August 2010 Chevy High Performance Q & A - Performance Q & A

Kevin McClelland Jun 17, 2010 0 Comment(s)
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All Dried Up
Several weeks ago, we were racing our wagon in bracket mode at Auto Club Raceway in Fontana, California. This was our second race back with our pump-gas LT4 350 engine under the hood, and Daniel and I were both racing the car in the same class under a double entry. Over the two days of racing, we made more than 20 runs. As I would have expected, Daniel went one round deeper into eliminations each day!

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I usually go to the line to watch his staging technique and the launch of the car. On Saturday, I noticed a very slight drip of fuel coming from our MagnaFuel 275 pump just as he was about to stage. Getting back to the pits, we could let the car idle, shake it, run the fuel pump alone, and it wouldn't leak. I tightened the pump cover slightly (nothing was loose), and off to the next round we went. I ran at the beginning of eliminations that round and Daniel didn't see anything, so I thought we had it fixed. Well, as Daniel was staging that round, there was the unsightly drip again, only it caught the attention of the starter. Luckily enough, with the amount it was leaking it wasn't an issue.

Now that I have the pump off the car, I think I've figured out the problem. I certainly don't blame MagnaFuel. I attribute it to the fact that we run both Rockett Brand 111-octane race fuel for the stocker engine and Chevron's finest 91-octane pump gas. The amount of alcohol blended into pump gas these days is tough on seals, non-stainless lines, and steel-braided lines. Pumping the system dry to switch over from fuel to fuel is also taxing on the fuel pump shaft seal, where it appears the leak was coming from.

This will be the last time I'll be pumping it dry. I stopped pumping as soon as the fuel was out of the system, but even that was too long and I've since resealed the pump with a fresh rebuild kit and it's happy again. Please keep an eye on any steel-braided lines you may run on your street cars. I've seen the lines fail and leak right through the braiding. If these are anywhere near hot exhaust or spark, it could be the end of your toy-or worse yet, someone could get hurt-so be smart and be safe out there.

Head Play
Q: I am putting a ZZ502 into my '67 Malibu, and I got rectangular-port heads with it and don't know what compression ratio I will end up with. All parts are factory and have never been started. The heads that go with this ZZ502 are PN 12363390 oval-port with 110cc combustion chamber, 110cc exhaust, and 290cc intake. The heads I have are PN 12363400, also new, with an 118cc combustion chamber, 110cc exhaust, and 300cc intake. The 502 with the oval-port heads are 9.6:1 ratio. I guess what I am saying is I don't want the ratio to get too low. This car is just a street machine, driven a few times during the summer. If you could get back to me with your thoughts, I would be eternally grateful as I am about ready to put the heads on if you think they will work OK. Thanks a bunch in advance.
Richard Griffith
Via email

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A: Very cool car-'67s are a favorite two-year body style. Stuffing a ZZ502 in one only makes it better. If we were you, we'd keep the oval-port heads on the engine. Let's get into the reasons why.

The rectangle-port GM Performance aluminum heads you have are based on the oval-port heads on your ZZ502. The only difference is that the port entrances are opened up to the rectangle shape. This is why the port volume is only 10cc larger than the oval-ports. We've spent many hours with a grinder, porting the GMPP rectangle heads just to get them up to where our good cast-iron rectangle-ported heads are-we were hoping for much more.




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