Porting my plenum on my 85 TPI!

Nelson84

Nelson84

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Car
1984 Z51
After:
Porting plenum
Air foil
SLP cold air intake
Coolant bypass on throttle body
Under drive pulleys
Hypertech chip
Air pump delete
10 mm plug wires
Catalytic deleteB&B catback
3.54 gears
Adjust fuel pressure

I'm guessing a 5 - 8 hp gain.

Then rear hatch wing should be at 35 hp
 
Hopefully the porting plenum is the first step on the list.....

Nelson84 said:
After:
Porting plenum -Not worth it unless you're doing runners or swapping out the runners. Runners first and then port match.
Air foil 0.5hp if anything
SLP cold air intake -I have this but can't say how much of difference it made. The improved filter over OEM is the difference. 3hp
Coolant bypass on throttle body -No gain, no loss
Under drive pulleys -Very noticeable difference as this modification affects all points of the power band. 10hp
Hypertech chip -85 ECU sucks, chip won't do much. Upgrade ECU and get 10hp
Air pump delete -Cleans up the engine bay. 3hp
10 mm plug wires -0hp
Catalytic deleteB&B catback -if no headers in place 15hp
3.54 gears -I went to 3.07 and really felt the loss of torque down low... wasn't as fun and actually lost time at the 1/4. I'm sitting on a SuperRam intake which should complement the 3.07 better.
Adjust fuel pressure -Noticeable difference on car without tune. 5hp

I'm guessing a 5 - 8 hp gain.

Then rear hatch wing should be at 35 hp. Ditch the wing and get the Z51 front lip
Click to expand...
 
you would have to dyno it, or take to the track see the results. Once you start opening the ports, or larger intake manifold car looses bottom end in exchange for top end sometimes.
 
88blackz51 said:
you would have to dyno it, or take to the track see the results. Once you start opening the ports, or larger intake manifold car looses bottom end in exchange for top end sometimes.
Click to expand...
yes you are right about loss of torque when you open intake etc..to let it breath..if you want to build a tpi (which is a great motor) you must commit urself to improving every part to achieve maximum results...its normal to think more air more gas = more power but the way the tuned part of the tpi works is as soon as you modify/improve the air flow you lose torque which can ruin the fun of the car..so having said that the long laundry list will be more air, more gas, and there are a ton of ways to skin that cat but almost more important is replacing the low end torque that you'll lose and there are 3 ways to do that (1) is moooore cubes (383 or more) which will give you mechanical torque (2) is more gear higher numerical number (3) is both...I am struggling with whether to keep the stock appearance or go for the more modern upgrade and ls swap it...I am old skool myself so am leaning towards keeping it stock looking
 
I wouldn’t worry too much about loss of torque. Yes you will be down in torque in the low rpm’s but only for a second so you probably won’t even notice. I didn’t.
When I swapped in a mini ram the DYNO showed a loss of torque at 3750 rpm but at 4000 rpm I started making more torque than the high flow tpi did.
 
If you’re just porting out your tpi, you won’t loose bottom end torque.

A tpi is “tuned” by the length of it’s runners. If you don’t alter the length, you don’t alter the torque/rpm relationship. Fyi: the runner length isn't just the visible exterior curved tubes, it’s the total length from the upper plenum to the rear face of the intake valve. It works out to somewhere around 21 inches. Thats one heck of a long intake runner!

If you siamese the runners or the base, you are effectively increasing plenum volume and decreasing runner length. That will move your torque peak up the rpm range.

If you “open up” a tpi, you actually gain more torque everywhere, but you stay rpm limited becuase the same runners that use wave tuning to ram air into the cylinders at certain rpms cause a restriction at higher rpms. Since you don’t alter the length, you don’t alter the chsracteristics. If you open up the tubes and manifolds, you can cram more air in there but the runner length still limits the rpm range. You make more power, ut at the same rpm limits. Thats why most tpi engines “lay down” around 4500-5000 rpm: runner length.

