3.1 with SUs - worth the effort?

[Guest nustad]

Howdy,

 

My short term plan is to build a 3.1 and put my ztherapy SUs on it so I have a stock but torquey engine. Later on I may go to triples

 

Is it worth the effort or should I just rebuild my 280 engine without the LD28 crank etc?

 

At this stage I have 280z engine and spare 240z rods and need to source the crank and pistons

 

This is to go into a street 240z which is used for open road driving and not racing

 

Cheers

 

Glenn

[Guest bastaad525]

Stock bore SU's are really not flowing enough air even for a 2.8... but it's workable... they're gonna choke a 3.1. It may run okay for daily driving or whatever, but depending on the compression you may also have lean run issues and detonation, as the SU's dont exactly supply enough fuel for 3.1L either, maybe not with the much loved SM needles. A 3.1 motor is a lot of work... and the extra .3 litres isn't necessarily going to give you some huge leap in torque. Save the money you were gonna spend on turning your motor into a stroker, and put it into headwork, which is where you can really free up a lot of power on an L6, and then if you have enough left eventually your now-high-flowing-motor will benefit from upgrading to triples or better yet for a street motor, get the big bore SU's that Rebello sells for about the same price as the Ztherapy carbs. Trips would probably yield more top end but big bore SU's can make a lot of power as well and still keep their 'civility' of the regular stock SU's. Porting, polishing and a mild cam... should get you about 200hp at the rear wheels, and much easier than doing a stroker. Add better carbs and you could be up to 220 or even more. Very fun in a ~2300 240z, should get around a 6 second 0-60 time and low 14-high 13 second 1/4 mile time.

[zolorin]

bastaad525, good info, now the question is can I use the SUs to break in the 3.0 stoker (use it for the first 2000 miles of the break in) since they are easy for me to tune and then install stand alone fuel injection (megasquirt) What would be a suggestion on that, thank you

[Dan Baldwin]

SUs on a 3.1 makes a KILLER street motor. I drove mine that way for years, LOVED it. Mash throttle and GO. At the track it hit a wall at ~5500. A hotter cam pushed the wall up to ~6000, and going to 2" SUs moved it up to maybe 6500, in my case. Going to triples totally eliminated the wall, and peak power is at 6500 now. Still makes good torque at the7000 rpm rev limiter.

 

Long-short, I would highly recommend a 3.1 with SUs, then you can build it up for track usage if you like, or not. IMO, the added cost of a diesel crank and KA pistons ($40/ea from Lynchburg Nissan, ask for Riley) isn't that big a deal if you're rebuilding anyway.

 

DO IT.

[Guest norm[T12SDSUD]]

Stock SU's on my 2.9L stroker was good for 12.94 @ 104 mph.

I wouldn't exactly call that choking the engine.

 

If you can afford the triples then go for it, but on a street engine I'd suggest staying with the SU's for economy and low end torque.

 

 

Later,norm

[akeizm]

Really, a single can perform as well as a triple. It matters if you can get it tuned right.

[Z-Gad]

SU's and mechanical fuel pump are working great on my 3 liter daily driver 240z.

[Guest bastaad525]

Norm, we all know how fast you ran with the stock SU's, but they ARE choking a 3.1L engine, especially if the engine is setup up to flow well (good cam, headwork), no matter what you say. Sure it can run, and run well, and make a fast car, I never said it couldn't, but the SU's will NEVER be able to flow as much air as a well built 3.1L would really be able to make use of, therefore they ARE, TECHNICALLY, choking it. However, this would really only effect high RPM operation, and I agree and have ALWAYS agreed that SU's, particularly the larger bore ones, make a GREAT setup for a primarily street driven car, and I always suggest upgrading them last if at all, and never swapping out the SU"s before doing some good headwork... I always stand fast that this is where real power can be had on any L6. I will usually tell anyone that is driving their Z on a daily or several times a week basis, that I do NOT recommend tripples, but usually get flamed for that, so was trying to be more openminded

 

Regardless, on a good flowing motor, SU's will be maxed out in flow long before the motor hits it's limit, this can go for a well built 2.8, let alone a 3.1. There will always be more power and more revs to play with when switching to triples unless we're talking a bone stock setup, in which case triples can actually hurt driveability significantly.

 

Personally, if it was me, I WOULD run the SU's, because I like how easy they are to tune and maintain, and I like their street manners, the couple cars I drove equipped with triples screamed on the top end but had no low end grunt, which I don't like. You can argue wether or not these particular cars were tuned properly or not, I don't know and don't really care. I ran SU's for a year and loved them on my 2.9L motor, and put down decent power with them, and had a really fun street 240.

[Guest nustad]

Thanks guys - pretty much seals it for me - will look for a crank - should be able to get one for $25 - $100US in New Zealand - not much demand for them here.

 

Cheers

 

Glenn