L98 plenum porting
Thread Starter
Racer
Joined: Sep 2015
Posts: 261
Likes: 24
From: Israel
Team Owner
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From: Phila., PA burbs
Le Mans Master
Joined: Aug 2015
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From: St. Charles MO
The primary flow limitation on any TPI intake is going to be dictated by the long runners and resonance. That pretty much guarantees your flow drops off a cliff a little over 4000rpms, no matter how much you hog the runners and base out. There's just no getting around that unless you completely change to another intake.
Race Director
Joined: Nov 2003
Posts: 12,220
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
Best I could tell (from feedback over the years), the larger AS&M or TPIS or Accel runners -- combined with a larger-bore base would add ~20hp to a 350. That was confirmed by .2ths in the 1/4m. Porting doesn't add much... And really, if you want even LARGER [long] tubes than AS&M, you should be looking at a FIRST or even a SuperRam.
Larger tubes are "mandatory" for anyone building a TPI stroker....because the original tubes weren't even designed for a 350...but a 305.
Siamesing either the tubes or the base are the better ways to change WHERE power is made. And, as noted, power made at higher rpms moves the car faster. The unclear part about siamesing is how/why reversion waves can be disturbed in adjacent tracts. But, I was also convinced that siamesing isn't necessarily as promising as it seems either.
Flat-out TPIs can be an expensive engine to modify. Largely, that's because of the intake. They aren't really worth spending much time on. If you want more power, look at other intakes.
Larger tubes are "mandatory" for anyone building a TPI stroker....because the original tubes weren't even designed for a 350...but a 305.
Siamesing either the tubes or the base are the better ways to change WHERE power is made. And, as noted, power made at higher rpms moves the car faster. The unclear part about siamesing is how/why reversion waves can be disturbed in adjacent tracts. But, I was also convinced that siamesing isn't necessarily as promising as it seems either.
Flat-out TPIs can be an expensive engine to modify. Largely, that's because of the intake. They aren't really worth spending much time on. If you want more power, look at other intakes.
Last edited by GREGGPENN; Jan 24, 2017 at 08:24 PM.
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Team Owner
Joined: Jul 2004
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From: Hartford WI
Anything can be done but the question becomes "Why"? What is your "risk vs reward"? Sure, you can port it but as mentioned, headers would yield better results. Cat, not so much other than the ricer effect, aka more noise especially with the LT headers and the Borla mufflers. Probably have to have the thing tuned to maximize the headers. I don't know if the HSR will work for your case but IIRC, some have mentioned benefits with the shortened HSR (don't remember what name) it went under. I'd decide on the intake before I do a dyno tune.
Instructor
Joined: Nov 2016
Posts: 138
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From: Watertown South Dakota
available parts?
Are the FIRST pieces available currently in retail? I know you can buy a TPIS mini and the ACCEL casting, but the ACCEL doesn't fit under the hood, correct? The Edelbrock base is out of production? AS&M is still operating? Are there others? Has anyone tried the Edelbrock ProFlo XT with LS throttle body on the stock ECU? I'm new to TPI and reading thru the old posts makes me feel a little bit out of the loop, like I'm 15 years too late!
Team Owner
Joined: Jul 2004
Posts: 28,378
Likes: 3,261
From: Hartford WI
Are the FIRST pieces available currently in retail? I know you can buy a TPIS mini and the ACCEL casting, but the ACCEL doesn't fit under the hood, correct? The Edelbrock base is out of production? AS&M is still operating? Are there others? Has anyone tried the Edelbrock ProFlo XT with LS throttle body on the stock ECU? I'm new to TPI and reading thru the old posts makes me feel a little bit out of the loop, like I'm 15 years too late!
Thread Starter
Racer
Joined: Sep 2015
Posts: 261
Likes: 24
From: Israel
Anything can be done but the question becomes "Why"? What is your "risk vs reward"? Sure, you can port it but as mentioned, headers would yield better results. Cat, not so much other than the ricer effect, aka more noise especially with the LT headers and the Borla mufflers. Probably have to have the thing tuned to maximize the headers. I don't know if the HSR will work for your case but IIRC, some have mentioned benefits with the shortened HSR (don't remember what name) it went under. I'd decide on the intake before I do a dyno tune.
