Twisted46

So I had to use a catchy title.
Anyways I am new to the forum and decided to join to get aome help setting up and tuning my motor. I figured you guys would know a thing or two.

I have a 74 Datsun 260z and finally got tries of the L6 twin SU carb setup. I spent north of a grand on carbs and tuning equipment and still had a motor that didn't run great and made about 160hp. So I gave in to the whispers and left my "keep it pure" mentality behind. I bought a swap kit and found a good condition 84 L83 motor with super low miles on it. That's it's V8 Z time!

Anyway this is a purpose built track car with very limited street use. Before I put the L83 in I am going to regasket and go over everything. While I'm at it I am planning to do a few upgrades (like cam and lifters.) My goal is to make 250-300 crank hp starting out. I don't need a lot of power in a 2400 lb car. Desired power band is 3000 to 6000 RPM.

The Motor:
1984 L83 with 23K miles on it.
Weiand 8004 dual plane intake.
Holley 8007 390CFM carb.
All else is stock.

Drivetrain:
700R4 with 2500 stall.
R180 3.36 rear end.

I have already done some reading and found out that my intake should be okay for what I want but will be at it's limits at 5500 to 6000 rpm. The carb is undersized and I can't understand why the PO would do that. I couldn't find a lot about the L83 but learned that the heads are nearly the same so I have been researching based on the L98.

Now my questions are:
1 - Is there any hope for this 390 or should I count my losses and buy a bigger carb?
2 - Would a 282/292 .46 lift cam be any good for this setup?
3 - can the above mentioned produce atleast 250hp?

I know that the manifold and carb are not ideal. I should mention that I plan to do a vertec swap after a season or two of dialing in the V8 car. I don't want to spend too much money on a temporary setup.

I really appreciate any feedback guys.
Feel free to badger any stupid things i say, I am nee to the sbc world.

Tom400CFI

I think for a track only (mostly) car you should use a bigger carb.

I think with a carb, your combo and headers/good exhaust you should expect ~300 chp. Should be a riot in a Datsun 260. Vortec heads and a Vortec "RPM" type intake should get you around 350 chp IMO.

Edit: 350 chp...not 250


.

Twisted46

Hi Tom,

Thanks for you answer.
So it sounds like I should be okay just keeping the stock heads and a mild cam.
I will see what i can get out of the 390 carb, it's too bad because it looks brand new.

I was checking out these two sites:
http://4secondsflat.com/Carb_CFM_Calculator.html
http://chevellestuff.net/tools/rpm_calculator.htm

And it looks like the 390 would be just outside the low end of getting to 5000 RPM.
With the gearing combination and light weight car this should be fun

Tom400CFI

I agree. I'm building a "VETTE KART" right now. It's still got the stock L98 so 245 hp (plus, I live at 7050' elevation. I think the car is ~2100 lbs and dude....it is AWESOME. With light cars, you hardly need any power for it to feel wicked. Throw on some loud exhaust you you've just created a rollercoaster ride experience that you control. . Your car is going to be so freakin' fun! Post up when you get it done, would you?

84 4+3

The stock l83 heads will limit you. The 390cfm carb will as well. That being said, I agree with Tom's numbers and it'll be fun in a light car. Some 180ish cc heads and a carb in the 500cfm range will allow you to get up in the rpm range. Again people have done some crazy things with stock 624 heads too.

JCrock

I ran a 390 Holley on a 350 Olds engine in a '76 Cutlass many years ago. What you will find is that it gives you great throttle response and gas mileage but it would run out of breath about 80-90 mph or so. Since it was a daily driver that got a lot of miles on it the gas miles and throttle response made it perfect for my purpose. I reckon you will find it to be good for cruising.

Twisted46

Hey everyone thanks for the great feedback.

This is what I will need the car to do:
hit 90 in 3rd which is about 4500 rpm
hit 130 in 4th which is also about 4500 rpm

300 crank hp is just a number that sounds good to me and 30-60mph and 50-90mph times matter way more. If you guys think it will make power up to 4500 I may give it a try and see what happens. At worst I still buy a new carb.

I actually don't want to make too much power because that means a whole pile of torque this old frame was never meant to handle.

