I just put on a ported TB in place of my stocker and I can feel a difference. I didn't feel any difference from swapping the stock tubing/hooker catback for the LM2 so I think my SOTP dyno is pretty accurate. I also have the stock descreened MAF and am planning on raising my shift points to 6200rpm and wanted to know the optimal intake size.

I'll try to answer this myself below for a 346ci LS1 with 0.92 volumetric efficiency and hopefully help somebody decide a setup for their car. Feel free to point out something I did wrong. I looked up some CFM numbers at 28" from multiple sources:

Stock MAF: 790 CFM (updated)
Descreened MAF: 840 CFM (updated)
SLP 85mm MAF: 895 CFM
Descreened SLP: 1000 CFM

Stock TB: 885 CFM
Good ported TB: 945 CFM
85-90mm TB: +/-1050 CFM

Required intake air flow for the LS1 at rpm levels: (92% VE est for my setup)

6000rpm: 552.6 CFM
6200rpm: 571.1 CFM
6500rpm: 629.8 CFM

The optimal pressure drop for the engine is 10" or less. The engine would need a crazy vaccum to achieve the above MAF/TB numbers. Here is the pressure drop of the above parts for 6000/6200/6500 rpm. (10.0" optimal)

Stock MAF: 13.49"/14.41"/17.53"
Descreened MAF: 11.94"/12.75"/15.51"
SLP 85mm MAF: 10.67"/11.40"/13.86"
Descreened SLP: 8.55"/ 9.13"/ 11.11"

Stock TB: 10.91"/11.66"/14.18"
Good ported TB: 9.57"/10.23"/12.43"
85-90mm TB: 7.75"/ 8.26"/10.07"

This shows that, at 9.57" @ 6000rpm, my throttle body is flowing optimal and even after I raise the shiftpoints to 6200rpm that at 10.23" it is still close enough. Looking at the bigger throttle body results it looks like overkill for anything under 400rwhp.

My descreened MAF to these results is only capable of giving enough flow to the engine at 12.75" Most likely no more than 5hp.

 

Does anybody with experience think my estimated 92% VE is too high or low? I also saw installuniversity tested a bunch of intake pieces assembled. looking at their results vs my setup of free mod/ kandn/ slp lid/stock MAF/ smooth bellow/PTB it should flow roughly 289 CFM @ 2" or 646 CFM @ 10.0" showing my setup flows enough.

 

NO you do not need a bigger MAF/TB. You are a cam only setup with a full exhaust. the P/P TB, Descreened MAF and LS6 Intake is getting plenty of airflow in. if you really want more air into the engine, get a ram air or cold air kit

 

Thanks, Hitmanws6. What about after I put my 243's on the car? It should still just be enough flow right?

I think most of the missing hp from my dyno was in the stock throttle body because I did feel a small difference. Since I dynoed I did the SLP LM2, flowmaster merged custom y, and P/P TB. I think it should be 375/375 now up from 350/360. Hopefully with the 243's and cometics I could hit 410 locked.

 

On my stock 346 LS1 i have the follwoing for incoming air

home made FTRA
85mm Lid
85mm Z06 MAF
Stock 74mm P&P TB
Stock LS6 Intake
Custom 228/232 cam

 

I do not believe your CFM numbers are at 28"(Hg?)
drop and would like to know the source; Usually CFM
ratings are at a fairly negligible drop like 2"H2O. And
I have seen no testing other than my own, admittedly
crude.

All you need to know is, how much does your MAP
reading drop from (say) 3000RPM WOT to redline?
That (MAP3000-MAP6000)/MAP6000*100% is all that
is left on the table, to improve by inlet tract. For
example 100kPa dropping to 97kPa at the top end,
is about 3% maximum possible airflow gain if every
element forward of the manifold plenum, were made
of smooth shiny too-big pipe and nothing but.

Now improving heads, cam, displacement, exhaust
all increase the motor's ability to draw down against
that inlet lineup, and what is not-worth-bothering
on a stocker, may well become important later on
(as bigger deal restrictions are removed, they bubble
up the list). But there is a very good chance that
your choice of air filter doesn't mean jack, until you
are very, very far into mod madness.

