Internal or external balanced flexplate - Team Camaro Tech
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post #1 of 13 (permalink) Old Oct 5th, 09, 08:57 PM Thread Starter
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Internal or external balanced flexplate

Ok so im getting rid of the old tired 305 in my camaro and installing a 400 sbc. my 305 was bolted up with a powerglide and the 400 was bolted up with a 4 speed muncie transmission. my question is will i need to buy a new flexplate for my engine if all im doing is just swapping engines. i talked to a couple guys and they told me that i will be ok by using everything that was with the old 305 such as the torque converter flexplate and starter. all im planning on doin is using the 400 with my powerglid but will the starter and the flexplate be usable with my 400? and how do i know if i need an internal or external balanced flexplate? any input is greatly appreciated. Thanks a million!
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post #2 of 13 (permalink) Old Oct 5th, 09, 09:18 PM
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Re: Internal or external balanced flexplate

A 400 uis an externally balanced motor, so you will need a "weighted" flexplate with the 400...

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post #3 of 13 (permalink) Old Oct 5th, 09, 10:32 PM Thread Starter
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Re: Internal or external balanced flexplate

ok so my other question is will i need to buy the 168 tooth flexplate or can i use a 153 tooth flexplate. i got both starters i just need to know which on i will need to use.
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post #4 of 13 (permalink) Old Oct 6th, 09, 04:33 AM
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Re: Internal or external balanced flexplate

I believe 400's only came with 168 tooth 14 inch flywheel.

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post #5 of 13 (permalink) Old Oct 6th, 09, 04:55 AM
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Re: Internal or external balanced flexplate

youll need a 168 tooth flexplate and a staggered bolt pattern starter.
(everything on the 305s lower end cannot be used (balancer-flexplate etc)


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post #6 of 13 (permalink) Old Oct 7th, 09, 07:07 AM
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Re: Internal or external balanced flexplate

I concur.400's use a special 168 tooth weighted flexplate or flywheel.The 305 stuff is no good to you on the 400.Good luck.
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post #7 of 13 (permalink) Old Oct 7th, 09, 09:29 AM
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Smile Re: Internal or external balanced flexplate

You will also need the 400's harmonic balancer. If you are using a stock one.

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post #8 of 13 (permalink) Old Oct 9th, 09, 05:01 PM Thread Starter
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Re: Internal or external balanced flexplate

Ok. it becuause someone told me that the flexplate from a 305 will work for it if i use the same starter. I thought that i didnt need a weighted flexplate because the flywheel that came off the engine wasn't weighted. im just swapping the engines so why would I need to change the balancer? i thought that the one that the engine came with would work? another question that i had was will the 168 tooth flexplate fit with my TH-350?
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post #9 of 13 (permalink) Old Oct 9th, 09, 05:51 PM
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Smile Re: Internal or external balanced flexplate

Well the 400 SBC is an externally balanced engine. Which requires an externally balanced flywheel and its mating Harmonic balancer. No other small block (that I am aware of) is externally balanced. If the 400 that you have was rebuilt as an internally balanced engine, then you could use the parts from the 305, otherwise No, you can't. If the 400 engine came with a Harmonic balancer, you should be able to use it, as long as it is for an externally balanced engine. Since it came from a 4 speed car you can not use the flywheel. You need an externally balanced flex plate. You can buy aftermarket flex plates that are 168-tooth or 153-tooth.

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post #10 of 13 (permalink) Old Oct 9th, 09, 09:50 PM
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Re: Internal or external balanced flexplate

talk to the person that built the motor (if you know who), and find out if they internally balanced this 400...if they did, it is out of the ordinary, but not "impossible"...

I woould guess, however, that whoever put the 400 in their car and used a non-externall balanced flywheel, did not realize the motor was externally balanced...

Keith
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Muncie M-20
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post #11 of 13 (permalink) Old Oct 9th, 09, 11:22 PM Thread Starter
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Re: Internal or external balanced flexplate

Ok then ill order the weighted flexplate. i now have a clearer picture and idea of what i can use on this engine.as i said before in my previous post im in high school and im planning in becoming a mechanic and problems like these are what i like because i can learn from them and become smarter on that certain thing. hopefully ill get my car running by tuesday because it takes until monday for my flexplate to arrive because its the weekend. ill keep everyone posted on how my engine swap goes. thanks a million to everyone who helped me out.
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post #12 of 13 (permalink) Old Oct 13th, 09, 01:08 AM
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Re: Internal or external balanced flexplate

Make sure you order a weighted flexplate for a 400 SB. The BB454 also used a weighted flexplate and it will bolt up to your SB, but the weight is different.

The 1 piece rear main seal SBC also used a weighted flexplate, but with a different bolt circle than the earlier 2 piecers.


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post #13 of 13 (permalink) Old Oct 13th, 09, 10:56 PM Thread Starter
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Re: Internal or external balanced flexplate

Ok i ordered the flexplate and bolted it up. My car finally runs ! it sounds amazing. I installed a dual exhaust I bought from a buddy for $25 and it sounds just like how i always wanted it to. I just want to thank everyone who helped me with my flexplate problem. Its amazing how such a simple weight can cause a car not to run properly. Ill try to take a video so u guys can hear my car rumble with the 400. Once again thanks a million!
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