The V8 Owners Forum -

Hi guys, basically I want to know what you think about what size eddy I should be using. Its a 4.0 with 4-71 SC atop (or it will be soon!) and I currently have a new 500cfm performer for it, currently jetted for a 3.9/4.0.

The supercharging book I have says jet an extra 10% primaries & 20-25% secondaries as a starting point and so its not too lean, the 500 should handle that fine but I'm just not quite convinced that (when looking underneath it) those tiny little butterflies are going to let enough through to feed the thirsty lump! I am hoping for near enough 300bhp, and I also have a nitrous plate to sit under the carb which I am hoping to rig up for a 75(ish)bhp shot.

Main concern is I dont want to start it up for the first time lean as dont want to bugger anything in a completely fresh build! So should I richen it up a bit and try it then decide or do I need a bigger carb?!?!

You should be well in with a 500 mate. Running Nasp my 500 easily feeds my 4.6 engine. I dont need to worry about more airflow on Nitrous for obvious reasons.

See here

http://www.buicks.net/shop/reference/carb_cfm.htm

Helpful chart, I just cant believe so much air can flow throught those tiny little holes! (not enough to feed something the size of the blower anyway!)

The primary venturi(?) things seem extrememly massive in my eddy, all the other pics I've seen show them to be a lot smaller- they must be blocking so much airflow!!

topcatproduction wrote:The primary venturi(?) things seem extrememly massive in my eddy, all the other pics I've seen show them to be a lot smaller- they must be blocking so much airflow!!

The venturi boosters are big (I think that's what they're called) This is to restricted the carb to 500 cfm. The 600 carb is the same body size but one of the differences is that the boosters are smaller and therefore less restrictive.

double post

I just want to bump this up if I may as I have been searching about edlebrock sizes.

I'm running a 500 on my 3.5 at the moment and was wondering if the 500 will be adequate for my new 5L stroker engine. I think it might be a little bit borderline but would save cash if I could use the current 500.

sidecar wrote: The venturi boosters are big (I think that's what they're called) This is to restricted the carb to 500 cfm. The 600 carb is the same body size but one of the differences is that the boosters are smaller and therefore less restrictive.

Is this true about the 500 and 600. If I change the venturi boosters and the jets and so on, I'll have a 600?

Adam/Tom

MarkMGBloke tried a 600 on his track tuned 285BHP 4.6 and it lost power.

The 500 was designed for engines of 5L + so should be fine except for all out race engines revving in excess of 7000 RPM

The modest primaries on the 500 give good drivability, torque and economy at small throttle openings, and when you floor it the secondaries should provide all the flow you will need.

Kevin.

Perhaps.

Using the CFM calculator though with a VE of 90% and max rpm of 6500 It's above 500cfms.

Am I likely to get anywhere near 90% with decent heads (possible Merlin heads) and decent cam? Is 85% more realistic?

If the heads are good aftermarket castings then you should get in the region of 90% VE at 6.5K with a goog cam and exhaust system, doubt you would 80% with flowed rover ones.
Mike

Dn't forget that with a large capacity long stroke engine you won't be revving much past 6000 RPM and peak power will be at around 5500 unless you fit a cam that will make undrivable on the road.

I think Real Steel showed a Dyno graph of their stroker engine fitted with Merlin heads, can't find it at the moment but I thing it peaked at fairly modest RPM which is no bad thing.

Kevin.

Yeah seen that graph, you have a point they only rev the engine upto 6K on that graph and it peaks at 5500.

No harm in experimenting tho if I can make a 500cfm into a 600cfm one cheaply without buying a new carb.

I did indeed try the 600 doing a back to back test on a rolling road.
The 500 drives so much better and mads more power!

I would swap my 600 primary venturis for the 500 ones.
Seems to be the only difference between them apart from jet sizes.

Cheers

mark

Hi Mark,

Good to here from you, we've got a bunch of MGBV8 guys going to Santa Pod in July, fancy bringing your beast along, should be a fun day with a friendly bunch and a chance to see what your car will do in the quarter.

Kevin.

Kevin
Never been to the Pod or done the 1/4 mile could be interesting, let me know.
v8mg@blueyonder.co.uk
Cheers

Mark