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turbogrill

Why more horsepower with a carb

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Not trying to do a carb vs EFI thing here! 

 

BUT! I it seems like putting carbs on a stock L28 engine will improve HP? Or is that not the case?

 

If so why? On a stock engine the EFI system should be able to perform a similar task?

Edited by turbogrill

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I'm not certain how true your statement is (and by how much HP/trq), but there is at least one thing that I think could influence this..

 

injected engines are relatively more modern, and were partly used to help with the emissions.  that means not wasting any gas that will end up in the air we breathe, which also means making certain things are as lean, or as stoichiometric as possible.

 

carbs, on the other hand, being from an earlier time where emissions were as interesting as a shaven chest on a straight guy, might be more generous and allow for a richer AFR.  it's a fact stated and supported elsewhere that having a 13.5 afr is better for acceleration/torque/hp producing than say, the ideal 14.7.....  

 

that being said, though, anyone ale to tune their injected engine (aftermarket ECU) should be able to negate this advantage, however..  possibly even make injection more powerful since the gas would be better atomized/mixed, in theory.  

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Please be aware that the EFI units used on the L series engines are analog and not digital.

 

Also the use of an AFM instead of a MAS creates a restriction.

 

I have yet to see an instance of a modern EFI system properly tuned NOT providing more hp, torque, driveability and gas mileage throughout the entire power range vs a carb setup.

 

In the case of high horsepower/rpm setups operating in a narrow range a carb setup can work just as well and be simpler.

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As Brad says, the limiting factor with the S30 EFI is the analog nature of the FI system. It's set up for stock stuff, so if you put in a cam, it can't adjust. Original S30 FI systems are 40 years old and have issues with bad connectors, etc, that a switch to carbs negates. A perfect running factory EFI unit should compete well with stock 240 SUs on a stock L28 engine. The other issue might be restrictions in the factory intake manifold, but if you compare hopped up engines with cams and headwork, etc and then ran the same intake manifold, say ITB EFI vs Mikunis or something like that where everything else is relatively equalized, you should do better with EFI than with carbs. When you start looking at those options, a motor swap becomes more and more cost effective.

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Its easier horse power vs. installing a new programmable ECU . Most guys opt to throw triples on then bigger injectors and a method to tune them. In the end the cost probably even out , and even the learning curve for some might be the same. Myself- I am about ready to do away with carbs and go for power the other route.

There isn't that many builds here that I have read that go for NA FI power with a programmable ECU . Most stuff is turbo style

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Funny you say that Madkaw.

 

I'll be taking the SU''s off my Ported L28 and installing a stock FI manifold and megasquirt this fall. It would be nice to get proper needles for the current setup and get it on the dyno to do a nice comparison. Half the reason for going the Ms route is not dealing with the needles.

 

Not many people seem to modify and keep the stock system. I'm curious to see how it turns out.

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Posted (edited)

Some news here?

Would be interesting to see some dyno sheets of some kind.

L28 EFI vs. L28 tripple weber

 

Of course you get more mileage out of the EFI setup but what happens to hp/torque.

 

Am I understanding it right, that when you change the exhaust and to an other cam that its hard to tune the stock EFI to it?

Edited by PrincePaul

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On 3/13/2018 at 10:50 AM, PrincePaul said:

Alright, that pretty much concludes what I thought/read over the last days.

Probably go tripple weber than. For myself I can`t justify the price of a modern EFI with the old ITB or carb look.

Especially as I`m not planning to run 300 HP.

 

It all depends on what you want to do, imo it makes sense to convert stock efi to carbs for hot street or race.

 

I did a megasquirt conversion and it takes a lot of time. But its awesome if you are on the geeky side :)

 

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The costs of the triple carbs are now almost identical to a set of ITB's.

Comparing stock EFI plenum to Triple Mikunis or DCOEs is a serious 'apples to oranges' comparison.

The dyno sheets WERE up here, in regards to our Bonneville L28, which ran, in turn, a Predator Four-Barrel, 45DCOE's, and then TWM ITB's.

