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

[zredbaron]

99% track only car. rare demonstration to a friend on an empty road.

 

what part of the alternator mount needs to be reinforced? how did you do it? [picture?]

 

i have the nissan comp. pulley, so at least one of the steps is complete.

 

regarding the exhaust, the headers (stahl included) have a max of 2.5" inches on the collector as per the surfing i just did. adapt it up to 3"? the weakest link would remain 2.5"...? the exhaust step will likely have to wait for next year. those headers are quite expensive.

 

thanks john.

[Daeron]

wow what a GREAT build thread!! I thought I had read through this one cover to cover, but I just started from the beginning and I think I stepped out before this one finished.

 

Its been four years... many many others have made the jump to ITB with aftermarket standalone EMS. Have you given any thought to using a setup like that? Webers are only SO great without the jetting kit needed to tweak them. Otherwise trying to pull max power (200+ gross horsepower goal out of a U-20 roadster engine, 2.0 liter 4 cyl) is difficult. Don't get me wrong, I HIGHLY respect the decision to stick with the carbs, but with this cam you are stepping into true big-league territory.

 

 

Besides, since this car is your wife, its easy for me to play pipe-dream games with your money!!

 

I don't know how complete my uncle's collection O' jets is in this size range, he has them for his roadsters and I can't even recall right now if they are mostly 40 or 44s.. but you mentioned long-term plans of traveling to Florida earlier. (you know, four years ago? EARLIER.) If you are ever coming down towards West Palm/Fort Lauderdale/Miami area, drop me a line and I will see if we can't set up a "butt-dyno" tuning session.

 

All that was mostly gas, I just wanted to subscribe to the thread and give you my compliments.

[zredbaron]

All that was mostly gas, I just wanted to subscribe to the thread and give you my compliments.

 

haha. at least you're livin' in the real world! thanks btw.

 

i had previously toyed with the idea of the ITBs, and they may very well be superior, but i'm likely to remain stubborn on this one. the challenge of tuning carbs to this cam and the reward of hearing it sing is something i can't turn away from. that and the nostalgic cool factor.

 

and yes, this car *is* my wife. she def. gets my paycheck.

 

as for Florida, i had lived there for about 1.5 of the last 4 yrs. a little late on the tune session, but it would have been fun. i'm now in norfolk, virginia flying helicopters for the navy.

[Daeron]

no FAIR!! you get to be married to a racecar AND you get to fly! *jealous*

[johnc]

I had to replace both alternator mounts. Ended up building two news ones out of 4130.

[johnc]

Regarding the exhaust, the Stahl header is a 3 into 1 (6 into 2) design with 2.5" collector outlets.

 

 

You need to merge two 2.5" inlets into a 3" outlet. The merge collector needs a specific minor throat diameter along with a specific length 3 or 7 degree transition to the major throat diameter (3").

[Careless]

been reading.

 

exhaust valve should have an extra bit of clearance due to heating of the stem as it gets washed over by the exhaust gasses. they can elongate enough to make contact. Even the pressure wave of them being OH SO CLOSE to the piston fly-cut can cause the stem to take some pressure deformation.

 

common note in two of the top-end engine building books i've got.

[zredbaron]

thanks for the info, john. i plan on investing in exhaust next season. one question: why not take the two 2.5" collectors and run two 2.5" pipes all the way back? i know there isn't much room, but it looks like it can almost be done. ever tried this or know anyone who has?

 

...or does the straight six run better with a single pipe due to the pressure waves from each combustion helping to pull the next exhaust stroke gases more efficiently (waves are tighter)?

 

that probably could have been worded better. anyone know the term for this effect?

 

with regard to the valve clearances, jim advised the following minimum valve clearances: .070 - .080 for intake, .090 for exhaust. his reason for the exhaust clearance needing to be higher was when you remove load (ie lift or push in the clutch) at higher rpms. he said the engine trying to spool down would have a transient that would lag slightly and that the exhaust valve would be most likely to float a little.

 

perhaps the high temp / elongation theory is a different explanation for the same phenomenon of the exhaust valve needing more clearance. i'd have to say i find the valve floating theory a little more plausible; if the exhaust valve elongated enough to cause clearance issues, i imagine it would also cause issues with not getting a good seal when closed.

 

but hey, that's me and i honestly have no idea what i'm talking about. i just look like i do on TV.

[Daeron]

The "twice pipes" exhaust setup does, in fact, suffer from a lack of proper exhaust pulse scavenging. At least, that is "conventional wisdom" when speaking in abstract theory; there are BOUND to be setups with Brand A twice pipes that would outperform brand B six into one... but the rule of thumb is that without having a collector somewhere you DO lose some scavenging.

