Siamesing HSR base??
 

I just had an idea about the HSR base. For those that need abit more flow and breathing room up topend for big motors, obviously shorter runners are needed and the effects of this can be seen on TPI bases that have been siamesed.

I was just looking at the HSR base in a picture and thought about siamesing out the top of the runners where the plenum bolts down.

Grind out the center wall (red line in the picture) to join the two seperate runners (cylinders 1 and 3 with 2 and 4, and likewise with 5,7 with 6,8) and then digging down the individual runner or green line in the picture (aka taking out the divide between the runners for cylinders 1 and 3, or 2 and 4, etc)

this way you expand plenum volume abit and then shorten runner length. From the looks of it, you have just enough room to do so. atleast enough room to seperate the divide in the runners to each pair of cylinders (ie 1 and 3, 2 and 4) and take out the wall seperating the left and right side of the motor.

What are your thoughts on this and what gains do you think this could have? the center wall tho may pose a problem as it doesnt look very tall. Might not beable to grind it down alot before you port through it and have a hole goin to the lifter valley

Re: Siamesing HSR base??
 

Wholeheartedly agree with the concept, been thinking the same thing for a few months now. These reportedly work fine on the 383 as is, but I'm looking at bigger cubes (up to 434). The alternative is a single plane, but I think the siamese approach could open up flow quite a bit. Should not be a negative effect on torque with the extra cubes coming in to play.

Re: Siamesing HSR base??
 

thats what i was considering since the HSR i have is only setup for 1205 ports and needs material added to be opened up to 1206 ports. 1206 ports are commonly used on alot of 215+ CC heads which are perfect for 406's and larger motors.
that way you can possibly keep a 195-200 cc head with a hell of a port job but still 1205 gasket size, and siamese the HSR to gain more flow where you need it at 6000+rpms

Re: Siamesing HSR base??
 

well here is a pic of how I modded mine

Re: Siamesing HSR base??
 

looks good. I figured as long as the HSR has been around, someone has done some kind of porting/siamesing to that area

Re: Siamesing HSR base??
 

Not too sure about the knife-edge though, wouldn't it create some shear in the flow? Better off rounding it over I think.

Re: Siamesing HSR base??
 

From all the research I have done you would be better off with a rounded port to the runner entry instead of the knife edge. Think of the leading edge of and airplane wing.

As far as cutting down on the runner length you need to look at the total runner length to the back of the intake valve and look into picking up the 3rd harmonic wave. Also you need to ask yourself what rpm you intend to run the motor up to as that will play into the harmonics and runner length.

Re: Siamesing HSR base??
 

Yes, you would want a rounded edge rather than knife edge. Rounded on the leading side (where the air is coming from), knife edge on the trailing side (as the air leaves). If you had access to flow equipment or a wind tunnel you could quantify the difference but I'll save you the trouble and let you know I've seen both shapes in a supersonic wind tunnel and the rounded edge is better than knife facing into the airflow path, less resistance that way (as measured in practice).

Re: Siamesing HSR base??
 

My thoughts were ( for lack of a better visual aid), take out a large bit of the center divider, done as if I had an over-size juicer, like juicing an orange. That's pretty crude, and without one in hand I can't see how deep I could go without busting through as Orr89 pointed out. But it would open everything up for a larger cube motor. Could probably even cut 1/2 to 3/4 inch off the top of the tunnel stack for those with hood clearance problems (me) with no negative effect.

Re: Siamesing HSR base??
 

I had the same idea, as far as taking about 3/8" to 1/2" off the top of the tunnel for the hood clearance. But I cant make the math work on the affected RPM range and the 3rd wave concept.

1989GTA what exactly did you guys mean by "S" in...

"L = (1100 x S ) / N where S equals the valve closing point. N equals the rpm. L = the length of the runner from the intake valve to the first open area which is usually the plenum"

You got me stumped here buddy haha.

Re: Siamesing HSR base??
 

S equals the advertised intake valve closing point ABDC. In my case it was 65 degrees. Also my runners turned out to be around 14 inches long for a 3rd harmonic peak at about 6000rpm. I will be shifting around 6300rpm with my setup.

It is not necessary to capture the 3rd harmonic but it is nice to get the little extra horspower boost it provides. In competition racing you want to get every available horsepower and this is one of the "tricks" people do.

With TPI they used the 2nd harmonic wave. However you need long runners and it occurs lower in the rpm scale as you know.

Re: Siamesing HSR base??
 

And you got my interest. Where can I follow THAT discussion?

Re: Siamesing HSR base??
 

well what is the total effective runner length on the HSR setup? do you measure it from the start of top of the base where the plenum sits on, all the way down to the back of the intake valve?

Re: Siamesing HSR base??
 

To the back of the intake valve. You would need to know the length of the runner in the head plus the runner in the intake manifold and if you have them like tpi the actual runner length.

Re: Siamesing HSR base??
 

Subsonic flow (which we operate in) loves rounded edges (corners), while supersonic loves knife edges.

If I were to siamese the HSR, I would take the inner walls down about one inch and put in a full round on the top edge surface.

Re: Siamesing HSR base??
 

Aha I see, Priceless info. IMO modding a car is great and all, but building a winner the first time...is priceless. Thanks man!