In each iteration there was an increase in power and civility of the exact same engine--a very important fact to realize is ALL that was changed was intake type (the TecII Ignition merely ramped identically to our recurved distributor):

The Predator made 217 Hp and just didn't pull well over 6,500 rpms, it idled at 2,200 rpms.

The 45 DCOE's made considerably more HP, with a power peak of 7,500 rpms, it idled at 1,700 rpms.

The 45mm TWM ITB's made 17~20 more Horsepowerthan the DCOE's at 7,500 rpms, and 40 HP More at the new power peak of 8,250 rpms. Idle was wherever we wanted it: it would pop along at 450 rpms, and start easily in 39F weather on a 1,900 fast idle, and come down as it warmed up to a curbe idle of 950. 

This can be attributed to pumping loss restriction? Below 6,500 a four barrel seems to be competitive, above that Triple ITB's or DOCE/Webers are the power kings. You will always need a larger carb to get the same HP as an ITB. We could have made this same power with 55 DCO's, but they would NOT have been applicable to run on our L20A later when we switched classes downsize. That's a lot of money to pay for something you can only use on one of two engines you have!

 

 

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I don`t know for what price you`ll get a efi setup with ITBs but tripple weber (just the hardware) is about 1500 +- 250€, and the efi ITBs alone is about 3500-4000$

https://www.efihardware.com/products/c388/Nissan-6-Cylinder-Throttle-Body-Kits

The jenvey kit is not much cheaper where you have the weber look with injection.

 

than you don`t even have all the sensors and the ecu.

 

But as I said Weber for a mild performance gain together with cam, exhaust and intake is probably a good way. For myself I`m also kinda a nerd with electronic hardware and do a lot of pc related stuff. But thats why its even more appealing for me to do a carb conversion as of the modern cars have enough electronic to play around with. And my daily will always be such a car. So to go back to the roots - at least for me - is really interesting ;)

Thanks for the comments anyway, I just wanted to rectify that I don`t loose power or make the overall performance worse with converting from stock EFI to tripple Weber.

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ITBs with little use are up on ebay all the time in the $1500-2000 range.
Which happens to be about what triples sell for when they are decent.

ITB's don't need the attention carbs do, you have to work very, VERY hard to get a bad set of ITB's. It is VERY EASY to get a bad set of carbs that ends in a money pit.

Sensors, a pfennings, and an ECU to run them is $475 from DIY Autotune look up "Microsquirt" they work JUST FINE!

Just to screw with your head, fact of the matter was I bought a 76 with an L28, header, and triple DCOE 40's on it. Made ALL the right noises, brutally accelerated and made a whopping 85 horsepower to the rear wheels.

Replaced them with a stock EFI setup that was pulled off another 76 that had 176,000 miles on it. Ran the full intake ducting, including the silencer the only change being a K&N Filter Element as the CAI that I originally used hissed loudly and generally made too much noise. I removed the header, and installed the stock 76's cast iron manifold using an MSA downpipe to convert from the iron manifold to the MSA Exhaust that was on it. I ADDED another muffler under the car by the transmission to quiet it down further.

With the EFI on it, felt kind of doggy. But it did whip the dyno to 146 rwhp, and consistently runs the 1/4 mile in 15.30-15.50 seconds. All that quiet is deceptive.

So no, you won't automatically make more horsepower with triple webers, and chances are if you simply bolt them on to the car like the previous owner did with my set, you WILL lose copious gobs of horsepower! Might sound good...but that is why we say the Butt-Dyno is a worthless evaluation of ANY performance addition.

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Oh, and just to point it out, I believe it was RHD Japan that was selling the Sangyo Kiki EFI set complete for like 1800 yen equivalents...whatever size you wanted, 40, 45, 47, or ??? 
Brandy new, in the box complete including TPS...all you needed was cheap GM MAT, MAP, and CLT sensors for the Microsquirt and you were complete...

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Posted (edited)

I use the microsquirt and it works very well. It took quite some time to get the harness done but you can buy a premade harness from softztop on this forum. That should save you some time.

 

Tuning with Mircrosquirt is very fun

Edited by turbogrill

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