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.
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 spent a LOT of time on our engine dyno and have have been very successful in making this type (VERY large) work on our road-race cars, but only at VERY high RPM– meaning above 9000!
Anyway – this page is written assuming the 6-ports are going to remain active (rotating sleeve installed). By leaving them in, and porting (like below), you will get a pretty decent power increase at mid rpm and up, with no loss of bottom end torque. If the sleeves are left out, or locked in the open position, you will be sacrificing bottom rpm torque.
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.
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.|