Zordak buys a C4 Vette.

Arctic cold here right now. I can not get out and work on the power steering leak(hoses maybe). I want to boost the power a bit, looking for around 20-30 hp without killing the low end torque. Now internet says the tpi was developed for the 5.0L  and is the limiting factor on the 5.7L. Looking on ebay, the aftermarket runners are running $500-$1000 for just the runners, not to mention the cost of the lower intake. But while I was looking I saw an ad for a runner expansion kit, $70. Looked interesting so I splurged and got one. Turns out to be a 1-1/2" steel ball and 5 pcs of 1-7/16" wood balls and you are supposed to open up the flange area  until the steel ball is past the flange then pound everything through. Now on the video the seller works out a badly dented runner tube and beasts up the flange in the process. He then takes a file and smooths ou the flange. This kinda annoys me so I thought of making a plate to bolt to the flange and push the balls through. Also he at one time made another kit to open the runners up even more. Using a calipers the actual runner tube is around 1.475- 1.480 so this will open it up a little and I think I can get a little more by getting a 39mm(1.535) ball and repeating the process. Photos and report of what happens when I try this on the spare runner I have from the Firebird project.  

Now that is interesting. "Runner stretch"

Yeah pretty much all the aftermarket TPI upgrade parts for the stock system are no longer made. Port your upper and lower when you have them off rather than throwing down $1000-2000 for SLP runners and the Edelbrock or Accel lower (that still want to be ported).

Yeah the idea is to get a second tpi manifold and modify it then swap them over a weekend. There is a set around here listed for a little less than going price on ebay. 

Is there enough wall thickness to "extrude hone" the runners? And will you have enough cam and exhaust to use more intake?

I've heard of factory LT1 intakes reworked to fit a TPI - supposedly gives a bit of a performance increase, and it's easier to find than the aftermarket upgrades.

Very interested to see your results with the runner modification, subbed

AngryCorvair (Forum Supporter) said:

Is there enough wall thickness to "extrude hone" the runners? And will you have enough cam and exhaust to use more intake?

I've never handled stock runners off the cars, but with the number of dents I've seen in them they are probably too thin for extrude honing. Even stock 305 cars see a benefit from runners and porting with the 350 F-bodies seeing more. Now on a Corvette with their better exhausts there should be even more. I can't remember if the Corvettes have hotter cams than the equivalent F-body though. The Corvette heads are better as well.

We wound up with ported tpi, then a miniram on the 383 in the c4. The porting of the stock tpi on the stock l98 made major improvements. 

MadScientistMatt said:

I've heard of factory LT1 intakes reworked to fit a TPI - supposedly gives a bit of a performance increase, and it's easier to find than the aftermarket upgrades.

Is there any advantage to reworking a LT1 intake, as opposed to swaping in the whole LT1? A bit cheaper, I guess, a bit less wiring and labor; and of course not Optispark... but there are ways to improve that!

I guess I'm asking if the intake alone helps enought to justify not going full swap?

O.K. the LT1 was, if I remember correctly 276hp, the L98 is 248hp, so I am only looking for 30hp or somewheres near. I really like the look of the TPI, so I am trying to keep it. Now I am not trying to remove any material, except near the mount flanges, just stretch the pipes out. Wall thickness is around .09", and the reason they dent easily is the material is somewhat soft. If I go to 39mm (1.535") I should have about .05-.06 wall where I have to grind out to get the ball started other wise I do not believe the rest will be that thin. If I get the intake breathing better it should allow the engine to rev higher and faster with the limit being the MAF and the stock air cleaner. I am still deciding what to do about that. On thirdgen.org there is a discussion thread about going to an OBDII from an '01-'02 vortech to get a few advantages there but not sure I want to go that route. Right now just looking to lessen the intake restrictions of the TPI.

After doing some other things I got a little time in on opening up the ends of the spare runner. It took 1-1/2 hours to rough out the step from the tubes to the flange then try to get the 1-1/2" ball past the flange so I do not crack the flange. I am going to try something else to do this. I spent most of the time working one tube out to get close. I am thinking of getting a set up in a cnc mill and using a teardrop cutter to finish out the flanges. Once I get this figured out it should only take around 15-30 min to do each hole.

O.k. I took the runners to my secret fortress of fabrication and made fixtures to hold the runner in a cnc mill and after some tweaking I got the ends opened up to about 1.54 dia. I also made a 1.537 dia steel ball. Now at home I had this:

I made a bracket to push the ball through instead of pounding on them. Looks like this in use:

Now cranking on the 1/2"-13 screw was not hard, about spark plug tight. I got the 1-1/2" ball through just fine so I decided to push the 1.537" ball through and that went fine until I got to the upper flange and was left with this:

Now I need to make a new plate to push the ball back so I can grind out some more material to get the ball through. I will just have to be sure on the others that the upper flange is cleared enough to allow the ball to pass through.  The tubes are soft and malleable and seem to strech ok. I will not be able to stretch them to my calculated dia of  1.575 but I can get them alot closer.

Great idea on the threaded push fitting. Following along...

Very interesting.

It's really not that hard to get TPI to make stock LT1 HP. The torque is already there and just about everything you do to TPI unleashes even more torque. And on a Corvette it's even easier. Getting one over 325hp is the tough part with stock displacement. People loved 383s in the '90s and early 2000s since that would get you to the coveted 350hp without going to a Stealth Ram or MiniRam.

After a bit of work I got the 39mm ball out. I think I need to re-machine the ends to get batter clearance for the 39mm ball. In other news I scored a complete TPI set up for $140. (including all 9 injectors). I am going to try to look everything over and make decisions on how to port everything else to get the flow I want.

On the upper porting is pretty much knock down the walls, gasket match and siamese the runner holes if you have siamesed runners. Now the rest is where the creativity comes in.

I got the new runners at the Fortress and noticed they are different from the one I was playing with, also a little larger. Working on opening up the ends for the ball procedure. I think I will just be using a coarse sanding drum on an extension to open up the base and for the plenum I think just some extra hand work similar to what I did before just more of it.

Kitchen remodel project has gotten in the way again. Spent the last 2 weekends installing some new cabinets then making large drawers fo one so the wife doesn't have to bend down to look in the lower cabinets. Any way splurged on a new pair of cable to release the rear of the convertible top. Not sure of the wisdom of the purchase, the cables look a lot cheaper than the originals and the originals were pretty cobbled up. If these fail I am going with the "design different stuff from less expensive but better materials" plan.

Not much in the way of work on the vette, Just getting it out and enjoying having a nice convertible to cruise around in.

A small up date. I finally found a way to clean the carbon/gunk out of the runners. I filled them with mineral spirits and let them soak for a week, then using a flexible brush and wadded up paper shop towels I got 95% of the stuff out. Now that they are mostly clean I tried to push the 1-1/2" ball through. I barely got it through, it seems the  wooden balls absorbed the oil and got soft and compressed and are now too big to go through the tubes easily. I have a fresh batch on order from Amazon. Other than that I have been just driving the vette and enjoying having a fairly good handling convertible.

Final update. Sold the vette on Sunday got $6500 for it. Looking to get a 4th gen firebird convertible. The "no dogs" thing did not work out so I need something with a back seat.

I few things on these vettes. The digital dash may look good especially going from the blank black to lighting up when turned on, but the first thing you see when looking down is the information area with volts, temps, tip odo and fuel milage. It takes a little extra time to do a glance for speed(steet use) or the tach(track use). I find this annoying. It also seems to be a trend on modern cars. I hope auto makers figure this out and put tach and speedo at an easy glance again.