Hey All,

I was talking to a local mechanic and was asking him what mods I should be doing to my car for starter. He told me I should upgrade my intake cuz the stock snorkel intake is not even sufficient for a V6 and I should open up the exhaust cuz the stock 2.25" pipe isn't even enough for a 4cyl. Wel I did all that. I am now running the Mr Gasket chrome open air element with a K&N HiFlow Filter for my intake. I haven't done the ultimate TBI mods yet because I plan on getting a 670cfm holley TBI. As for the exhaust I basically installed hooker headers, 3" down pipe, Magnaflow 3" HiFlow cat, 3" intermediate pipe into a 3" Magnaflow Muffler going out 2 3" chromed out tailpipes (They look sweet).

My car really honks on bobo all the way up to around 3000-3500rpm and then seems to peak out around that area. Could this be a cause of the stock heads? Maybe a stock 305 CAm issue? What about the TBI? Could this also be due to the onboard computer not being tuned to the new gear? Any responses as to what I can do to get it to continue to pull throughout the whole RPM Range.

Oh I should probably mention..my car is a 305 TBI. New plugs, wires, cap, rotor, O2 Sensor, EGR solenoid, EGR Valve, AC Delete and Stock 305TBI injector.

Thanks for the input.

 

Do you have raised fuel pressure?

 

Your car is peaking there because of the crappy stock heads and cam. A cam combined with proper chip tuning will increase your power band significantly.

 

Dude, i gotta know, what the hell does "honk on bobo" mean?

 

the stocks heads and cam suck, but still should not peak at only 3000, especially with his mods, he should peak atleast around 4000.

 

Yea I agree with that. The difference however between 3 and 4 k is minimal. He could have a fueling problem. This is where an inline fuel pressure gage comes in handy.

 

Sounds to me like hes going rich.

 

Not at WOT. He would feel a lack of power down low if he was rich. The stock fueling systems on our cars cannot make you run rich enough at WOT to make a difference in performance and feel.

 

My first build up (6 years ago)

Stock tbi 350, execpt comp HE 268 cam, and porrted heads, w/headers. Stock tune execpt for rasied fuel pressure to 15 psi.

Drove good, but at WOT it would hit a flat spot at 3800rpm. Would still rev to 6000rpm, but just not pulling.

Lowered pressure to 13 psi, everything was fine.

 

Do you have an aftermarket fuel pump?

 

No, stock pump.

He hasn't replied, but if hes raised his pressure up, I'd be willing to bet thats the problem.

 

No offense to you shifty, but I think you jump on the fuel pump issue way too often. The stock pump can take you a lot farther than you are lead to believe. An aftermarket fuel pump should not be a requirement to go fast in these cars. There are a few cases where I believe they are needed, but it's far from the norm.

 

Well I may be harsh on it but that is because I haven't really seen any succesfull WOT tuning done without one. This is with heads and cam of course. Cam alone you can get away with it but you need to monitor it. Some heads and camed cars can get away with the stock pump if they have a perfectly running one. Most GM pumps are junk and really lose their umph fiarly quicly. When my car hit 28,000 miles by pump could only muster 6psi at idle. The same thing happened to my buddy who for the life of us couldn't figure out why he couldn't tune his vortec/LT1 cam combo. A ton of data logs and a inline gage showed the pump was ok and working fine(at idle, couldn't check at WOT). He replaced it with a Walbro and low and behold tuning became so much easier and all of his part throttle and upper rpm lag dissapeard without changing the prom he had previously burnt. It is just a safe measure that I like to stress and isn't to much of a cost for added measure. Even Dewey went with the Walbro when he did his first cam swap because he knew he was on a fine line.

 

A dying pump is one thing, but a good pump should be adequate. I have over 100,000 miles on mine and it's just dandy. I won't be going through all that bs to change it until the thing dies, and I plan on pushing 375 hp with it. We'll see if it's enough, but I am positive on a stock or mild tbi car the stock pump should be more than enough, ofcourse in good shape. A dyning pump is a whole nother story.

 

With some 90# injectors the stock pump could probably make some good power.

 

Yeah I'd say if you have really big injectors you could hold it with the stock pump at low psi. But 375hp? on a stock pump? That just won't happen, I don't care how good of condition that pump is in. Most stock pumps can barely hold 15 psi. You try to take a stock pump in perfect condition above that 15 psi, closer to 20, I doubt it can hold the pressure.

 

Why not, you take a bolt on L03 with well over 200 flywheel hp and add 125 shot of nitrous which has been done numerous time before on the stock pump. You don't think the stock pump can support that much?

 

You beat me to it. The only way you can make the pump go farther is by going with some huge injectors running low PSI. If you want to run anything over 15 PSI at wot with a motor making 375, you are going to need a high flow unit.

 

Any built engine will need at least 15 psi of constant pressure. Stock pump may be able to hold that if in perfect condition. If you have say a 250 horse n/a motor, you are pushing the pump to its limit (ie 15 psi, maybe more depending on the setup). Then you want to throw a 125 shot of nitrous on that and expect the pump to be able to put all the added fuel that nitrous needs in as well? It just won't happen. If you're willing to chance the life of your engine over a $90 pump then be my guest. I would never ever throw nitrous on a decently powerful motor with a stock pump. They are known for going bad, what if you shoot the nitrous in and your pump can't hold the pressure it needs to for even a few seconds, boom there goes your engine. Not worth the risk.

 

oh well, it's been done before more than once.