NA 3.1L=>head & camshaft questions. No shortcuts, max

[zredbaron]

I gave Jim at Sunbelt a call and he's looking into whether or not I would need valve reliefs in my pistons to clear the valve lift. I bought the big bore kit directly from Nissan Competition in 1998. (R.I.P.) Does anybody know if those pistons can clear .525-.550" valve lift? The catalog I bought the parts from say that the pistons have a positive deck height of .025", but I have no idea how to use that information.

 

Chances are it will have to be measured since there is no way of knowing the history of shavings, especially since I will likely use a 1mm gasket. Chances are that I will just have to get a set of custom forged pistons. And I thought at least my block was done right. How dissappointing.

 

On the bright side, it will give me a chance to swap in some prettier pulleys for the re-balance, getter some better paint on the block, and gut the engine bay to clean up the wires and give it a fresh coat of paint.

 

Might as well do my planned tranny and ATB 4.11 diff swap then, too.

 

As for John Bs idea of dyno plots, why not start a stickie where each graph submitted also has the member's comments with the cars setup. One for NA, one for Turbos? I'm sure this isn't a new idea. Administrators?

 

Damn, this is gonna cost some serious cash...I may have to wait a bit to get it done. Okay what really happens is a loan gets taken and paid off later while I'm out to sea. Let's be honest here....

 

...I can't wait...

[johnc]

I'll be more disiplined in trying to join in on the next thread ,again everyone, I apologize for the confusion John seems to think I've brought.

 

Ease up. Check the site guildelines in the Announcements forum. Although thread hijacking occurs here its not really something we encourage.

[JMortensen]

JohnB, if you've got a 4.44 rear gear, why are you trying to find a cam that works at 2500 rpm? Seems like you could get a cam that doesn't start til 3500 or 4k and still keep it in the revs with that diff.

 

Or were you asking rhetorically? If you find that cam, BTW, let me know...

 

Jon

[gramercyjam]

Slow second gear corners mainly. I'd like to stay out of first. Seem to be getting a lot of those lately. The 4.44 gears make that possible, but I run out of second gear quick now too so some times up to third for just second or two, then back to second, brake and start turning in all at the same time. I'm not coordinated enough to do all that turning and braking and shifting at the same time. So if I could just stay in second (like an S2000) on the tight courses, maybe they won't beat me anymore.

[Dan Baldwin]

(R.I.P.) Does anybody know if those pistons can clear .525-.550" valve lift? The catalog I bought the parts from say that the pistons have a positive deck height of .025", but I have no idea how to use that information.

 

Valve reliefs are required for .550" lift! When I first installed the Sunbelt cammed head, I ran the cam a little retarded to get decent intake valve clearance (.040"), which I checked with a lump of clay. Unfortunately I didn't check the exhaust side. A year later when the motor had to get rebuilt, we found deep dings (~.080") on each piston from the exhaust valves! That was with a 2mm gasket. Abacus Racing did the rebuild, and did the valve reliefs in the new pistons. Chuck at Abacus is GREAT, very conscientious, and experienced in building serious (GT2) L-series race motors. He checked all the clearances and mocked up the assembly a few times to get close to the CR I wanted. VERY tight, even with the reliefs.

[JMortensen]

Wouldn't the duration determine whether or not you need the reliefs, not the lift?

 

EDIT--Dan, did you have to turn your spring retainers down on a lathe so that they didn't hit the stem seals? I recall that you have Schneider springs and retainers, and I had to have mine turned even with my .490 lift cam. Also, did you cut the spring seats flush with the head, or was that not necessary?

 

Jon

[JMortensen]

Anyone know the answer regarding the Schneider retainers?

 

Jon

[zredbaron]

Dan:

 

Thanks for the valve lift details. I'll call Sunbelt again tomorrow.

 

Well, since all L28s were fuel injected from the factory you're not compromising the "purity" of the engine by going with FI. Throttle response has much more to do with reciprocating mass then the fuel system - carbs do not have any advantage over FI. If you build a 300hp NA L6 I think the FUN will be there regardless of the fuel system. Sound is a subjective thing and I agree that a triplet of Webers at full song is beautiful....Regarding fuel injection, you *could* open up your wallet and go with 3x2 50mm throttle bodies and have all of the sound and fury of triple carbs.

 

Okay, Dan. I have to admit that I'm actually toying with the idea knowing that my 40dcoe's are too small. I know nothing about FI, but you say with that setup that it would sound like my webers do? You also say I wouldn't lose any throttle response? If those are both true than I just may go with FI! This 3x2 50mm throttle body setup...are you talking about FIs or DCOEs? How much cash are we talking about?

