TheMonaLisa Posted December 28, 2018 Share Posted December 28, 2018 I am ordering a BNM unequal length header and now must decide on the primary tube size. The header uses a 4 to 1 collector with a 2.25" output. I am using a Grimmspeed standard up-pipe and VF52. This is an autocross setup so spool is very important. A) 1.5 sch10 which has a OD of 1.9, ID of 1.68 B) 1.5 sch40 which has a OD of 1.9, ID is 1.60 Area of 1.60 in = 2.01 in^2 Area of 1.68 in = 2.22 in^2 Area of 2.25 in = 3.98 in^2 Link to comment Share on other sites More sharing options...
JmP6889928 Posted December 30, 2018 Share Posted December 30, 2018 Spool is better with ELH. Also, comparatively speaking, the VF52 is slow to spool for AutoX. If you're only going to use it for AutoX, believe it or not, the Td04 is an excellent choice as it spools extremely quickly and you'll never use it all the way up. The Custom VF40 is also a good choice-slightly slower spool (about 100-200 rpm) but it pulls much harder in the middle and again, you'll never run it all the way out to redline. Link to comment Share on other sites More sharing options...
TheMonaLisa Posted December 31, 2018 Author Share Posted December 31, 2018 Spool is better with ELH. Also, comparatively speaking, the VF52 is slow to spool for AutoX. If you're only going to use it for AutoX, believe it or not, the Td04 is an excellent choice as it spools extremely quickly and you'll never use it all the way up. The Custom VF40 is also a good choice-slightly slower spool (about 100-200 rpm) but it pulls much harder in the middle and again, you'll never run it all the way out to redline. I still have the stock VF46 that came on my Spec.B, it's currently installed on my daily LGT. The VF52 that I'm running on my auto-x Spec.B you actually built for me years ago. So I could swap turbos between cars, put the stock VF46 back onto the auto-x Spec.B and put the VF52 onto the daily LGT. The auto-x Spec.B is a 6 speed so short gears and runs on E85. Anyway, I'm leaning towards the smaller ID header primary tube. At 1.6" ID, they will still be 0.1" bigger than the exhaust ports on the heads. I know there are benefits to equal length header but I just can't do it... Link to comment Share on other sites More sharing options...
TheMonaLisa Posted December 31, 2018 Author Share Posted December 31, 2018 https://legacygt.com/forums/showthread.php/spool-study-between-vf46-and-vf52-198675.html VF46 vs VF52 spool study Link to comment Share on other sites More sharing options...
JmP6889928 Posted December 31, 2018 Share Posted December 31, 2018 Good comparison and excellent information in the thread. A Custom VF40/46 spools quicker and pulls a lot longer and harder in the mid than the OE style though and it would be probably the perfect mix/upgrade to what you are doing. Link to comment Share on other sites More sharing options...
TheMonaLisa Posted January 4, 2019 Author Share Posted January 4, 2019 I decided to go with 1.6” ID primaries and a 2” ID post collector. The ports on the heads are 1.5” and the Grimmspeed up pipe this header will mate to has a 2” inlet. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
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