Fuelish MattersMy question concerns the gas tank on my '70 LeMans. It's a plain-jane convertible that I purchased from an estate. It came complete with an aluminum walking cane and mesh baseball cap-yep, a whitewall-tired, hub-capped, AM-equipped Grandpa cruiser.
I was having gas-to-engine problems and found that some of the fuel hoses were cracked, so the pump was sucking air. An easy enough fix, I thought. Then I discovered some type of venting apparatus at the rear of the tank. It has two inlet fuel hoses from the tank and one screened outlet. It's a clear plastic piece about the size of a matchbox, now stained yellow. The tank sending unit has only one hard gas line leading to the engine. Well, this venting part has a crack down the seam, and I can't identify the part in any catalog. Can this piece be eliminated, or is there a company that sells replacements?
The car runs when gas is poured into the carburetor, but this vent piece has to be replaced since my wife refuses to sit on the inner fender and feed my 350 the gas it needs to drive. What the heck is this thing called, and who sells them? The Honda Pilots at my local parts stores are of no help, and duct tape won't do it for this repair. Thanks for your help.Bob MitchellVia Internet
Quint Stires responds:What's wrong with the duct-taped external fuel unit? Talk about getting into shape. Grandpa's clear hoses worry me. Where did they come from, and are they for fuel? Have they broken down and are now causing havoc?
Your fuel system should have a 31/48-inch gas line and a 51/416-inch return line coming out of the sending unit. To the right side of the car, there should be a 11/42-inch vent line, which simply goes into a clip on the body and vents the tank. At the neck of the fuel tank is a 51/416-inch vent line as well.
Get some of the free GTO supplier catalogs, and order a new sending unit for around $100. Purchase some fuel-rated 31/48- and 51/416-inch black rubber hoses, as well as new clamps, and replace all the aged and cracked fuel lines. Make sure the fuel pump is pumping, and replace the gas filter. You and your wife will be a lot happier and maybe now she can ride IN the car. Sounds like you have a diamond in the rough right now-good luck with it.
What's Wrong With My 389?I have a '66 GTO with a 389 and a four-speed. I rebuilt the engine with stock heads, a new Edelbrock Performer RPM intake, new Edelbrock series carb #1407, a Unilite distributor, a Promaster coil, Hooker headers, a Flowmaster exhaust, ACCEL wires, and an 068 cam. The car runs great-if it was a six-cylinder. I've taken the car to shops, and everything seems to check out. Help!AnonymousVia Internet
Jeff Kauffman responds:A few quick things you can check are:* Wide open throttle-This is an easy one to miss. We assume that the throttle linkage travels enough, but sometimes it doesn't or it has a bind. I've seen this many times.
* Fuel supply-Does there seem to be any dead spots in the acceleration when getting on it, or is it slow from the start? Fuel pumps and/or lines can be a power killer if they have restrictions.
* Carb adjustment-Is the carb correctly dialed into the combination to provide a proper mixture via its jets and metering rods? It should be close out of the box, but further tuning can reap benefits.
* Ignition timing-Where is total timing set? What type of curve does the mechanical advance have from idle to full advance? The curve should come all-in by no higher than 2,500-3,000 rpm. For your setup, you should have approximately 30-34 degrees of total timing.
* Engine health-Even though the engine is rebuilt, you may want to perform a leakdown test, or at least a compression test, to ensure that all the cylinders are sealing properly.
* Rearend gearing-What's the ratio in the rearend? A good ratio for your car would be in the 3.55-3.90 range. This can make a big improvement in performance of the engine.
Other than these few things to look over, I would have to see the car/engine setup to further chase the power issues.
Cylinder-Head Alphabet SoupHow can I get knowledge of cylinder-head ID numbers? I'm putting together a '68 400. I don't want to use the original heads that provide a 10:1 compression ratio. I have a pair of 4X-1Hs, but I'm concerned they'll lower the compression too much. Around 9:1 or 9.25:1 is desired. This will be my daily driver, not a steroid mill, and aluminum heads are way over my budget.
Also, who makes an adapter to mate a 200-4R to the 400? I've built up a 200-4R and like its ratios and compactness.Tom KoniarzMesa, AZ
Rocky Rotella responds:Since D-port cylinder heads can be interchanged easily, many owners have elected to replace their engine's original high-compression castings with common lower-compression castings and are enjoying their pump-gas-friendly Pontiacs even more!
A quick compression calculation reveals that your current 4X-1H heads yield a compression ratio of about 7:1 on a stock-bore 400. To reach your compression ratio goal of 9:1 with your 400, you need a combustion chamber volume of approximately 80-82cc. But since Pontiac didn't produce a casting in such volume, start with a larger-volume casting and mill it to the desired range. While there are suitable larger-volume castings from the early '70s, those from the mid-to-late-'70s may be more logical from an economic and availability standpoint.
We prepared a highly detailed article on the "smog-era" heads (June '05 issue) in which we gathered several different castings and physically measured those areas typically associated with performance. We measured chamber volume, intake port volume, and flow-tested the various castings and found little variance amongst the group. The article also includes all the casting numbers and secondary application stampings of the various heads from that era. So it may be wise to reread that article before making your decision.
Taking what we learned in the article, I suggest you locate a pair of 5C-4 or 6X-4 castings if you want your 400's compression ratio in the 9:1 range. Either will contain 2.11/1.66-inch valves, threaded rocker studs, and an approximate chamber volume of 93cc. After milling the block surface roughly .060-inch, chamber volume should drop to around 81-82cc. A valve job may increase volume 1-2 cc, but the total effect will put your 400 in the 9:1 range. And because the Pontiac V-8 is a 90-degree design, the intake surface must be milled the same amount.
Regarding the 200-4R transmission, there are a number of aftermarket companies offering block adapter plates for bolting a Chevy-type transmission to a Pontiac engine. However, it's much easier to simply locate a 200-4R with a BOP bolt-pattern as most had them. Since they were used behind various Buick V-6 and Olds V-8 engines throughout the '80s, you may be able to locate one of these and save the cost of the adapter plate.