 

The term for the phenomenon is the Helmholtz effect, and I am probably mis spelling that. Honestly, you found a way to describe what you were talking about in FAR fewer words than I could have done

 

And also, it sounds like you and careless were both indeed talking about virtually the same thing regarding exhaust valve clearances.

 

 

See?? You already know more thank you think you do

 

For the record, MSA sells a twice pipes system (I own one but haven't installed it yet) that runs from a 2.5" collector/Y-pipe (the one with the system fits right onto the MSA 3->2 headers) and then splits into two, 2 or 2 1/4" pipes all the way back, side by side. From what I have gathered (read: all internet hearsay) this type of design should preserve the "proper" exhaust pulse scavenging effect that a straight, "(3 cylinders into one exhaust pipe) times two" exhaust system would lose. I am not 100% positive on the piping size, either; it may be a bit larger. If the main pipes are larger, I will say for a certainty that it would be an easy affair for a competent welder or exhaust shop to modify it to use a 3" collector rather than what it comes with.

 

 

Sorry my recollection on the sizes is so poor; its been a while since I actually laid eyes on my exhaust, but that will all change soon enough.

[zredbaron]

good info. i think i'll stick to the tried and true re: johnc. 3" pipe after the 2.5" collectors sounds good. probably sounds good, too. whee.

 

everybody likes pics, right? not good, but good.

 

the cam from sunbelt arrived. man, that thing's rough:

 

 

can't wait to hear it turn over. [and burn my starter motor out!]

 

pulled the engine... i think i found the problem!

 

 

 

hah. fred flinstone racing anyone?

 

 

been setting up shop here the past few days. just had to share this setup i've got with my trailer. and yes... thats an evaporative cooler at the back of the trailer behind my engine stand! hot and humid. or dark and raining... i can be out there if i want to be!

 

 

 

 

opened up the engine and took a look see. several problems...

 

 

 

to start with, this is the intake valve that failed the leakdown test miserably (#6). you can make out that half of it isn't seating properly.

 

 

 

cyl. #5 failed the leakdown test too, only this one leaked past the piston rings. pulled the piston and found this:

 

 

one of the rings sheared! still havent found the missing piece. i went digging around in my oil pan for it and found... A SPRING!!??!?!

 

my only guess is that its from the check valve in the oil pump but who knows? the damn thing is like 2.5" long and .5" in diameter. HUGE metal piece to be just hanging out in my friggin oil pan!

 

holy hell, batman. so yeah, it only gets worse! back to the block, the #5 cyl. wall is badly scratched. not sure if honing the wall will be good enough. i'm dreading the machine shop will utter the word bore. sigh.

 

 

as i'm sure you noticed, my valves have been tapping the pistons as well.

 

it's a damn wonder that i've been RACING on an engine that is in this condition... as you can see, all of the cyls have been hitting.

 

 

so now i'm wondering if this is the kind of power i've been making with an extremely overworked engine, what the HELL is it going to be like when its tight, let alone tuned, let alone upgraded?!?

 

too bad its going to cost so damn much.

 

not good. but good.

 

good to find the problem(s).

 

so, on to the solutions. obviously i'm ordering a complete set of valves since these are all bent slightly. check.

 

as for the pistons, one of them at a minimum is getting tossed. it has scratched grooves going down both sides. additionally, the pistons (part of the nissan 3.1 kit) seem cast aluminum, and isnt all that thick. if i cut the calculated .170 out, thats uncomfortably thin. so now i'm thinking i need a whole new set of pistons. can pre-cut pistons be ordered for our L6s? if so, where? forged, of course.

 

the plan is to take all the parts to a machine shop, assuming they say honing the cyl wall is good to go and that boring isnt necessary....

 

any advice on how i should proceed would be greatly appreciated...

 

thanks.

[Careless]

On the topic of tubular header exhausts... what size exhaust runners are people running before the 2 collectors and the final 3.0" collector.

 

I know that all engines, even given their displacement, flow different numbers in both intake and exhaust but I'm just trying to find what a good number to start with for a high-po 3.0 i6 would be.

 

Is there a calculator' hangin around the net?

 

 

As for the engine, what kind of power were you making? I remember printing this thread out and reading it on the street-car downtown... Then some old foggie had a convo about his datsun, and then rambled off about some 3500 square footage of land he owned or something...... drunks (LOL!)

 

Can't really remember what kind of power you had though...

 

 

And now about the pictures you posted:

 

Your non-sealing intake valve seems like it was never cut properly, or the valve stem stretched some how. Either that or the spring itself is not seating right... possibly not adjusted properly from the beginning. Carbon deposits? Running rich on the far 2 cylinders for the first couple of hundred miles? I don't think that would make it seat that oddly though. :-/

 

Tough scratches on the 5th cylinder... I hope you can hone it out, but I would hone them all and look for new slugs :-/

 

I would be worried that the Feet-Per-Minute that you're slinging those pistons at, and with the thin casting... your pin bosses are going to have a hell of a time keeping themselves together with the new cam/rev range you'll be shifting your power upto.

