Pontiac 428 +boring or 455?

Lonnie J. Borntreger

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Oct 22, 1997, 3:00:00 AM10/22/97

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Howdy,

I have a '67 GTO hardtop with a '68 428 in it. The 428 needs to be
rebuilt (something about loss of power due to out-of-round cylinders --
go figure :). I'm looking for a result of good reliable low end and
mid-range power (no circle track, 8 sec., or 7000+ rpm engine needed
here).

Here's where your opinion is requested: given my starting point
(chassis, engine) and my target (low/mid power), would I be better off
overboring the 428 and using oversized pistons/rings (keeping the 428
crank/rods/etc.), or boring it out far enough to make it into a 455
block (I think it's +.060) and replacing crank/rods/pistons/rings with
455 parts. (The second option would be to just get a 455, but that's
near impossible without giving up your first-born, and I like my kids.
:)

I'm wondering what the impact of stroke length, etc. would be on the
response/power combination.

(Assume that all else intake/carb/etc. are the same for both setups)
Just for info (in case it helps) I have (and am keeping) a setup with a
Edelbrock dual-plane intake, Holley vac-sec 750 (3310) carb. I haven't
determined if I'll replace my Crane cam (288/292 adv. dur., 488/510 lift
- I think - I've had it a while), yet.

Of course, if anybody knows of a reason (or the possibility) to
re-sleeve it and keep it a 428 (uniqueness is valid :), let me know.

Looking forward to all your thoughts.

TTFN,
Lonnie Borntreger
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Oct 22, 1997, 3:00:00 AM10/22/97

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The 428 is a 4.12 bore x 4.00 stroke
The 455 is a 4.15 bore x 4.21 stroke
Bore your 428 .030, drop in a 455 crank, your rods will work with this
crank. You will need to know the cc's of your head to select
the appropriate compression ratio. If you have the 68 428 heads
you already have 10.75/1 compression. If you want to run
92 octane, find a set of 6x heads off of a 76-79 400. this will
get you about 9.10/1 compression.
The torque is greater with a cam of around 273 intake, 282 exhaust
and .406 lift. Remember these are not Chevy's. they dont need
a lot of valve lift.
I swapped a cam with the above specs for one with 308 intake,
320 exhaust and .469 lift. low end almost disappeared, but it revved out
easier.
also gained a pretty lopy idle, which is what I was after.

Good Luck
Mark

Lonnie J. Borntreger <lon...@netwave.net.spamthis> wrote in article
<344DA50E...@netwave.net.spamthis>...

Lonnie J. Borntreger

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Oct 22, 1997, 3:00:00 AM10/22/97

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The casting number on my heads is "62". They were just reworked not too
many miles ago.

My idle quality was quite lopey. I don't mind it since I think most of
my problems were due to lack of vacuum and compression from the leaking
cylinders.

Thanks for the ideas.

John W. Schulze wrote:
>
> Lonnie,
> The 428 is a good engine to have. Boring it over .30 would bring you
> to 433cu.in. What is the casting number on the heads? As far as the
> bottom end, keep what you have unless you have some extra money. How
> is your idle quality with that cam shaft? A little head work and some
> balancing, you will have a nice power plant. No sleeves for the 428!
> --
> Sincerely,
> J.W.Schulze
> HOLE IN THE SKY SOFTWARE SERVICES
> jsch...@mindspring.com

--

mands-v

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Oct 23, 1997, 3:00:00 AM10/23/97

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"Lonnie J. Borntreger" <lon...@netwave.net.spamthis>
wrote:

snip:

i saw the word rev's above: i used to have the 69 / 428
/10.75:1 what an amazing motor !!!!!!!

i think that engine in fresh condition would be enough
to keep anyone happy on the street !!!

*********************************************************
just be careful, the rods are factory weak and you
should have them: shot / fluxed / beams polished /
resized -- to get a dependable run out of them.
paramount !!!!!!!!
**********************************************************
good luck with the engine...i know mine gave me many
smiles !!! ( and NDE) near death experiences** LOL

regards,

mands-v

Pete Duncan

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Oct 23, 1997, 3:00:00 AM10/23/97

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I agree, the difference will likely not be missed...Think about it...
30 extra cubes at a really good state of tune, giving 1 hp per cubic inch,
results in 430+ hp vs 460 or so... 7.5 percent... you *might* feel this
difference if you built both and ran em back to back, but if you just
build up the 428, you will be very pleased I'd wager...

The answer would be different if you said your goal was all-out rotate-the-earth
power-unlimited budget...but you imply that the $400 saved is important...save
it...

Enjoy, pd