Thread: Got a hi-po small block chev?--what are you running for plugs?

My Vega’s been running a bit crappy so I thought I’d try changing the plugs out. Basic specs are: 383 stroker, 671 blower, dual Holley 750 blower carbs, isky blower cam, msd ignitioin. Motor is not hi-compression, revs are kept under 6k and blower is putting out around 4-6 lbs. Car is mainly driven as a cruiser with the odd trip to “Mexico”. Motor tends to run on the hotter side. Current plugs are Autolite 3924-gapped at .040”. I did a bit of research and found few sites recommending Autolite 3910x plugs—these are classed as race plugs, would they be too much for a street car? Can someone recommend a better plug and what to gap it at?

What are the specs on the cam and what is the actual compression ratio? Running on the hot side of what? Like 200 or 220? Are you running an CDI ignition box like a MSD 6 or something

Jeff

Edit: also what heads are you running, and are they stock or highly ported or what. Way too little info to recommend anything.

I can go with the 3910s on a mild boost application. Are you seeing a fuel foul condition? Assume you are running a MSD box and hot coil? AFR?

Car was bought off auction so I got very limited info on build. I did talk very briefly with the owner and he was supposed to send me a spec sheet but he was about to move to Asia-got too busy and didn't follow thru. What I do know-- Motor was built by a pro shop in San Hose-- it's a balanced, blueprinted 4 bolt main motor with forged crank and probe pistons with h-beam rods ( I had pan off and verified this--but probe pistons are marked on tops so couldn't get compression #). It has aluminum heads but I can't find any brand name on them to id them. Motor was built for blower and nitrous so compression was kept low--how low?--don't know. It has has 175 shot 16 line nos system hooked into the race fuel only (has 2 separate fuel systems)- pump gas runs off holley 125 pump thru 1/2" line to dual holley 750 blower carbs. Has a MSD-6al box and blaster coil. Custom Isky cam on rollers. Owner said he spent $18K on the build. That's about it.

Originally Posted by 02 WS6 TA

I can go with the 3910s on a mild boost application. Are you seeing a fuel foul condition? Assume you are running a MSD box and hot coil? AFR?

Motor is crapping at top end and suspect I may be going lean with the holley 125 pump--brand new but might be undersized for the carbs. I accidentally overfilled the oil by a quart after failing to seat dip stick properly and probably fouled the plugs in the process. (motor was crapping before this) That's why I want to start with new plugs and start eliminating problems. Doesn't have an afr gauge. Just bought timing light to check things out but the dam thing is a piece-o-crap and won't flash. I ended up getting the 3910x's for $32 so I'll try them out. if they have problems idling too long and fouling, I'll use them as race plugs for those trips to Mexico. Also motor tends to run about 210-220 in traffic probably due to the rad not having a proper shroud enclosure--very limited space between the blower pulley and rad--maybe an inch if I'm lucky. It's running 2 electric fans on the outside of rad but they don't seem to handle the heat. I'm trying to find someone to fabricate some sort of shroud.

Hmmm. Holley Blues have always worked well for me. I assume you have either a pair of external gauges, or isolated gauges in house? What fuel pressure are you seeing at WOT?

Originally Posted by sugaryuk

I'm trying to find someone to fabricate some sort of shroud.

Randy, contact my buddy Barry, 604-451-1760. He owns Allen Autotech in Burnaby, and has been building racekarz for years. He can fab like mad and might have some insight in your other issues.

Originally Posted by 02 WS6 TA

Hmmm. Holley Blues have always worked well for me. I assume you have either a pair of external gauges, or isolated gauges in house? What fuel pressure are you seeing at WOT?

It used to have a Holley blue but it was leaking so I thought it'd be a good time to upgrade to the Holley Black. It was leaking like a sieve when I first got it so I didn't get a chance to see if the blue was performing properly. It does have fuel gauges for each system but they're currently mounted on the motor so all I can see id idle pressure--which iirc is about 5.5. Remounting them on the hood vents is on my "list of things that I should do but never seem to do."

Originally Posted by Bronco Boy

Randy, contact my buddy Barry, 604-451-1760. He owns Allen Autotech in Burnaby, and has been building racekarz for years. He can fab like mad and might have some insight in your other issues.

Thanks for the info Chris. I know I a guy who used to work at our sheet metal shop who also is into cars and he might be able to do it for me--if not I'll keep your bud's name on file.

5.5 is a teensy bit low for carb'd roots application, I'll bet a dime to a dollar it drops hard under WOT. I'd verify you are feeding at least that under full throttle before making any major changes. Also assuming the car has a sumped cell?

You assume correctly sir. Hopefully I'll have it back on the road this weekend and do a little testing--redoing tierods at the moment.

Sounds like a plan. Keep us posted. Cool car.

Originally Posted by 02 WS6 TA

Sounds like a plan. Keep us posted. Cool car.

Well it turns out that it wasn't the plugs after all. My #5 plug boot is wrapped in header wrap due to clearance issues with the headers and I had assumed all was well underneath the wrap--- oh how I was wrong! The boot was almost completely disintegrated!-- I guess previous owner put the wrap on as a quick fix and didn't bother replacing the single wire- the rest are in perfect condition (only 2k on the them). Anyways I had already ordered the 3910x's so I ended up putting them in. Motor ran great, for about 20 minutes, then she decided to snap the crank! see my other post in this section under alt belt... going to be a long summer.

Forgot to mention about what I discovered about my "magical dipstick". After the crank snapped I go to check the oil again and it shows zip on the dipstick!! This is just after I had the problem with over filling it by a quart-- something definitely loopy going on. I check it again and it shows exactly on the full line--wtf??!! So I check it again--empty! This time I get my flashlight and watch as the stick goes into the tube (well not a tube, it's actually made from steel braided hosing--another custom job from previous owner)...anyways-- as I'm watching I actually see the dipstick poke out from the tube/hosing and slide along the outside of the tube- hidden from view by the headers!! I thought I was loosing my mind after all this time of seeing my oil level go from full to nil in a matter of seconds, turns out there's a small hole in the tube. I wonder what other surprises are still in store for me??

Ohhhhhhh dear, not good, you have my condolances!