Am I running out of carb ?

kris

Ir is this some other tuning issue ? Ive never been impressed with the performance of the last few 360's Ive had. My current fresh build and my previous one both ran/run an Engle k52k54 (INT489"lift, 254dur/EXH501"lift, 260dur) cam with a 112*lsa installed straight up. Previous engine had a 727 behind it, this one has a manual. Both have run the same '89 vintage 2150. There are no venturi size marks on the body but they are larger than the 1.08" body I have here. Mains are 56, power valve is a 2 stage that came in the rebuild kit from NAPA and running EGR. Also running a MSD distributor, coil, and 6a. Timing is 12* at idle and I unfortunately had to slow the advance curve down over the summer due to pinging, but max should be in by 3500rpm. With the latest engine its running the SilVoLite pistons and we cut .020" off the deck. Pistons are about .005"-.008" in the hole. Final CR is about 8.5:1. I finally got around to hooking a vac gauge up in the cab to see how things are looking. Idle is 17"hg at 750rpm, Im happy with that. Cruise in 5th gear at 70 on flat ground is 2500rpm and 10"-14"hg. Not impressed, but at least its off the power valve. At WOT, 3rd or 4th gear on a moderate grade is the worst. It reads 0-1"hg at 2500 rpm, 2-3"hg at 3k and about 4"hg at 3500 and thats where it seems to not want to rev any more. Basically runs out of steam. With 35's and 4.56 gears performance is still not a word I would use to describe how it runs. Its gutless. In first gear at idle, its hard pressed to break the tires loose on dirt when floored. Various "desktop dyno" runs say this combo should be putting out 240-250hp and 330-350tq. It doesnt feel anywhere near that. In fact, the 150,000mi MPI'd 4.2 in my YJ pulls harder and revs better than both 360's. The YJ only weighs about 1000lbs less. Have I missed something ? Any thoughts ? k.

tufcj

I'd go to a performer manifold and a 600-650 CFM carb with Vacuum secondaries (NO double pumpers). You might be running out of both fuel and air at higher loads or WOT. Have you ever run a sniff test under load (on a dyno) to see if you're running lean? Lean mixtures will sap the power quicker than rich mixtures, and can do internal damage too. You said you had to slow the curve to stop pinging. That would indicate to me you're running lean. Bob tufcj

kris

tufcj wrote
I'd go to a performer manifold and a 600-650 CFM carb with Vacuum secondaries (NO double pumpers). You might be running out of both fuel and air at higher loads or WOT.

I am unfortunately in an enhanced smog test area of Kalifornia. This means tested on a dyno, and non approved aftermarket parts (eddy manifold and carb) are a no-no. Judging by the vac readings Im sure Im running out of carb around 3500rpm, I just wanted a confirmation.

tufcj wrote
Have you ever run a sniff test under load (on a dyno) to see if you're running lean? Lean mixtures will sap the power quicker than rich mixtures, and can do internal damage too.

The first engine was run on a dyno with this carb and jetted accordingly. So its in the ballpark. If I go more than a step or two up, the exhaust starts to stink.

tufcj wrote
You said you had to slow the curve to stop pinging. That would indicate to me you're running lean.

Bob

Yes. I had originally had full advance in around 2500rpm, and it was pinging on hot days under load. Full advance comes in around 3200-3500 now and although I may sense a slight drop in power its nothing Id consider worrying about. Now that the temps around here have cooled off, I could probably get away with putting it back. I could also go a step or two up in jetting but it doesnt seem to gain anything more than stink, and I am due for another test in January.

Im more concerned right now with the lack of overall power. With everything that went into this engine I really thought it would get up and go much better than it is. The cam is a lower rpm (under 4500rpm) cam and if vac readings are a reliable way to check for carb efficiency, then I should be good under 3500rpm.

I have heard that people that have gone to TBI with a 500cfm TB havnt noticed any power gain, so mabye I expect too much. If it really does just need more carb I may be out of luck.

With the small carb, would a longer duration cam help ?
Could I get away with a 260-270 duration cam and not affect the low rpm power ?

ironman_gq

can you use aftermarket parts with the carb exemption numbers? a lot of efi kits have them and will run cleaner and make more power than your 2150. depending on your intake you might be running out of flow there too not just the carb.

kris

ironman_gq wrote
can you use aftermarket parts with the carb exemption numbers? a lot of efi kits have them and will run cleaner and make more power than your 2150. depending on your intake you might be running out of flow there too not just the carb.

The way CARB exemptions work, is that they specify years they can be used on. The Eddy manifold has a CARB number but it is for early 70's vintage vehicles.

The Howell TBI kit is the only EFI legal in CA on an 89. But at $1400+ without even controlling the timing, is it an option ?

tufcj

I'm running a Howell system on my 360 powered CJ. Other than a failed O2 sensor (probably due to water), it's been flawless for nearly 10 years. Starts easier, idles smoother, and runs at any angle. They can control spark if you use one of the HEI distributors, and specify that when you order from Howell. Mine just uses a Mallory Unilite (slightly recurved), and it hasn't been an issue. Could you use a later cast iron manifold and a Motorcraft 4bbl carb? Maybe slip it by under the factory air cleaner? I don't know how closely they look at equipment. Bob tufcj

kris

I figured it out... I had to replace yet another leaking 2 stage power valve (2nd in the last year) a few weeks ago. When I had everything reinstalled, I had started it up with the top of the aircleaner off to check the choke operation. When it was warm enough I blipped the throttle by hand to bring the idle down, and thats when I saw it. The evap air door (the inner door in the air cleaner snout) moved. I then gave it a hard blip, and it closed almost completely, then opened right back up. The diaphragm that controls it is leaking and it wont hold vacuum. I did check the delay valve on it and it is good. Since it is connected to manifold vacuum, every time I floored it the door was closing due to low vacuum, effectively choking the engine. Sheet metal screw fixed it just fine. :mrgreen: All is well, lots more power, and much better vacuum reading under load. k.

Holeshot

I BELIEVE the pinging MUST be addressed! I know traditional theory is to lower the CR to stop the ping, I say HORSEPOOP! First, the chamber HAS to be free of anything that would cause hotspots, naturally. Second, you NEED to keep the piston-to-head clearance to .040~.045" with an iron head! Much more and the super-heating, molecular reaction called quench doesnt happen. A red light went off when I saw your internal specs, piston too far in the hole! In my experience, nothing pings worse than an 8.5-1 CR engine. I had a fully, professionally built 390, by a real good race shop, where they had turned down the center 3/4ths of the pistons, dropping CR to around 9.1 by the math. I have to believe they did this due to the owners insistence that he needed less CR to use pump gas. So he ended up with a 060" clearance pinging sob. Had to use race gas 50-50 to stop ping. Bass-ackwards, yes?

ironman_gq

couple ways to deal with pinging. you can dial back the timing, change your cam to reduce your dynamic compression (you'll lose some power), add fuel to run a little rich, change your ignition timing curve to make it a little less aggressive.