Is it normal to lose alot of bottom end after a header install on an otherwise stock engine? Would intake mods help bring it back? I'm running Hooker 2149's with an upside down factory cat and a flowmaster catback, the engine is otherwise stock except for a cut airbox and TB airfoil (It came in the car). Have an auto trans with 3.07 rears. The car is not throwing any codes, it just lost its off the line rip and kick going into second.

 

:lurk:

This has me very curious, after all I've read here about doing full exhaust mods as the single major bang of the buck performance increase one can do for the L98 :confused: I hope some others with good experience can address this.


[Modified by bradvette, 10:54 AM 9/24/2003]

 

Yeah,

If you got headers with bigger than 1 5/8" tubes, you will notice a big drop in bottom end. Even with 1 5/8" tubes, it hard to notice a difference in performance with a stock motor. The benefits in better upper end breathing that good long-tubes provide is negated by an intake system designed for a 305 C.I. engine. Since your stock engine probably falls on it's face anyway at around 4900 RPM, that's the bottle-neck in L98 performance, IMO.

Even with a fresh rebuild and a CompCam 501-8 roller, mine still didn't want to pull beyond that. After taking it apart again and porting everything including the heads but mostly the plenum and base manifold (but not the runners, I'll just replace those) and an AFPR set to 46 lbs did the engine wake up. The porting increased all parts of the powerband- from a dead stop to 5500 RPM. It will seriously smoke 315 tires all the way from a roll in first gear and keep smoking even after shifting into second. Not bad for an automatic. And I'm running the stock exhaust manifolds untouched with just muffler eliminators as the only exhaust mod.

Maybe I'm to the point where long-tube hearders will help me now.

Unless you get rid of the stock whimpy cam and start upgrading the intake system, your headers at this point was not the best performance dollar you could have spent, IMO.

BIG JIM

 

In general people lose low end torque because they don't tune the engine to the change.

Try using and AFPR to optomize fuel flow at WOT to match air flow and think about a new hi-flow cat.

 

I had the pre cats gutted out... does any one here think this might of made my car loose low end power ?

Doesn't the ECM ajust itself after making certain non drastic mods? I though it would only need to be upgraded if the internals of the engine was modified or that the engine in general had a lot of mods.

I have a 383, with gutted cats and Flowmaster cat back... would installing header be a good idea? I also have stock ECM.

I was told installing a highflow cat would also be good... but am I going to also loose low end power?

 

I have a 6-speed.

I put on Hedman 1 5/8" headers, 2.5" dual exhaust, no cats and dynomax mufflers, removed frisbee, took out the wall behind the throttlebody in the plenum, k&n, cut stock air box, cap, coil, rotor, ignition module, spark plugs, wires, removed the air pump and upped the fuel pressure.

I did not notice any loss of low end tq. maybe it's because I have the 6-speed. it's more powerfull across the entire usable range of the engine and puts down 254rwhp and 354rwtq.

BTW, I changed the exhaust to 3" with an H-pipe and could not feel a seat of the pants change.

 

Its normal to lose the 'feel' of the torqueyness when you do headers, yes. Especially if you go with 1.75" on the L98.

That torque peak, that youre used to being at low rpm, has been moved up to a higher rpm, and she loses the 'umph' off the line a little.

Its not going to make you any slower, its just a 'feel' thing. Perfectly normal.

 

:iagree:


I've got 1.75" TPIS headers on my Xfire. Its pulling over 347rwtq@3700rpm and has 300+rwtq from 2000-4500rpm.

 

Here's my Vericom times before and after headers:

Time/mph stock --- Time/mph headers --- Distance
13.75/111 --------- 14.61/97 ------- 1/4
9.2/84 -------------- 9.5/77 ----------- 1/8
6.2/65 -------------- 6.3/61 ----------- 330
2.6/33 -------------- 2.5/32 ----------- 60

Stock I rolled on the gas from the start, with the headers I just mashed it to the floor. Temps were 60ish both times, same stretch of road.

After an AFPR, what else should I do to get this car running like it used to? Will a high flow cat help any, or would the reduced backpressure hurt the car even more? I'm really upset that I've spent almost $800 on this car to make it slower. Maybe I just should have bought an electric supercharger and some stickers instead. :)





[Modified by shotchkiss, 7:56 PM 9/24/2003]

 

Other track considerations can come into play, track temp, barometric pressure, etc.

But if you lost that much time, there's something up with how you put it back together, or you have a more serious problem. Might wanna check out all the electrical connections.

No way in hell would losing backpressure add on .6-.8 to your car.

 

do you have a heated o2 sensor? im sure its in the collector now, isn't it?

 

The only things I had to hook back up were the sparkplug wires and the O2 sensor wire. It doesn't seem like it's missing, all the boots clicked back on. I put in new spark plugs, they were gapped to spec. I'm using the original O2 sensor with 1 wire from it, it is located about 1/2 way up the #7 collector tube. I have an AutoXray scanner, are there any values I should be looking at?

 

:lurk:

 

I would check your base timing. Should be 6* BTDC.

Your '89 uses the MAF system, so it should compensate some for the increased airflow.

If you can scan a run, look for knock retard, you seem to be losing all your power after the 1/8 mile wich seems to me to be a timing issue (computer retarding timing at high load).
Also look at the O2 milivolts while at full throttle

If you're getting timing retard, raise you fuel pressure.

 

Thanks I'll try to get a scan done tonight, I can capture 30 frames of data with it, so I'll see what it looks like. It's calling for rain, so it may take a few days. Hope to get an AFPR in the next week or so, will have to buy a fuel pressure gauge too because I have no idea what the base pressure is at now.

 

I'm planning on getting a set of hooker 1-3/4" headers for my '86 auto I have ran a 13.5 with the following mods flowmaster cat back, K&N with an open air lid, gutted main cat, manual fan switch and a 160 degree thermo stat. Will I lose any off my 1/4 mile with these headers if so what else could I spend the money on to increase performance?

 

I read in David Vizards book "how to build perfomance on a budjet " that to big headers is not very good.

I can't remember what was said in the book, but I read that even stock ported headers is better then putting on very big headers.

If any of you guys needs this quoted out of the book I can quote it for you tomorow.... I don't have the book with me at the moment.

 

1.6 roller rockers would be good! :seeya

 

Lots of talk in this post about going slower with Headers.

But, my results are completely the opposite.

I installed Hooker 1.75" headers and picked up ET and MPH.
No loss of bottom end at all, the 60's remained the same.

This was the only mod I did at the time. No other changes, I haven't even played with the fuel pressure and timing yet.

Vic

 

Got some 0-60 WOT runs in tonight, my O2 sensor reads around 800-840 mv,
I am getting about 5 or 6 knock counts per run, it's retarding the timing up to 12deg to compensate. How do I go about getting rid of this knock? Will increasing my fuel pressure help this out?


[Modified by shotchkiss, 6:22 PM 9/25/2003]