[Mateusz]

I am researching everyday but i am not sure what should i do if someone can help me i would really appreciate that.I have a 4-bolt main 350 short block bored 60 over, 8.5-1 compression with 64cc SRP forged Aluminum pistons, 5.700 Eagle forged light weight I-Beam rods with ARP rod bolts, Eagle crank with 3.480 stroke, SB Chevy 262-400 Nitrous HP Hydraulic Flat Tappet Camshaft - .462" Int .480" Exh lift (1600-5900 RPM)Lobe Separation 114. I wanna make around 500HP with this setup. What kind of blower should i use for that? Is 6-71 too big? What heads would work the best too do that? Should i lower the compression ratio? How much boost should i run to get 500? What kind of carburetor? And i wanna use unleaded fuel.

[471A]

I run a 355 SBC in a Model A sedan and have used a blower on it for several years. Initially, I used and enjoyed a Weiand/B & M 144 blower, with a single four barrel, and ran a best 1/4 mile run of 11.37 at 118 in a 3200 pound car. Chassis dyno numbers reported 485 foot pounds of torque and 475 hp. This was with static compression of 8.5 to 1, similar to yours, but 76 cc heads. Your 64 cc heads may give you static compression over 9, whatever your pistons may have been intended to yield, and lead to serious detonation problems. The cam I ran, and still run, with a blower is Crane hydraulic roller HR-230/359-2S-12.90 IG with lift at the cam of 359 intake and 372 exhaust, duration of 230 degrees intake and 238 exhaust.

Currently, I have gone to a Weiand 250 Powercharger (similar in swept volume to a GMC Roots 4:71) with the same cam but two boost referenced 600 cfm Holleys and Ross pistons yielding static compression of 7.6 in combination with Dart 72 cc aluminum heads. Engine stand dyno on this combination yielded 515 hp and 485 foot pounds of torque. However, dialing in the carbs and exhaust has been a headache. I miss the simplicity, throttle response, and reliabilty of the single Edelbrock 800 TVS cfm card on the the little 144 c.i. blower. The big downside, however, to the little Weiand is that it is overdriven at or above 2 to 1. If you wish to run at an NHRA track, overdrive on a Roots style blower is limited to 1:6 or 1:7 to 1, making the 144 illegal. The 250, which I currently am trying to make streetable, uses a 1:33 to 1 pulley as its baseline ratio, well within NHRA rules.

[471A]

Adding a further reply, with static compression no higher than 8.5:1 and aluminum heads, boost not exceeding 10 pounds is likely to be safe using premium gas (octane lf 93 or higher) . If you are using iron heads with static compression around 8.5:1, the safe upper end of boost is likely to be 8-9 pounds. Since aluminum dissipates heat much better than iron, engines with iron heads will detonate sooner, and at lower boost levels, than the same engine set up identically except using aluminum heads.

[Mateusz]

I think im gonna go with aluminum heads with 72cc, is my cam good for around 9 pounds of boost? what cfm carbs should i need to use for one carb blower? Making 500 hp. Or how about a 6-71?
Thanks for all the info.

[cobalt327]

IMHO, you will be right at the safe limit of your rods. This is one case where a little heavier- as long as it's used to make them stronger- would have been a better trade-off.

Most street-driven blower engines are not high RPM deals, so a lightweight rod/piston combo isn't needed, for the most part.

That said, as long as you don't get crazy w/boost, you'll be OK. If your crank is cast, it will thank you, too.

[471A]

If you enter "swept volume 4:71" as search terms within the Hotrodders Bulletin Board, it will lead you to a helpful and interesting 2005 thread which included input from legendary hot rodder Jim Davis. The thread contains useful comparison among blowers of different sizes as well as recommendations on static compression, cams, etc. Second, the website for Blower Drive Service
includes a thorough "Tech Info" section which addresses the "Most Asked Questions About Blower Motors". Third, for a street blower, basically you want a cam with more lift and duration on the exhaust than on the inlet (about 10 degrees more duration) and lobe centers at 112-114 degrees.