with so we will see. I got untill the 3rd to make up my mind. Thanks for the info guys. And if you can think of anything i should ask the shop who will be doing the work please let me know. More information the better.
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Complete Engine Compartment Discussion

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