Outer Limits 4x4 Board

well, i have finally got my engine togeather after new waggot cam, lifters, cam chain and gears (old ones were about to trash themselves )

Anyway, fired her up and it idles sweet but when i throttle it it will bog and die... if i only just touch the reves up slowley it will rev out ok?

now i was thinking at may be a problem with the accelerator pump shooters, either to big or to small? any ideas here?

PS. its a 600 cfm vacume secondry. carb is newly reconditioned and has no leaks, blocks etc.
any help would be highly appreciated!

Cheers, Joe.

A 600 holley is way too big for a 3.5 even with small jets, you want a 450 or 390 or even a 465. Some people have had good results with quaddies as they have very small primaries and large secondarie vebturi's.

nah, 600's ok. i just want to know if anyone has ideas on this problem i am experiencing??

Joe.

could be many things...

maybe timing ?, excessive vacuum openings your secondarys early or too much fuel... and why are you so sure you havent over carb'd you car so to speak? if all you have changed is the timing of the motor then a 600cfm carb WILL give you too much fuel and bog down exactly like your describing.

Simon

I still reckon a 600 is too big, you are flowing too much air/fuel mixture or your power valve is incorrect.

Take the vac. line of your secondaries and try it, you should be able to smell if your overfueling anyway, 600cfm holley is way to big, and a crap carb to use anyway

What The...!

600 is waaaay too out there for a 3.5 . IF this engine sees 7000rpm in a race car, then maybe it would work, but be undrivable at low revs. Too much air, and if you've ported the heads( opened them up) it will be worse at low revs, and prone to bogging as the airspeed into the intake runners is slower when the runners are bigger. Good for outright revs, but lousy for torque and throttle response.
The 450 square bore or 465 spread bore holley would be better, but the best is Quadrajet with the small primaries. These suckers will flow 700 CFM at full opening, but will allow low speed response and good fuel economy(!) on the primary circuit.

JC

well, have put this on the back burner for a while, latley been making an exhaust system up.....
anyway...

a 600 vac.sec. holley is really 2X 300cfm carbs in one. the motor will run fine on the primarys, and if it develops enough vacume (which it enevidbly will) it will pull the secondrys open creating more flow.... this is only if it requires it. This is the beauty of the vac. sec. design.....

If i was to use a double pumper, the car would still run quite well at mid to high rpm's, although it would black plugs down low very quickly........

I spoke to a guy today who is running an 11 second drag car with a 308 Holden running a barry grant 1150cfm carb! yes lots more cfm than required, but it works by jetting down and having the knowledge that being a double pumper it will black plugs quick at idle, so keep it nailed!

Joe.

On paper a 600 vac sec should work but it comes dowm to the intake velocity, i was talking to a very switched on mechanic/ auto engineer and he was saying the trick to rover V8's is keeping the intake velocity as fast as possible by keeping the port and venturi sizes small. so although it sounds ok in reality not so good.

Exactly. Too much port enlargment and carb venturi sizes equals poor low end response and flooding.

One of the torquiest 3.5's I have driven was a bog standard 3500S with the 10.5:1 engine and SU carbs. It has standard early 3.5 heads with factory mismatched manifolds. It went well and pulled from 20 MPH to 110MPH in 4th gear.


JC

600 Holley is too big for a 3.5
I tried one on my 4.4 and it was still too big. You can get restrictors for the throats which in effect makes it around 500cfm which was just right for my 4.4, however in the end I gave up tuning the Holley and fitted a Carter AFB which is a 625cfm but they have a different way of metering and work a lot better than Holleys in my opinion, even though it was still too big. 350 Holleys work real well on a 3.5 and 4.4, you don' t need a 4 barrel. The ports and valves are HEAPS smaller than a 253 Holden, they need a smaller carb to keep the velocity up.

It's a 3.5 not a 5.3! It aint gunna happen