Hi all,

I have an issue with WOT on my slant . My setup is as follows:

* An Aussiespeed Hurricane Long Runner intake manifold
* A brand new 07448 - Holley 2300 (07448) 350 cfm carburettor
* Dual Dutra Duals front and rear
* 2 inch pipes from the Dutra's to a Flowmaster 2 inch in 2.5 out Y connector scavenger pipe
* single 2.5 inch straight out the back through a Flowmaster 50 Delta Flow.
* a set of 6x new spark plugs, new spark leads, high voltage coil, electronic ignition, new distributor
* K&N air filter

Otherwise the slant is fairly standard for an Aussie built 225.

She has the most power at about 3/4 throttle and will keep pulling up to 100mph without too much trouble, but if I put my foot flat to the floor anywhere, even at say 50 or 60 mph, the power dies out. Even if I'm at, say, 80mph it doesn't like WOT or much past 3/4.

80 mph + is plenty fast enough, but given it's very hilly (or mountainous) in NZ and most passing lanes run up hill, it'd be good to get a bit more power at WOT around the 50 - 60 mph mark when needed. It feels like it has plenty more in it... Not that there are any camper vans to pass at the moment...

I'm guessing that it's either too much or too little fuel at WOT but I am unsure which. Possibly an accelerator pump, jets, power valve, etc. on the 350 cfm holley 2300 (07748) carb jetted with 58s, orange accelerator cam. (I have read this is not an ideal carb, but seems to be o.k otherwise ).

Any ideas on what is causing this issue and on what the the ideal jet size etc might be for this setup?

If necessary, I can get it back on the dyno to try and iron this out.

Cheers
Mark

Hi Mark,

Thanks for the detailed rundown.

What are stock jets for a Holley 350? Do you have an accel pump cam kit for Holley carbs?

As I mentioned before, a WB O2 gauge can be your best friend...

All the best,
Lou

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Home of Slant6-powered fun machines since 1988

What I'm seeing from Holley is 61 main jets and 8.5 power valve. 31 pump shooter.

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“Buy the ticket, take the ride.”
― Hunter S. Thompson

The early version used to be #562 jets, Red acc pump, and #31 shooter with 8.5 PV

The new ones are #61 or #612 close limit jets, Red Acc Pump, #31 shooter, 8.5 PV...they also are manual choke...so you might make sure
that the butterfly isn't stuck partly shut...

Besides the O2 gauge and sensor, you need a vacuum gauge plugged into the vacc port under the bowl
so you can monitor the reading where it will show you throttle position.

Street Long Ram Manifold need more fueling to cover the delay in the throttle opening and the air/fuel making it
to the valve... a 4 barrel would help transition the things under demand better...the small 2 barrel is gonna be outside
it's comfort zone, FYI.

If using a holley, you are going to need a holley tuning book and a master kit so you have an assortment of acc pump cams
and PV's...(and bowl gaskets... and a couple pairs of jets #60, #62).

If the engine is a 9:1 RV cam build... I would start at #60 jet, try the Orange cam in #2 position, shooter size is fine...
If the vacc reading fall off going up an incline or under load in high gear at low rpm... you may have to go to a pink cam
in #1 position for a long stronger pump shot... the pink profile provide gas from the acc pump all the way to WOT,
the Orange one tends to drop off about 80% throttle (where it's expected that the secondaries would be opening to
fatten the mix up and if still low vacc...the PV will be open...) If the PV needs to come on sooner a #10.5 picture window style
PV will be the ticket... you might need to go up to a #62 jet...

Check to make sure that the spring is set correctly on the acc pump arm.


Best of Luck.

Good, there are some things to try. I will say that I ran this exact intake on a relatively racy motor with a 500 CFM holley 2bbl. It was the best responding engine at low RPM that I've ever run with a large-ish cam. However, it would not rev to very high RPM. I really like the 500 2bbl and have run it on stock Slants with great results.

Lou

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Home of Slant6-powered fun machines since 1988

I've never run a 350 Holley but like Lou I have run a 500 and it ran great right out of the box on a near stock and on a built engine. All I ever changed was jets.

_________________
“Buy the ticket, take the ride.”
― Hunter S. Thompson

Thanks for the backup, DrGonzo. I have told people this exact thing for 20 years and basically no one listens to me. I have heard way more people happy with 500s than with 350s.

Lou

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Home of Slant6-powered fun machines since 1988

Thanks all,

That is helpful and I few things to try when the shops here open again sometime in the future.

