New stroker motor bogs down at full throttle
Thread Starter
7th Gear
Joined: Dec 2008
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From: Glen Elder KS
New stroker motor bogs down at full throttle
I recently installed a 475 hp stroker in my 86 corvette. It has 26lb injectors, K&N filter and a upgraded computer. I broke it in for 500 miles. The problem is when the motor winds up over 3/4 throttle it bogs down and losses power and blows smoke out the exhaust. Any help would be greatly appriciated. Thanks
Thread Starter
7th Gear
Joined: Dec 2008
Posts: 7
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From: Glen Elder KS
The smoke is from too much fuel. When it idles it runs rich. I reset the computer by disconnecting the battery for a hour. Then started it up put it in drive and held the brake for 15 min. It ran good for about 6 miles then started acting up again. When it acts up the gas mileage goes from 20 mpg to 8 mpg. The computer is off of ebay.
Race Director
Joined: Apr 2000
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From: Texas
Needs a tune for the idle issue and the injectors are probably too small at the higher rpms.
Resetting the computer temporarily changes the fuel trims back to 128. They'll stay there until the ECM begins learning and updates them based on o2 sensor feedback.
Resetting the computer temporarily changes the fuel trims back to 128. They'll stay there until the ECM begins learning and updates them based on o2 sensor feedback.
Race Director
Joined: Apr 2003
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From: moraga ca
A wideband will tell you what is going on. When it bogs, you can see for sure whether it is too rich or lean and where. Then have your computer calibrated. Is there a dyno near you? They will also be able to check with a wideband.
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Race Director
Joined: Apr 2000
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From: Texas
Lowering the fuel pressure will at best solve the idle issue but make the WOT bog worse. 26# injectors on a 475hp stroker engine are woefully inadequate even if he is running them at 50psi+
Race Director
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From: moraga ca
30# or 36# would be more in the ballpark but would make the idle worse. Custom tune needed.
Team Owner
Joined: Jan 2003
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From: Summerland B.C. Canada
I know if I crank up my fuel pressure, mine will bog at WOT.
Race Director
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From: Texas
At 6000rpm my stock 28# injectors were at 100% duty cycle at WOT on a 425hp engine with a 13.1:1 A/F ratio. 26# injectors on an engine with 50 more hp aren't going to cut it. People with stroker engines, self included, run a minimum of 30# injectors and some run larger.
Needs a datalog, needs larger injectors, needs a tune.
Melting Slicks
Joined: Aug 2003
Posts: 3,401
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From: Lakeville MI
At 255 gm/sec airflow, 26 lb injectors are sufficient for a 10:1 AFR. They certainly could be enough to bog the motor.
It could be going rich if the tuner went overboard with PE and if the motor isn't really flowing that well to begin with. However, it is not very likely that the ecm is actually tuned to provide an actual AFR any richer than aprox. 11:1, since this requires some special changes and know-how.
Does this 475 hp stroker still have a tpi intake?
It could be going rich if the tuner went overboard with PE and if the motor isn't really flowing that well to begin with. However, it is not very likely that the ecm is actually tuned to provide an actual AFR any richer than aprox. 11:1, since this requires some special changes and know-how.
Does this 475 hp stroker still have a tpi intake?
Last edited by tequilaboy; Mar 21, 2009 at 05:06 PM.
Race Director
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From: Database Error Indiana
If its blowing black smoke, the O2 sensor may be fouled. A new one will get contaminated quickly if the tune is that far off. I am not a tuner but I have replaced a couple O2 sensors.
Team Owner
Joined: Jan 2003
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From: Summerland B.C. Canada
He's going lean at WOT and it's likely the cam has so much duration/overlap that the computer can't compensate at idle.
At 6000rpm my stock 28# injectors were at 100% duty cycle at WOT on a 425hp engine with a 13.1:1 A/F ratio. 26# injectors on an engine with 50 more hp aren't going to cut it. People with stroker engines, self included, run a minimum of 30# injectors and some run larger.
Needs a datalog, needs larger injectors, needs a tune.
At 6000rpm my stock 28# injectors were at 100% duty cycle at WOT on a 425hp engine with a 13.1:1 A/F ratio. 26# injectors on an engine with 50 more hp aren't going to cut it. People with stroker engines, self included, run a minimum of 30# injectors and some run larger.
Needs a datalog, needs larger injectors, needs a tune.
Could be oil for all I know, the OP is not giving much info.
Thread Starter
7th Gear
Joined: Dec 2008
Posts: 7
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From: Glen Elder KS
The car has the stock tune port injection it was mildly ported and polished on the inside of runners and gasket matched. It has been bored (not sure how much) mild cam, cast steel Eagle crank, I beam rods, flat top hypereutchic speed pro pistons with speed pro moly rings. The heads have been ported and polishied with a 3 angle valve job and heavier valve springs. I'm not sure what else was done to it. I bought a new o2 sensor today. I will see if that helps in the morning.