Autox and SR powered Z

[logr]

A little background first.

I have SR20Det's in 2 240SX's. One is a daily driver and the other I use for autox and the occasional track day. I do very well in it in Street Mod. A co-driver just won a National Tour in it against the Canadian National Champion. The engine/ecu is completely stock with a T28 on it. The power is great and I have to weigh in at 2480lbs to be legal.

 

I also own a 240Z with an L28 which I believe needs an SR. The more efficient engine and better mileage along with the power and light weight just seem to to be the ticket.

 

My Question.

Has anybody here autox'd an SR Z with any success? The class would be SM2 and around here we combine SM and SM2 so with the Pax. I would have to beat the SM cars by about half a sec. to actually beat them. A friend has a 240Z with an L28et which is great and smoother power but I want an all around car. The mileage on the L28et is terrible. I'm leaning toward using a T25 on the SR for the smoother power and 240ish HP is plenty in a lighter car. I have the SR and am just about ready to start. I'm doing the swap but was just wondering how much it lightens the front and how much it affects the handling, good or bad. I'm sure lighter springs in the front will be needed and subsequent chassis tuning but has anybody done this already and had success? Thanks for any input, Mike.

[m4xwellmurd3r]

you can get near 30mpg with an L28et if you tune it right with megasquirt. I think for a high performance turbocharged car that's pretty damn good. I'm not sure what it would do to the handling, but from what I understand, a stock Z with the stock engine is pretty close to being 50/50, so lightening the front may upset that balance. you can probably find a lot of answers to your questions by searching a bit.

[johnc]

I don't think it would much (if any) of an advantage over the 240SX in SM. You still have to hit the same weight number and a 2,400 lbs. 240Z is a heavy autocross 240Z. You would have to add ballast.

[logr]

In SM2 the weight can be 200 lbs lighter. It would have to weigh 2280 lbs.

It weighs 2350 right now on an unofficial scale.

[johnc]

Oops, forgot about the weight differences between SM and SM2. A SR20 swapped 240Z fully prepped to SM2 should come in between 2,050 and 2,150 lbs. You'll have to ballast up to the minimum weight, which isn't too bad a thing.

[logr]

In case anybody is interested there are 2 videos on utube of my sx running autox. Search Logger Mike. Gotta say I really like SR's. Seems to me that a SR20Det in a Z has got to be a great handling car. Mid engine weight without the engine behind you. More balanced and less likely to snap spin like MR2's.

[Armand]

Ever since I swapped an SR in my car its an absolute pleasure to drive in the turns, it simply has gobs of traction, plus the way it enters and exits the turn feels much more graceful and poised. I can simply power out much quicker out of a turn with the weight of the car feeling much more centered. I've never had a car with this power to weight ratio before and I am still getting used to utilizing all the power coming out of the turns. It can be quite a handful sometimes. Although I have a 3.7 clsd and Falken Azeni's in 225's, it still doesn't take much to get the rear end out with a quick blip of the throttle. I'm running 13-14lb's on stock turbo/ecu. I also still have to corner balance my coilovers and get a proper alignment so the best is yet to come.

[logr]

Armand, I really like that intercooler set up. I did that on both my SX's and was thinking I would do it on the Z. I have experienced heat soak from the rad. at autox. I plumbed the windshield washer to the intercooler front and use it in grid. It solved the problem and also makes sure the engine never overheats. I've never had that problem though. I was thinking, with all the room left in the Z in front of the engine, I would separate the intercooler and rad. a bit more.

 

On my SX, I have kept softening the rear, for traction. I also eliminated the rear sway bar and added 1/4 in. toe on the rear. It helped tremendously. I have a helical rear so if you lift a rear it goes open, not good for autox. It now works great and I love the helical. Nothing to wear out.

[wheelman]

Hey Mike,

Good to see you on the board, This is Ken from the TriCities.

 

When are you planning to start the swap and have you given much thought to what you'll do with the suspension? I think the car you're working with has the Tokico springs I sold to Poorboy. They're OK but I didn't care for them, they lowered the car more than I wanted and the fronts are progressive while the rears are linear. The lower ride height probably came from the V8 in my car, you may have the opposite problem with the SR.

 

If you search this site you'll find a couple guys who've swapped in an SR. I think they all used a cross member setup for the motor mounts due to the thin nature of the frame rails in the Z. After my accident last year I replaced mine with .120 wall 2.5" square tubing, might be an option if you want to strengthen the front end but it's a lot of work.

