Buick GSX Engine Rebuild Alan Haime (WA Buicks)
This article is for the serious Buick performance person who wants’ to get the most out of
his engine, not just the occasional burst but reliable tub-thumping enjoyment over and
over again on the road or the race track. We all know the temptation to push the old girl
along now and then just to see what it can do, with the result that there are usually oil
leaks, smoke, rattles and other undesirable outcomes that make us wish we hadn’t tried it.
If you want reliable high engine performance you must pay attention to every conceivable
detail at every step of the rebuild – the more performance that you aim for requires an
exponential rise in attention to detail. If your aim is to restore your Buick engine to factory
performance level, this article will provide some useful points for you to consider. If you
require more performance this article covers some fundamentals for increasing torque and
horsepower yet still maintaining reliable performance.
I base my article on the Buick 455 cubic inch engine. It is not well known in Australia that
the 455 is a classic muscle engine in the USA. In its day it ate more than its fair share of
427 Hemis on the track and this soon cemented the engine’s place in the annals of
motoring history as the “Hemi-Killer”. In 1970 GM finally lifted its corporate ban of engines
larger than 400 cubic inches in the intermediate A-Body cars and Buick responded by
fitting an all new 455 cubic inch engine into its restyled GS. The 455 boasted more
displacement, larger diameter valves, and a more aggressive camshaft than the 400 it
replaced. It was mated to a cold air induction through functional hood scoops. The 455
was factory rated at 350bhp, with a stump-pulling 510 ft-lbs of torque. This was the
highest torque rating of any production engine at the time, aside from Cadillac’s 472 and
500 cube V8s. No other engine achieved that level of torque at a lower rpm (2800). To
take things up a notch, Buick introduced the Stage 1 package which featured a more
potent cam, bigger valves, and a re-worked carburetor (Buick claimed this engine
produced 360hp but most people in the know believe this to be closer to 400hp).
My interest in aiming for a higher-than-factory performance 455 engine was kindled after
attending the BCA Buick Centennial in Flint in 2003. There were a number of immaculate
GS455s and GSXs on display with high performance engines. The owners recommended
TA Performance as a reliable source of specialised Buick aftermarket equipment and
parts for 455 engines. Lois and I were travelling down Route 66 and happened to call into
TA Performance on the outskirts of Phoenix Arizona and when I saw the range and quality
of their stock, I was hooked. On returning to Perth I obtained a spare 455 engine and
transmission, ordered pallets of goodies from TA Performance and began the rebuild.
I had to overcome a few problems with the engine, as will be discussed later in these
articles. I eventually sorted these out and resolved that I really needed a nice looking
muscle car to do the engine justice. Lois and I were attending the BCA 2007 National in
Seattle and decided that we would take time to search for a 70-73 GS with the right body
and finish. After arriving at Los Angeles we drove to Las Vegas on our way to Seattle and
lo-and-behold there sitting in the Imperial Palace Auto Classic Museum on the Strip was a
72 GSX clone with “buy me” written all over it – how could I refuse. The next day the car
was mine and on it’s way to Fremantle. Lois and I were able to enjoy the rest of our road
cruise to Seattle without having to look any further for a car. After arrival in Perth the
engine was fitted and modifications were carried out on the new GSX and in March 2009
she did an 11.49 second @ 118 mph quarter mile at the Perth Quit Motorplex. It runs on
98 octane pump gas and drives well on the street and strip.
Working the Engine
In the beginning you need a good strong block. I decided that rather than work on my
matching number Stage 1 engine I would purchase a second engine as insurance against
the unthinkable. The Buick 455 engines changed little between 1970 – 76 and most parts
are interchangeable. The important engine and gearbox bellhousing mountings are the
same as are the head, manifold and timing cover bolt holes patterns. Post 1970 engines
had a 5/8” oil pickup tube and 9/16” oil suction passage in the block which is an
improvement over the earlier ½” oil feeds. One of our Club members had a spare 1974
455 engine lying around and although not too happy about seeing it used for the workover
I proposed, soon came round when the readies rustled.
