New 250 Super Charger jetting question.
 

Ok now we've installed new 250 superchargers from The Blower Shop with Barry Grant Demon 850's on 454's Gen IV, .030 over on pistons and we are getting a pop on top end through carbs. Had this with Holley 750's before the blowers and ended up increasing jets to 88's all 4 corners; pop went away and we learned we were definitely lean on the top.

Barry Grants' came with #83's in primary and #88's in secondary. Changed the primaries to 88's since that solved the problem with the 750's before blowers.

Question is, what are some of you guys running for jets with similar blowers and set-up? Cams are Comp Cams with duration @ .050 Intake 230 and Exhaust 237. Could the 3/8 fuel lines now be a problem? Fuel pressure was noted at 5 psi when pop occurred at 4500 rpm. Also running stock 90 gph fuel pumps.

Any thoughts would be appreciated.

Re: New 250 Super Charger jetting question.
 

upsize all fuel lines and tank pick up. lean conditions under load are fatal for supercharged engines

Re: New 250 Super Charger jetting question.
 

Thanks for the reply. Changing to 1/2 from tank pick-up on should be the much trouble. Any thoughts on the right se-up on jets? What about the stock 90 gph mech. pumps? Is it ok or do I go to say a Holley 120 gph pump?

Re: New 250 Super Charger jetting question.
 

I just put a B&M 250, superchiller and dual 750's on a 502 30 over. Teague said to start at 80/82 jets. Running it in the driveway seems a little rich. Heading on the water next weekend to test.

Re: New 250 Super Charger jetting question.
 

I'm running the Grant Demon 850's; normal jets are 80 and 88's. I had given them mmy engines specs. (cam, lift etc) and I would guess that's why it came witht eh 83's and 88's. Though increasing the primary to 88's would add some fuel but perhaps I should take the secondaries up a couple of jet sizes since that's were it appear to be running lean, on the top end. Also notice some bubbles in the primay bowel sight glasses. Mean anything to you?

Re: New 250 Super Charger jetting question.
 

mine did the same thing on the top end, went to 92s in rear never popped again. lean is mean , better to be alittle fat.

Re: New 250 Super Charger jetting question.
 

What were you running on the front jets? What fuel pump were you running?

Re: New 250 Super Charger jetting question.
 

i think 84s frt 92s rear, go up two sizes on the rear try it there, i put demons on my fountain 502 w/good internals listened to the shop where i bought them they said bolt on and go, yea right. went up to 90 in the rear felt like at 5000rpm it hit a wall and wouldnt go any faster, went to 94s went 5500 rpm sounded crisper, made night and day diff. play with the jets . remember alittle fat is better than to lean.

Re: New 250 Super Charger jetting question.
 

Thanks again Boatman for the response. Will give the rear jets a try.

Re: New 250 Super Charger jetting question.
 

The bubbles in the sight glasses make me wonder if your fuel supply system may be the problem. I removed the 3/8 fittings and lines from the tank and installed 1/2 into a dual outlet billet fuel filter. Paralleled the Stock Mercrusiser fuel pump with an Aeromotor electric with #8 lines into a manifold, then #6 lines to each carb.

Jim