Cams! Cams! Cams!

[DavyZ]

I took a look at the MSA catalog, but they don't seem to list if the cams are "emissions legal" or not. My advice would be to call Crane Cams and speak with a tech about that. Invest in a "cam oiler" to preserve the camshaft, bearings, etc. You could have your head shaved (from the car) to boost the compression a little, and install a larger, performance cat-back exhaust system. If you have the $$$, you can also put in a freer flowing catalytic converter and a performance throttle body. A K&N air filter is a good idea and so is a cold-air induction system. By the time you are through making a fast N/A L6, you could have had a V8!!!

 

HTH,

David

[Guest Anonymous]

yeah i know, but it's my daily drive, so i kinda gotta keep it more or less on the road...what kinda stuff does it take to get a chevy small block emmissions tested in one of these cars? Won't they balk at an engine swap?

[DavyZ]

Well no, not if you use a motor that's a 1976 V8 or newer and keep the emissions equipment intact. There is a link to JTR on the Forum's main page. The book will tell you everything you need to know about the swap. Then again, maybe not quite everything--so this is why we have a forum

 

David

[Guest Anonymous]

thanks guys. Think i'm gonna go ahead and get just get my valves done, and maybe get a stock replacement cam, i'm almost sure i've got a flat lobe somewhere. Probably go ahead and get all my suspension done. Then I'd have to go and do brakes, right before building myself a nice, powerful small block...

[DavyZ]

Sounds like a really good plan. You can completely set up the car for the swap--not much to do really if you are upgrading everything performance wise anyway. Good luck with your project! And again, get the JTR book--most V8 swappers here give our 100% recommendation!!

 

David

[Kevin Shasteen]

Racnoth,

 

I've recently worked out the kinks to my new toy (Crank/Slider Mechanism) which allows me to know what comp.ratio is needed w/any given camshaft chosen based on location of piston in relation to the rotation of the crankshaft degrees (sounds fancy-not really once you understand it).

 

Before I begin-when milling any OHC engine-regardless if it from the block or the cyl.head-if too much is removed then you will have to use Cam Tower Shims (just a reminder).

 

Anyho; the L28 engine has:

 

Bore x Stroke = 3.385 x 3.110

-or-

168 cu.in engine

 

You have two choices-The Stock Set up or the L28 w/L16 con.rods: (all spec's taken from How to rebuild your Nissan & How to Hotrod your Datsun books)

 

Stock Set Up:

Block Deck Height = 8.183

Stock Connecting Rod = 5.125

Piston Compression Height = 1.496

1/2 Stroke = 1.555

Add this up: 1.555 + 1.496 + 5.125 = 8.175

*NOTE-This leaves you .008" piston deck to block deck clearance or you may wish to mill a portion of this for squaring up your block.

 

The L16 Rod/Piston Comp.Height:

Block Deck Height = 8.183

L16 Connecting Rod = 5.236

1/2 Stroke = 1.555

*Note-This leaves you .014" piston deck to block deck clearance to mill for squaring up your block (or more room for using pip-up pistons)

 

To maintain a 9.0:1 Comp.Ratio you will need a camshaft whose Intake Valve Closes 38* ABDC ("*"=Degrees) or less 37*, 36* or 35* ect.

 

To maintain a 9.5:1 Comp.Ratio you will need a camshaft whose Intake Valve Closes 47* ABDC or less. Any cam w/Intake Closing later than 47* & you're enterine the world of High Octane Fuels! So keep that in mind.

 

For the life of me-not one of those previous mentioned books listed combustion chambers for the L24, L26, L28 engines for comparison with the numbers I came up with-they only listed comb.chambers cc's for the 4bangers(?).

 

My numbers indicate you need a 53 to 54cc Combustion Chamber for the 9.5:1 Comp.Ratio set up.

 

You'll need a comb.chamber of 57/58cc for the 9.0:1 Comp.Ratio set up.

 

Remember-the actual combustion chamber in the cyl.head can be less than listed above-after you factor in the cc's from the dish in your piston, the deck/block clearance in cc's and the head gasket crushed thikcness in cc's....all this will add to the actual combustion chamber/tell your machinest what you want & let him discuss the final measurements required.

 

Hope this helped-I'm not a 6 banger guru/so maybe someone else can chime in about the piston's Dish/Dome & the actual combustion chambers required to make a performance engine run.

 

I almost forgot:

 

Your 280Z-if its weight is @ 2800lbs w/you in it requires 165FWHP to run the 1/4mile ET = 15.9/86mph. I dont know your tire size or I'ld give you your RPM's as well.

 

Good Luck & have fun.

 

Kevin,

(Yea,Still an Inliner)

 

PS: IM ADDING THIS AFTER THE FACT, I MADE A MISTAKE ON RACNOTH'S HP NEEDS. THE 165HP IS ACTUALLY RWHP...SO HIS ACTUAL HP NEEDS ARE 195 FWHP. ANYONE READING THIS MAKE NOTE-RACNOTH ACTUALLY NEEDS 195 FWHP & IF HIS ENGINE IS AT .85% VOLUMETRIC EFFICIENCY THEN THAT TRANSLATES INTO 165 RWHP. MY MISTAKE-SO SORRY.

 

[ June 10, 2001: Message edited by: Kevin Shasteen ]

[Guest Anonymous]

tires are uh...i mean...oh yeah! 215/60/R14

[Kevin Shasteen]

Racnoth,

 

My calculation puts your 86mph 1/4mile time at 4235rpm's.