The Buick 455 blocks are great for standard performance, being some 100lbs lighter than
the Chevy big block. This weight advantage comes at the price of thinner castings all
round including the webbing, particularly to main bearings #2 and #4, and around the lifter
bores. For serious horsepower and engine rpm the rule of thumb amongst Buick
enthusiasts is that should you require 600+HP and/or 6000+rpm performance a 455 block
girdle is a must to stop the block flexing excessively under the unintended tortuous
conditions. In my experience, following multiple replacements of damaged main bearings,
I would be more conservative and recommend that you go for a block girdle for 500+HP
and/or 5500+rpm applications. Since fitting the block girdle my mains have remained as
good as new. I also fitted a lifter girdle, which strengthens the lifter bore walls and protects
against the additional sidewall stresses when using a roller cam.
The block girdle should be fitted by your machine shop; it is not a job for amateurs. The
girdle mounts to the block using the existing oil pan bolt holes. The bearing caps must be
machined to fit inside the girdle and the whole assembly line honed to ensure the bearings
line up exactly. Buick bearings are relatively large diameter (3¼”) and the main bearing
clearance is critical. Buick specifies .0007” – .0018” main bearing clearance – it takes very
little main bearing misalignment to throw the main bearing clearances out of whack. My
machine shop insisted that the main bearing clearances should be around .002” which is
probably not a bad thing, provided the oiling is adequate. This brings us to the next critical
item, namely the oiling system, to be covered in the next part of this article along with
more on the engine rebuild.
Buick GSX Engine Rebuild – Part 2
Alan Haime WA Buicks
In Part 1 of my article I discussed the desirability of fitting a block girdle to a high
performance engine and the need to ensure that the main bearings are line honed for
precise alignment. The next critical item to consider in a rebuild is the Buick 455 oiling
system which should be upgraded for a high performance engine. This can be achieved
1. Using a 5/8” oil pickup tube and drilling out the diameter of the oil suction passage
from ½” to 9/16”on 1970 455 blocks – not necessary on later year blocks which
already have a 5/8” oil pickup tube and 9/16” suction passage.
2. Enlarging the oil pressure passage from the oil pressure sender hole to the LHS lifter
gallery from 3/8” to 7/16”, making sure that it is clean and without restrictions. Serious
users drill out this passage to 1/2” or even 9/16”, however care must be taken to
ensure the hole is not drilled too deep and into the cam bearing gallery.
3. Installing double grooved cam bearings to increase the oil flow to the LHS lifter gallery.
The double grooves are on the outside of the cam bearings, allowing extra oil to flow
between the bearings and block surface. Normally the oil is fed via a groove in the
camshaft through holes in the bearing, which is adequate for normal performance
engines, but can lead to LHS lifter and valve train oil starvation on high performance
4. Increasing the maximum oil pressure from around 60 to at least 80psi at high rpm.
This requires a new pressure relief spring in the oil pump. Adjustable units are
available which are ideal for setting the required pressure. Obviously the oil pump
should be in good condition – I purchased a new timing cover and oil pump assembly
with larger than stock oil passages and an adjustable higher rated relief spring to be
sure. Don’t be put off by “rules of thumb” that say 80psi is too high and there will be oil
leaks and so on – the high pressure works just fine. Some really high performance
Buick engines, well beyond my league, run on more than 100psi oil pressure!
5. Although not essential, I installed more secure threaded front gallery plugs in place of
the freeze plugs used by Buick. Care needs to be taken to ensure that the plugs do
not protrude into the oil passage behind and interfere with the oil flow.
The block girdle drops the oil pan by about 1” and you need to take care that there is
sufficient clearance to the front cross member, especially if you intend using a deep sump
pan. After spending a lot of time trying to raise the engine slightly with things like shims
under the front engine mounts, I bit the bullet and had my oil pan remodeled to ensure
sufficient clearance. Raising the engine slightly also had the disadvantage of reducing the
air cleaner to hood clearance, which was tight at the best of times.
