455 block and head number questions and transmission mount - Pontiac GTO Forum
User Tag List

 
LinkBack Thread Tools Display Modes
post #1 of 6 (permalink) Old 10-12-2012, 02:50 PM Thread Starter
 
Join Date: Oct 2012
Location: Texas
Posts: 554
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
455 block and head number questions and transmission mount

I absolutely understand that a th400 is far superior to any 2 speed transmission, and I've had several th400's over the years in Cadillacs, Chevy's, etc..., but remembered the old gearheads actually liked the powerglides for the torque? (maybe I was just dreaming). Having resurrected this Lemans slowly for the past straight year, I guess I am getting lazy, and was hoping to just slap the 455 right in, bolt the existing exhaust manifolds on to avoid flange swaps, and attach the torque converter to flywheel bolts to avoid the trans. mount and driveshaft thing. (already been there,done that-"we do it nice,'cause we do it twice"). What about the driveshaft yoke? Is there a common swap for this part? Also, this 455 was sold to us as a 1975 motor, however, the #'s on the distributor pad say do51, with a large 71 next to the dist. hole.(is this 4/5/71 ?). Near that on the right rear is # 485428. On the front right of the block are #355304 yc. I've tried to look these up, but have had limited success. Heads are 4x with # g203 (7/20/73 ?). Cylinders are 30 over with flat top pistons, with stock cam. What kind of hp roughly would this put out? Thanks very much. More questions to come...
gjones is offline  
Sponsored Links
Advertisement
 
post #2 of 6 (permalink) Old 10-15-2012, 09:16 AM
Former Moderator
 
68greengoat's Avatar
 
Join Date: Sep 2005
Location: Northern Wisconsin
Posts: 3,523
Mentioned: 0 Post(s)
Tagged: 1 Thread(s)
Quoted: 1 Post(s)
You're correct on the date codes. '71 motor and '73 heads. That motor originally came with #66 heads which is comparable to the 4x except the 66's had slightly bigger exhaust valves.

YC A-body 71 455 325 Turbo 400 L-75 1x4 485428 2 GTO
YC B-body 71 455 325 Turbo 400 L-75 1x4 485428 2
YC B-body 71 455 325 Turbo 400 L-75 1x4 485428 2



SOLD.....
462ci, 4spd
Performer Intake, Mild Cam
Pertronix Ignitor III
Accel Super Coil, Accel 8.8mm Wires
68greengoat is offline  
post #3 of 6 (permalink) Old 10-15-2012, 01:26 PM Thread Starter
 
Join Date: Oct 2012
Location: Texas
Posts: 554
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
That's good news for me! Thanks! So the 355304 yc means it was originally was installed in a GTO? What does L-75 1x4 stand for? Is this a HO engine? I've tried to look up the 355304 yc number through old threads-someone else had a similar problem, with very conflicting results. I've tried other sources, with dismal results. THANKS!!!
gjones is offline  
 
post #4 of 6 (permalink) Old 10-15-2012, 10:22 PM
Former Moderator
 
68greengoat's Avatar
 
Join Date: Sep 2005
Location: Northern Wisconsin
Posts: 3,523
Mentioned: 0 Post(s)
Tagged: 1 Thread(s)
Quoted: 1 Post(s)
Very good news. '75 hp ratings were in the toilet(and they didn't make a YC in '75..). A YC was installed in GTOs and B bodies(Grand Prixs etc......). 355304 is the unit number which would match the PHS if it was the original motor which it's not. So, it could be either. 1x4 is a single 4 barrel carb. L-75 is the RPO#(Regular Production option). I believe the L-75 stood for a 455, 4 barrel V8.

It is not an HO. They were WC, WL and YE blocks with casting #483677.



SOLD.....
462ci, 4spd
Performer Intake, Mild Cam
Pertronix Ignitor III
Accel Super Coil, Accel 8.8mm Wires
68greengoat is offline  
post #5 of 6 (permalink) Old 10-16-2012, 12:48 AM Thread Starter
 
Join Date: Oct 2012
Location: Texas
Posts: 554
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
excellent info. A '71 455 had a base hp of 325, I believe.(I hope). With 30 over flat top pistons in her, and most all other components stock and at specs, what kind of hp boost would that equate to? It's not like we're going to the drag strip with it every weekend, but want that punch out of it on demand. Only paid $900 for engine & th400. , and helped the guy pull it out of a '50 Merc. Runs great. In the process of stripping paint & priming the block & heads now, then sticking it in the 66 Lemans convertible. The old 326 is tired and in need of a complete rebuild.
gjones is offline  
post #6 of 6 (permalink) Old 10-16-2012, 08:46 AM
Super Moderator
 
BearGFR's Avatar
 
Join Date: Aug 2008
Location: Springtown, TX
Posts: 5,742
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 122 Post(s)
Garage
Quote:
Originally Posted by gjones View Post
With 30 over flat top pistons in her, and most all other components stock and at specs, what kind of hp boost would that equate to?
A +0.030 455 works out to 462 inches. Expect the HP boost to be in the single digits - nothing that you'd feel or would show on a time slip.

Bear

BearGFR
Springtown, TEXAS
BearGFR is offline  
Sponsored Links
Advertisement
 
Reply

  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Complete Engine Compartment Discussion

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Pontiac GTO Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
Block Casting Number Question jedward1 1964-1974 Tempest, LeMans & GTO Technical and Electrical Wiring 8 02-16-2012 01:05 PM
455 block casting number picture par4n1 1964-1974 Tempest, Lemans & GTO General Discussion 10 01-18-2012 09:11 PM
Head Casting Number Help dillon14 1964-1974 Tempest, Lemans & GTO General Discussion 12 04-07-2011 04:49 AM
Anyone know the part number for the A4 tranny mount? Robk46 2004-2006 GTO General Discussion 3 08-24-2010 04:47 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome