blackbeauty

About a month ago I had Hedman's headers installed in my car (see https://www.thirdgen.org/techbb2/sho...hreadid=264657 and I was hoping for a nice performance boost. However I was disappointed, the car didn't go any faster down the track at all. I might as well have kept the old manafolds.

The exhaust isn't 3" all the way to the back. Not too far after the Y pipe it goes back to 2.5" and the factory pipes that go over diff are still used.

I know that a 3" exhaust will support 400HP and since my LG4 is nowhere close to making that kind of power I'm wondering whether or not the rest of my exhaust system is stopping the car from running to its full potential. Is it worth going 3" ALL the way to the back? I don't want to spend the money if it's not going to do anything for me.

Note that the 15.788s time I did with the factory manafolds, just when the weather turned cold. I've never got anywhere near that time with the headers.

If it's not the exhaust that's the problem could it be my valve springs or something? My vacuum gauge needle jumps around violently when I hammer the accelerator to the floor.

Thanks for any thoughts

adambros

iTrader: (2)

There is definately a bottleneck where you kept the factory exhaust. How much it is actually hurting performance currently is another question.

I didn't see in you sig anywhere, but if you're still running with the stock intake manifold and heads, I'd say thats why your not feeling, seeing and hearing the difference.

blackbeauty

This is what I'm wondering...

I still have the stock intake and heads, but I've read of people doing x, y and z to their cars that didn't include intake and heads and got their 305 cars to do low 15s. Unless they did something else to their cars they didn't mention.

MrDude_1

if the vac gauges is moving at WOT, you have a engine problem.

CaysE

You already said the problem... you've got good flow going to the same flowing cat-back that you had before. Get everything matched up on your exhaust. Hell, just take off the catback at the track and see what happens. Are you still using a cat? If it's the stock cat, that could definitely cause problems if it's getting clogged.

LG4 heads aren't exactly the best flowing things in the world to begin with, anyway. Did you do any port matching when the headers were installed?

biff85ta

This is where I would put my money.

CraZ-28

Yeah, seriously. Your gauge should not move at WOT.

blackbeauty

I didn't do any port matching with the header install. I don't have a cat on the either. That went ages ago.

If I have engine problems what is it likely to be? The instructions that came with my vacuum gauge told me that if the needle bounces around at WOT that I've got weak valve springs. Does this sound like something I should look at doing with regard to improving performance etc, or might it be something else? The engine has 116,000 miles on it.

MrDude_1

assuming the throttlebody linkage or carb butterflys arnt acting funny, the valves is where i would start.

paulmoore

At what RPM does the needle start to jump around? If it starts to happen at 5000+RPM, then I might lean towards weak springs and the possibility of valve float. The valve hanging open at higer RPM's will cause a loss of cylinder pressure, and cause engine vacuum to fluctuate greatly.

blackbeauty

There isn't a specific RPM that it happens, I just slam my foot to the floor anytime and then the needle begins violently fluctuating roughly between 0-5 inches of vacuum. From memory, I think sometimes it dances between 0-7 inches.

I do know that I need new valve guides cos of the blue smoke I sometimes get on start up, that's a job for the Christmas holidays.

paulmoore

Take a look at this.............

http://www.iwemalpg.com/Vacuum_gauge.htm

paulmoore

The one you will probably look at is the one where the reading fluctuates as rpm increases. Like the site said, a misfire, bad head gasket, or a weak or broken valve spring. I highly doubt that it is a broken spring cause you would have a definite misfire on that cylinder plus alot of noise as the cam tries to open the valve. Have you replaced the plugs and wires lately? If not, try that along with a new distributor car and rotor, it's cheap insurance. Does you distributor have a vacuum advance canister? If so, is it hooked up to the correct vacuum post(I'm pretty sure that it should be hookd up to timed vacuum and not ported vacuum) Have you done a compression test? If not, try it out and see what readings you get. Pull out all the plugs, screw in the compression gauge and hold the throttle wide open while someone cranks the car over. Let it turn over for about 4 revolutions and note the reading. Do all 8 cylinders, and they should be withing 10% of each other(the diference between the higest and lowest readings) If one or more seems low, squirt some oil in that cylinder and try it again. If the numbers come up then the rings are going bad and losing tension. If the numbers don't come up, then there is a good chance that the rings aren't sealing like they should or the vavles aren't seating or there is a problem with either the head gasket, or head itself. Either way, a low compression reading could lead to that needle jumping because at higher rpm the rings or head/gasket will allow some if not all of the comression to blow by and can result in a dead cylinder or a cylinder that is not making peak power. Sorry for the long post, I just got on a roll and figured I'd forget if I didn't type it out. hope you figure it out, Paul Moore

blackbeauty

Thanks for that link, very interesting reading.

