1 5/8 vs. 1 3/4 Tuesday, 30-Jan-01 13:13:20 Message: 206.98.143.250 writes: At what point do you guys graduate to a 1 3/4 header from a 1 5/8? I know that may be a hard question to answer considering the thousands of different combinations that are out there. However, is there any sort of general rule of thumb people go by or is it just trial and error as to which one works best for your application. I mean I see 2007cc motors running 1 3/4 while other 2275cc motors running 1 5/8. I know heads, cam etc. play a big part. Any thoughts? I'm running a 2175cc, 48's, Engle 130 with 1 to 1 rockers, heads that flow 155cfm at 6Krpm's with a 1 5/8 header and a Bugpack single muffler on the street. Don't know if graduating to a 1 3/4 would help? I also don't wish to buy a new header if it's not going to make any difference. Comments please! Adam from Atlanta

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A lot will depend on the heads/valve sizes, cam, carburetion, compression ratio, and RPM range used. For a 2 liter running at the track and using up to 8,000 (or more) RPM the 1 3/4" would probably work better. For a street car and mostly street use, the 1 5/8 would probably work better. For any particular engine, the only way to tell which is best would be back-to-back dyno runs. Just my opinion (n/t) (george brown) (30-Jan-01 13:22:05) Re: Adam, could you e-mail me? Gotta question about your combo... (n/t) (Ron Bullard) (30-Jan-01 13:33:15) Re: 1 5/8 vs. 1 3/4 (Keith Seume) (30-Jan-01 13:40:49) My mistake - FK8 smaller than 130. use 1.25s with the 130 for the gains yyou need (thanks to Dave and Judy Kawell for pointing out the error of my ways on that one!) (n/t) (Keith Seume) (31-Jan-01 02:33:56) Re: 1 5/8 vs. 1 3/4 (n/t) (good to see keith on the web sight. Jose Medrano) (30-Jan-01 17:27:35) Re: 1 5/8 vs. 1 3/4 (Phil Norman) (30-Jan-01 18:25:59) I run a 1-3/4 on the street with my 2007cc (K-10, Berg 861 heads 40x37.5, 1.45 ratio, with 42 DCNF Berg specials) I had to go that big, 'cause the motor wanted more breathing room the way I drive (even on the street!) I did lose a little bottom end grunt, but the top end really comes alive hard at 3500 and runs strong to 7500 or so.Got tired of replacing exhaust gaskets every week. (n/t) (bugly) (30-Jan-01 19:32:09) Bugly, try the new copper exhaust gaskets from Bugpack. Aircooled.net has them and they work great. (n/t) (Steve Arndt) (31-Jan-01 12:36:01) I second that, bugpack copper gaskets rock. (n/t) (Billy) (31-Jan-01 13:43:35)

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Re: 1 5/8 vs. 1 3/4

Tuesday, 30-Jan-01 13:40:49

195.102.198.179 writes:

I would say that, with your combintion, the 1 5/8 header should work fine, offering plenty of torque etc. However, you would probably do yourself a favour by replacing the single Bugpack muffler with either a set of dual quiet-packs or a single A-1 style turbo muffler. Those 48s (I presume IDFs or Dell'Ortos) could do with a little more cam. maybe an FK-8 (or a set of ratio rockers - anybody any experience there on a 130?). As it stands, your set-up with 44IDFs would make a great street motor, with a ton of torque. iIm just afraid that the carbs are a little big for the cam and exhaust. Maybe I'm wrong!

Keith Seume

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I gained 6hp changing from a 1 5/8 to 1 7/8 on my 2165 48idf fk89'd motor.

Phil Norman