 

Kevin,

(Yea,Still an Inliner)

[Guest Anonymous]

Ok fellas! Been referred to this board by the guys at Zcar.com. Gonna get my head rebuilt, stock 76 280z two seater. 4 speed manual. R200, 3.54 rear. Took off the ugly and heavy front bumper. Shooting for at least a 15.9 in the quarter. And I need to pass emmissions. Would a cam swap help me out much? And would i get through emmissions? If not, what could i do to run a 15.9?

[DAW]

Whoa...you're not going to make power without compression on a naturally aspirated engine. Your L28 has 8.3:1 compression ratio and that's not going to cut it. Here are some options: 1) You can swap your cyl head (N42) for an N47 from a Maxima L24 ('81-'84), as it has a smaller combustion chamber and will provide a modest increase in compression (I'd guess at about 8.9:1). Get the Maxima exhaust manifold too. 2) You can swap your piston/rod assemblies for those from a '81-'83 280ZX (flat tops) and retain your cyl head (N42) which will yield about 9.8:1. (you can swap pistons/rods with the engine in the car). 3) You can have your pistons removed from your rods and have the rim of that 10.9cc dish machined down until it's gone and you've created a flat top with less compression height than the 280ZX piston. This allows you to install L24 (Zcar not Maxima) rods which are 2.6mm longer than your L28 rods, and increases the rod/stroke ratio at the same time compression ratio is increased. Clearly, the Maxima head swap is the easiest. While not a dramatic change, there will be a noticeable difference in performance. With a change to 9.8:1 c.r. you'll notice a dramatic difference but you also have to increase mixture richness, run colder plugs, etc. You won't get much bang for your buck from a performance cam unless you've increased compression ratio.

DAW

[DAW]

You lift up the engine (mounts unbolted) in order to drop the pan and, with the head off, can push the piston/rods out through the deck. You are going to have to pull the front cover because you'll need to rotate the crank and therefore can't block the timing chain. Remember, the top-end of the engine can be removed as an assembly, there's no need to unbolt components, i.e., intake manifold, exhaust manifold, etc, just pull it as a unit.

DAW

[Guest Anonymous]

Oh, wow...guess I'm just too used to American small blocks...duh...hello...inline six...got it now, thanks!

[Guest Anonymous]

ok, ya said I can change rods and pistons with the engine in the car....do tell more...please?

[Kevin Shasteen]

Hey DAW,

 

What are the cc's of the Combustion Chambers in the N47 Maxima L24 (81-84) cylinder heads?

 

And, how much of the piston tops need to be milled(?)...just till their dish is gone(?) & what is the piston comp.height after the dish has been removed?

 

Kevin,

(Yea,Still an Inliner)

[DAW]

I'm not sure of the exact cc's of the Maxima N47, I've relied on the specs in "How to Modify Datsun/Nissan Engines" book and that head is not specifically mentioned, just the N47 head from the 280Z. I have seen the numbers before in these postings and it's a modest difference. One could work backwards if the Maxima L24 dish and c.r. were known, and knowing the 280Z c.r. of 8.3 and dish of 10.9 with the comb chamber cc of the 280Z with the N47...it can be calculated.

 

As to the alteration of the compression ht and removal of dish on the '75-'78 L28 pistons, I had my machinist take down the dish edge carefully until it was just gone. The last pass left machining marks across the entire top of the piston but so superficial that you could still read the factory "oversize" markings on the piston tops. I wrote down the new compression ht measurements which, with a recent move, I can't find at the moment...however, they were approximately the same change from stock 38.1mm as the change from L28 rod = 130.4mm and L24 rod = 133mm, giving no significant change in deck ht, loosing 10.9cc of combustion volume, and increasing rod/stroke. The key question is whether the top ring is placed too close to the deck by this change. I think that distance has been growing less anyway on newer cars as this space is a source of emmissions from what I remember reading somewhere.

I'd like to know the Maxima combustion chamber cc too, anyone??

DAW

[Jason81NA,82RBtt]

What are the differences between the N47 Maxima head and the N47 head from the 280z/x, if any?

[DAW]

combustion chamber size (Maxima is smaller); at least that is what I've read many times on this and other forums.

DAW

[BRAAP]

Maxima N-47 Combustion chamber size is only 40 CC, TOO small, (read too high of compression) for a daily driven pump gas L-28, even with the factory dished pistons. As for the L-series 6 cylinder heads, I personally love the Maxima N-47 with it’s biased intake port, nice radius short side exhaust ports, almost perfect chamber shape/design for a 2 valve head, (I have built several Maxima N-47’s for many racers including my own personal race car), and if you have the disposable income to afford a set of custom pistons, with the dish machined directly under the chamber in the head so as to retain the squish the Maxima head has AND bring the comp ratio down to a respectable level for pump gas, for a mild to hot street head, the Maxima N-47 would be my first choice, hands down.

As for compression ratio, yes, more is better up till the point of detonation. With that said, the 8.3:1 compression ratio of the L-28 can make some decent power. I.e. my person ’75 280 Z weighing in at 2800 lbs with half tank and driver, runs the ¼ mile in 14.4 @ 97 MPH. Engine is a BONE stock Naturally aspirated L-28 with Z car N-47 head that I massaged, (I reshape the combustion chambers for more air flow which in turn dropped the comp ratio down to and even 8.0:1), STOCK EFI retuned to take advantage of the freer flowing head and exhaust system, STOCK ’78 camshaft, header, light flywheel stock ign with recurved advance, Jacobs wires and coil. This same car also achieved measured 28-30 MPG on the freeway at 65 MPH, (the variance was due to hills). Those performance numbers along with its fuel mileage are pretty respectable numbers for an L-28 that only has 8.0:1 Compression ratio, though I have no doubt that the performance would only be better with something closer to 9:1-9.5:1.

 

Just thought I’d throw in my $.02

Good night guys,

Paul BRAAP Ruschman

Rusch Motorsports