 

Add the fact that your ring busted... cheap rings? sounds like a cheap piston package.

 

RacinJitter turned me over to a good point.. use Total-seal gapless rings.. our N/A engines make all their power on the premise that they use vacuum to suck in, and not forced induction... keeping minimal blow-by sounds like a good idea. seal it all in! As for a Forced Induction engine, blow-by is a good thing in most cases.

 

Some say you might need new pistons when switching to gapless rings because of their design... adding them as an upgrade to old pistons doesn't let them sit right because of the profile of the piston/ring contact surface.

 

Now's the time to upgrade. you got almost all the hardware to run it all nice and purdy like =)

 

Alls you need now is something to keep it beefy down low.

[zredbaron]

power? well if you follow the history, i didn't make much at all for years. over the last year or two though, its realized much more, about 225 rwhp until it started acting up a few months ago. the valve tapping cant happen suddenly (can it?), so i'm assuming it's been that way (perhaps even leaking) since the head was installed. the miles finally did the cyl. wall in. that's my theory, anyway.

 

that said, it was almost always the fastest straight line car at my autox events (only about 50 cars). only the Z06 that showed up occasionally could hang.

 

...i thought we ALL had the fastest Z?

 

 

as for cheap piston package, this is horse crap. i can't disagree with your assesment at this early stage... but this kit was bought from Nissan Competition directly, back when it was still known as Nissan Competition. one would think that a $3000 kit from Nissan Competition would *NOT* be cheap.

 

thanks for the info on rings. the more info the merrier.

[Daeron]

First off, that cam looks AMAZING. the asymmetrical lobe... words fail me.

 

Secondly, regarding the pistons, search Ross racing.. I cant recall where through (possibly Jegs?) but there is a place where you can order custom ross forged pistons for about $500 or so, custom bore, custom pin height, just don't tell them its for a Nissan. Order by measurement and quantity and somehow, its cheaper.

 

Regarding the Nissan comp pistons, I may be wrong, but I wouldn't bust on them too hard. They obviously never gave in; the engine somehow had a piece or two of metal flying around; the ring, AND the spring both could be the cause of your scoring and piston scratch. The lack of machinability (ie, thin material) also translates to light weight, and it is VERY possible that you paid for a very technical lightening and balancing of your pistons. If you have at least four useable ones, there may well be a 510 or other 4 cyl datsun guy somewhere who would LOVE em, who knows.

 

If they DID screw you out of your money, rest assured you aren't the only one

 

HTH, I am looking forward to hearing this engine.

[zredbaron]

Regarding the Nissan comp pistons, I may be wrong, but I wouldn't bust on them too hard. They obviously never gave in; the engine somehow had a piece or two of metal flying around; the ring, AND the spring both could be the cause of your scoring and piston scratch. The lack of machinability (ie, thin material) also translates to light weight, and it is VERY possible that you paid for a very technical lightening and balancing of your pistons.

 

great points. i admit i think i'm being a little harsh. a kit is by definition designed to work with itself, not to be customized further. and it did have over 10k on it. used to be my daily driver.

 

i'll post my findings on pistons. thanks. any other advice out there?

 

i can't wait to hear it either. here's how it sounded about 6 mths before being disemboweled. highlight is at about halfway through.

 

http://www.markhaag.com/media/cold%20start.mp3

[Careless]

as for cheap piston package, this is horse crap. i can't disagree with your assesment at this early stage... but this kit was bought from Nissan Competition directly, back when it was still known as Nissan Competition. one would think that a $3000 kit from Nissan Competition would *NOT* be cheap.

 

You basically paid for "Sketchers" pistons, at a "Nike" price.

 

There is no way in hell I would pay 3000 for a piston/pin/lock/ring set... unless it's made of titanium or some other space-aged metal, or was forged by Mojilnor under the watchful eye of Thor. Not even if it was from Nissan Competition branded.

 

Lets say that was what... 10 years ago?... LETS JUST SAY.

 

I don't want to bring the passed into this, but I bet there were cheaper and stronger pistons at the time. But THAT is not important now. The pistons held up, but I think they're passed their time. Giving them to an L4 datto guy at a good price is a great idea that didn't even cross my mind.

 

You got your fun out of them, 3000 is good for the fun you had I'd bet... and they're still alive. But... i would just get newer forgies. They're way cheap now. And can be made with the proper pin-boss sizing so that you can keep you rods that you got.

 

2618 alloy for a 99% track duty engine is what you should be running, with a semi-loose fitting. The heat will get'em to fill the bores when at operating temp and the gapless rings will hold them tight and leak free.

 

Are you running any sort of fuel "monitoring" devices? AFR Guage? EGT Guage?

