hello I just transformed my iroc into somthing very fun and I am looking for some educated guesses on the hp output, and where it is on the power curve.
Here is the specs:

383 rotating kit from eagle
comp cams 276hr
9:3:1 compression
1:6 roller rockers
headman 1 5/8 coated shorty headers
rpm air gap performer intake
vortec cylinder heads
750 dp 4779 holley

my assumption is it is very similar to the twister motor chevy high performance built but they used a comp cam 282hr. they made 449hp and 486ftlbs at 5400 rpm. also my tranny was from gear star and is suppose to shift at 5500rpm but on my tach it is 6000rpm. Just wondering if my tach is slightly off at this end of the scale or should I look into recalibrating the shift points back to 5500rpm. Or is this setup liking 6000????
The other twister motor setup was with the lt4 hotcam and made 416hp and 466 ftlbs at 5600rpm. I assume I am in between the two combos...thanks greatly...... Ryan

p.s. Iam getting 16mpg with this and am driving it daily

 

I think the 1-5/8" headers are going to kill the power with a 383. I'm thinking anywhere from 400-425 HP at approx. 5500 RPM. I would leave the 6000 RPM shift point.

The only way to trully know though is on a dyno.

 

i would have thought the same thing on the headers. chevy high performance tested their twister engine with bigger headers and the power was better with the 1 5 8 headers. must be to do with the vortec heads...as i have read this alot. i am hoping to find a chassis dyno outfit in maine so i can dyno it to find out the power to the wheels.

 

I've seen la few dyno comparsions with 383 and 400 sbc where going from 1 5/8" to 1 3/4" headers lost about 15-20 lb.ft. of torque and only gained a few horsepower up top.

I'd stick with the 1 5/8" for a daily driven car

 

update: 6200rpm on shift points with a new tach installed. boy that factory tach is all over the map next to this new tach.. car seems to like this high rpm. I put a different governor in it and it shifted 5700rpm and it did not seem as powerful. does this make sense really?

 

If it is mainly street driven and if it is true dual I would stay with it.1 3/4 might give you 5-10hp but you are going to lose 20ftlbs or more in torque.1 5/8 are fine for a true dual street driven 383.Unless you were running a bigger cam I would say it is not worth changing.If it is not true dual you are losing a little more hp and torque.