Aggravated4life

Hey everyone,
Wanted to make a little discussion on what works for the L98 TPI motors.

Having said that,as far as the L98 goes,it appears that a larger intake manifold offers no real gain but larger runners like ASM does.Even though GM built the TPI for suiting a 305,it's TPI flows enough VE(volumetric efficiency) of air to feed a 350 motor for its powerband to runner length size.

Installing larger runners seems to have a positive effect for a little more HP and Im guessing its because of the change of pressure.

Does anyone think that maybe larger runners,ported plenum,etc will make more gains with a stock manifold compared to a larger manifold?

My idea is that maybe the increase in mass of air in the plenum and runner volume will charge the intake better,improving velocity.
A larger intake,while being able to flow more air over time,wouldnt have that filled charge the stock intake would get.
(Just a guess,any other ideas,chime in)

One of the reasons I say this is because,a few examples Ive read over the years have shown no real gains with a larger manifold.When the larger runners were bolted on,10-15 HP was recorded.I think Vic here has an example of this,but not sure if it was him.

I wouldve thought with a larger manifold,larger runners,at least 25-30 HP would be seen.I havent seen this yet so wanted to know your thoughts about it.

Has anyone seen a 10-20HP gain with a larger manifold and another 10-15 HP with larger runners?

Keep in mind im speaking of a stock motor with only bolt ons.Im gathering info. for a small project I want to do and wanted to hear some real world data.Dyno graphs posted by catalog companies do not impress me.Every car is different and subjected to different conditions while sharing the same components as similiar models.

Any ideas,corrections,feedback,is appreciated.Just want to hear others thoughts on the subject.
Thanks!
:)





[Modified by Bill's86Coupe, 9:47 PM 5/16/2002]

scorp508

Vic gained 0 from the larger intake, but then made gains when he added the AS&M runners. The runners are really what is holding you back as far as I'm concerned.

SurfnSun

depends on how the motor is built. More cubes= larger intake a must

65Z01

Vic'89 did one half the experiment: base alone=0gain; base + runners=15hp
I don't know if anyone has done the other half which would be runners only.

I have L98 mods data that predicted about 15hp gain from base & runners.

You might want to try just the AS&M runners to see if they make a nice gain with stock base. You can always do the base later if not satisfied.

Vette9d1

All I know is after I installed LPE runners, Accel intake manifold and ported the plenum my car feels a significant amount faster starting at about 2300 rpm all the way up to 5300rpm. Before it was a waste to go above 4600. Unless there is something wrong with your car you will notice a difference!

Aggravated4life

Thanks for the replies so far everyone.

Its good to get different ideas on what has worked for some.
I would imagine as with what scorp said,the runners may be the main restriction when it comes to the stock set up.

I do know that more engine mods would require different intakes and such,but im keeping this subject in particular to stock motors with the basic bolt ons.

Also,if the siamese stock intake makes more HP,Id magine with larger runners it may be better,and then we can save 375-450 instead of buying a larger manifold.

However,Vette9D1 brought to my attn that his mods has helped his car pull better in the upper range so cant rule the larger base out yet.
While I do know the intake manifold has been considered the main restriction for TPI for years,it appears a larger manifold did any better for the stock engine unless maybe there were larger runners with it.
Keep em coming people.

:)

SonnyinVA

has anybody put an LT-1 intake on a L-98?? what results would you guys expect from this swap??

Dr. Evil

Maybe my car is a freak but I did before and after dyno tests on just the accell manifold. I still have the stock runners/plenum/throttle body. I did however mildly port the accell manifold before installation. Just a good cleanup. I got a solid 15 rwhp gain. I have a dyno sheet but it's not scanned in. I think it all has to work in conjunction, the manifold/runners/plenum. I'm hoping to get a SR upper sometime on here to see what that will do on a stock longblock L-98. Mods are in sig.

Vic'89

Bill,

As stated by the other members and yourself, I have some track data with the Accel base + stock runners + ported plenum vs. the Accel base + the AS&M runners + ported plenum.

The reason I did the base first was because of the dyno data that redsixspeed has. I wanted to see if I would see a gain also. I didn't dyno it, but track tested it. There was no gain in ET or MPH.