 

Wheelman

[logr]

Ken, I will probably wait for bad weather to start though I might finish building the SR in the meantime. I need to get alot done around here and we have 2 more race weekends which take up much of my time. I plan on using a crossmember type set up for the engine mount with the stock SR mounts if possible. I like your torque but light is might.

 

Are you going to come up for our next event?

[johnc]

A SR20DET 240Z can win SM2 nationally, but it has to be built as a pure autocross car. Compromises for the street (like rubber/oil filled engine mounts) will reduce its capabilities.

[Six_Shooter]

you can get near 30mpg with an L28et if you tune it right with megasquirt. I think for a high performance turbocharged car that's pretty damn good. I'm not sure what it would do to the handling, but from what I understand, a stock Z with the stock engine is pretty close to being 50/50, so lightening the front may upset that balance. you can probably find a lot of answers to your questions by searching a bit.

 

My car, which is an L28E (F54/P90 flat top pistons), Borg Warner turbo from a 6.5L diesel, non intercooled, N47 intake 30 lbs/hr injectors, GM EMS, with a still rough tune (rich pretty much accross the board) was able to get 25 MPG on the last tank, I know I can pull a lot more out of it once I get the tuning closer, switch it over to closed loop and enable lean cruise mode.

 

I'm still swapping to a lighter powerplant in the future, but so far, I'm quite impressed with how this has turned out.

 

There's something about an SR20DET in an S30 that is just so appealing though.

[johnc]

FYI... a SR20DET swap is not any lighter then a NA L6 install. The added weight of the turbo, intercooler, and intercooler plumbing pretty much negates the weight advantage of an SR20DET swap over a NA L6. The SR20DET does save weight over an L28T swap.

[wheelman]

Ken, I will probably wait for bad weather to start though I might finish building the SR in the meantime. I need to get alot done around here and we have 2 more race weekends which take up much of my time. I plan on using a crossmember type set up for the engine mount with the stock SR mounts if possible. I like your torque but light is might.

 

Are you going to come up for our next event?

 

Mike,

As of right now I'm planning on coming up but with work as busy as it is things may change. I also just checked the weather and looks like it's going to be perfect.

 

I know what you mean about things to get done, I've got a project car I'm working on for some friends I need to get done and then I need to prep the house for paint (that'll probably end up waiting for next spring).

 

Yes, the torque of a V8 is tough to argue with, it'll be interesting to see how our cars compare once you get the SR swapped in. At some point I would think the suspension setups will be similar, we'll have to make sure to run an auto-x at that point and see what happens. Maybe we could talk Cody into driving both and give us a review, then we could post it here for all to see.

 

Wheelman

[logr]

FYI... a SR20DET swap is not any lighter then a NA L6 install. The added weight of the turbo, intercooler, and intercooler plumbing pretty much negates the weight advantage of an SR20DET swap over a NA L6. The SR20DET does save weight over an L28T swap.

 

This really surprises me. I'm still all for it because I think I can move the weight back and the more efficient engine with more power is a win, win situation but it sure seems like it would be lighter.

Do you mean the SR isn't lighter than an L28? I have both engines in my shop but no easy way of weighing them. Essentially you are saying that the total weight is the same but relocated? Quite a bit of work/money to relocate 100-150 lbs.

 

It is also interesting that you think a Z, with it's 30 yr. old suspension design can win SM2 Nationally. My SX is very fast, with the right driver, but there is a vette with a built small block that cleans our clock most every time we race. It revs like no other. Now I'm intrigued.

 

CODY and MikeyV (our local super drivers) both say my SX is the most fun and best turning car they have driven. We took 1st,2nd and 3rd at the vette club autox this last weekend, all in my car. They beat their fast times in their cars, with one run each in my car. Mitzy also beat her best time in the cobra with mine. We were swapping around a lot.

[johnc]

The combined weight of the SR, the turbo, the intercooler, and associated plumbing make the SR swap very close to the weight of a NA L6. And you can move the L6 back in the engine compartment and get the weight distribution close to the same as an SR swap.

 

There's a thread here that compares the NA L6 I built for myself with a SR20DET swap I did for a customer. Overall weights were within 10 lbs and the weight distribution was within 1%. The SR swapped car made 100 more hp then my NA L6.

 

I was originally building my 240Z for SM2 back when Dennis Grant and others had just created SM. Talking with Howard Duncan convinced him that a two seater sports car version of SM would be a good idea. Unfortunately, SCCA got some bad information about potential participants and started messing with the weight/displacement/aspiration formula before any car had made a run. The original specs made a NA 240Z at 3L run at 2,100 lbs. My car came in at 2,150 lbs. in SM2 legal trim and made 320hp.

