How would an L98 engine perform with a ported plenum and fully siamesed stock runners. I was thinking that they can be made fully siamesed with some sheet aluminum and a good welder. Any thoughts, or has any body ever done this? Wouldn't this increase the plenum size close to that of the super ram?

 

I think if you can increase the cross section of the runners like you want to, it would effectively increase the plenum size. I'm not sure what happens to the velocity of the air and how it affects the overall results.

TPIS has done some testing with siamesed runners and from their results, these runners only began to work better than large tubes after 4500rpm.

 

TIPS "Insider Hints" compares their Siamesed runners with LT runners; the Siamesed runners play catch up from 2,000-4,250rpm and peak at 5,000rpm while the Siamesed peak to 366hp at 5,250rpm and have 37hp more at 5,500rpm. While the LT runners peaked at 5,000rpm with 345hp. So this data, though from a 350cid motor, was not from a stock L98.

Remember that the TPIS Siamesed runners are larger in dia than stock runners too. In fact they are made from the TPIS LT runners.

I'm not sure if it would be called an extended plenum or a double tuning effect. Certainly the air velocity in the Siamesed runners would be lower than in the intake base runners. That is likely what reduces the ram effect at low rpm and accounts for the initial reduced HP as seen above.

 

Dick Guldstrand built the GS80's when TPI came out and cut the runners open and welded the aluminum backings to them to make a full set of runners.Same idea youre thinking now.
So its basically an older way they did to increase more usable rpm.Keep in mind they did other engine work,headers,cam and etc.
Not sure how this idea would work with a stock roller cam.
Power output was pretty good and the peak HP came in closer to 5250 rpm but began to fall off a bit after.Thats still better then the low 4400-4800 speeds the stock runners peak out.However these engines were worked and made over 375 HP so power falling off after that didnt hurt it much.
Prob. wont hurt to try an experiment like that.
:)

 

I was looking at them and it looks like you could siamese all the way down to the hole for the plenum to intake bolt, you would have to leave a little indentation in them in order to get a torx bit in there to instal. That would basically leave about 2 or 3" of runner divider, so it might not cause a huge loss of torque. How much divider is left in the SLP runners?

 

The SLP Divider starts at near the top of the runners and goes all the way down to the bottom, a very thick wall.I cut them open once to knock the wall out but havent gotten them welded back up.I knocked the wall out down to the lower bolt hole where its a divider now.

I also have a spare set of stock GM runners,I cut one runners open to see if this welding idea was feasible and it is.Doing it this way would give you a short runner divider at the bottom just above the lower bolt hole as you described.I still have these runners sitting in a box,never was able to find the time to duplicate the GS80 runners that was made or what TPIS experimented with.Would like to try them someday with a full siamese plenum opening.

The SLP's divider doesnt even come down nearly this far in stock trim...so these alone can be or mean more volume.
In short you can almost make a SR effect with cutting and welding but using a narrower stock plenum above.(of coure we know the SR is the king)

Btw, a rumor I heard, TPIS when experimenting with their full siamese runners,removed them from their catalogs because they had problems with the welds holding.
I can imagaine that because aluminum tubing isnt exactly the easiest thing to weld.
Sure it can be done but will it crack at the seams later?
I dont know if the runner tubes have enough material in them to make a thick weld when needed.When I cut the runners open, it was like paper thin.
But if GS80's had them and they held up,maybe the GM pipes were thicker then the ASM runners that TPIS sells as their own.

 

There's a thread at third gen- a guy just did that and said he'll post his new hp and tq #'s after they're on. There's some pics there too. check out http://www.thirdgen.org/techbb2/show...threadid=46659

 

It might be possible to braze the runners together. Brazing should provide the durability needed for the job. Another idea is to take the runners and cut the down so they are half their original height. Then get an explosion proof electrical junction box and mate it to the the runners. Maybe weld the setup. Finally machine the box for the throttle body. This would give you a superram type setup. Its just an off the top of my head idea.

 

I think if you could get the runners cut as straight as possible, maybe a dremel or some kind of saw, and had the plates match the holes as much as possible, you could get buy with a very small bead, I don't think it would burn through the metal. I was planning on getting the SLP runners anyway so I am very interested in doing this if I knew it could be welded back with no problems.

 

KY,
If you want to see the SLP runners slightly ported on one side and not the other to gasket match them to large tube gasket size, go here:
http://community-2.webtv.net/TunePor...ODS/index.html

I made that page a while back,but didnt finish them.I also cut the divider wall much farther back since then.

The SLP runners are VERY thick so Id bet you could get away with welding easier then trying to weld the thin tube stock or large tubes other people sell.
Keep in mind theyre cast aluminum runners as well.

LOTSA meat on them to grind and port away to your desire.Once I opened them up to Large tube size, I was suprised how big the insides diameter began to look.
I also think JAKE on the forum has these SLP's and extensively modifed them as well and has them on a 415 ci. motor.
Hope he chimes in and lets us know how well they work.

Btw I did 90% of my porting and cutting with a dremel tool and cutter.They cut/port fairly easy.

:)

 

Thanks for the pics Bill. I think I am going to get the aluminum and start fiddling around with this idea. If I don't get some headers next week I will get the SLP runners and try the full siamese job.