: Increasing Displacement



hoser795
01-19-04, 07:26 PM
I know the N* motor is aluminum with press in iron cylinder liners. Does anyone know of any large bore liners (similar to what guys are doing in the LS-1's...pull the stock liners out, bore the aluminum block, and put in new thinner liners to increase the bore). Also...is anyone making long stroke cranks (preferably forged)?

DaveSmed
01-19-04, 11:48 PM
From what I've heard, it's hard to get any rebuild parts for Northstars. I'm not even sure if you could even get .030 pistons....

growe3
01-20-04, 08:37 AM
The cylinder liners are cast in place, not pressed in.

In my opinion the Northstar was designed to be a strong, leave it alone, high performance engine. There is little you can do to it, aside from head gasket repair, try to funnel cold air to the intake and open the exhaust up (Corsa).

The crank is not allowed to be turned, the cylinders are not allowed to be bored, the cost of any head work is prohibative. To repair anything major, other than the head gaskets, is not cost effect, you just get another engine, complete from oil pan to the heads.

This engine was so well optimized from the factory, it is difficult to pull much more power from it, for dependable street use.

I have run a few computer dyno programs and a small increase in valve sizes and camshaft overlap, along with a few more cubic inches and this engine can really produce a lot of power.

I would also question the driving safety of putting more than 300 HP in a front wheel drive car. In a rear wheel drive car that would be different.

Probably the best way to gain power is by supercharging, but that effort seems to have died.

One source of aftermarket Northstar power is at:
http://www.chrfab.com/

BeelzeBob
01-20-04, 09:55 PM
It is difficult to significantly increase the displacement of the Northstar engine. It was designed for a specific performance envelope for the FWD Cadillacs and the displacement and output was designed "at the limit" to minimize the package size of the engine for the TFWD arrangements.

The diecast aluminum block as cast in place cylinder liners...not pressed in liners. The cylinder liners are designed to allow a 1mm overbore. The standard bore is 93 mm for the 4.6 engine so a 94 mm bore nets only a 0.2 liter increase. There are currently no oversize pistons available from GM but there may be aftermarket parts available from sources such as www.chrfab.com (http://www.chrfab.com) Custom pistons are another alternative that are not that expensive considering what you are undertaking.

Given that the Northstar engine is built on a 102 mm bore center ... with 93 mm bores that leaves only 9 mm between the bores for the head gasket to seal. Pushing beyond the 93/94 mm bore mentioned puts great stress on headgasket sealability.

Similarily with the stroke, look at the piston and the piston clearance to the crank when at BDC. It looks like a 'stroker" now everything is so close. Every opportunity was taken at the design phase years ago to shrink wrap the lower end around the crank to get he minimum possible deck height to minimze the package volume of the engine.

In order to stroke the engine even slightly it will be necessary to do a lot of custom machining and some tight clearances will result. The piston pin is near the top of the piston as is so moving the pin higher to get a longer rod into the engine nearly impossible as the rod will hit the underside of the crown.

Sorry , but the engineers that designed the engine from the git go did their homework and packaged the engine very tightly and optimized it for the 4.6 displacement....that was their job...not make it easy on hot-rodders later.

A stroke increase will require a custom billet crank ($$$$) as the cast nodular iron crank cannot be offset ground due to the filler rolling operation performed on the crank. The nodular iron crank is very very robust in the Northstar in part because of the heavily rolled fillets. Rolling the fillets imparts a very high residual compressive stress in the crank pins which makes them very durable and resistent to cracking and fatigue failure... Unfortunately, this high residual compressive stress causes the crank to distort when offset ground due to the uneven residual stress left from the offset grinding...plus the crank will crack quickly in the fillets due to the left over uneven residual stress. Unless the crank can be stress relieved, ground and re-rolled it cannot be reworked practically speaking.

Understand that over head cam engines , especially dual over head cam engines like the Northstar have large cross section cylinder heads. Unavoidable. To combat this the block is designed to keep the deck height at a minimum to minimize the overall package volume. This is one of the inherent advantages of pushrod engines...the heads are much smaller in cross section so the deck height is not nearly as critical. The deck can be raised artificially to allow for "stroking" and displacement changes later on.

In addition, the overhead cam engines have the necessity for a cam drive system at the front of the block at overhangs the front cylinder bores for clearance to the head. This requires that the engine be as short as possible to allow for the timing drive....requiring putting the cylinder bores as close together as possible. Another area where cam-in-block engines have an advantage...the timing drive to the single cam can be tucked in between the front cylinder bores taking up very little overall length. This allows the bore center of the cyliner bores to be opened up...allowing "bore increases" later in life for displacement changes.

All engine designs have pros and cons. The ability to accomodate a lot of different displacements on the same block architecture is not one of the strong points of the dual overhead cam engine.