L7 Cam

[4DrSportsCar]

I put an L7 in a small chamber (sss) head and bolted onto an L18 short block. Th short block is newly rebuilt with the stock dished pistons. The engine pulls nicely up to about 5500 and then starts to slowly taper off. I'm running stock header running into 2" tailpipe, with the Offy dual plane intake with a Weber 38.

 

This engine just feels tight and does not rev freely. Is the bottom end too weak to push the rpm higher? Te engine feels like its being held back once it hits 5500. I'm not an engine builder, so I don't profess to understand all this, but does this cam profile just not make sense on a street car where I'm looking to have a little fun going from traffic light to traffic light....?

[HRH]

Which cylinder head did you use? (Casting number, open or closed chamber)

What jets are you running in your 38/38 Weber?

[MicroMachinery]

If you only have one small carb, it could be that it's starving out on the top end. I don't think w/ the 38/38 this would be the case, but if the jetting is wrong, it will. I tried using a 32/36 on an L20b, and it couldn't hang. The power would drop off around a little before 5k. I'm sure there was more to it than just carbing, but I know it would lean waaaay out. Make sure your jets are correct.

Do you have specs on your cam? That makes a huge difference.

[MicroMachinery]

Beautiful 510, by the way. I love the color and the front spoiler. More pics?

[datzenmike]

By his description (SSS) it should be a 219 / V912 which were all peanut chamber.

 

 

There's nothing much below the head that will 'hold it back' or be 'too weak'.

 

Engine strength (or how well it stays together when you pound on it) is determined by everything below the head; block, pistons, rods, bearings and the crank. How well they are built and assembled and how strong the parts are.

 

Engine power is determined solely by the head. How well it breathes: valve size, port size, combustion chamber size and shape and most of all by the cam that is chosen.

 

To a somewhat lesser extent the carb (in) and exhaust (out) system, but this can all be lumped under 'breathing'.

[HRH]

The specs on the L7 cam are .475"/270 deg dur. You did get the .160 lash pads to go with that cam, correct?

[HRH]

By his description (SSS) it should be a 219 which were all peanut chamber.

 

 

Yeah, but you know how everyone always says they have a SSS this or that, and it turns out not being. And me, I'm not that impressed with the SSS head. As my second in command Datsun racing guru says when anyone mentions it, "Triple-shitty head!" :D He had one for a while but got rid of it for custom stuff. He also has a Gerolamy head. I about creamed my pants when I saw it.

[datzenmike]

The SSS is a 'bit much' for a stock L16. Huge ports with low port speed.... ok for 7k running but around town.... not so good.

[datsunfish]

You have only specified it as a sss head. What is the actual casting #? No offense to your but I see a87 and w53 closed chamber heads reffered to as sss when they are not. The 38 weber is more than enough for an L18 btw. They have the small intake ports that could restrict airflow. I am unfamiliar myself with what a L7 cam is. Is it a regrind or a brand name new cam? Had a .450 regrind in my 521 with open chamber head and L16 and it would rev past 7k and make power up to 6500 but all together it was way too weak with the L16. The L18 should rev past 6500 with no problems with a good breathing head and produce decent torque. I ran a 210 head on my old L18 for a bit as an experiment for gas mileage and it did what yours does. Power curve dropped around 5k and felt totally restricted but thats small port,smaller valves and smallest cc.

[4DrSportsCar]

Yes the cam specs you cited are what I have, and I did use the lash pads you specified also.

 

I am running the stock Weber 38 carb and jets, except I used larger idle jets (60's?) to get it to idle smoothly and not have that lurch at take off. It will idle smoothly when warm at 600 rpm, has very smooth power delivery up to 5500. The head is the closed chamber head, for sure v912. I'm running stock distributor with timing set at 12 degrees btdc. The mixture seems a little rich to me simply based on the exhaust, but if I lean it out would this not restrict the power further? The entire valvetrain is new: valves, inner and outer springs, cam, rockers, lash pads, head.

 

I don't know who in the midwest would be able to diagnose this further, if anyone knows a good speed shop in the midwest I'd be willing to take it there. Sounds like a good reason for a road trip. Obviously I've not had this on a dyno.

[RoadRace]

Yes the cam specs you cited are what I have, and I did use the lash pads you specified also.

 

I am running the stock Weber 38 carb and jets, except I used larger idle jets (60's?) to get it to idle smoothly and not have that lurch at take off. It will idle smoothly when warm at 600 rpm, has very smooth power delivery up to 5500. The head is the closed chamber head, for sure v912. I'm running stock distributor with timing set at 12 degrees btdc. The mixture seems a little rich to me simply based on the exhaust, but if I lean it out would this not restrict the power further? The entire valvetrain is new: valves, inner and outer springs, cam, rockers, lash pads, head.

