EMPI HPMX carb for 1745cc - now 2021cc

[Ravivos]

Hi,
well, since y'all where so great with your advices about part selection for my engine, i've decided to present one more questions.
waiting for the parts to arrive, i'm building a 1745cc engine 76x85.5 with a W100 cam on the stock heads,
planning on porting the heads and intake manifold a bit.
now, i want to give the engine a proper breathing, so i've decided to go with the EMPI HPMX carbs kit, its a double carb with the flat air filters that would fit under the T-34 lid,
which one do you recommend that ill get, the 40mm or the 44mm ? is the 44s too much for such engine? any other input on that subject?

as for exhaust, will probably go with the type 3 "over the top" style muffler.

Thanks.
Ravivos.

[gearheadgreg]

Again - I haven't built a hundred of these, but I have had first hand experience with the EMPI carbs. The sets that the local shops have dealt with have needed lots of work to make right, and a few sets that for some reason, never could be adjusted to run correctly. So I would vote for a set of used Weber/Dellorto carbs in good condition over new EMPIs, until they are proved better.

Second - 44s on your motor are way too big IMO. The old rule of thumb on an IR (individual runner = one carb throat per intake port) was to size it the same as the intake valve. So if you have 40mm intake valves, choose 40mm carbs. There are exceptions of course, with very high rpm motors, etc. but that gives you an idea. Porsche's 356 engine used Zenith 32NDIX carbs (four 32mm butterflies) for 1600 engines making more power and rpms than you are likely too.

My opinion, for a mild engine like yours, choose a mild carb setup - dual single barrels. Weber ICTs/Baby FRD Dellortos, or even Kadrons, which are available in 40s or 44s and should be more than enough for your engine. Dual 40 or 44 IDF/DRLA style carbs would be more than your engine needs, and more complexity. Maybe some 36DRLAs, but I would still vote for the ICTs or FRDs.

On my 74x88 Baja engine, I used a single 40mm IDF - it starts right up, idles great, and runs cleanly to high RPMs. Would it make more top end on dual 40s? Yes, but it's a Baja and low end and mid range response is more important - I get the feeling your engine is the same way.

[Ravivos]

Hi Greg,
Thanks, but i have a rule of thumb that i'm trying to follow - don't buy someone else's problems...
buying a second hand/used set of carbs seems a bit problematic from that point of view,
just as i wont be buying a set of used pistons or crank.
now, the HPMX will set me back at about 800$ at my door (shipping+tax, its a nightmare) and that is considered a low price comparing to other carbs on the market.
will definitely go with the dual setup, and the EMPI HPMX sounds like the correct way to go when on a budget.

beside, it seems that almost all people that chose using this set are pleased with it and it looks like a good value-for-money comparing to other (new) sets out there.

so, a 40mm it is, how about jets? should i order a set of different jets for it? the original set comes with 115 mains and 50 idles, should i go with the 130-135 for mains?

it seems i need to get myself a set of wideband o2 sensor (innovate LC-1) and hook it up to my laptop for proper tuning of the carbs, looking for the sweet spot at 14.7 AFR...

[madmike]

Try the 115's first and see 130-135 will be too big, I'd get some 120-125's,200 airs and 50-55 idles should get u in the sweet spot

[Ravivos]

Try the 115's first and see 130-135 will be too big, I'd get some 120-125's,200 airs and 50-55 idles should get u in the sweet spot

Hi Mike,
Thanks, will try the original 115's and will order a set of 125's as well.

any recommendation for a Wideband O2 sensor beside the innovate's LC-1?
any other input regarding the proper jetting?

Ravivos.

[madmike]

Sorry,I've never used a wideband ,Madmike

[Ravivos]

Hi Mike,
Thanks.
anyway, ordered the 40's type 3 kit with additional 125s and 130s mains.

[Ravivos]

Well, it has been a slippery slope trying to get the parts for the engine.
ended up with 2021cc , CB performance 42mm heads, Norris336s cam

since i already bought the carbs, and want to use the ones i have, was wondering how can i make the HPMX 40s to work on my engine?
looking for a nice flat torque curve, not going to spin it a 6K.
should i replace the venturies? any ideas on how to re-jett it?

Thanks
Ravivos.

[gearheadgreg]

What venturis are in it now? I don't think 40s will be too small at all - especially when you are looking for response and a torque motor vs. a top end screamer.

[gearheadgreg]

As an aside - my 2276 build has shrunken to a 2180 or 2074 - and I plan on using the dual 40mm IDF setup I have - along with 40 x 35.5 mild ported heads. I think it's a good combo.

[Ravivos]

Hi Greg,
currently, have the original 28mm venturies... haven't ran them yet as i am still building the engine.
would love to hear how the 40s performs on a bigger engine.

the 2180 sounds like the perfect engine, highly reliable using the 92TWs with a 40mm head, it should be a great street engine.
actually, the 2180 is on my "build list" and will probably go on one of my next T1 builds.

So, 40s with the 28s would run o.k? or should i get a set of 32mm venturies? will probably need to re-jett the carbs accordingly, any recommendations?

Thanks.
Ravivos.

[gearheadgreg]

They're easy enough to change. If you've got ported stock valve heads, I'd probably lean towards the 28s. If they are 40x35's, the 32s.

If you think your engine combo will make power over 4500-5000rpm, I'd say the 32s, but that's just by the book. Marc or someone has to have more real world experience with a setup like this.

I had a mild built 1800 Water-cooled 8V VW engine with 40mm DHLA Dellortos - 33mm venturis (weird size, I know). [9.5:1, ported 38x33mm head] It idled and ran great, but it also pulled to 70000rpm routinely, even with a mild cam. Those engines are undersquare, though with a much longer stroke, may affect the comparison

[Ravivos]

since the cam is rather large, with a 290degs duration (Norris336s) and a (to0) big intake valve 42mm, it seems that the 32s will be good.
so i went ahead and bought a set.
any ideas on how to re-jet them? maybe just the basic rule-of-thumb?

Thanks.
Ravivos.

[gearheadgreg]

The 336S is actually a pretty mild cam - it has softer ramps and easier on valve train than a similar mild to medium cam, part of the reason I will be using mine with 1.25 rockers.

[Ravivos]

thanks
1.25 is the way to go... i have the solid shaft set from EMPI.
i just hope that the 1.25, with the 336 and the dual springs on the valves, wont be too hard on my pushrods, but will probably replace them with chromoly pushrods once the engine is built.

so, any idea on the jetting?
2021cc,
Norris 336s
CB performance 044 42x37
HPMX 40 with 32mm vents



Ravivos.