Next I added the AS&M runners and did some track testing. There was a .15 ET gain and 1.5 average mph gain in warmer weather.

For $800+, the gain is NOT huge. For example, for $90, I gained .10 from a crank pulley.

If people are expecting it to make a night and day difference, they should consider another mod.

Vic

grumpyvette

read this, http://www.thirdgen.org/newdesign/te...meseport.shtml
I bought and ported the slp siamese runners like these and ported the stock plenum and base and got about the same improvement that the others got (1.5-2 tenths in the 1/4 mile the big mouth TPI base added later gave another .05 to .1 improvement so you can figure about a solid .2-.25 improvement for 12 hrs porting and $850, now the super ram and the HOLLEY STEALTH RAM both take less work, have a far greater effect and can cost about the same or less with careful shopping, (installed and running) if your willing to put a hood bulge/scoop on your vette and do the work on the hood and engine yourself you can install the HOLLEY STEALTH RAM for under about $650 not counting paint, I did it for even less, but don,t bother on a stock engine the intake works great,( Im getting more and more power as I learning to tune to its far greater airflow potential) but its designed for the 3500rpm-7000rpm range, that a stock engine spends little time in, for a engine with no other mods the super ram will prove to be the better choice, read this, http://forums.corvetteforum.com/zerothread?id=300678


[Modified by grumpyvette, 3:26 PM 5/17/2002]

Aggravated4life

Thanks for the replies everyone!!
I appreciate it...it brings a little better idea of whats working for stock bolts on.
Vic and red90,thanks for chiming in.

For the person that asked abut the LT1 intake mod,I havent seen anyone here do that but its been done on the http://www.thirdgen.org board for F-bodies.
I would imagine it would increase HP nicely for the mods.

Grumpy,
Ive done the SLP mod too but never finished them.Its on hold for now.The Stealth ram also sounds great but as mentioned,has hood clearance problems so im looking outside that right now,but thanks for the heads up.
I can imagine with a good cam,it would make nicer HP numbers up there without doing any major head work.Of course with head work and etc would be better.

Back to the mods,Most large tube runners are said to see a solid 10 HP gain on stock motors.If the larger intake mod is done,and HP is 15,then its safe to say youll net maybe 5 HP combined with the runners.
Unless the base doesnt do much and the runners add the 15 HP to the package.
:)

PhilPolaski

I'd add up all the components before any dyno testing! Air lid, MAF, Base, Runners, and oh ya a bigger TB>>>> ;-)

More air and then add some fuel... FPR...

160 degree's to keep things cool.. and on and on..

If your going to pull the intake install a cam...

-Phil

Dr. Evil

I got to thinking about this over and over and wondering why I posted a gain where as Vic didnt. I was very careful to match the intake to the heads, gaskets also. I removed allmost all the cast flashing from the inside of my accell base before I put it on. I actually ported it a bit and got about 1 cup full of metal shavings out of it alltogether. My plenum had allready been ported before I installed the base. As for the runners, I DID flare the lower ends on them so it would be a smoother transistion from the runners into the base. By flare I mean I used a die grinder and removed a little bit of metal from the thick flange area where they bolt up to the base. I kept pretty good notes on everything and on the dyno sessions. I made sure my timing was the same as well as my fuel pressure. Same plugs etc etc. I also thought that maybe there may have been something wrong with the car that maybe I wasnt aware of that got fixed without me knowing it when I swapped the base in but the stock dyno showed 216 rwhp and 317 rwtrq and succesive dyno sessions were right in line with where the car should have been at any particular level of mods. I really expected you to pick up a solid tenth at the least Vic. [scratches head] I'm left wondering if somethings amiss. FWIW, I dont drag race that often but enough to know that I picked up a solid 2 mph from mine.

Vic'89

Redsixspeed

You have to remember that we both did different types of tests.
Maybe on the dyno there was some gain , I have never dynoed my car, so I don't know. Also, I didn't touch the stock runners at all, no porting or anything.

There were a few other people that installed the base and didn't record any gains. They chimed in on my "intake - no gains" post.

Vic