 

I don't know who in the midwest would be able to diagnose this further, if anyone knows a good speed shop in the midwest I'd be willing to take it there. Sounds like a good reason for a road trip. Obviously I've not had this on a dyno.

12 deg with the vacuum advance hooked up? whats the total advance, and at what rpm? single or dual point dist? if dual, which set of points are you running off? is the OE points switch still there on the linkage? larger idle jets generally aren't required as you can tune the idle and idle to part throttle transition fairly effectively with the mixture screws. But the vacuum gauge has to be hooked up to do it and you keep it hooked up when setting the timing, with the vac adv off and plugged. the valvetrain may be all new, but that does not guarantee that it was put together correctly.

 

the casting number on the head is not as important as the guy that did the work to it - ie porting, machining, assembly. a 210 can out flow a 912, a U67 can have a smaller chamber than a 219, etc...

[datzenmike]

I would assume the Weber is much like the Hitachi in that the vacuum advance is ported. There is no vacuum advance at idle so it does not need to be disconnected to set your static timing. Vacuum advance is irrelevant at 5,500RPMs as at WOT there's almost no vacuum anyway. There would be static (12*)+ centrifugal (20*-23*) for a total of about 33*-35* above 3,000 RPMs. The centrifugal advance could be sticking?

[banzai510(hainz)]

Maybe timming chain is off a tooth ?

ck timming marks on head. Maybe installed chain off

[HRH]

Here's a question: What intake manifold are you using? Cannon? Did you match the size of the intake ports on the head to the larger intake manifold? If you have small ports on your head, and your Cannon manifold is bigger than those, you will have problems. Exhaust pulse reversion, tumbling effects, weird crap. You can go small to big, but not big to small. Don't ask how I know. :D (Younger days) Just a thought.

[banzai510(hainz)]

Datsunboy in New Zealand had this proplem and find out the chain was off 2 links when he put head back on.

[4DrSportsCar]

Thanks for all the feedback. As for the intake manifold, I'm running an Offenhauser dual plane manifold whose ports are smaller than the head ports to which they match. This was one concern when I built it, but from your post I read that if the intake ports are smaller than the head ports things should be ok. I think the Offy was built to match up to the stock L16 (210) head, but this head I'm using has larger intake ports and valves.

 

Other comments have been made regarding the timing, and so here's' the rest of my dirty laundry: I'm running a rebuilt single point distributor, the original engine was a dual points set up. So I'm just 'ignoring' the lead for the second set of points. From what I've read, that second set of points was to cut emissions, and would not impact 'performance'. I plead insanity on this point.

 

The spark is strong, the engine fires up immediately, and idles very smoothly when warm. The exhaust does smell rich, the engine has no sputter nor backfire, and will bark the tires in gears 1,2, and 3 . But when the rpm's 'hit the wall', it just seems that something is off. I don't know how to check if the certrifugal advance is sticking, as has been suggested. I'll check the tooth alignment on the timing gear--but if I flubbed that then I'll forever throw out my metric sockets and return to tomato gardening.

 

What's wierd is that the engine does not seem to 'cross over' beyond the peak power band---it hits 5500 and continues to pull, but just very slowly. The guys at Rebello told me this set up i.e., the sss head with the L7 cam and their competition valve springs should really come alive at about 4500, and it does, but then it just sort of stays at 5500-5800 as if a governor were put on it.

 

I'd be willing to convert to an electronic ignition set up if someone can advise me about that. But I don't want to just start changing things blindly hoping for a miracle. Thanks to all.

 

I did this same thing 30 years ago on my first 510, except I used the stock head and carb. That baby pulled hard past 6500, and seemed to rev much more effortlessly than this situation, so I have a point of reference. Something has to be amiss.

[datzenmike]

This engine just feels tight and does not rev freely. Is the bottom end too weak to push the rpm higher? Te engine feels like its being held back once it hits 5500. I'm not an engine builder, so I don't profess to understand all this, but does this cam profile just not make sense on a street car where I'm looking to have a little fun going from traffic light to traffic light....?

 

 

Hainz brings up an excellent point about cam timing here. To check that the cam is properly timed and how much chain slack you have:

 

 

Set at TDC on compression stroke, remove valve cover. Look through the top hole in the cam sprocket. The back of the sprocket will have a notch possibly V shaped. Behind the sprocket is the cam thrust plate and on it there is a small horizontal etch mark. See picture below:

 

 

Your cam timing is correct if the notch is below the etch mark or slightly to the right of it.

 

It's very important to set the TDC by turning the crank in a clockwise direction to keep the chain tight on the tension side. I use a 27mm socket and bar on the crank bolt. If you over shoot TDC even slightly, back it up to well before TDC and try again even if you take 4-5 tries. The more accurate you set this the better your chain slack reading.