I am hoping to set the motor in next weekend.
it sits lower and farther back than the L6 so it will handle great.

Twisted46

Well I made an interesting discovery today, I don't have an L83!

The guy I bought it from bought it out of a 1984 vette and he was certain that it was an all stock motor.
Me not knowing anything and this guy having at least 5 SBCs in his shop just made me say "okay" and roll with it.

Well today I got the motor out of the crate and onto the engine cradle and started looking up the casting numbers.

GM 3970010 on the back of the block, numbers not visible on the front of the block.
Heads are 416 305 heads.

Then I also found what seems to be an aftermarket service tag (attached picture).

What do you guys make of this?

I am going to work on getting the cam out to see what it is, pistons look like OEM dished.

84 4+3

It would really stink if you ended up with a 305... with 305 heads I'd lean toward it could be a thirdgen crossfire. Iirc they stuck it on 305s.

Tom400CFI

Tha't's likely a possibility. They did put CFI on the 305, for three years; '82-'84. I had one in a TA that was an '83.

If *I* had a 260z with a 305, I'd make the best of that because it's CHEAP (you already have it) and a 305 is or can be better than good enough in that light car. It's a V8 in a light car...it'll be a hoot no matter what it us, IMO.

rjacobs

100hp is but a button push away...

Twisted46

Well luckily it is a not a 305, it is for sure a 350 but I am still mad at myself for not questioning the guy and asking for proof of numbers.

I dropped the pan and found the crank number is 3932442.

The heads are definitely not the heads that came on it and I can tell they were worked on (looks like large valves maybe?)

The block and crank combo is some generic 78 (based on date code) 350 probably a truck.
I am pretty upset, mainly that I over paid the guy, but at least the motor is in very good shape and hopefully will still make 250CHP.

84 4+3

Well... gm had enough cranks and rods from the 70s that they left them in the 80s... my stock crank shares that casting number, I just checked my photos from the cam swap. So it could be a 84 block with the wrong heads...

Edit: a quick search shows that the 416 heads with some work can be decent... so maybe you have stumbled onto something interesting.

Twisted46

I can live with the setup as I dont need a ton of power. Just sucks whenbyou don't have what you paid for and can only blame yourself.

Anywho I can tell the heads have been worked on and the intake valves look pretty big. My main question now is what pistons I have. The are a deep circular dish with no valve reliefs.

Once i vet the cam pulled ill decide where to go next. Right now i have no idea what CC or compression this setup gives.

Twisted46

Okay I got the cam pulled out today and I cant find any of the cast stampings online.

960 is stamped between loves.
GM20 and D20 are cast a lobe above 960.

Also found there number cast into the block behind the timing cover:
010
509
776
512
G30

They are not in sequence but scattered around the area.

Any ideas?

84 4+3

Look around the distributor gear for other numbers... there should be more. For the block I have no idea.

Twisted46

I had a look at the cam again for more numbers and the only additional casting was the CWC foundry mark near the dist. gear.
Also a 5? but I couldn't really read it.

Everything about this motor is a mystery...
I hate to buy a new cam when the inside of the motor looks brand new but if I can't ID it then I don't want to leave it in there.

Twisted46

So for the first tip I would love to but I don't have the equipment. I may drop it off at a shop to see if they can do it.
Sadly I read up on the first tip to try to ID the motor but that pad has been milled smooth. I took a razor place and acetone to make sure I wasn't missing some faint engraving.

At this point I don't think it matters too much because the heads are not original and what I have found online indicates that the brass tag is from and aftermarket re builder.
My goal this weekend is to pull one of the valves to see what size they are and if any porting was done to the head.

Hot Rod Roy

The camshaft in that engine might even be better than stock! If I have my numbers correct, the stock '84 cam specs are: 202*I/206*E @ .050, .403I/.415E valve lift, and 115* LSA. IHBD, can you confirm my numbers?

Twisted46

Hey guys, I first want to say that this is probably the best forum I have ever been on you are all great and helpful.

I have some family in town the next two days but then I am deep diving on this motor. I just finished prepping the engine bay so I can dedicate more time to the motor.

Looks like with my piston/head combo the motor will be around 9.5 - 10:1 CR.