Theres also not a lot of sense in “porting” a stock tpi. The lower manifold is the biggest restriction in the intake system and theres not enough “meat” to port it out the way it needs to be. If you want to modify a tpi lower (at least to where it makes an improvement) you need to have the roof of each runner welded to add material to port it out. Other than that, your best bet is to find one of the “big mouth” lowers (edelbrock, accel, etc) that went out of production a while ago or cough up $1500-2000 for one of the FIRST tpi systems. The older lowers are hard to find these days and very pricey. The FIRST system makes a metric s-ton of power, but you’re going to have to pay through the nose to get one.

Now, if you do the lt1 intake, super ram or stealth ram install, you make more hp at higher rpm but it costs you at low/mid rpm. The reason is you are installing shorter runners.

This is one of those “pick your poison” things. Higher rpm hp or low/mid range torque. It’s not a “dog” either way you build it, it just means you need to choose the right power delivery for what you want to do with the car.

Don’t forget the cam. Most of the big power lives in the hewds and the cams.

Lets also not forget that you can only go so far with the hard parts before you need to get into the ecm and tune to the new parts. Even the MAF system can be over-taxed by mechanical changes and need some “tweaking”.

Good luck.

:)
 
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Tourmax is spot-on. I’d only add that an engine is a glorified air pump. Anything you can do to help it breath is beneficial. I had my TPI unit (runners, base and upper plenum) given a respectable porting just for this reason knowing full well the inherent limits of the intake.

Don’t go overboard on a ‘big mouth’ TB. The TPI as you have it won’t be able to make use of it.

Later,
 
korvette klown said:
ok then that's where gears and a converter come it to play...but that's what I was sayin b4 unless your committed to improve every where you wont get what you want and if u do commit big money
Click to expand...
Again, yes and no.

Porting out an intake or heads is not a simple process. “Gasket matching” is, but actual porting is not.

If you mess up the port you can negatively affect everything from port velocity and cylinder filling to turbulence and even inadvertently adding restrictions. Something as simple as wall finish makes a significant difference and even that is differnt depending on the engine (ie: wet or dry manifold, etc).

If you get it wrong enough, it won’t make a difference on what you do with gearing, stall speeds or cam profiles. If the cylinder filling is buggered, you can’t make it back. You either have to fill it (ie: welding, epoxy, etc) and re-port or chuck it out and start over.

The scary part of it is that it doesn’t take much to get it wrong to the point where you turn the engine into a “dog”. Make a port too big, change the profile too much, raise a runner roof too much or even smooth out a bump or casting thats there for a purpose and....bingo; poorly flowing port and a dog until you spin the living bejesus out of it (and even that might not make a diff).

Toss in a TPI manifold and it gets 10x worse. They are very easy to mess up because of thier tuned “ram effect” and the fact that GM left virtually no room anywhere in the casting to hog out. They were on a weight savings kick chasing MPG’s and it showes up in every part on the car. The intake didn’t escape the accountants pen any more than the rest of the car did.

For example: there’s no way to significantly improve the lower intake manifold unless you get a couple pounds of Aluminum welded to the runner roofes and raise the injector bungs. Which means you need to rework the fuel rails and the feed lines. Then you have to get into the ecm to make sure your VE and BLM tables haven’t gone out the window.

We haven’t even gotten into the problems you’ll run into with the connecting pipes and upper plenum...

Once you find out how the engine runs after “porting” the lower, upper and connecting tubes, you can get into matching cams, TC and gears....although you CAN do calculations before hand and chnage out the cam, gear, TV, etc and hope your math matches reality (it almost never does, close, but not match).

Porting isn’t a simple thing. It’s a big change that can make it stronger....or it can kill it completely....
 
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If your serious about supercharging and keeping the stock ECM, give Greg at Blowerworks a call and ask about their MAF and tune for stock engines. The factory MAF is far too fragile to hold up for long in a forced induction application
 
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