jmortensen

There is NOTHING you can do to an L28 that should make it get 10 mpg while driving casually. If you're getting 10 mpg, something is WRONG.

If you look up "oversquare" "undersquare" and "rod/stroke ratio" on Google, you'll find some reasons why you don't see many stroked L26's. Plus the L28 block is basically the same but with a larger bore as has been stated, they're dirt cheap, and it's a bigger displacement engine to start from, so why not?

If you mixed 50/50 109 octane, I can't see any way possible that the formulation of the gas could make the car bog. It would have plenty of the aromatics that Tony D referred to at that point and the octane should be sufficient for 12:1 compression, which I don't think you have based on the info that was on that website I linked to. That's why I think you have some other problem going on. You could put a stock head on the engine. That would pretty much return everything back to normal as far as the engine is concerned. Then you'd have to figure out what kind of mods were done to the fuel injection to make it work in the racey configuration. Do those two things and it should run on 87. At cruise you want stoichiometric ratio, which is 14.7:1 air to fuel. At WOT (wide open throttle) for NA you want about 12.8 to 13.4:1 for max power.

About 120 whp would be what I would expect from what I've seen on the net, but I've never dyno'd anything. Never had the $$$ to spend on a dyno. You might consider a Gtech or other similar product as they will give you 0-60 and hp estimates. At least you can tell if your last modification helped or hurt.

The 4 speeds have the widest gear ratios of the Z transmissions, and have tall gears to enable the cars to cruise comfortably at freeway speeds. This means a big rpm drop between shifts, which is not desirable. What you want is the rpm drop to be smaller so that it doesn't drop you out of the engine's powerband when you hit the next gear. The early five speed has a little bit closer ratios than the 4 speeds, but is also relatively widely spaced when compared to the ZX 5 speeds. So still a relatively large rpm drop between gears. The ZX 5 speeds, particularly the 1980 model, have the closest ratios of any of the Z transmissions. They also came with the lowest rear end gears. This is the best combination for twisty road driving with a normally aspirated Z. The ZXT came with the T5, and it's ratios are very similar to the original 4 speed with the addition of the overdrive 5th gear. This is a particularly bad combination for acceleration with an NA engine, but it is much better suited to a turbocharged engine. All of the parameters like how much rpm drop is preferable and speeds at shift points can be determined with a dyno sheet and a spreadsheet that shows the gear spreads like this one: http://www.geocities.com/z_design_studio/ Basically in the ideal situation you want to be running over the top of the hp curve, shifting, and then hitting the next gear as close to the top of the hp curve again as you can. By driving over the top of the hp curve in each gear you're maximizing the hp to the ground. If shifting to the next gear drops you down the hp curve too far, you end up accelerating through a longer portion of the rpm range where the engine is not making maximum power, and that takes longer, which basically means you're going slower.

On the timing issue you'll probably want full advance in the mid to high 30's. You can test this on the dyno and figure it out. If you have a timing light with an advance dial you can figure that out just by setting the light to say 36 degrees, revving the car up to 3000 rpm and then setting the timing to hit the 0 mark on the pulley. Then you can adjust it on the dyno to get it dialed in right where you want it. I'm guessing it's the way that the rest of the motor is built that is holding you back. Timing might help to optimize what you've got and you might pick up a few hp, but I think you're going to need to step it up in the compression or cam area (or both) to see a bigger jump in hp.

If your air and fuel are between 12-14:1 that's the important thing. You could maybe tighten up the range a little bit, but I don't see how that is going to make a huge difference in power. Maybe there is another reason you aren't making more power. Maybe you need different timing, a bigger cam, more compression, bigger Webers, etc. Did you dyno it before the Webers and after? Personally I don't think 40's make very much power over SU's, as I stated before...

I don't think you've done anything "wrong", it sounds like you just want the car lower than is practical without sectioning the struts. Most people like a little rake too (front lower than the back) so that means that the fronts usually end up with less available travel than the rear. Sectioning the fronts is usually more necessary for this reason than sectioning the rear, although it seems like most people do them both at the same time. Another idea to even them up would be to section less length out of the rear than the front. Again, not something that is commonly done, but there is no reason that it couldn't be.

Put simply, that don't make no sense. I would suggest at this point that you take it to a mechanic who knows Z's. Bogging shouldn't have to do with octane. Pinging should have to do with octane. 109 octane is ridiculously high for what you have there. Since your Z still apparently runs stock FI, I doubt that the issue is the specific gravity of the fuel. I think it has some other problem with the FI that's causing your hesitation.

Octane booster is Tolulene or Xylene or a mixture of both. You can buy a gallon from the hardware store (it's also used as paint thinner) for ~$12, or you can buy a 16 oz bottle for $8. Tolulene is 114 octane and Xylene is 118 octane. When the bottle says it raises octane one point, that actually means .1 so it will take 92 octane to 92.1 octane. You can do the math in oz as shown in my previous post to see what the actual effect is, and it's basically nil. There are site's with homebrew octane booster recipes, and I think it's been talked about here before. If not it's come up a couple times on Hybrid Z if you want to learn more.

1/2 and 1/2 with 87 should give you 98 octane. Figure 16 gallon tank so 1/2 tank = 8 gallons. 8*87 = 696 + 8*109 = 872. Add those two together and divide by the number of gallons, 1568/16 = 98. That's enough for 12:1 compression in all likelihood. I still think you could get down to 95 or so and be OK, based on the info we have.

I found something VERY interesting when I tried to read your plugs. Look down at the bottom...

Why do you have two threads going on the same subject? I thought my first response never made it in here, then I find this other post and here it is. You should post once in one forum only.

If they would pull the head to install the new gasket, why not just pull the head and clean off the tops of the pistons, and while they're at it, maybe see if the oil rings or valve stem seals are bad and causing the problem in the first place.