 

I think a 400 to 450 hp 240Z running 285/30-18 V710s and some triple adjustable Penske's or Ohlins would win SM2 with a good shoe.

[wheelman]

Ken and MikeyV (our local super drivers) both say my SX is the most fun and best turning car they have driven. We took 1st,2nd and 3rd at the vette club autox this last weekend, all in my car. They beat their fast times in their cars, with one run each in my car. Mitzy also beat her best time in the cobra with mine. We were swapping around a lot.

 

Mike,

Which Ken are you taking about here, cause it certainly wasn't me.

I wish I had the time to attend more events like that, it sounds like you all had a blast.

 

So, if I let you drive the Z can I drive your SX?

 

BTW: There's a young guy who lives in Spokane that's building a 2+2 Z turbo. I mentioned the event this coming weekend and told him I could let him ride along a time or 2 if he comes out. He said he might have his car ready so there may be another Z showing up.

 

It's also looking better work wise for me to be able to come up. Isn't there a guy up there that runs an F-Prepared 240? I think he ran with us once last year, came down with Cody.

 

Wheelman

[logr]

Sorry Ken, I fixed it. I meant Cody. Please Register for this weekend.

Yes, there should be an FP car with a Robello engine. 300hp but not enough rubber and pretty touchy power, also 14/1 compression which means 9.50/gal. fuel. It's alot like big turbo power from what I hear. I does run hard though.

 

JohnC, I will look for that thread. It still surprises me. I was hoping to get the weight to the minimum with 55-58% or so on the rear. I like the 285's and have thought of them for my SX but I really like the 275/35/15 for the shortness. I can run most tight courses in second and have unreal pull out of the corners without shifting. I put in a 4.6 and 23in tires. 2nd at 6 ft. and stay there most of the time. I do use 3rd quite a bit on faster courses and even hit 4th at Top Gun in Helena. The Top Gun video has Cody saying I forgot to shift to 4th. Sometimes it is more shifting but it is SO much easier to hit 2nd than first and 2nd and 3rd are so close together that the jump is minimal so the power is always right there. I can fit the 275's under the car with no flares but need more tire if I up the power at all. We usually run 10-12lbs with gain at 10% to slow up the boost hit. I have some really light rotating parts and maybe should have saved my money. The spin up is so fast that the tires can't keep up and part throttle is hard to do smoothly on a turbo.

[johnc]

I was hoping to get the weight to the minimum with 55-58% or so on the rear.

 

That would be impressive. Best I've measured is 53% on the rear with an SR20DET swap.

 

Regarding tire size, the 285/35-18 is where the tire manufacturers are spending their development time. Originally Hoosier built the 275-15 by adding a strip to the middle of their 225. That carcass wasn't designed from the start to be a 275 but they may have redone the tire to be a dedicated 275.

 

If you're really thinking out of the box, I suggest you consider a Powerglide for the transmission behind your SR. With a good torque converter and rear gears in the 4.88 / 5.12 range you should be able to build a top gear range of 30 to 80 mph while still being on boost.

[logr]

I like "outside the box" in all of life. I blew up so many Powerslides that I had to learn how to rebuild them while still in high school. My parents were not impressed until I could fix them also. Guess that may date me a bit.

I have never even considered an automatic for autox. I watch the karts spin every time they try to power out of a corner with that snowmobile clutch set up and dismiss it. That said, it is an interesting idea. If you could get the gears right, the torque converter could take care of the low speed manuevers with slip and the top end needed might still be there. I'm just not sure how I would like the "hit" when you give it gas coming out of a tight manuever. Left foot braking could make a big difference. I've always thought it could be a big help on a turbo anyway but I seem to never be able to remember to do it at the important times. With no clutch to worry about though, hmmmm. Auto AND Turbo, hmmmm.

 

As for weight balance, don't forget the minimum of 2280lbs. Ballast in the tool kit holes and battery in the back and it might be close. Powerglides are very heavy. The converter weighs close to what an SR trans weighs. I would most likely stay with manual. This car was to be a driver that I might autox too. My SX is so close to being a very good autox car. I have been considering the 285's for it for a while. The PDM car we beat at the tour was a very nice car and he had 275/17F and 315/17R. He was running a turbo'd KA with 460WHP. Cody (my codriver) was the only reason we won. I would have loved to see Cody drive that car at the Nationals. Don (the owner) may do just as well but giving Cody a chance would have been interesting. Don said he was giving up on the SX and building a 510 all out. I'm sure it will be done right.

 

Anyway, this sure gives me food for thought. Winter is coming up and I need something to build.