My plugs are not quite a year old and the leads are about 2 years old and are in good condition. I've owned the car for 2 and a half years roughly.

My distributor doesn't have vacuum advance, it's done by the ECM as I have a CC QuadraJet.

I did a compression test a while back (I've had this fluctuating needle problem for ages), and I got 190-195psi on all my cylinders, none of them was noticeably low with respect to the others. I figured then that I didn't have a compression problem.

I did replace the dizzy cap a while back, but not the rotor.

I agree, I doubt I have a broken spring, if I had to guess at anything I'd say it was weak springs.

330hp_91RS

Start small before you go into the heads and do the springs....

#1 check for a vacuum leak

#2 Check your timing and ignition parts (especially coil)

#3 Check your valves and make sure they are properly adjusted (could be too tight)

#4 Think about doing the springs...at which point I'd just as soon get some better heads to put on there.

1QWIKZ

Well, getting back to no gain in performance have you richened up the carb like changing the metering rods? Because when you run headers over manifolds it will run leaner with the same tune as what you ran on the manifolds.....Something to look into...

blackbeauty

How can I go about checking the coil? Is a visual inspection enough, and what do I look for? I'll have to get a friend to help me check the adjustment on the valves.

No, I haven't done anything like changing the metering rods. I have noticed that since having got headers my car sometimes idles a little rough, as if it's going to stall or something. Maybe that's from being to lean?? Thanks for the thought, I hadn't considered that.

paulmoore

I have got some questions for you. What kind of vacuum reading do you have at idle? Does the needle jump around? What about at idle with the car in gear? Does the engine idle smoothly or does it stumble? What does your gauge do if you rev up the engine in park or neutral? If you are cruising at highway speeds, what does your vacuum gauge show? What about your fuel pressure? Most carbs need 7-8 psi max. At idle you should have around 7-8 psi and under heavy acceleration it should not drop below 4 psi. If your engine does check out to be in working order, then I would say valvesprings are your enemy.

blackbeauty

Originally posted by paulmoore
I have got some questions for you. What kind of vacuum reading do you have at idle? Does the needle jump around?

At idle I can have anywhere between 20-22 inches. Some days the needle will be rock steady, other days there can be a little movement of the needle with a deviation of about an inch.

What about at idle with the car in gear? Does the engine idle smoothly or does it stumble?

It's usually smooth. I think sometimes my carb linkage might flex a little which alters the output voltage of my TPS and carb butterflies which might cause the occassional stumble and low RPM (500RPM), and in such circumstances the needle bounces around. If I bring the RPM up a little (say to 600RPM), the needle becomes steady and the car is happy.

What does your gauge do if you rev up the engine in park or neutral?

It does bounce around.

If you are cruising at highway speeds, what does your vacuum gauge show?

Depending on things like head winds, inclines in the road and therefore my foot and stuff like that, usually 18-20 inches. That's at 60MPH, in OD with the converter locked. The needle doesn't tend to fluctuate a whole lot.

What about your fuel pressure? Most carbs need 7-8 psi max. At idle you should have around 7-8 psi and under heavy acceleration it should not drop below 4 psi. If your engine does check out to be in working order, then I would say valvesprings are your enemy.

I have no idea what the fuel pressure is like, I've never measured it on my car.

What's the verdict Doc?

paulmoore

Honestly, sound like the valve springs. If you have steady vacuum at idle, and at cruise rpm, there is no real possilibity of a vacuum leak that is can see. Otherwise, your gauge would be floating around at idle and steady cruise. Wth everything else looking good that sounds like the only plausible explanation. The reason why I asked you what the vacuum needle did when revving the engine in park or neutral is this. Sometimes, you can get a vacuum leak when the engine is under load. The vacuum under load causes either a gasket to unseal or soemthing to unseat, things of that nature. With no load, and revving up the engine, you should not have that much fluctuation in the gauge. It should dip momentarily from the initial throttle tip in, but usually restore itself. In that case, the only thing that could cause that would be the valves not sealing compression. Another thing that might remotely cause that is the lifters. If the hydraulic lifter is bleeding down as rpms increase, you will have less lift at the valve, less combustion, uneven power balance, and can cause that condition with vacuum. Sometimes, if a lifter goes bad and bleeds down you can hear ticking from the plunger bottoming out at the base of the lifter. Worst case scenario, get some new vavlesprings(it's a good investment anyway) as well as some lifters. Reset them to 0 lash then 1/4 turn past to set your preload, and get a new tune to work with your headers.

blackbeauty

Thanks for that. I'll get some new and better springs and install them over the Christmas break.