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1990 Toyota Corolla Headers and mileage

Tiny
JACKOLSON
  • MEMBER
  • 1990 TOYOTA COROLLA
  • 4 CYL
  • FWD
  • MANUAL
  • 90,000 MILES
I'm working on a stock 4AF carb toyota engine, 1.6L 16valve

The first upgrade we did is we installed a 4-2-1 header and straight thru exhaust

4-2-1 design
primary pipes - 32" long 1.5" diameter (sequential pairing, 1-2 and 3-4)
secondary pipes - 22" long 1 5/8" diameter
short 2" collector
no cat, no resonator, no muffler - just straight thru exhaust pipe 2.5" diameter about 6' long
all are mild steel

after install, I had to dial a richer air fuel mix almost 1
1/2 turns more than the stock
now I know that lowers the mileage but is it normal?

the car runs great with peak torque coming in at about 3500 rpm then stays high until about 6000 rpm
i realize it has more top end power now but sometimes it bogs down when WOT @ 2nd gear only

any idea on this one please? Thanks and more power
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Saturday, October 16th, 2010 AT 7:42 AM

7 Replies

Tiny
MMPRINCE4000
  • MECHANIC
  • 8,548 POSTS
Most likely it is too rich.

Headers alone will give you some power, but I would say MAYBE 2-3 hp.

Only way to get more power is to increase air into engine.

Camshafts, heads, or forced induction are traditional ways of doing this.
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Saturday, October 16th, 2010 AT 7:53 AM
Tiny
JACKOLSON
  • MEMBER
  • 67 POSTS
Thanks,

but one last thing, why does the engine bog down when at WOT particularly when using 2nd gear?

Thanks again
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Saturday, October 16th, 2010 AT 8:39 AM
Tiny
MMPRINCE4000
  • MECHANIC
  • 8,548 POSTS
Other than timing, it would be a rich fuel mixture.
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Sunday, October 17th, 2010 AT 8:40 AM
Tiny
JACKOLSON
  • MEMBER
  • 67 POSTS
Thanks, I heard that a gas analyzer can be used to determine the correct A/F ratio. What readings on the analyzer should I aim to get for a good A/F mix?

Thanks and more power again
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Sunday, October 17th, 2010 AT 9:17 AM
Tiny
MMPRINCE4000
  • MECHANIC
  • 8,548 POSTS
You can use a wide band O2 sensor on a chassis dyno, that would give you AF ratio under load.

Generally under WOT you would want an AF ratio of 12.5-13.0.
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Monday, October 18th, 2010 AT 8:29 AM
Tiny
JACKOLSON
  • MEMBER
  • 67 POSTS
Thanks. What should be the AF ratio when idle?
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Monday, October 18th, 2010 AT 9:22 PM
Tiny
MMPRINCE4000
  • MECHANIC
  • 8,548 POSTS
ECM will try for a 14.6 AF ratio at idle.
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Tuesday, October 19th, 2010 AT 8:50 AM

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