 

If this is as good as it sounds, I'd also be able to use my Electromotive igntion to its fuller potential. Not to mention tuning based on seasons and climate wouldn't be hard at all.

 

I do have one rule about spending significant amounts of cash regarding something I know nothing about: I make sure others agree.

 

You other NA voices out there agree?

 

Again, thanks so much for your time, guys.

 

-Mark

[JMortensen]

Triple TB's are awesome. You can run a 50mm and still get decent low end. Seen 2 Z's with triple TWM's, both REALLY haul @ss. Sound is exactly the same as triple carbs, because you have the same open hole from the air horn to the valve, so you get the same noise. Easier to tune or have tuned too, seems like there are more programmable FI experts than triple carb experts these days...

 

Jon

[zredbaron]

Wow. I think I might be sold (just checked out the TWM site).

 

So I guess my next question is...why have you only seen 2 Zs with a setup like this?

[JMortensen]

$$$

[Dan Baldwin]

Jon,

Sunbelt did the cam setup, they didn't reuse the Schneider stuff. It only now, two years later, occurs to me I should've asked for it BACK, they still have it (or threw it out). When I was running the Schneider kit, I didn't machine anything, just replaced the stock stuff with their stuff. The Schneider cam card listed 0-lash lift as .503", not .490". Weird if they have two L6 cams that close together, huh?

 

One note about Schneider cams, my first one wiped out a lobe just over a year after I bought it. They were great about it and sent me a new one after they got mine back. I checked the dribble holes on the new one, and lo and behold one of them wasn't *quite* drilled all the way through! I only barely caught it. I blew compressed air in to see if it came out at all the dribble holes, which it did, but the air coming out of that one hole felt like just a *tiny* bit less than the others. I'm sure that's what happened to the one lobe that got wiped out on the first cam from them. When using the internally oiled cam, check each dribble hole! Sunbelt set it up for internal and spray-bar oiling, btw.

 

I *think* lift should be as good or a better indicator of whether reliefs are needed, but either way it should be mocked up and the clearances (of intake AND exhaust valves!) checked. When I took the head off and sent it to sunbelt, there were very slight dings from the intake valves on the tops of the pistons. From the .503" cam, and a couple of stuck throttle overrevs to 8k(!). So I guess I'd say .490 is probably getting in the neighborhood of where it needs to be checked for sure.

[JMortensen]

I've got the Schneider springs and retainers, but my cam is an American Cams regrind, so that's why my specs are different from yours. Did you reuse the old valves when you installed the Schneider stuff? If so that probably explains why you didn't have to cut the retainers and I did. A new valve sits substantially lower in the head than a valve that's been cut once or twice.

 

Thanks for the info.

 

Jon

[Dan Baldwin]

Part of the quote you attribute to me is from John. Don't *totally* agree with the part about reciprocating mass affecting throttle response more than carburation or injection. If the carburetion or FI are spot on, throttle response will be good, even if you have large rotational inertia (not the same thing as reciprocating mass, but what I *think* John *means*). Poor carburetion or FI setup and throttle response will suck, even with a formula 1 engine.

 

Back to the main topic:

If you can afford it, and are eager to learn how to tune fuel injection, you should go for it. Carbs are a big compromise. I went with them cuz they were (relatively) cheap, and I didn't have time to figure out FI. I installed the carbs on Thursday, was at the dyno of Friday, and at the track on Sat/Sunday, where the ~30 hp gain was partly responsible for me beating 2nd and 3rd in my class by less than a tenth of a second! The only car faster than the three of us that day was a Formula Ford:)

 

My hp curve sucks, though, and parts are in Japan. I can't just program in a different fuel map.

[JMortensen]

I think throttle response will be better with FI because of the method of spraying the fuel. Anyone who has ever played with the accelerator pumps on triples (at least Mikunis) off the car can tell you that if you open the carbs you get 6 nice long pee streams of gas out of them. When port velocity is low there isn't enough turbulence to mix the air and fuel fully.

 

FI doesn't have this problem, so you get much better atomization at low rpms, and better throttle response at low rpms.

 

Jon

[zredbaron]

Thanks for the throttle response thoughts.

 

The more I look into this FI stuff, the more confused I get.

 

TWM offers a DCOE manifold conversion where you stick the throttle bodies at the end of your intake manifold where the carbs used to be.

http://www.twminduction.com/ThrottleBody/ThrottleBody-FR.html

I am referring to the 2900 series here.

 

I also see that Top End Performance seems to have put a few of these kits together successfully. However, I am weary of doing business with them again.

http://www.racetep.com/ztripdcoe.html#twmtbod

The picture at the very bottom is what looks to me to be the DCOE replacement.

