cygnusx1

Good decision. Period correct modding is always fun. I run 40DCOE18's on my stock '76 L28 with 32mm chokes. I think either carb will work for you. Obviously the 45's will ultimately give you more top end. Remember, smaller chokes size flows faster at low engine speeds for easier low end tuning (street).

OK I discovered that two of my pistons lost their skirts. So I will definitely need pistons. So much for the budget...I called a local machine shop and they will prep the block, boil, bore, hone, deck if needed, for $400. I suppose that really is wise money spent.

Little by little I make headway. I finally got the motor on a stand and pulled the oil pan to the sound of clank, clink. Yep, #4 and #5 pistons decided to cross dress, so they removed their skirts. I suppose JB Weld is not the right solution here, so I guess I'm definitely buying pistons too.

My P90A measures 4.248. My E31 measures about 4.255

Hmm, maybe welding my R200 and installing some skinny tires is not such a bad thought. fun fun fun

I had a friend of mine stop buy to look at it today, he is a fairly experienced engine builder who taught the subject at a local tech school. He feels the same as I do about it, but stressed that it's imperative that the block and head are also checked for flatness, which I already plan to do anyhow. His thought was that if the block is flat, then leave it alone. If not, then it needs to go to the shop anyhow.

Really thinking that Nissan probably didn't even have it much closer than what I am finding. I quickly measured above the swept area tonight, and it was out by just about the same amount. I am thinking that I am well within the "functional zone" for an engine that will never see competition. Or, I am seeing block distortion from not having the head on it.

Pete, I am waiting on an engine stand and I'll dismantle and inspect all the parts. Right now I have the head off and measured the bores mid stroke, and 1/4" from the top, wide, and long. As expected, they are wider perpendicular to the crank by about 0.00010" and the worse case is #4 at 0.0015" mid bore. I am confident in these numbers as I double and triple measured. The motor ran great before, other than some oil consumption, some from the turbo, and some from the rings for a total consumption of about 1qt for 1500 miles or so. The head is new for all practical purposes. Here is a photo to show how clean the bores appear.

I got the block out today and will go over all the measurements again. I'll look for the worst out of round, and measure piston clearances all around. I certainly understand the benefits of pouring money into every detail but I want this thing back together as soon as I can, with as little dough that I can put into it. It survived 6 years as it was, running 14-18 psi, so I think with new wear parts, I can get a few more years+ out of it at 16psi with a real dyno tune and maybe a knock sensor loop. The head is almost brand new, and my hunch is that a fresh lower end, even stock with that little ovality, is very strong. My gray area is the initial question, of how much am I REALLY giving up with the bores ever slightly over-oval spec. I'll spec the pistons and bores out again carefully to make a final decision. Thanks for the thoughts and suggestions!

I will definitely look into that. This is an opportunity to upgrade the MSII firmware as well. Thanks.

Found an informative article discussing cylinder dimensions and wear. http://www.realclass...ch05031600.html He says that in his experience cylindricity up to 0.005" is workable (on a morotcycle bore), so I should be fine at 0.0012 and just expect slight oil consumption..which will undoubtedly be better than it was with the old rings anyhow.

Converting a P90A-H to a P90A-S has no disadvantages over a P90, that I can think of.

So I measured the bores carefully today and found that they are oval on average by about 0.0012" and the max allowable spec in the FSM is 0.0008". The bores are extremely clean with zero scoring. The taper and maximum bore is within spec. I am on a very tight budget so I plan on doing a re-ring, bearing shells, and a timing kit. I had planned on flex honing and calling it a day. Should I fret over the oval spec? I know leaving it oval is not the "right" thing to do...but what are your opinions. What am I losing with slight oval? Ring sealing compromise? Piston slap? I am going for an OEM L28ET rebuild on my current setup, which is in the 320-350rwhp range at 16psi boost. I am not too concerned if the side effects are minimal. It was running great, albeit, a bit oil consuming (1qt every 1500 miles or so), but that could be due to the 160k mile rings that were in there, no? I didn't do a leakdown or compression test before the motor blew the head gasket. The plugs showed signs of oil too. The downside to boring it is that it will add machining costs and piston costs to the budget, which is a significant cost increase for this particular project.

Some photos as I work... Look at that crosshatch! Could that be original at 160k miles? The bores are not over bored at all.

Haha, yeah this makes you appreciate what those 24 hour race cars need to deal with.

Ryan, I was over budget thousands of dollars ago.

My tux rental deal fell through David.

So I pulled off the top half of the motor today. #4 and #5 had some fire ring push out, and #4 had a shatter in the fire ring that exposed the nearby coolant passage. The head, block, and pistons look great so far. Tomorrow I'll pull out the lower end and take a closer look. I still can see crosshatch on all the cylinder walls. With a caliper I measure 3.387 +/-0.003 but I am getting a bore gauge tomorrow to check them all the way around. What I found amazing was that the exhaust side of the turbo had about 3/8" radial play in it! The turbo was spooling fine and making its setpoint of 18psi with no strange sounds. So far the turbo looks fine and I already have a rebuild kit for it on the bench. Plan: -"A" N/A E31 Cam conversion, externally oiled -Full bottom end rebuild with new OEM turbo pistons -Rebuild turbo -Dyno tune -Maybe replace the 15 year old radiator, pro actively.

Very cool article. I always noticed that I could "steer" my car in corners with the brake pedal. Brakes on = oversteer, Brake off = understeer. I always attributed it to the loading and unloading of the front tires.

OK then I will work on the rear toe when I get the motor all sorted out again. I run Poly T/C bushings with OEM rubbers behind the T/C bucket.

At the latest HPDE event I went to at Lime Rock Park last week, I really began to feel one with the car and was starting to play with later and harder braking. I began to feel the rear end start to wag around a little during real heavy brakes. Unfortunately, my motor blew the gasket before I could experiment with bias. Those with track and setup experience, can you point me in the right direction? I figure first I need to get an accurate rear wheel toe reading, and then set some rear toe-in with the eccentric bushings I have. Secondly, would moving the brake bias around, have any effect on rear end stability? Thirdly, is there anything else I should know about it? Rear control arm uprights flexing around? The car runs stock 280Z suspension hard parts, with 1" drop tokico springs, illuminas (#3 rear and #2 front), st sway bars 7/8" and 1-1/8", and eccentric alum/delrin LCA bushings f+r.

Converting the head to solid is fairly easy with thread adapters for the solid rocker posts. Then just install the new cam, and check the wipe pattern. My P90A head happens to be factory solid. I didn't convert this one. I always reference this chart for cam info. The early A is not drilled for oil, I am not sure about the later A cams. http://www.atlanticz.ca/zclub/techtips/cam/index.htm

I am installing an E31 "A" Cam, rockers, and matching external oil towers with spray bar into my L28ET/P90A solid "lifter" (rocker post) engine. The full engine rebuild will start today and proceed for the next couple of weeks. Based on the info here, I should have a nice gain in top end with some possible mid range torque gains. Will report my butt dyno results, of course. Any word from the OP and the "C" cam?

Can you do a 50% partial refund in good faith, stating that if the part arrives within X more days, or doesn't, then the balance of the debt will be settled, depending on what happens. If it does get lost, with no tracking or insurance than there is not much you can do.

If you took those two braces in the OP and X-crossed them horizontally across the bottom of the diff, you would really stiffen up the rear uprights. Welding them at the intersection would be even better. Without getting under the car and looking, I am not sure there is enough air-space to do an X brace under the diff.