305 falls on face after 4k rpm
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Car: 1991 Vert Z28
Engine: 305... LS1 waiting to drop in
Transmission: 700-R4... soon 4L60E
Axle/Gears: 3.08 posi nine bolt
305 falls on face after 4k rpm
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
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Car: 87 Z-28
Engine: A worn-out 305
Transmission: T-5, until it dies
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..
run K&N filters, and gut your airboxes. All of this will help..
#3
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Car: 88 IROC
Engine: 350 TPI
Transmission: Pro 5.0 shifted T56
Axle/Gears: 10 bolt 3.73 posi
welcome to GM TPI
torque monster below 4k
cement block after 4k
torque monster below 4k
cement block after 4k
#4
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Car: 1991 Vert Z28
Engine: 305... LS1 waiting to drop in
Transmission: 700-R4... soon 4L60E
Axle/Gears: 3.08 posi nine bolt
Thanks, hey is that edelbrock lower emmissions legal? Also do you have part numbers or a web page w/specs and prices?
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Car: Tree Huggers
Engine: Do Not
Transmission: Appreciate Me.
50 state legal, search summit or use google, there is a bunch in our database and somewhere in our faq/articles section.
#6
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Car: Red 1987 IROC Convertible
Engine: 305 LB9 TPI
Transmission: T5 5-Speed
Axle/Gears: 9-Bolt 3.45
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!
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!
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Car: projects.......
yep
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.
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Car: 1991 L03 700r4 RS
Engine: 1987 WS6 Trans AM Lb2
Transmission: Th350 red neck Performance 3k stall
Axle/Gears: 95 Mustang 8.8 built with 3.73s
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.
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Car: 88 IROC
Engine: 350 TPI
Transmission: Pro 5.0 shifted T56
Axle/Gears: 10 bolt 3.73 posi
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Car: 1986 Camaro Z28
Engine: 305 TPI
Transmission: Who orders an auto in a Camaro??
Axle/Gears: Economy gears..once again, WHY?!?
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Car: 1985 Z28
Engine: 85 L98
Transmission: 700r4
Axle/Gears: stock 10 bolt-3.73 eaten posi
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
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?
#17
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Car: 1991 L03 700r4 RS
Engine: 1987 WS6 Trans AM Lb2
Transmission: Th350 red neck Performance 3k stall
Axle/Gears: 95 Mustang 8.8 built with 3.73s
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.
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Car: 84 Z28 / 91 Trans Am
Engine: LS1 / 5.0 TPI
Transmission: T56 / 700R4
Axle/Gears: 4.09 / 2.73
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
#19
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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
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
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Car: 1991 L03 700r4 RS
Engine: 1987 WS6 Trans AM Lb2
Transmission: Th350 red neck Performance 3k stall
Axle/Gears: 95 Mustang 8.8 built with 3.73s
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.
#21
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Car: 1991 Vert Z28
Engine: 305... LS1 waiting to drop in
Transmission: 700-R4... soon 4L60E
Axle/Gears: 3.08 posi nine bolt
Re: 305 falls on face after 4k rpm
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!
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Car: '89 formula,'88 Iroc
Engine: 350,305
Transmission: 700R4
Axle/Gears: 3.73
Re: 305 falls on face after 4k rpm
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
#23
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Car: Red 1987 IROC Convertible
Engine: 305 LB9 TPI
Transmission: T5 5-Speed
Axle/Gears: 9-Bolt 3.45
Re: 305 falls on face after 4k rpm
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.
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.
#24
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Car: 1991 Vert Z28
Engine: 305... LS1 waiting to drop in
Transmission: 700-R4... soon 4L60E
Axle/Gears: 3.08 posi nine bolt
Re: 305 falls on face after 4k rpm
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
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Car: 91 Camaro Z28 Convt.
Engine: 305 TPI (built)
Transmission: 5 spd
Axle/Gears: 3.08 posi
Re: 305 falls on face after 4k rpm
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 ..
----------
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 ...
Last edited by Adrians91Z28; 02-23-2008 at 04:30 PM. Reason: Automerged Doublepost
#28
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Car: 1991 L03 700r4 RS
Engine: 1987 WS6 Trans AM Lb2
Transmission: Th350 red neck Performance 3k stall
Axle/Gears: 95 Mustang 8.8 built with 3.73s
Re: 305 falls on face after 4k rpm
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.
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