I initially experienced a number crankshaft thrust bearing failures. After considering a raft
of reasons for this happening, I found that it narrowed down to the type of torque
converter I was using. I started with JW hi-stall converters, made in Florida and supposed
to be the ant’s pants for drag racing. Each time I wrecked the thrust bearing I found my
transmission fluid was full of bronze filings from the JW converter. JW make their
converters to fit both GM and Ford boxes and there is a redundant bronze bush not
required for the T400 gearbox. Somehow this bush was making contact where it shouldn’t
and apparently exerting excessive forward thrust on the crankshaft, as well as polluting
the transmission fluid with bronze. I swapped to an Australian made Dominator converter
designed specifically for the T400 and had no more problems. To be on the safe side I
had my machine shop drill a 2mm hole from the centre main bearing oil passage to the
thrust bearing surface, thus supplying plentiful oil to the thrust surface. I also had my
crankshaft nitrided to provide an extra hard finish to the bearing surfaces, including the
I used front and rear neoprene crankshaft seals in place of the factory rope seals. The
front seal came fitted to the new timing cover and has proved to be ideal. The rear seal
was a different story. After wrecking a number of seals that either spun and/or melted at
high rpm, I was advised to remove 0.015” from the crankshaft rear bearing surface. This
was another costly exercise getting the crankshaft out, machined and re-nitrided; however
it worked. Evidently for standard engine performance enough oil is splashed onto the
neoprene seal to keep it cool, but not at high rpm. Shaving the crankshaft reduces the
seal bearing pressure sufficiently for the oil to keep it cool whilst not allowing oil leaks.
Whilst on the subject of oil leaks, big block engines are noted for creating high crankcase
pressure which in turn can cause annoying leaks around the oil pan and bearing seals.
The crankcase pressure is caused in part by piston ring blow-by which can be quite high
especially prior to the rings fully bedding-in. Normally the PCV system will take care of
excessive crankcase pressure however I found I needed something more. I used moly
rings, which exacerbated the blow-by problem as they take longer to bed-in than the
standard cast iron rings. To reduce the crankcase pressure I had a crankcase vacuum
pump installed on the engine in place of the PCV system – see Photo#1. The pump runs
off the crankshaft pulley at half engine rpm and delivers between 4 to 10 inches of
crankcase vacuum via the PCV valve port on the intake manifold.
1. Crankcase Vacuum Pump and Oil Catcher on RHS and LHS of alternator, respectively
I retained portion of the original Buick valley pan metal gasket and installed a baffle plate
on the inside of the manifold to limit the amount of internal oil splash reaching the
underside of the PCV valve port as shown in Photo#2. An oil catcher was required to
collect the small amount of residual oil sucked out through the vacuum pump. Draining the
oil catcher now and then is preferable to leaving annoying oil puddles from engine leaks
each time I park the beast. Care must be taken to ensure the crankcase vacuum is not too
high otherwise it will do nasty things such as suck in gaskets and seals. The crankcase
vacuum can be adjusted via a bleeder valve installed in place of the mechanical fuel pump
on the timing cover. Care must also be taken not to over rev the vane type vacuum pump
hence the large pulley on the pump.
Now to take a look at the top side of the engine. I used replica Stage 1 aluminium heads,
SRP notched racing pistons, Crower forged rods and decked the block to zero, giving a
compression ratio of 11:1. The car runs on pump gas without a hint of detonation/pinging.
The roller camshaft is suitable for street and track with strong mid-range to top-end power
and fair idle. The camshaft specifications are 0.576/0.584” intake/exhaust lift at valve with
1.6:1 roller rockers, 238°/248° intake/exhaust duration at 0.050” lobe lift and 112° lobe
2. Baffle Plate on underside of Intake Manifold
I experienced repeated valve stem seal failures when I first used the aluminium heads.