I wrote here once regarding the thins I've done and want to do. current setup:
- 1985 automatic with stock engine and geabox.
- modified air box lid with K&N air filter
- de-screen MAF
- no catalytic converter.
- Borla mufflers
- relocate temperature sensor from plenum to in front of the MAF.
Few weeks ago I run a test using dynolicious fusion (R.I.P). I inserted the car weight+driver+fuel before the run/test.
For my original question, can I gain few HP by just increasing the plenum volume.
P.s.
Just found these:
http://www.jegs.com/i/Edelbrock/350/7137/10002/-1
The dynolicious results are in metric. HP is wheel HP
Last edited by Yariv; Jan 24, 2017 at 11:18 PM.
Team Owner
Joined: Jul 2004
Posts: 28,378
Likes: 3,261
From: Hartford WI
I'd like to gain much HP as can without an overhaul.
I wrote here once regarding the thins I've done and want to do. current setup:
- 1985 automatic with stock engine and geabox.
- modified air box lid with K&N air filter
- de-screen MAF
- no catalytic converter.
- Borla mufflers
- relocate temperature sensor from plenum to in front of the MAF.
Few weeks ago I run a test using dynolicious fusion (R.I.P). I inserted the car weight+driver+fuel before the run/test.
For my original question, can I gain few HP by just increasing the plenum volume.
I wrote here once regarding the thins I've done and want to do. current setup:
- 1985 automatic with stock engine and geabox.
- modified air box lid with K&N air filter
- de-screen MAF
- no catalytic converter.
- Borla mufflers
- relocate temperature sensor from plenum to in front of the MAF.
Few weeks ago I run a test using dynolicious fusion (R.I.P). I inserted the car weight+driver+fuel before the run/test.
For my original question, can I gain few HP by just increasing the plenum volume.
I wouldn't have descreened the MAF since that does nothing at best and screws up the airflow at worst. You aren't going to need any air more more than what the MAF with the screen does.
Don't think the cat is the big issue unless it is clogged up. Removing it does not really help. Again, I think you are opening it up to flow more than what you need or will help. With LT headers, it will be noisy for no real reason.
Borla mufflers, see above. Headers are going to make a difference as will a dyno tune.
Relocation of sensor is to fool the ECM into thinking it is colder than it is or so the theory goes. ECM might do what you want for a couple of times but might compensate for it by changing things in the long run. Not sure but I haven't seen anyone report long term gains other than the sellers of that sort of snake oils.
I'm not a big fan of those sort of apps to tell HP. I much prefer a dyno where we have correction for air, pressure, etc.
C
Thread Starter
Racer
Joined: Sep 2015
Posts: 261
Likes: 24
From: Israel
Maybe a couple HP with the ***** cut out in the airbox. Probably your biggest gain without a tune and headers.
I wouldn't have descreened the MAF since that does nothing at best and screws up the airflow at worst. You aren't going to need any air more more than what the MAF with the screen does.
Don't think the cat is the big issue unless it is clogged up. Removing it does not really help. Again, I think you are opening it up to flow more than what you need or will help. With LT headers, it will be noisy for no real reason.
Borla mufflers, see above. Headers are going to make a difference as will a dyno tune.
Relocation of sensor is to fool the ECM into thinking it is colder than it is or so the theory goes. ECM might do what you want for a couple of times but might compensate for it by changing things in the long run. Not sure but I haven't seen anyone report long term gains other than the sellers of that sort of snake oils.
I'm not a big fan of those sort of apps to tell HP. I much prefer a dyno where we have correction for air, pressure, etc.
C
I wouldn't have descreened the MAF since that does nothing at best and screws up the airflow at worst. You aren't going to need any air more more than what the MAF with the screen does.
Don't think the cat is the big issue unless it is clogged up. Removing it does not really help. Again, I think you are opening it up to flow more than what you need or will help. With LT headers, it will be noisy for no real reason.
Borla mufflers, see above. Headers are going to make a difference as will a dyno tune.
Relocation of sensor is to fool the ECM into thinking it is colder than it is or so the theory goes. ECM might do what you want for a couple of times but might compensate for it by changing things in the long run. Not sure but I haven't seen anyone report long term gains other than the sellers of that sort of snake oils.
I'm not a big fan of those sort of apps to tell HP. I much prefer a dyno where we have correction for air, pressure, etc.