[Daeron]

I'm pretty sure the 3 grand included rods and a crankshaft, as well as pistons and rings. There wasn't a whole lot in that catalog, and it was pricey.. but it usually performed once you put it together right

[Careless]

Ahhh, i've never had the chance to look at the nissan competition catalogue.

 

If it's 3000 for a full rotating assembly, then I'd say that's a fair deal... considering they're OEM performance branded internal parts, one would expect to pay that much and get pressure cast aluminum pistons, proper rods, and a set of new bearings/rings/fasteners.

 

I'm not discrediting the fact that they work well and they perform as advertised, and as shown...

 

but if it's "no shortcuts" this time around... I'd put my money on a well cut box of 2618 slugs with gapless rings, and a proper bore/hone to get the wall clearance as tight as possible to avoid piston slap and as loose as possible to avoid ring bind.

 

Heck, even a set of 4032 or the TRW VMS-75 alloy would be better suited than cast pistons =/

 

 

*taps arm*.... *injects veins with "while-im-at-it" drug*.

aHHHHHHHHHHHhHhHhHhHhHh

[zredbaron]

i took a look at my nissan catalog, and i have the price of $1800 penciled in the margin next to the 3.1L kit, not 3000. now that i've paid for the replacement parts, i'd say that was a damn fine deal since it included rods, pins, bearings, rings and the LD28 crank. and you guys are right... i'd say i got my money's worth.

 

quick update:

 

the block was honed and is ok. so that's good.

 

all parts have been received. i ended up with a set of custom forged JE pistons spec'd by dave rebello. i intended to work with sunbelt, but i have to say that i've been quite frustrated with them/jim. ordering the cam was extremely painful and i never once was called back when promised (well over a dozen times i'd say). dave rebello on the other hand was very prompt and to be honest seemed more active/experienced with our L6s.

 

anyways, i was thinking about sending the pistons out to get a teflon coating on the sideskirts of the pistons. anyone have experience with this? opinions?

 

regardless, i have a new competition dampener as well. obviously everything else is being replaced: coated bearings, new valves, springs, the cam of course, timing chain etc etc. going to 12:1 compression.

 

side note, evidently the 1mm gasket is unavailable. (according to rebello, anyway). i'll be using a .6mm gasket. (!)

 

*taps arm*.... *injects veins with "while-im-at-it" drug*.

aHHHHHHHHHHHhHhHhHhHhHh

 

hah. got a good kick out of this. [case in point...]

[Careless]

good update mark.

 

I am in to researching the chemical coatings as well for the piston sides and whatnot. Only problem is I have not found a suitable person in my hood to do it, and I would not trust any regular person to do it.

 

most often it requires scuffing/blasting of the piston skirts, and then coating and baking the pistons at precise temps. powder coating, really.

 

I also know that if you choose to use a coating of somesort, you will have to rebore your block if it's required by the coating.

[zredbaron]

update time again.

 

well, with any luck my new engine will come to life this weekend! then again, i've thought that for a few weeks now...

 

regardless, here's a couple more pics of the new parts. i didn't get a pic of the .6mm gasket, but i couldn't believe how thin it was. like 5 pcs of paper i'd say.

 

i was also really impressed with the damper from rebello racing. to my suprprise, they also seem to be proponents of electromotive ignition, so i went ahead with their magnetic wheel that they've designed to go with this damper. here they are:

 

 

as expected, i was also impressed with the je forged pistons' craftmanship. as per the sideskirt coating discussion, they came with a wear-in texture on the side thats specifically designed either for coating or for wearing gently in with the piston cyl walls. the pictures don't show it, but it was some seriously precision machining:

 

i ended up not going with the sideskirt coating simply because it was a tight enough fit already that any coating would require the pistons be slightly reduced in diameter to allow for the coating. i decided that perhaps a future rebuild when the walls are honed again or the pistons have worn a little. if they do...?

 

 

and of course, here are the valve reliefs. they weren't as deep as i thought they'd be with that cam i've got.

 

 

...which were one of the reasons for the delays. they WEREN'T deep enough. my machine shop clayed the reliefs and turned it over and basically the clearance was ridiculously tight. calculation error prob from the combination of the head being shaved at some point and that crazy .6mm gasket. we went ahead and had another shop cut them .080" deeper. now they really do look like they're going in a race car...

 

my master mechanic buddy thinks i'm going to see a 100 rwhp gain. me, i think he's got a rather lofty number in his head, but hey. we'll see. 12:1 compression and an aggressive cam certainly won't hurt.

 

regardless of the numbers, it's going to be a little bit on the nasty side and i'm anticipating it's going to be REALLY hard to tame on 225/50R16 DOTs. and therefore insanely fun.

 

i'll try and post a video or two on youtube next week if all goes according to plan. hopefully one idling and one racing this sunday!