This was both puzzling and frustrating until I discovered that it was caused by the dual
valve springs moving around on their seats in the head and rubbing up against the seals,
resulting in almost instantaneous seal destruction followed by the predictable and
embarrassing oil burning. It turns out that the heads were supplied without spring locators,
a shortcoming that the vendor has rectified since. Meanwhile I sourced suitable locators,
had them installed to stop the springs moving about on their seats and hey presto, no
more damaged seals.
Buick GSX Engine Rebuild – Part 3
Alan Haime WA Buicks
Following from Part 2 of my article where I covered the necessity of using valve spring
locators to prevent seal damage, the next item of concern was the valve train, including
the lifters, push rods, rockers, valves and springs. Initially I used a hydraulic cam with
standard lifters and valve springs, and roller rockers set with 0.004” valve lash. Until I
invested in a roller cam and heavy duty springs I had nothing but trouble keep the valve
train under control at high rpm. This severely limited the top end performance of the
engine and it did not sound very healthy either. Evidently the valves were floating and
rattling like a charity collector’s tin on a Friday. The horsepower and torque reached a
respectable 485HP/510 ft-lb as shown in the Figure 1 dyno curves but nose-dived noisily
beyond 5000rpm. Removing the valve lash and using anti pump-up lifters made some
improvement but did not fix the valve train float problem. The second dyno curve showed
that considerable improvement was made by replacing the standard hydraulic lifters with
solids but with the same old valve springs and hydraulic camshaft unhealthy noises
prevailed at high rpm.
Figure 1. Initial dyno curves with hydraulic cam.
The installation of heavier dual valve springs, solid roller lifters and roller cam soundly
fixed the valve float problem once and for all. The springs were shimmed to provide 280lb
closed and 600lb open pressure taking care to ensure they were compressed to no more
than 0.1 inch before bind. The resulting dyno curves in Figure 2 clearly shows that the
engine now revs effortlessly to 6000+rpm producing a meaty 563HP/559ft-lb and without a
peep out of the valve train – note how the curves are smoother than the early ones. The
engine is now far more reliable and the car has repeatedly run a sub 12 second quarter
mile at the track with an 11.49sec/118mph best result. The car has plenty of scope for
upgrading the camshaft and moving into the 600+HP category…..but as Lois will tell you
that is another dream!
Torque & Horsepower
Torque is what the dyno measures. Horsepower is derived from
torque using the following formula:
Torque (ft − lbs) x RPM
At 5252 rpm HP is equal to torque. That is why all HP and
torque curves using the above units cross at 5252 rpm.
For an interesting and informative discussion on horsepower
versus torque visit:
Figure 2. Final dyno curves with roller cam and solid roller lifters.
The 455 engine performance is dependent on valve and ignition timing. Getting these right
usually requires a bit of vendor advice together with some trial and error – and luck. I
purchased a double roller timing chain with multiple keyways for adjusting the timing.
Since changing the valve timing involves serious engine work I decided against the trial
and error approach and had the valve timing set to the vendor’s recommended 4 degrees
advance during the engine assembly (evidently the stock Buick timing sets had a built-in 4
degrees advance). For the ignition system I purchased a Mallory distributor with
mechanical but no vacuum advance. The mechanical advance is set to 14 degrees
maximum at 2,600rpm and the idle ignition timing to 20 degrees, giving the 34 degrees
advance that flat-out Buick engines love. As for the valve timing I have not messed about
with the ignition timing – I guess I have been satisfied with the performance.
Before I carried out the engine modifications I found that my stock 800cfm Quadrajet
carby was not up to scratch, “bogging” badly each time I attempted hard acceleration from
standstill. I invested in a Holley 950cfm HP Series double pumper and single plane intake
manifold which overcame the bogging completely and simultaneously drove down my fuel
consumption. Some may argue that 950cfm is excessive for my engine, however I have
never experienced a hint of top end power loss due to restricted airflow. The engine is
probably not as “sharp” as the purists say it would be with a smaller, say 800cfm, carby at
lower rpm but this has not given me cause for concern. The engine has plenty of room for
higher 6000+rpm performance should the need, and permission from Lois, arise.
