88L98

ok as most of you know i have siamesed the intake ports on my base manifold and got pretty good power gains from it. as of now ive got something that i dont like, i have an air/fuel ratio gauge it shows im running lean in Park. once i put it in drive though it bounces around in the normal range. i dont know if this is due to my shorty headers not heating the o2 sensor or not, but i will look into it. i used a G-tech last night, from a friend that i had borrowed it from before i did this mod and i ran a 13.98 at 99mph, and last night i clicked off several 13.3X-13.4X at 103-105. the times were very consistant with the g-tech, all being within several hundreths of a second. (very low 13.4X, to very high 13.39). im gonna go jack with it while i have free time and go buy a heated o2 sensor to see if i can fix that lean reading in park.

GRX

Awesome. Now do you 'feel' you've bounced the peak HP rpm up a bit???

john25

Did you port the stock base or an aftermarket base? Do you have any pictures of what you removed and before and after pics?

88L98

oh yeah the car pulls and makes good power to 5300-5400

its a stock base

here is some pictures http://forums.corvetteforum.com/zerothread?id=153200



[Modified by 88L98, 12:42 PM 9/22/2001]

GRX

So if you got a 'big-mouth' manifold with SR and siamesed the SR runners?
Wonder if that would peak close to 6000rpm? ...and still be smog legal!


[Modified by GRX, 11:04 AM 9/22/2001]

NoWorries

Which 02 sensor are you running right now? My A/F guage is being run off of a cheapy NAPA brand sensor and I cdon't get readings until about 5 minutes after the car has been started up.

I adjusted my fuel pressure for a heated up idle(computer leans out the mixure) and smelling the exhaust at a cold start-up, the mixure still smells a little rich, but its better to be rich than lean...

As for the times!!!!! Thats awesome!

AquaMetallic94LT1

99 mph to 103 - 105 means increase in peak hp. The QTR mile time increases are impressive.

88L98

*UPDATE*

i just got back from doing some more playing with the fuel pressure, and doing some runs. i managed to get a best of 13.26 at 104. the thing that i was surprised on these last couple of runs, my tires are chirping on the 2-3 shift now too. it never did that before. i had to order the heated o2 sensor so i dont know if its gonna fix it yet. maybe i just need some chip tuning to enrichen the park idle mixture a tad.

88L98

noworries, i am running a napa o2 sensor also. i know it shouldve been warmed up because i looked at the air/fuel gauge after i got home from doing the 1/4 mile runs, and it stayed in one spot on the lean side. so i threw it in drive and the gauge started bouncing around in the stoich region. then i put it back in park and it went back to the lean constantly staying in one spot again. maybe the increased airflow needs a little more fuel at idle.

65Z01

Though I'm sure you already posted, what are your mods again?

And have you upped the FP since the base mod, or was that when you inserted the quarter to bump the FP?

Sorry, but the memory is the 2nd thing to go...now what was the 1st...:confused:

Chris@SD

How old are your O2 sensors? I have seen this a few times in cars with non heated O2's. It is because they are not hpt enough. When you put it in gear, the load on the car makes it a little hotter. That is when it will start bouncing from lean to rich at idle.
Most of the time new O2 sensors will clear up the problem, but it looks like you have already gone with a heated one, which will also fix the problem.
Good luck,
PS, what you have essentially done is create a second plenum, effectively shortening the runners. I have though about this before, but I have never tried it. I was wondering how the air would react to building velocity in the runner and then stalling in a second plenum and then picking up air speed again.
If you have before and after dyno or actual track times, I would love to see them.

88L98

i have shorty headers, muffler eliminators, k&n filter, the adjustable fuel pressure mod with a nylock nut tacked on like you suggested. i also ported/polished the heads while i was doing the manifold too. im about to get some semi-siamesed runners and port the dog chit out of em pretty soon too. the motor is a new stock longblock from Scoggin Dickies part center in lubbock texas. my motor seems to be running the best at 50psi at WOT. i was at around 46-47 with the quarter in the regulator, then i used your idea and raised it to 50. i ran the 13.26 with the 50psi that i just did today. man i can understand the feeling of being close and wanting to break into the 12s now! :cool: im gonna get some real track times and a dyno as soon as i can find some free time.


[Modified by 88L98, 6:09 PM 9/22/2001]

65Z01

Thanks much for the feedback, this concept obviously has realy peaked my interest. Though I may not see gains like yours since I'm still running stock heads I think I could benefit from this mod (and just when I was done for the season).

It's good to hear that AFPR idea is working well for you. You realy need to be able to adjust it as you've found out. In fact I think the next time out I may try another 2psi.

Now that you have her breathing better up top, have you tryed upping the shift points? If not this may be your ticket into the 12s, along with good weather. I expect your trap speeds will be a little below those with the G-Tech, from what I've heard. But still your relative gains are very impressive.

Aggravated4life

Very :cool:
How much did you knock down into the manifold? DId you say 3 inches down or so?
Its almost amazing the super tuners never caught onto this, or maybe they experimented but saw no gains at the time.

I also dont think there would be a air fuel ratio problem n the cylinders any more then the stock set up, since you still have a few inches of runner divider wall left inside the base.But its good you looked for that since someone else said they thought they had a problem with it due to the mods.

Im also thinking this mod,with siam. runners that are ported will increase manifold pressure and volume providing alot more air then before.In fact, all the engine could inhale.

It would also be great if there was a way for us to see the VE of the airflow from 4,000 rpms-5,500rpms as compared to the stock set up.(thats usually where the TPI begins to choke)

Aggravated4life

One more question...when you siamesed the intake, how did you shape the divider wall after cutting/porting? Did you leave it flat (___|__)or a crescent shape(__)__), or more sharp knife edge cut?(__>__)

Hope the little illustration helped what I was asking.

Chris@SD

Speaking from an aerodynamics point of view, you want to leave the divider fat and round for the best air speed and flow. Knife-edging is a no-no.

Aggravated4life

...Thanks for posting that.Wasnt sure myself what the best way to do it was.That makes alot of sense since it seems all the best aerodyamic machines in the world are rounded off and not knife edged or pointy.

88L98

bills86, i knocked down about 3 1/2 inches into the manifold. i first had it at a squared edge about 3/8 of an inch wide but i rounded it down real smooth with a dremel.

65Z01, my heads are the stock/ZZ4 aluminum L98 heads. they are just ported and polished now. i havent played with the shift points yet, but im gonna be putting in a ZF6 sometime this winter. ill play with the TV cable tommorow since im gonna be free.

good thing now though, i got the oil leak at the rear of the manifold fixed. i still have the same o2 sensor issue, but i dont idle in park for very long so i dont think its gonna hurt anything. i guess its not hot enough cause the sensor is less than 6 months old.


[Modified by 88L98, 8:56 PM 9/22/2001]

88L98

hey 65Z01, about that spark plug mod, you just grind it down until it is just barely overhanging the center electrode? that 10hp might get me that much closer to the 12s :cool: i think im gonna do that tommorow along with the TV cable

65Z01

Yep, that's the deal. I haven't experimented (yet) with grinding it back past the edge of the center. It'll definitely up your trap speed (HP).