Hi guys , If I build a 489 ,can I use the 1 3/4" headers I am using now ? or the big inch motor need a 2" primary tubes ?

your cam timing, compression ratio and rear gear ratio will effect the correct answer, but Id seriously doubt that a street driven car would see any huge restriction due to just that primary header size since your running an exhaust behind the headers anyway...especially in the low or mid rpm ranges and even above 6000 rpm or so ID suspect the differance to be minor since your running an exhaust behind the headers

I just posted the correct primary tubes I am running , Sorry .

the motor will be

10:1 CR
990 HEADS
3:90 or 4:10 ring pinion
TH350 or th400
402A7Lun solid flat tapped

Do they even match the exhaust port? Most don't, and that will hurt.

stick with the 1-3/4".....if they dont match the exhaust port, start grinding ;)

I personally think 1 3/4 with Rec. port heads on a 489 would be a mismatch. I would run 2" if it were mine. JMHO.

hi,

i use 2 pri...with 489 now
before stroker kit...i use both 1 3/4 and 1 7/8 with 454
cam :solid roller 287-295 990gm heads 10.25:1 comp

1 7/8 has more tq and responds from low to middle, with 850 cfm on 454
1 3/4 has much more throtle respond,i didnt like 5800-6500 rpm

2 kills low tq,but good to top , i need little more compression and better heads

here a small video 489 with 2 pri 3 collector and 3 mandrel bend borlas

http://www.youtube.com/watch?v=C05oOfyIXuo&mode=related&search=

regards
sami

I want to say that the late John L. used to say that 1.75" and 1.875" were fine for up to a mild 540 engine b/c they helped build low and midrange T over the larger 2" and bigger sizes.

But I may be off here?

I have the old RHS store's Hedman Hedders 1.75" el-cheapo's on my 496"er b/c i was worried about fitment issues AND I still had fitment issues!!

pdq67