I have read every thread root blowers on this forum, including the excellent tech article on how to do it. But i do have some questions: goal is a pretty streetable car with lots of punch when asked for. no money remains to replace the heads, carb, etc. the trans has been slightly stengthened at this point, rear end is off a 92 camaro, i cant off hand recall the gearing, prob about 3.5 or 3.7 range. tires are 275s all around. We have torn down the 383 to rebuild...block is mid eighties, 4 bolt main, ARP bolts, good machine work on the stroker crank. new blower pistons to be installed, any suggestions, make, part no on these? Im planning on going for 8.0 CR. cant afford the best, just need reasonable ones, blower cam selection ideas? lookin at Comp cams or Crane 700R4 trans...Running also World Sportsman II Iron Heads..we are having some mild p&p,3 angle valve grind on the heads, 1.5 RRs, Edelbrock 750 carb. with vacuum secondary, electric choke.. any issues on using this carb on a blower? any mods to make or other considerations? suggestions for metering? Would anyone suggest that I would greatly benefit from a meth injection system? If so, how to hook up the spray nozzles on this? Anyone have photos of accel. brackets when using this type of blower, or part nos? any suggestions on proper ratio pulleys? finally, i'd like to hear some RWHP predictions, as we go to the dyno when assembly is done...and I'll let u know. thanks guys, Pics later... mark

I hope you have the 72cc chamber size heads. With 64s getting down to 8:1 is almost impossible with a 383. I use AFR heads with 74cc chambers and used a -28cc dished piston to hit 8:1.

I'm using KB Hypers but I wouldn't recommend them to a first-timer with a roots blower. It's way too easy to step over the line into detonation and blow hyper pistons to pieces. JE has a line of Sportsman forged pistons that are adequate for what you're doing and have a big enough dish (I think they offer a -31cc dish for a 383 with 5.7 rods last time I checked). Speed Pro pistons would be a cheap forged piston but I don't think they offer anything with near enough dish (or I'd be using them myself).

Don't go nuts with the cam. The blower is by far the limiting factor in making power. A Comp XE 262 Nitrous grind cam would work just great without breaking the bank. Don't worry- it'll work great with a blower, too. Here's the link:

http://www.compcams.com/Technical/Se...umber=12-556-4

Chances are you'll need to step up from the supplied 6" bottom pulley to the larger 7" bottom pulley for a healty 383 with decent heads and a little bit of a cam. That's what I'm using on my 383 and I'm still only getting about 5PSI on the gague. The only step further than that is the smaller 2.85" upper replacing the stock 3.07" one and that's it- there ain't no more pulleys left.

I think an Eddy carb could work just fine if it's tuned right. I'm using a QJet that was never intended to run on top of a blower and, with a little tuning, it runs just fine. Go up about 4 jet sizes from stock on both sides of the carb to start with- make sure it's nice and safely rich. Ditto the accelerator pump- there's no such thing as too much pump shot. You can always lean it out later if you find you went a little too far.

Thanks so much for the info. Im glad someone responded to my thread. i checked the price of a 7 inch pulley is like $170 at jegs...doubt if i can afford that now. but will if i get a good deal on one somewhere, none on ebay.any idea what the hp torque numbers should be on your car. If you get any pics, it would be helpful. thanks again, Mark

I know exactly what they are but I won't tell you.

Just kidding.

On a DynoJet I laid 390HP to the rear wheels @5800 and torque was about 420. I say "about" becuase I have an automatic and when you get too low in the RPM band you start seeing the effects of the torque converter multiplying torque rather than true engine output. Some spikes were over 500, but 420 is about what it was once things leveled off and stabilized.

So, flywheel horsepower would be somewhere around 450-480, depending on whose conversion factor you believe. Dyno operator said most stock factory-rated 450HP Vipers laid down 390-400HP on that same dyno.

i layed down 380hp and 483ft lbs on the dyno with my setup

Crane cams #113801 (HMV-278) is a great cam for a 144blower. No need to order a special Blower/NOS grind. This one is it.

if you're adventureist crane mechanical #113841 (F278-2) is a "just right" street solid cam for the 144 blower.
Mild manors, lots of power and rpm.