[banzai510(hainz)]

Im not in to those dual plane manifolds. Maybe those dont work with a 38/38. maybe a reverb happaening in there or soemthing.

What I did is get a stock intake and get a SSS or a Felpro intake gasket as they are 1.5 inch ports and increase the port size of the intake. More or less match port the head to the intake ports. Thats should be good enough.

 

I would ck my cam timming right off the bat. dial the crank to Zero keeping the chain on the tight side then open up the valve cover and see where the marks are at. The V notch should be right under the dash on the timming plate or the V nottch slight right but still under the dash.(maybe you know this already).

 

olddatsuns.com has my cheezy ved on how to ck this.

[HRH]

Oh yeah! Just forgot. YOU NEED A #4 HOLE!! Cam's too retarded. I found that out when running my L7 copy regrind, but completely missed that last night. Put the cam sprocket on number 3 if you haven't already. That should make a big difference from #2. If it feels good, take it to your local machinist who long ago made a copy of a Nismo comp gear with the 8 holes, and have him add a #4 hole. As seen on this page of my website:

 

http://www.mattalbertson.net/camgear.htm

 

I had the very same problem when I first built this motor. Ran it around and it seemed ho-hum.

[datzenmike]

Hainz, that dual plane manifold only works if you have a vacuum secondary or a well delayed mechanical secondary. The primary barrel feeds the smaller half of each runner so the port velocity is nice and high at low speeds and when it's well revved up the secondary opens into the larger half of each runner. Course the speed is only increased in the manifold. As soon as it dumps into the head port it slows down again.

[79D50]

Im not in to those dual plane manifolds. Maybe those dont work with a 38/38. maybe a reverb happaening in there or soemthing.

What I did is get a stock intake and get a SSS or a Felpro intake gasket as they are 1.5 inch ports and increase the port size of the intake. More or less match port the head to the intake ports. Thats should be good enough.

 

I would ck my cam timming right off the bat. dial the crank to Zero keeping the chain on the tight side then open up the valve cover and see where the marks are at. The V notch should be right under the dash on the timming plate or the V nottch slight right but still under the dash.(maybe you know this already).

 

olddatsuns.com has my cheezy ved on how to ck this.

 

The 38/38 is your problem. I have an OFFY dual plane and did much research, including calling Offenhauser and Rebello.

The dual plane on the offy has two different diameter chambers. It was designed to be used with a primary/secondary carb setup like Hitachi or Weber. The smaller primary chamber is for the 32 and the larger secondary chamber is for the 36. A Weber 38 is dual synchronous meaning both chambers open up at the same time all the time whereas the 32/36 does not.

 

Also, do not use a high rise plate on an offy if you have one installed. Rebello advised me not to use the Offy intake if I was going with a larger CAM and had extensive head and port/polish work done. They say to get dual carb setup to take full advantage of the head work.

 

An offy does have advantages with a mildly built or stock motor as you will have an increase in low end torque and MPG. It only works with a header (meaning stock mani won't fit) so a good quality tri-y will complete the package.

 

I would advise getting a hogged out L18 Manifold with your Weber 38 and trying that.

[banzai510(hainz)]

It only works with a header (meaning stock mani won't fit)

 

 

You sure about that one. Otherwise they should sell it with a "header pakage"

 

maybe the heat riser L20s that had the intake and exhaust bolted together.

[79D50]

It only works with a header (meaning stock mani won't fit)

 

 

You sure about that one. Otherwise they should sell it with a "header pakage"

 

maybe the heat riser L20s that had the intake and exhaust bolted together.

 

Good Point - Not sure on an L18 as I haven't messed with installing my OFFY or Tri-Y.

I'll take your word for it on the L20.

[79D50]

Ok...i have confirmed the fitment of the OFFY and Header. Here are the pics. Sorry to thread jack but it may be pertinent to the original post regarding fitment....

 

 

 

Here is the intake and my block of plate for the EGR I made...

Here is another shot showing there are no mounting holes on the low side - Requires dished washers that share the mounting surface with the header...as seen on next pic.

Here is the header...this is a california model with the emission plugs. These will get plugged and the header will get ceramic coated. Note the installation points - Half Moons...

Here are the 2 peices together...

These are other peices that have been bead blasted....everything posted will get polished eventually...

Better pick of Tri-Y

[banzai510(hainz)]

sorry for th thread Hijack as I cant PM

79D50 I bead blasted my front cover and it didnt last more than 40K miles before it cavitated. I dont know if Nissan puts a coating on there. But I got mine ceramic coated if I ever use another front cover.

 

Maybe I just had bad/old anti freeze but it was a perfect front cover with no holes and looked like Termites wen thru it 2 yeards latter