 

I used more than just this source to come up with the numbers to make sure they were right but this is from GMhightechperformance, " SLP's 85mm MAF (part No. 23060, $160), said to flow 895 cfm at 28 inches of water--90 cfm more than the stocker."

http://www.ajlc.waterloo.on.ca/gnttype/200207/111
Here it says 747cfm stock and 800 descreened

http://www.gmhightechperformance.com.../photo_31.html

I think my numbers are a little low for the stock and descreened MAF. I'll redo the math for 790 CFM and 840 CFM

I also saw a post where you recommended getting a 85mm GM MAF, with 410rwhp is there going to be even a 5hp gain?

 

Your numbers made me lose any though I had about needing a bigger TB, still thinking on a 85mm MAF though.

 

Huh? didnt understand what you said

 

Since you made 419rwhp with a 228 cam and bolt-ons which I think is very good shows a stock ported throttle body definately flows plenty for sub 425rwhp cars.

 

This sounds like the old days when people would put a Holley 850 on a cammed 350 SBC, your engine can only ingest so much air, period.

If you do anything, put a GM truck screened 85mm MAF on and save a but load of money over SLP. They make an adapter harness for the install.

 

Yea, this guy at work had a baldwin motion 68 camaro with a 850 or something when he was a kid, he went down to a 750 and picked up a couple tenths down to 11.7.

I'll stick with my ported TB and descreened maf, Maybe the GM truck screened 85mm down the road. Thanks to replys.

 

I tuned my car with the MAF still in the intake tract. Then decided just to see if there would be a difference, so I cut a small section of 3.75" pipe and replaced the maf with it. I did not retune it or anything just went out for a drive, the SOTP dyno was very very pleased. The car went from falling off at 5800 to pulling all the way to 6500. And suprisingly low throttle was unchanged or even a little bit better. Im guessing it was a huge restriction for my setup because it felt like I added at least 15rwhp up top.

 

It could also be attributed to the MAF not being tuned properly. 15hp, not likely.

Go do a back to back at the track and see what it does.

 

JimmyBlue gave you the proper answer on how to help figure out if you have an intake restriction or not. Don't buy **** you don't need.

 

A properly tuned MAF will almost always make identical power to a SD car, so 15hp id say would only be possible if your maf was way out of wack, Most NA cars have no problem running a MAF, the only way i can see a 15hp difference if your maf was tuned properly would be if your car was FI.

 

It was SD tuned with the MAF just in the way, I didnt change the tune at all. 80mm is 3.14" so I added about .4" (ID) worth of intake. Maybe its not 15whp, but it definatley is alot more than it had before. It wasnt an issue with just the cam but porting the heads opened up a whole new can of worms. I had to add injectors and do this to see the full potential.

By removing my maf from the intake tract it basically went from spinning the tyres in first to absolutely frying them off with no potential for grip at all. 3rd gear pulls all the way to 6500 now without a hickup where as before it would fall off at 5800rpm. As soon as I can get some radials and a new windshield I'd gladly test it out back to back since its a 2 minute swap without any other changes.

 

Haha

This is good advice! (and obviously so is Jimmy's about MAP drop).

 

With the mods that you have, with a properly tuned VE table and a properly tuned MAF table (both tuned independently in OL and then married back together) you are fine . Any SOTP gain is attributed to something being wrong in the MAF tune. Your not moving enough air NA, you can't port the heads to that extent to open up that big of can of worms.

 

There was no difference in the tune. There could be nothing wrong with my MAF tune cuz I havent had one in years. The MAF was simply just a connector for the Lid and TB. I never Maf tuned my car with the cam, I used the Maf with all the bolt ons, but just decided it was one more step I didnt feel like doing when I did the cam. So I tuned the cam in SD and havent looked back. I then ported the heads (flow 300 @ .6 and 290 @ .5) and added QTP's (versus my old hooker's).

To each their own I guess. It was a free piece of pipe I had laying around and the results really were mind bottling It was like adding headers and exaust all over again. I understand I shouldnt need it but it definatley liked it up top. I wonder if the previous owner snuck in an LT1 Maf before he sold it? If that is even possible.