Other useful bits and pieces include electric fans, headers and a lightweight starter motor.
The electric fans have completely overcome the overheating problems that I have
experienced with the stock mechanical fan and shroud – so much so that I am seriously
considering fitting electric fans to my Riviera. I do not believe that stock 455 fans were
ever seriously designed for heavy airconditioned cars in the desert! The 2 inch headers
with 3½ inch collectors fit very snugly and help scourge the exhaust gases through hi-flow
mufflers and 3 inch pipes to the outside world. The lightweight starter turns the engine
faster than the stock motor and can easily be supported with one hand whilst installing –
no more juggling the stock monster into place!
Figure 3. GSX Engine on dyno machine
The transmission and wheels must be capable of delivering the performance engine
torque to the road or track. As mentioned I use a Dominator 3000rpm stall converter. My
T400 transmission is stock except for a smaller modulator and a slightly higher pressure
relief valve spring to smarten up the gear changes, which are effected by a B&M ratchet
type floor shifter. A 6000rpm shift light is fitted to the steering column to indicate when to
shift gears. The rear axle is the stock 3.73:1 posi-traction with 15×10 inch rims, street legal
275×15 slicks and Edelbrock anti-hop bars. A tailshaft hoop is fitted, as required for sub-
12second cars to prevent the “60ft pole vault” should the front universal fail. The break
locker is useful for locking the front wheel whist warming the rears, whilst a five point
driver’s harness is fitted should things go pear shaped.
Table 1 summarises the GSX specifications and Table 2 provides an indication of current
engine parts costs in US dollars. Machine shop costs can be significant and personal
hours spent are through the roof. But at the end of it all, the satisfaction of having a
reliable high performance car is worth the cost and effort. And don’t be put off by age – I
was over 65 when I ran my first quarter mile at the track and I enjoy every second of it.
Racing the GSX makes me feel young again in fact I’m becoming younger as the days go
by, doing l the things I couldn’t afford when I was a teenager!
Table 1. GSX Specifications
– Engine: 1974 Buick 455 cubic inch block bored out 0.40” with SRP notched racing
pistons; Crower forged rods; TA Performance ported aluminum (aluminium if you
prefer) Stage-1 11:1 CR heads; block and lifter girdles; TA single plane manifold; 950
CFM Holley double-pumper; Mallory distributor and ignition; 2” headers with 3½”
collectors; electric fans; deep sump baffled oil pan; crankcase vacuum pump.
– Cam & Valve Train: Roller cam, 0.576/0.584” intake/exhaust lift at valve, 238°/248°
intake/exhaust duration at 0.050” lobe lift, lobe centre 112°; solid roller lifters; Crane
push rods; 1.6:1 roller rockers; dual valve springs 280/600lb closed/open; 3/8” stem
stainless steel valves; Teflon valve stem seals; cam bumper.
– Timing set at 34° BTDC at 2,600rpm; cam advance 4°; bench run-in on dyno,
producing 563HP/559ft-lb using local 98 octane pump gas.
– 3-speed T400 auto, B&M shifter, 3000rpm hi-stall converter, 3.73:1 posi-traction
limited slip diff, tailshaft lop; anti-hop bars, brake locker, hood tacho, front discs, 15 x
10 inch rear sports wheels with street legal slicks, 5-point harness.
Table 2. Indicative Engine Parts Costs in US$
Stage 1 Aluminum Heads with Valves & Springs 2450
Racing Pistons & Moly Gapless Rings 1000
Forged Rods 775
Heavy Duty Dual Valve Springs 300
Roller Cam 700
Roller Rockers 750
Roller Solid Lifters 700
Intake Manifold 400
Block Girdle 500
Lifter Girdle 400
Distributor & Ignition System 700
Carburetor 950cfm 720
Oil Pan Deep Sump 450
Starter Mini Size 300
Electric Fans 250
Crankcase Vacuum Pump 300