 

TWM also has manifold/throttle body kit (throttle bodies built into a custom manifold they manufacture) that will be available for L6s later this year. The website says march 2004, but an email I got today said it will be closer to september.

http://www.twminduction.com/ThrottleBody/ThrottleBody-FR.html

I am referring to the 2000 series here. TWM estimates the kit will be ~$3k when it is released. It would include fuel rails, fuel regulators, and injectors.

 

BTW, TWM seemed to think that 48mm would be better for me since I don't plan on pushing 8,000 rpms full time like a road racer would be.

 

Just thought I'd share my internet/email findings thus far. I will make some phone calls tomorrow to get some of my questions answered.

[JMortensen]

TEP's stuff is obviously TWM, so why the wait until Sept??? They already have the manifold and the throttle bodies and air horns. All you would need are injectors and SDS or Tec III or MSS or something and you'd be done, which is what TEP has.

 

Ask them what you'd be waiting for that you would get in Sept that you couldn't buy now...

 

Jon

[zredbaron]

Yeah that was one of my questions for them when I call this afternoon. Another is do I need a TEC 3? I don't think I would, I think my HPV-1 would do the trick.

 

Anyways, like I said, I'll let you know what I find out...

[Dave240Z]

I have a 3.0L n/a Rebello sitting under the hood using 45MM DCOEs and a TWM manifold. At the time I had the engine built (1997), FI was an option but I wasn't impressed with the complexity and narrow range of choices. TEC-II was the only real option at the time but it was fussy and difficult to program, let alone the fact that not many people really knew what they were doing with it. Since I was already familiar with multiple carb setups and Webers in particular (this harks back to my automotive beginnings working on modified VWs and 911s) I felt comfortable to settle on a set of 45MM DCOEs instead. It's been working well ever since and I have no plans on changing it. It also has the feel of nostalgia which I like and most people are quite impressed to see a set of triple carburetors under the hood of anything on the road these days. Younger people (those less than 30) tend to shrug it off as "old technology" but they have been schooled on a few occasions that old doesn't automatically equal obsolete.

 

Fast forward to today, with the myriad of FI setups available, the ease of tuning via a laptop and fancy GUIs makes an ITB FI rather attractive although it is still rather costly. The main benefit of FI is that it has the potential to offer better low-speed drivability due to better fuel metering and atomization. As a case-in-point, I have been in another Rebello 3.0L car that used FI and I can say that the low speed drivability was noticeably better than mine. However, at the top-end there wasn't much difference between the two as they both seemed to pull equally hard. Of course this is just my butt-dyno evaluation but it does make sense given the similarities and differences between the two setups.

 

Which is better? Probably the FI from a purely performance standpoint as you can get great top-end power without sacrificing a ton of low-speed drivability. Coupled with the popularity of FI these days and the ever growing selection of products related to it and it makes even more sense. If, however you already have a set of carbs available there is no reason you couldn't use them. They won't be quite as expensive with regard to initial cost and are rather simple in comparison to FI since you don't have to worry about computers, wires, sensors, high pressure fuel pumps, fuel lines, etc...Ultimately it depends on what you're more comfortable with.

 

Edit - Added gratuitous pic

 

[zredbaron]

Thanks, Dave.

 

I am one of those younger drivers you are talking about. I got my first 240z when I was 16, I am on my third now at 24 (same one since 18 ).

 

When I started, I didn't even want to go to an L28. I wanted to keep the L24 and overbore it a bit. I eventually decided that I would later regret having the smaller displacement, and I am glad I went with the stroker. I liked the idea of keeping the car as pure as possible, and I loved how carbs looked.

 

However, no one in my family knows anything about cars. Everything I know has been taught third person (which ain't much) . I don't have any friends that know much about cars, just friends that like them.

 

I have had on hell of a time getting my carbs tuned. I managed to accidentally find a mechanic in arkansas (where the car is) who used to run 240s on a track with triple webers back in the 70s. He owns an import repair shop and although he could have tuned them well, he needed jets to play with. I got some jet sizes recommended to me, it ran better, but as my numbers show, not as well as it should be. Again the cause is the head, but the carbs still need better tuning.

 

Every time I go home its a new season and with humidity and temperature changes, it runs different and I have to play with them. I used to just screw them up, but now I get it a *little* better.

 

So for me, having no experience or resources, FI makes more sense. I can let my ignition account for changes in season and elevation. Additionally, I am in the Navy and I see several geographical moves in the next five years. Here to Baltimore, south to Florida, then west to San Diego hopefully. FI gets more and more attractive.

 

But my heart still wants the carbs, Dave. It's too bad. As for the initial cost of everything, even if I would stay with carbs, I would be upgrading them, so I might as well just get what I decide on.

 

I'm still sleeping on it. I'm not in a rush to make the wrong decision...