L98 TPI Porting Questions
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From: OBAMA IS HITLER
L98 TPI Porting Questions
The stock plenum was ported at the TB area to accomodate a 58mm TB. With headers & full exhaust upgrade, 1.6RRs (and possibly a cam, still out to lunch on this), archives here mostly point to keeping the stock 48mm on. Since the porting in the front of the plenum is larger now, will this cause issues with airflow, ie, will I lose bottom end?
The stock base was ported a little, mainly to open up the area more where the fuel injectors can give a full spray (L98 base seems to encumber the fuel spray into the cylinders somewhat. Is this a "full base" port, or not?
How important is it for the porting to be super smooth?
The stock base was ported a little, mainly to open up the area more where the fuel injectors can give a full spray (L98 base seems to encumber the fuel spray into the cylinders somewhat. Is this a "full base" port, or not?
How important is it for the porting to be super smooth?
Le Mans Master
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From: Kempner Texas
Re: L98 TPI Porting Questions (bradvette)
I did the same thing. Opened up the plenum for a BBK 58MM, installed it and, after a while, decided I didn't like the abruptness in throttle response it caused.
So I went back and reinstalled the stock 48. Ran it that way for several months without any problem at all.
I'm now running a 52.
"Full base" port or not?" Depends on who's defining "full base".
The most recent intake porting job I had done which I would consider "full base" involved cutting the intake apart, modifying the insides and welding it back together.
Wet flow and dry flow call for different surface finishes. Wet flow, with air and fuel mixed, need a slightly rough surface in order to keep the fuel in suspension. Dry flow - only air - likes smooth surfaces.
Polishing of the intake ports on the heads has seemed to fall out of favor because of the fuel separation it causes. Exhaust ports, I believe, like smooth.
Check out Air Flow Research's website and see if they have a Tech Article posted on this.
Jake
[Modified by JAKE, 12:25 PM 10/29/2003]
So I went back and reinstalled the stock 48. Ran it that way for several months without any problem at all.
I'm now running a 52.
"Full base" port or not?" Depends on who's defining "full base".
The most recent intake porting job I had done which I would consider "full base" involved cutting the intake apart, modifying the insides and welding it back together.
Wet flow and dry flow call for different surface finishes. Wet flow, with air and fuel mixed, need a slightly rough surface in order to keep the fuel in suspension. Dry flow - only air - likes smooth surfaces.
Polishing of the intake ports on the heads has seemed to fall out of favor because of the fuel separation it causes. Exhaust ports, I believe, like smooth.
Check out Air Flow Research's website and see if they have a Tech Article posted on this.
Jake
[Modified by JAKE, 12:25 PM 10/29/2003]
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From: OBAMA IS HITLER
Re: L98 TPI Porting Questions (JAKE)
Thanks Jake. Aside from the base you describe, it sounds like I have just what you explain. The plenum work is quite smooth, especially all around the runners as they meet in the base as well (plus flaring), and the base a slightly rough. My local shop is going to do a few finishing touches on it anyway before they do the install.
Le Mans Master
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From: Kempner Texas
Re: L98 TPI Porting Questions (bradvette)
Thanks Jake. Aside from the base you describe, it sounds like I have just what you explain. The plenum work is quite smooth, especially all around the runners as they meet in the base as well (plus flaring), and the base a slightly rough. My local shop is going to do a few finishing touches on it anyway before they do the install.
The difference can only be observed on the flow bench and sometimes very small changes have a radical effect on flow.
In the case of the manifold I mentioned, Bob Jones ended up cutting it open, modifying the inside and re-welding it a few times. Then, with that intake bolted to one of the Brodix heads (so they could be flowed as a unit just as they would run on the engine), he got 340 CFM @.700 (28").
That's really the only way to determine true flow. Bob explained that the intake manifold must flow MORE that the heads flow or the manifold will present itself as a flow restriction. So in our case, it wasn't the heads that needed the work, (because they flowed 340 already), it was getting the Mini-Ram to flow close to 400 cfm.
Bottom line: if you have a great set of heads that flow well, but bolt a weak flowing intake manifold on top of them, it'll pull the head flow down tremendously. Bob said even to a point that is BELOW what the intake would normally flow on it's own.
There are some airflow dynamics going on that I don't pretend to understand, so I have to trust in the superior knowledge of others.
Hope this helps.
Jake
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From: OBAMA IS HITLER
Re: L98 TPI Porting Questions (JAKE)
Thanks again Jake. Based on what you said, I should have no problem. I'm dealing with an intake that adds airflow over normal stock intake, my heads are D-113 stock that came in my 90 L98.
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Re: L98 TPI Porting Questions (bradvette)
How important is it for the porting to be super smooth?
