sack23

iTrader: (2)

Hi, hope I can have some guidance in increasing the RPM band on LB9. Not to fun shifting around 4400 rpm during track days.

My current set up is a 1989 TPI M5 3.27 rear's. With the following.

Mod Maf and ram air scoops
Air foil
Bosh II injectors
1.6 RR's
MSD Dist, Coil, Ignition box and wires
Edelbrock headers and 3 inch cat back
Fuel press regulator at 46 PSI
AC/Air delete
Small pulleys

Short term plan is to drop in a set of L98 aluminum heads along with an Edelbrock base that I have sitting around. Also the cam and spring will be replaced.

Also I'm considering buying a set of runners, but I'm not sure if it would be worth it.

Will the above combination increase my RPM potential materially or the gain will not be significant?

thanks in advance.
Sac

Drew

iTrader: (58)

The T in TPI comes from the runner length. You can do whatever you want, but if you don't change the runner length, the intake is still going to be tuned to the same RPM. That's where it'll always want to run best.

sack23

iTrader: (2)

Understood, basically an can increase my Peak HP but where it peaks will remain relatively the same.

Thanks

tealman92

Only way to increase rpm on the tpi engine is to modify the intake system. Aftermarket base manifold ported out, larger tube runners or full siamesed ( not longer) runners ,ported plenum. Stock throttle body for the 305. Tpi falls on it's face north of 4600rpm unless the intake manifold is modified. Bolt a miniram intake on and instantly go to 5500rpm with no other mods.

sack23

iTrader: (2)

Got it, so maintaining the same runner length, but increasing its volume can have a small increase in the RPM band.

Still not sure if worth buying aftermarket runners to go along with my edelbrock base.

Sac

tealman92

The edlebrock base is only slightly larger then the stock one. It needs significant porting to actually flow more then stock. Larger runners like the as&m runners with a ported to match plenum will make a very noticeable difference over stock.

sack23

iTrader: (2)

Will work on porting the base the best that I can. I will be matching it with Comp cams (08-502-8) 218/224 .528/536 with 1.6 RR's Hopefully this along with the L98 AL heads will help.

tealman92

5.7 heads on a 5.0 isn't a wise direction. Do a search on here about it.

chazman

iTrader: (4)

If you remove the wall in the plenum, behind the TB, you'll get an extra couple hundred usable RPM.

Thirdgen89GTA

iTrader: (5)

Just a question. How many miles do you have on the heads now? On a 5.7 the yellow line is 5000, and the red-line is 5500rpm. How much extra RPM do you want to run?

The springs may not be in good enough condition to sustain high RPM loads like a track day might generate.

tealman92

just because the tach has those colors on them doesn't mean you are actually making power up to the redline. Peak power is 4500-4800 tpi 5.0 or 5.7. once you hit around those rpm's the torque falls off and horsepower falls. Tpi makes it's torque and power down low and pulls hard to about 3300 rpm then it goes flat on the Dyno then tapers down after 4000 rpm. Do a search it's very well documented. Now take the exact same engine and bolt on a miniram intake manifold and you will see a big difference in rpm

Thirdgen89GTA

iTrader: (5)

I'm not talking about power.

I'm talking about valve train stability.

As an example. The valve train in my GTA is built to handle upwards of 7200rpm even though peak power is not going to be that high. The engine was built to play all day at a track like Road America where mid range and top end power is supreme. The main straight is 4100ft long, and there are two other sections where 150mph+ is possible.

sack23

iTrader: (2)

What I have is an 305 with roughly 60K miles. Engine starts to fall flat around 4600 I occasionally spin it to around 5200, but does not really pulls up there.

One of the reasons why I was thinking in using the 113 heads, was to put better springs and drop some weight along with a small benefit in flow. I know I was going to lose TQ but was hoping to at least increase my rpm band.

I will also port my plenum to get as much as I can.

Sac

Thirdgen89GTA

iTrader: (5)

You won't need anything wild, exotic, or expensive with a planned power band that sits under 6000rpm.

I was just pointing out my own concern over taking a 28yr old engine with a indicated redline of about 5500rpm to the limits it had when new. Age can have affected the springs and increased the possibility of a catastrophic failure.

I know the temptation that exists on track to ring the engine out.

sack23

iTrader: (2)

One of the reason I leaned to the 113 was the screw studs. I will replace the springs to match the cam. Hopefully the bottom end holds up.

Thirdgen89GTA

iTrader: (5)

I'd be less worried about the bottom end as long as the cranking compression is balanced across the cylinders.

sack23

iTrader: (2)

You think stock runners are ok for my setup?