Pontiac Performance Upgrades- Butler Built Bottom End

Bottom End

Block-
Stock blocks are all fine for the majority of Pontiac performance builds. Unless you want extreme, high horsepower that will be put to the test weekend after weekend on a track application then the stock block will work for you. Most Pontiac blocks are capable of up to .060" over bore and up to even .065". These blocks usually have thick main journals and can accommodate increased strokes to increase cu in.

The exception is the 75-76 400 block (casting# 500557 & 568557) which has thin main journal thickness. We recommend limiting the stroke on this block. You can read more about this in the 400 stroker kits on our web site.

IAII Blocks- If you are looking for a stronger block for higher hp applications and larger displacement then the IAII block is available. These blocks come in Cast Iron or Aluminum (less 85lbs). These can be 4.145 rough bore and up to 4.345 rough bore. They feature more material in the critical areas such as the lifter area, oil pan rails, cylinder walls, main areas, and deck surface.

Main Caps-
2 bolt main caps are fine for most street builds up to 600hp. If your application has higher hp and larger stroke then the 4 bolt main caps are a good investment. Some blocks come standard with 4 bolt main caps, while others they can be added. Some blocks are predrilled for 4 bolt main caps otherwise the block can be drilled to accommodate them. For the strongest 4 bolt main caps we offer splayed caps. On these caps the outer bolts are angled outward to offer a clamping force in another direction than the inside center bolts. The block would have to be drilled for splayed caps. When changing and main caps the block must be align bored and the thrust must be cut into billet main caps to match the block.

Crankshafts-
Pontiac factory crankshafts are strong and work well in most street applications. The journals of these cranks can me machined (turned) to remove imperfections and crate a very good bearing surface. Most cranks can be turned up to .030 but these bearings are getting harder to come by and are more commonly found in .010 and .020 oversized.

Aftermarket cranks come in cast or forged as well as billet. Cast cranks are now readily available in stock stroke as well as stroker cranks and are very good options for older stock cranks. Cast cranks can accommodate most strong street applications up to 550-575 hp and 4.250 stroke. Forged cranks are stronger and can work well when more power is being made and strokes up to 4.500". Billet is only used in race only extremely high hp applications.

All cranks must be balanced to your bob weight to ensure they do not have offset weight causing harmonics issues.

Rods-
Stock rods work well in street applications and when reusing stock rods a new set of rod bolts are always a good upgrade. If upgrading to aftermarket crank and using stock rods adding additional heavy metal to the crank may be necessary due to the cranks being cast or forged for the lighter aftermarket rods.
Aftermarket rods come in I-Beam and H-Beam styles in cast or forged steel. The cast I-beam are great upgrades for stock rods while the forged rods are stronger and can support higher hp. The H-beam is a slightly stronger design over the I-beam. Race application rods are full aluminum such as GRP.
Most rods come standard with 8740 rod bolts (180k psi) and if strength is needed they can be upgraded to ARP2000 (220k psi) or L19 (260k psi) rod bolts.

Cast I beam rods are good up to 700hp
Forged I beam rods are good up to 800hp
Forged H-Beam rods are good up to 850hp with 8740, 1200hp w/ARP2000, and 1500hp w/L19.

Our stroker kits usually come standard with Forged I-Beam or forged H-Beam that are more than capable of most street applications and bolt upgrades are also available.

Stock Pontiac rods are 6.625" with rod journals of 2.250" and a .980" pin size
Stroker rods are 6.700 and 6.800" with rod journals of 2.200" and a .990" pin size

Pistons

Piston material-
Options are cast and forged aluminum. Cast pistons work well in street rebuild applications and keeping compression ratio no more than 9:1 on cast irons heads. Forged pistons are used in stroker kits and can accommodate higher hp and larger strokes. We like to see compression ratios around 9.5:1 on cast iron and 10.5:1 on aluminum heads.

Piston Types-

Piston faces come in flat top, dish, and dome. Flat top pistons only have notched for valve pockets and usually net to a -6- to -8cc while dish and dome can be made in varying cc's. The dish increases cylinder volume which reduces compression and the dome reduces cylinder volume and increases compression. One of the most important factors is the piston type used in conjunction to the head cc. The compression calculator is vital in figuring proper CR for your application.

Compression Ratio-

Butler recommends no more than 9.5:1 compression ratio on cast iron heads with forged pistons (9.0:1 with cast pistons) and 10.5:1 with aluminum heads. Mid to late 60's had high compression heads usually in the 68-75cc range. It was common for compression ratio's to be in the 10's on cast iron heads. In that time this was ok due to the availability of high octane fuel at your local gas stations. This is no longer true with today's fuel and these kind of compression numbers on pump gas will cause predetonation, bearing failure, overheating, and timing issues. Choosing the correct piston based on your stroke, bore, and head cc is vital. We verify compression numbers on every head, piston, and rotating assembly order before shipping.

Click here for our compression calculator

Piston Sizes-
Pistons can usually be made in any bore you wish but commonly stocked in .030", .035", .040", and .060" oversized.

Why the 4.155 bore?
Here at Butler, we choose to stock one of ours in .035" (4.155) over so a stock 400 bore (4.120) can go .035 over for the first bore or a current .030" over can clean up to a .035" to keep from having to go to .060" over which is closer to the end of the life of the block. Because Edlebrock 87cc heads are a popular upgrade one of our stocking pistons is a flat top piston that makes a compression ratio of about 10.2:1 which is perfect for pump gas.

Rings-
Piston rings keep compression in the cylinders and there are different options but the most common are ductile iron rings. Ring thicknesses must match the pistons ring lands and will be specified in the product details. All rings must be gapped to the application. Larger gaps are needed in boosted and nitrous applications where there is more expansion due to heat/compression. Common street gap is .018-.020"

Bearings-
We sell only name brand bearings and keep a constant check on bearing to bearing tolerances by our machinists in our own engine shop. We sell what we use and include the correct main and rod bearings in each of our kits. Main journals for 326-400 Pontiac engines are 3.00 and 421-455 are 3.25".

Stock Pontiac rod journals take a 2.250" bearing and stroker rod journals take a 2.200" bearing

Stroker Kits-
Butler is one of the pioneers in making stroker kits widely available for Pontiac engines. One of the best things about stroke is that it produces instant torque.
So torque is better than horsepower you may ask?

That depends on application. Most people love to drive their cars daily so our common application is the street. Torque comes in when the pedal is pressed while hp builds. HP alone can't always be felt until you reach the optimal rpm's for that cam. Sometimes that can't be achieved from stop sign to stop sign or red-light to red-light. So a good mix of hp and torque is great for street applications. This is why our stroker kits are very popular. Our kits upgrade you from 3.75" stroke (326, 350, 389, 400), 4.000 stroke (421, 428), and 4.210 stroke (455) to the ost popular 4.250" stroke. This produces more torque that can move the car quickly. Larger strokes such as 4.350 and 4.500" are available for other applications.

Our kits are neutrally (internally) balanced so you will need a matching flex plate/flywheel. This means the crank does not need anything external to complete the balance. Pontiac stock (externally) balanced cranks so an offset weight flex plate/flywheel was required to balance the assembly.