If you're going to pull the head off, why not just clean the pistons rather than switching the headgasket out? You might also consider WHY they're so covered in crap. Is it bad rings, Bad valve stem seals, something else?

I read this information here: http://suncoastzcarclub.homestead.com/club_carz_Moschettos.html and while it is not particularly thorough, it sounds like the car should not be running anything too extreme in terms of compression. Flat top pistons, not domed, .040" oversize, shaved head. Doesn't say what head is being used. Do you know which head is on it? What the website info did tell me is that most of the compression is in the head because the flat top pistons are not REALLY high compression pistons. So rather than getting a new shortblock like hls30.com suggested, a new head would be the way to mellow out your engine. Either the P79 or P90 heads should drop your compression down to the high 8 to 1 range, and at that compression you can probably run 87 octane. I would expect compression for your engine to be in the 10 to 11:1 range. I think my own engine is at the high end of possible ratios for flat top pistons since I have an E31 head which has one of the smallest chambers. Mine is about 11:1, and my engine requires about 95 octane to keep from pinging. I trial and errored it out until I got the minimum octane that I could use with full timing advance and not ping. If you bought one gallon of the 109 octane and mixed it with 5 gallons of 92 octane, that would net you 94.89 octane. That should be pretty close to getting it to run without pinging. If that didn't quite cut it you could go with a 4:1 ratio for 95.4 octane. The lower your octane the more power you can get from the gas, so you should always run as low octane fuel as you can with the appropriate amount of timing for max power and not ping. I believe Dan Baldwin proved this on the dyno way back when. Upped the octane and lost hp, tried to increase timing, lost more hp. Anyway I hope that helps some. The more info you give us the more closely we can try to figure it out.

What is in the engine? Is this the V8Z or the 6 cylinder? Did he leave you with a list of mods done to it? Without more specific info we're just SWAGing.

If they're 45 webers I'd go for it. I wouldn't bother with the 40's. Too much hassle and not enough return on the 40's. I would estimate that I got about a 40 hp gain by switching to 44 Mikunis. My engine was somewhat similar. I had a slightly larger cam (close to MSA stage IV) and about the same compression ratio of 8.5:1. If you do buy the carbs, be prepared for some teething problems and don't let them get you too upset. You'll spend time and money figuring the Webers out, they're a lot more complicated than SU's. My biggest piece of advice would be to install an O2 sensor in the header collector. I used a narrowband one wire Bosch sensor and a simple volt meter to read it. Shoot for about .8V at WOT as that is about 13:1 air/fuel ratio. The O2 sensor works SO MUCH BETTER than trying to read plugs or smell the exhaust or whatever. Doesn't tell you how to fix the mixture, but at least you'll have an idea of what rpm range and load condition is lean or fat, and you can use that info to figure out what jets to change. Oh and if you're scared of the Webers the Mikunis are a lot easier to tune as they are much less adjustable.

Your cam has the duration rated differently. Yours has it listed at .050" lift or better. The ones that you're seeing with 290 duration are giving you the full duration to .001" lift. The theory is that the .050" lift is the more accurate at describing what the actual cam will perform like, but the logic is a bit flawed because it assumes equal profile cams, not assymetric like most Z cams are. Being that the cam is only .465 lift, I'd expect something between 260 to 280 duration if it were listed in the more traditional way. A larger cam will make it less likely to ping, and will also give you more top end at the expense of bottom end and midrange power. If you're building for top end power, I feel that a bigger cam is in order. When you go to a larger cam than about .470 or .480 lift, you run into several problems. Coil bind on valvesprings happens right around in this area for one, and requires aftermarket valvesprings to fix. Valve spring retainers hit the valve stem seals. Ford makes a viton valve stem seal that fits right on and is much shorter, and very commonly available here in the states anyway. I know I've linked to the Hybrid Z thread in the past. You can also use the Nissan A series valve stem seal, but here they're a lot harder to come by. At some point the pistons need to be notched for valve clearance. I don't know that there is a hard fast rule for this, since the head thickness and gasket thickness is variable. I am running a .490 lift cam with a slightly shaved head and have not had any issues, but I've heard that a .520 lift cam requires notching the pistons. I think the only way to really know for sure is to assemble it and check the clearance with modeling clay. The chambers on your head look decently polished out and valves unshrouded, that's a lot of work so that's nice to have done for you. I'd suggest a 5 speed swap and 4.11 gears to make the most of the triples.

They're both intermediate length runners which is good. They don't say how big the carb side opening is which is pretty critical. If they're 40mm you'll have a good solid 8 hours of porting to get them to match your 44s and taper nicely down to the head end of the manifold.

44's should do that for you. I'd probably swap the cam out for a larger one to make full use of them, but they should work reasonably well with the cam you have.

Twisted throttle plate, so one butterfly is slightly more open than the other when they should both be closed. It's not really too big a deal and you could just leave it alone, but there was some discussion about twisting the shaft via the flat section on the ends of the shaft, and some warning about how badly you could screw it up too. It came up not too long ago, maybe a couple months back. Search and you'll find it.

You can trim them down to about 1/2 length, but if you're really only going to get 2" of travel you should section the strut housings.

I really like snopes, but that was the worst effort at proving something false I've seen in a while. The acetone thing is obviously BS, but if they had access to a properly conducted test as they stated, they should have cited it and the results. Then they claim that acetone is a solvent and can damage the rubber components of the fuel system. In the proposed quantity??? I don't think so. I like the bit at the end though, that warns you that paint thinner can damage your paint. Gee, thanks for the warning. I checked, and snopes has no articles about octane booster, which is made from Xylene and Tolulene, which are... you guessed it... solvents and paint thinners.