EDIT: The text below is now old information.
Here are some pics of my new small port intake (SPI for ease of reference) versus the port size difference of the large port TVIS setup.
The TVIS is a little more than 1 1/8" tall by about 2 1/2" wide. I didn't measure the SPI, but you can see from the pictures how much smaller it is. It looks like it's about 60% of the TVIS size at first glance.
Problem there is that we have to subtract the area used to create the two separate 30MM round ports of the TVIS. The big problem is that the TVIS head has a port opening that is not divided, so the
flow disruption caused by the center divide has to wreak havoc at the point of transition from manifold to head.
Obviously there is so much material missing from the SPI that you have to fill in a lot of area if you even want to try to bolt this intake up to the large port head. There is a spacer available online that
seems to be about an inch thick (same as the TVIS plate thickness) and it's machined to make the transition from SPI to TVIS size in that inch. Again, I think this would create a serious flow problem to
make this change in such a short space.
The only solution that I could come up with involves cutting out the centers of the paired SPI ports several inches back to the point where they initially split. The plan is to then weld in a center divider and
build new roofs and floors for those parts of the port that have been removed. The end result will be port outlets that closely match the port openings of the TVIS head.
I will also open up the upper end of the ports into the plenum area to keep the port volume as even as possible. I may have to cut off the top of the plenum so that I can reach in to do all the porting - I'll
have to see how far up there I can reach.
Most of you know that I've been getting better results with the TVIS disconnected as far as driveability, power and mileage. From time to time, I've re-connected the TVIS just to make sure I wasn't wrong.
Each time the results were the same. (see the last paragraph also please)
So, last weekend the epoxy on my smallport intake was fully cured. (I epoxied the gaps between the 1&2 and 3&4 runners at the manifold face where it bolts to the head so that I could port match it to the
mid-port I've been working on.) Since it will be a few months before I can get back to the head work, I decided to swap the smallport intake on in place of the TVIS intake since it would now seal up
correctly (no vacuum leaks) just to see how it drives. I did that last weekend. The nice thing is, with the epoxy job, there was no need for spacers or anything else, so everything bolts up like stock, triangle
bracket, EGR, the works.
So I drove it around town a little on Sunday and during the week but only put 35 miles on it - all in town. Today was my first trip down to San Francisco (56 miles from home).
WHAT A DIFFERENCE !!!!!!!!!!
The car is far more responsive than it was with the TVIS connected or not.
It makes more torque at lower RPMS - pulls clean on the freeway from 2200 RPM in 6th gear (as low as I was able to get in 6th) where before it would just wallow and not really do anything at that speed.
There is a fairly steep hill approaching the GG Bridge that I was having to drop down to 5th for (while cruising at 70, 3300 RPM in 6th) to avoid loosing speed. Today I went up that hill at 70 in 6th gear
with no loss in speed at all, but with the same throttle setting. If I had done that before, I would drop down to 60 or less by the top of the hill.
At high RPM you could tell that the car was wheezing before. It would get to redline, but that last 1000 RPM was kinda pointless. Now it goes right to redline in every gear, no problem at all.
At low rpm in a tight corner (like city streets making a sharp turn at an intersection) it will spin the inside rear with less than 1/4 throttle quite easily. You had to TRY to do that with the TVIS intake.
No, I don't have new dyno numbers for you. I'm working 7 days a week right now and can't get back down to Su's. I may be able to go in May, but I'll have to see how work goes.
This is running so well as it stands right now, that I've decided to abandon my mid port setup for cost and time reasons. I'm going to just build the small port that I got last weekend, mildy port the head and
get a set of 256 cams, although the cams may even wait till later. I will bump up the compression while I have it apart and do a set of Sealed Power rings to keep it as efficient as possible.
I do have to say that I don't think this would make as much of a difference on a car with stock exhaust. The exhaust change on my car made more of a difference than this manifold swap did. I don't know if
that's because the old "stock" exhaust was absolute junk, or if the new one is that much better or what. Just keeping in mind the "package" idea - it has to all work well together.
Pictures below show the manifold as installed, and where it needs to be filled so that it can bolt on to the big port head without having
huge vacuum leaks.