When using the edelbrock carb on a blower make sure the power piston (metering rod) step up spring remains full up (rich) at high rpm. use the highest rated "stiff" spring tension. (8-10") a light tension spring may get sucked closed at high rpm. Recurve the distributor for more inital advance at idle and limited advance at high rpm. allowing 18+deg at idle and around 26-30deg at rpm/under boost. (limit the mechanical travel.) use cooler than stock non projected tip spark plugs.
I believe Sportsman heads use common .460" reach "peanut plugs" Champion #RV8C is "just right"
Hook up the vacuum advance UNDER the blower, on the intake manifold.
You may need a adjustable vacuum advance can . Limit the amount of vacuum advance travel to about 10-12deg and play with the "rate" so the ignition timing is modulated relitive to the manifold boost responce. If you get it all working together you won't need a boost timing retard system. start by getting the initial/ mechanical total right an then plug inthe vaccum and dial it in.
Something like 18-20 inital at 700rpm.....26-32 total at 3000+ under boost will work well.

Further install edelbrock .110" high flow needle and seat assembly. check and verify float height and drop. You can even raise the float level a bit. I find the Edelbrock right angle "banjo" fuel inlet fitting restrictive. But you can convert to dual fuel inlets by drilling and tapping the fuel inlet boss on the drivers side and install a second fuel fitting. If you have to use a banjo fuel fitting for air cleaner clearance I recommend this upgrade. Edelbrock even sells a braided dual feed fuel line. make sure you have enough fuel pump volume (not pressure) to feed your hungry blown motor.

i would set it up for a 2:1 to 2.4:1 pulley drive ratio. which I believe you can do with the stock 6" bottom pulley and a 2" to 2.5" top pulley. this will be about right for a street setup on high octane 92+ pump gas and 26 to 32deg advance.
I believe Weiand has more hi boost top pulleys in the "marine catalog"

A alky/water injection system will allow more (full advance and or more boost.

Summit cam/lifter set SUM-K1105 $69
makes a great cheap "blower cam" alternative to the crane HMV278 if $$$'s count. Works very well.

Ditto on the above, the summit cam is a great alternative to the more expensive units...As a matter of fact if you look closely it is a blower cam from a "reputable" cam company.....Its even grinded by the same people :-)


These roots blowers are terific but if you add a simple little alky nossle they change drastically...Especially if you run straight alcohol. In my car running the straight alcohol fogger nossles makes a HUGE difference in power. Its like running the blown motor at 100+ degrees vs. running it at 30 degrees weather temperature outside with more fuel. On my motor it feels like an easy 50-70hp more. (these things run hot). You might see a little less with a smaller blower.

On an Edelbrock carb definately use a .110 needle, you will need it! You will find as stated above that a blower motor can swallow almost any amount of pump shot.

Run it very rich at first and dial down from there!!! SLOWLY

Just seconding what everybody said here, is all good information so use their advice they know their stuff. :-)

There's some good info here!

I experimented with my dizzy curve today. My engine responded very well to 14° base using the Moroso HEI recurve kit using thier weights and 1-light spring and 1-medium spring to produce 32° total timing. I couldn't leave it like this because the engine cranked very hard on a hot restart. So I went back to 7° base, and 2 light springs to produce the same 32° total.

I do have a boost timing box so I may try adding a degree at a time up to 3° and see what that gets me. I may be able to get a good "middle ground".

After advice from Damon and F-BIRD'88 I also tried running a vacuum gauge on the carb itself. I run a QJet so I have the same power piston "dilema" you have. I found that when the manifold vacuum (under the blower) is at ZERO, the carb vacuum is right at 7". Right now I run a 7" spring on my power piston. I've been told that I need to run a spring that cuts in just before ZERO. So that would put me right at 8"-10". Basically the heaviest spring they have available for my carb.

...just thought that might help a bit...

I do have a boost timing box

Does it have a cranking/start retard function? Many do.
or does it have a switched input to activate retard?
You could engage the retard function during cranking to relieve the strain on the starter.
Check your starter for exessive resistance. Battery ground strap, and battery + cable and solenoid.
I run my timing Locked out (full advance at idle) and use a ignition cut switch to crank the motor over when hot. Get it cranking and throw the switch and it fires instantly without starter kickback.

Great info here, guy Thanks all! when i get the engine back from the builder, i ll post back with some updates. ill look into the cam selections and pulley gears.
mark

how about fuel pump? mechanical? electric? gph?