I'll need to do a Vac reading, when I can get a Vac gauge, but it makes sense to increase the power valve size from 8.5 to 10.5 so that extra fuel is kicked in earlier and it could well be that the main jet size is now too small (if it is she is starving rather than flooding at WOT). Apart from the WOT issue, she is pretty good through the range, except for a slight rough patch at about 30mph under light acceleration.

The main jets were downsized as I had an problem with a missing #6 cylinder when I first fitted the Aussie-speed long runner and Dutras. We thought jetting might have been an issue as well, as I'd read elsewhere that a 350 cfm carby can be "too big" for a slant. I now realise that was probably because people were talking about a stock build with no exhaust mods etc. The #6 miss was later remedied by new spark plug leads, electronic distributor and high voltage coil but the jets never re-"up-sized".

I am guessing that additional fuel should not be a problem, if what Lou says about a 500cfm carby is right.

I note the 500 CFM would be pulling in a lot more of both air and fuel than the 350 cfm. I am of course now curious what the performance difference would be between the two in terms of power/driveablity/fuel use. I suppose if changing jets etc above does not work, then I might swap in a 500 cfm as Lou suggested and let everyone know the difference.

Lou, I note that you say that your slant would not rev "to very high" RPM. I am not sure what "very high" means in this context and perhaps you could elaborate? - Note my VC Valiant is a torqueflight 3-stage auto (as built) and I'm mostly unlikely to drive over 80 mph, except for very short periods of time for testing purposes. If it was not clear from my above post, I mostly use this car as my road trip vehicle for holiday/camping trips around NZ on the open road (100kmh/60mph speed limit) and not as a commuter or for much inner city driving, although it is the only car I own.

I note from Holley the following carb specs:

350 CFM PERFORMANCE 2BBL CARBURETOR
Manual Choke
PART# 0-7448

Primary Main Jet 61 (mine is presently down jetted to '58 - it is a brand new carby and came with an orange accel. cam - In #1 position)
Primary Power Valve 8.5
Primary Pump Nozzle Size 31 (I note the Street Avenger - 0-80350 auto - choke version uses a 28 Primary Pump Nozzle)

500 CFM PERFORMANCE 2BBL CARBURETOR
Manual Choke
PART# 0-4412C

Primary Main Jet 73
Primary Power Valve 5.0
Primary Pump Nozzle Size 28


Cheers
Mark.

Not necessarily, the throttle plates may not need to be as open to get the same level of performance as they are on the 350 cfm model...

Just for your information the 350 is pretty small... the throttle bores are fairly similar to the primary bores of the 390cfm holley 4 barrel...
given the airflow test pressure drop conversion... the 390cfm holley 4 barrel...flows about the same as the 500 cfm 2 barrel...


Food for thought...

Very high means over 5400 or so. You will never see that with your engine, and it will not make meaningful power about 4500, so no worries there. I would start by jetting back up to the stock jets and see how runs there. FWIW, I have gotten fairly close in MPG with a holley 500 as I have done with the best tuned Edelbrock 500 4bbl, which matches just about anything (if you keep your foot out of it).

Lou

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Home of Slant6-powered fun machines since 1988

What you describe is classic rich jetting. However, what is your timing set at and how is your vacuum advance hooked up? What kind of air filter are you using?

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Official Cookie and Mater Tormentor.

Ok,

So the answer seemed to be to follow Aussiespeed's advice and put in a couple of small bits of welding wire into the enrichment holes under the power valve to restrict fuel flow when the PV opens.

I went to a 10.5 PV and used 0.8mm mig welding wire, 60 jets. A lot more go off the mark and at the bottom end. Still a small bog at just past 3/4 throttle, but sorts out at WOT now or if revs high enough. Maybe if I use slightly thicker wire it'll even our up all the way through and eliminate this issue - the next thing to try. Sounds dodgey but it works.

More info is here: down the bottom of this page https://www.aussiespeedshop.com/carb-tuning-help/

Hope that helps someone.

Cheers
Mark

Just a FYI:
I have noticed, that a Holley 4412 (500 cfm 2bbl) on my 170 engines, likes to pull fuel out the accelerator pump nozzels, at higher RPMs.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Cool ideas, folks. Thanks for the link too. My 500 richens up with RPM, more than I would have expected.

Lou

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Home of Slant6-powered fun machines since 1988

Try pluging the acc pump circuit, temporilly,(plug the nozzels) and see if it does the same thing. I talked to Holley about that several years ago, and they were helpless. If I remember right I put a heavier weight under the shooters, and also drilled a "bleed" hole in the shooter below the nozzels. I think I tried the anti-pullover shooters, but still had the problem. I never really cured it, but since a "racecar" I just adjusted for it at WOT. Very seldom was in the main circuit at part throttle.

_________________
Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225