Bigger throttle body

rs2000 · Post by **rs2000** » Wed Mar 08, 2006 8:52 am

I'm trying to get the maximum horsepower out of my cam/engine setup. I believe the weakest link in the setup is the throttle body being too small. I currently have a 50mm throttle body that i would like to increace to 60mm, which should stop it from being the limiting factor in the engine.

Would my VE table need a lot of work if a larger throttle body was installed? Originally i had thought it wouldn't need to be modified, but now i'm not sure as surely more power will require more fuel?

thanks

Andrew

whittlebeast · Post by **whittlebeast** » Wed Mar 08, 2006 9:20 am

What is your MAP reading at WOT and say 75% of full RPM and what is you MAP reading right before the shift. Also check your MAP reading when the squirt is on but the motor is not running. With those numbers we can give an opinion.

AW

rs2000 · Post by **rs2000** » Wed Mar 08, 2006 10:05 am

Ok rather than me choose whats important, i've just posted all the info i have ATM. If it would be easier for you to view i could just post the log itself.

Heres the numbers i got last time i dataloged an acceleration pull.. Between each reading the map fluctuates a bit. For example between 2300 and 2700 the map drops to 95 then comes back up (with tps steady at 100%). The only time the map value hits 100 is at 1900, 2100 and 2300. Unfortunately i didn't get a 'turned off' reading so it may not be much use. I'll do another log tomorrow and record the atmospheric pressure.

2300 100
2700 99
3000 96
3500 95
4000 95
4500 95
5000 95
5500 94
5800 95

Another pull from the same day has 2700rpm reading at 100kpa, everything above that the map fluctuates between 95 and 99.

My datalog didn't rev any higher, ideally max rpm is about 6500. This would make 75% of max 4875.

Thanks again

andrew

rs2000 · Post by **rs2000** » Fri Mar 10, 2006 3:59 am

whittlebeast do you or anyone else have any ideas? I believe i do need to upgrade as according to the megamanual i'm trying to make more power than the throttle body can support, just need to know whether i will need to modify my VE table.

thanks

andrew

whittlebeast · Post by **whittlebeast** » Fri Mar 10, 2006 4:49 am

see

http://www.ncs-stl.com/fuel/ReqInjectors03.xls

I like to keep air flow in the 100 mile per hour range or lower. The thing that throws me with your data iswhy the motor is down to 95 kpa early in the RPM band but does not get any worse. That is a little strange. The closer that you can get to 100 KPA at full throttle the better.

Most undersized throttle bodys that I see typicaly go from 100 KPA in the intake at low rpm and have a steady drop to about 91 KPA at high RPM. All at WOT Get too large and drivability suffers MAP Dot is the only way to tune AE and 98 KPA at full power is possible. Note all of these numbers assume you are near sea level.

Generally the VE table will not change a lot with a simple throttle body change. Please do not talke my word for it and change the throttle body and then jump on a dyno and nail the throttle.

AW

rs2000 · Post by **rs2000** » Fri Mar 10, 2006 5:43 am

Thanks for that.

I though my data was strange too.. The thing that is weird is the map fluctuates over a range of about 5kpa. At other times in the datalog it is steady so i don't think its electrical noise.

My Air flow is approx 102 mph according to that link. A 10mm throttle body size increase will drop it to 70 mph.

I will certainly check my AFR's after changing, a bit of tweaking is fine i just didn't want to put a new throttle body on and find my fuel map was completely off.. It makes sense when i think about it that it would still be close.

Thanks again,

andrew