C
This was before any modifications. 187 HP @ hubs. Going to re-run it soon again.
Last edited by Yariv; Jan 24, 2017 at 11:58 PM.
Race Director
Joined: Nov 2003
Posts: 12,220
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
I agree with aklim that porting plenum isn't going to provide much at all. I tend to agree with aklim about the removal of CATs too, but obviously exhaust mods helped...and I would conclude MOST of your improvement came from the CATs/mufflers. Maybe your cats were partially clogged?
FWIW, I have (on my laptop) a dyno of a stock 89 that I found in this forum a few years ago. It showed 210rwhp/300rwtq. I didn't think 85 was that much lower so you might have "corrected" a problem with your exhaust mods.
Keep up the passion and interest!
Did you do any retuning?
FWIW, I have (on my laptop) a dyno of a stock 89 that I found in this forum a few years ago. It showed 210rwhp/300rwtq. I didn't think 85 was that much lower so you might have "corrected" a problem with your exhaust mods.
Keep up the passion and interest!
Did you do any retuning?
Last edited by GREGGPENN; Jan 25, 2017 at 04:24 AM.
Thread Starter
Racer
Joined: Sep 2015
Posts: 261
Likes: 24
From: Israel
I agree with aklim that porting plenum isn't going to provide much at all. I tend to agree with aklim about the removal of CATs too, but obviously exhaust mods helped...and I would conclude MOST of your improvement came from the CATs/mufflers. Maybe your cats were partially clogged?
FWIW, I have (on my laptop) a dyno of a stock 89 that I found in this forum a few years ago. It showed 210rwhp/300rwtq. I didn't think 85 was that much lower so you might have "corrected" a problem with your exhaust mods.
Keep up the passion and interest!
Did you do any retuning?
FWIW, I have (on my laptop) a dyno of a stock 89 that I found in this forum a few years ago. It showed 210rwhp/300rwtq. I didn't think 85 was that much lower so you might have "corrected" a problem with your exhaust mods.
Keep up the passion and interest!
Did you do any retuning?
The cat was clogged. all internal stuff was taken off. going to install a resonator instead soon.
In the near future I'm going to test the 85' again using the same dyno.
I'll update.
BTW my Vette in an automatic. 230 in stock @ crank. I read for wheel HP you should reduce ~20%.
Safety Car
Joined: Sep 2001
Posts: 4,150
Likes: 552
From: Glenbeulah Wi
Hi,
The cat was clogged. all internal stuff was taken off. going to install a resonator instead soon.
In the near future I'm going to test the 85' again using the same dyno.
I'll update.
BTW my Vette in an automatic. 230 in stock @ crank. I read for wheel HP you should reduce ~20%.
The cat was clogged. all internal stuff was taken off. going to install a resonator instead soon.
In the near future I'm going to test the 85' again using the same dyno.
I'll update.
BTW my Vette in an automatic. 230 in stock @ crank. I read for wheel HP you should reduce ~20%.
Team Owner
Joined: Jul 2004
Posts: 28,378
Likes: 3,261
From: Hartford WI
All bets are off if it is clogged. However, there are 2 reasons that could become apparent in the future to suggest you should replace it with a higher flow cat. When you put LT headers in, the drone will suck. On that note, it becomes more apparent to Johnny Law to pull you over when passing his small town because it was loud. I have a Random Tech cat in place of the main one. Precats are gone because of the TPIS headers. I plugged up the inlet for the AIR hose and removed all of the AIR stuff with no ill effects.
Team Owner
Joined: Jul 2004
Posts: 28,378
Likes: 3,261
From: Hartford WI
Did the descreened MAF do much? A couple of tuners I talk to say that you can do that but it could throw readings off so best to have it dyno tuned. In stock form, it was said not to do much since the MAF will flow more air than needed unless heavy mods are done.
Safety Car
Joined: Sep 2001
Posts: 4,150
Likes: 552
From: Glenbeulah Wi
Side note: Before I could tune I had 4 different MAF's that I played with on the strip, one all stock and three descreened ones. The car would vary as much as 3 tenths of a second when swapping the MAF's out as the only change. The stock screened MAF was in the middle of the road, some of the descreened MAF's ran faster than stock and some slower. I was surprised at the difference between them when they all appeared to be the same.