This is a problem i see in my friends firebird as well. after 4k it seems like the power falls off the face of the planet. what is this caused by? is it because the runners are too small? what is the best way to improve top end power on a budget?(no giggle juice) also where can i purchase what i need to fix this? i searched and couldnt find this problem. Thanks

 

What I've done is: Have my plenum ported, as well as SLP runners (ported) and an Edelbrock lower. You can also
run K&N filters, and gut your airboxes. All of this will help..

 

welcome to GM TPI

torque monster below 4k
cement block after 4k

 

Thanks, hey is that edelbrock lower emmissions legal? Also do you have part numbers or a web page w/specs and prices?

 

50 state legal, search summit or use google, there is a bunch in our database and somewhere in our faq/articles section.

 

Stock runners are just fine for a 305 TPI.

To get more power at 4000+ RPM requires a different cam, better valve springs, and better exhaust.

My engine pulls hard to 5500+ with the mods I have listed.

Have fun!

 

yep

 

 

 

I second M. Hall. - They do make great truck intakes, especially when you push a blower through them.....

Anyhow, as has been stated, a little port work will go quite a ways, but to truely achieve high rpm power, you need better flowing heads, a bigger cam/springs, and a better flowing intake. The TPI just isn't designed for much above 4k. With the proper work it can support to about 55-6k, but a shorter runner intake would make more power at that level.

 

Your valve springs are probably dead, my car did the same thing and all the porting in the world wouldn't solve it. Replace those springs and you should see solid power past 4k. Just hope your cam doesn't look like mine with nice grooves cut in it.

 

A 305 isn't a high RPM engine to begin with. It doesn't matter what intake is on it.

 

my buddy had an 82 z with a carbed 305, he spun it to 6500 on a daily basis.

 

That's nice, and what numbers did it pull on a dyno or a race track? I could rev a 2.8 to 8,000rpm, it still doesn't mean it's making power at that RPM.

 

Nor was the 350 tpi....

 

the stock intake will work fine with your 305. port out your plenum and stock base. there are some tech articals on that in this site. some edlbrock performers and a healthy cam. what year is your motor?

 

Once again, I will almost garuntee your immediate problem is the valve springs. They're weak from the factory and running them hard pretty much destroys them. With a stock cam you'de be fine going with a generic set of "Z28" springs or any .550 lift genero springs. Now for the porting, I recommend porting the plenum and base to EVERYONE who owns a TPI, it's free power and there's alot to be had there. I have a semi tech article just look for the threads I've started in advanced search. I'm assuming your car's a 91 so your cam shouldn't be the issue, after the porting I'de be after a new prom, someone on the board can probably set you up with a mild performance prom for your car, that's all you should really need. Good luck with the mods.

 

valve springs could be a problem. i put a set of shorty headers on my 91 TA and it pulls better on the top end now. if you have the low output TPI 5.0 changing the cam would help. cam specs on the small one are like 179 @.050 intake .350 lift and 194 @ .050 exhaust .394

 

definately check springs and timing. while your at it, throw in a set of 1.6 roller rockers
by your screen name, i suppose you have a 91 Z28 which should have the L98 cam in it. 1.6 rockers will help that out. if you had a older car with the peanut cam, youd have to change the cam to spin the motor to 4500rpm +

but exhaust mods will definately help it breath up top end. also gut the air intake boxes to let more air in. those mod alone should make that motor pull to 5K easy. my 350 car pulls well to 4500. 305 should do 5000

 

Even 1.6 stamped rockers will be a nice step up. If you want to go full out pull the heads and port everything from the heads up and have a set of 1.94 valves put on the intake side. Headers and exhaust are pretty much mandatory on a third gen, and are usually the first thing people do. However good power could be made for completely free minus the bits, grinder, and time consumed by porting.

 

well i took everyones suggestions into consideration and tore my engine down over the last few months, what i ended up doing is shaving the heads putting new springs and roller tipped rockers. 1.94 1.55 valves (i think 1.55 im not sure need to double check) thinner head gaskets. heddman shorty headers. crane cams #CRN-104221. basic smoothing of the plenum interior and the intake base. It runs very nice but i cant drive it till the 2 two feet of snow and ice melts away from the garage door!

 

Yeah those motors really only make power up to 4k. cam and springs for top end power man.... Those 305's are high compression and are torquey motors. they are basically work horse motors

 

That should pull well to about 5300 RPM. I'd guess 250+ FWHP. Probably put you at a 14.5 or better 1/4 mi.

If you are still running stock fuel injectors you may want to get an AFPR and raise the fuel pressure a few PSI. The reworked heads/cam combo will flow better and allow more fuel mixture at WOT.

 

yeah i ordered an Adjustable regulator a couple days ago off summit it should be here tommorow. People keep telling me i should be around 14.5 but keep in mind i live at 4000 feet and my 2000 ss runs a 14 sec e/t

 

How exactly do your gut your airboxes?

 

if you got the one with two filters at the front .. all i did was unscrew the little "flaps" i think it was 4 screws per filter .. then put in some k&n filters ..


want to have some fun .. get a screw driver and undo the intake completely .. pulls like a **** then ..
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oh .. just thought of something ..

try a new fuel filter .. that caused me to have no power at all when i first got my 91' z28

there VERY easy to change out ...

 

fuel filter... check

 

Fuel filter, oil change, gut airbox, knock out EGR walls in plenum *port while you're in there* change valve springs, relash vavles, set timing, rev to 5000 without issue. If you have the 1986 style engine, change the cam. The cam's to weak to really make power past oooh say 3800rpm.