84-92 6-Port Intake Porting

The 6-port non-turbo engines (made from '84-'92) are a totally different story for porting. The front and rear side housings have the auxiliary ports in them, and the center housing has very small ports. Additionally, there is not a lot of casting thickness behind the upper part of the center port. This means if you go too far, you hit the water jacket, and the housing is now pretty much junk. At a later time, we will cover the method of adding epoxy to the back side, and filling in the EGR ports (86-88) to allow more porting for race engines (not recommended for street engines where longer term reliability is needed).

If the separate ports (in the end housings) are simply made into one large port, the bottom and mid-range torque suffer a lot, and the port velocity is compromised as the intake flows from the manifold into the intake runner. The intake port timing of this configuration is: later on opening than a peripheral port, but roughly equal to intake closing on a peripheral port! That's a LOT of timing and port volume for a street car. There are MANY combos that could be tried here. We have not been (nor have we heard of anyone) willing to build/port probably 8-10 different engines/port combos, and spend a few hundred hours on the dyno, to optimize these engines. We are talking big $$$ to do all that - in order to sell porting templates ???

Anyway - this page is written assuming the 6-ports are going to remain active (rotating sleeve installed). We tend to tell phone customers that 6-port engines are "not able to be ported" -- we frequently do not have the time (sorry - this is a confession) to go through the VERY long speech explaining how "that's not really true, they CAN be ported, gain is not very much, might hit water, epoxy behind the center ports, full explanation of the rotating valve, exhaust back pressure activation, port timing and volume problems with connecting the ports, intake runner cross section limitations, etc. etc. etc.". This page is going to make our life a lot easier by allowing us to refer them to this pictorial on how / why / where.

The images here are of an 84-85 GSLSE engine we did -- this all applies to the 86-92 engines also.

Use of dykem marking fluid, and tracing ports from templates, is shown on the 4-Port Porting page.

	Simple shot of end housing (with dykem applied)
	This is the outline of what we have determined as the "optimum, feasible, safe, valve active" port. We are sure others will go bigger, BUT, you can't go anymore on intake opening (right side of this view), and you should not go much more on intake closing (top horizontal line) because it is already very late timing, and the valve prevents effective use of much more.
	This is what the rotating valve looks like.
	Valve slid into intake port - this shows port open position.
	Porting Template for these ports, and for the center port as shown lower on this page. The template allows two different ports to be on the same piece of metal. The ports are scribed onto the template - you need cut and grind them out to the scribe marks. Part Number 49-2226P
	Valve in closed position.
	Valve half way open.
	Valve all the way open.
	Finished end port(s) with valve installed.
	Looking down the port runners of finished end housing.
	Simple shot of center housing.
	This shot is for comparison purposes only (center housing). The lower top line is intake closing on a stock 74-75 port, the upper top line is a street port. There isn't enough metal in the casting to go up to the "street port" timing, nor enough to match the bottom shape. Additionally, the height of the floor of the runner is nowhere near enough to bother even trying to go that low.
	This is the port tracing we are using for the center ports. There is enough metal in the casting to blend up to the top line, and the bottom arc goes in nicely.
	Center port roughed out to tracing.
	Center port about ready for final clean up and polishing. Sorry about changing the port we shoot - but we prefer doing increments of the same work to each port, and the shots are taken when time permits.
	Comparison shot of original sized port, and where it is when finished.
	Finished center port.
	Looking down port runners of finished center housing.
	This is just a shot of the GSLSE exhaust port with the street port traced onto it. Refer to our Exhaust Porting FAQ for the details.

Exhaust Porting

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