(1) Blown Header Gaskets - Every stock car that goes into the corner with flames coming out of the exhaust, every drag car that pops after the finish line, has the same problem, they all have an exhaust leak. The amount of power lost depends on the location of the leak – before the collector is worse than after. The most critical location being at the header flange. Use liquid Teflon on both sides of the gaskets and tighten them every week – you won’t have any more problems.
(2) Overfilled Oil Pan - With a properly located oil pump pickup most engines don’t need more than 5qts of oil. Want to see how critical oil level is to power? Test it: If you have an 8qt pan, run it with both 5 and 8. If it’s a drag car where it’s easy to see power changes, you’ll be shocked – the difference may be as much as 3 tenths of a second. Not only is there more power with less, but there’s also less chance of air mixing with the oil – which I’m sure you understand is a bad thing.
(3) Dirty Air filter - I’m embarrassed to admit it, but I’ve actually been tripped up by this one. It never crossed my mind that a dirty air filter could be the problem when I chased a bog in the car for weeks. I was using an oil impregnated air filter and was having the car painted. I’m sure all of you body guys know the amount of dust that is involved, how much of it ends up under the hood and exactly where it went when I fired up the engine. I had bought into the advertising on how long that type of filter was supposed to last before cleaning. Pretty dumb on my part. Anyway, I know it’s simple, but sometimes that’s just the thing that will trip you up.
(4) High Coolant Temp - It’s not the coolant temp itself that’s the problem, it’s the temp of the passage air must pass through. From a performance standpoint, it’s almost impossible to have the intake and heads too cold. Ever see the guys putting ice on their intakes? That’s taking it to the extreme. Now on the other hand, the bottom of the engine does need some heat, including the oil. Just remember, cold on top, hot on the bottom.
(5) Rusty Header Tubes - I watched a racer chase a miss in his car for half a season. Rust inside the headers ended up being the problem. I would have never believed it had I not seen it. I know a lot of you are thinking, just get the headers coated and there won’t be a problem. Wrong! These coatings do nothing to protect the inside of the tubes. Even if they were able to properly coat the insides, the heat would burn it off in a hurry. The best choice is a stainless steel header, the next best is to clean out the rust in the off-season - sandblasting being the easiest method.
(6) Engine Driven Fan - This can be the biggest power killer on the front of the engine. An aftermarket flex fan doesn’t help much either – do this test: take a flex fan and see how much effort it takes for you to straighten out the fins. That should give you a good idea the amount of work the engine must do to drive the fan. An electric fan is the best option, but you can also try a fan clutch or a flex fan with a shallow blade angle.
(7) High Inlet Temp - Everybody knows the cooler the weather, the better the car runs. The better way to look at it though is the cooler the air reaching the engine, the better the car runs. If you pull air from under the hood, you might be shocked to find out how much higher the temp is than outside the car. Any modification that brings cold air to the engine will make a measurable difference in performance, that is, as long as it’s not flow restrictive.
(8) Ineffective Cowl/Hood Scoop - The object is to not only bring cold air to the engine, but to create more pressure in front of the induction system to allow the engine to more easily pull the air/fuel mixture in. It’s hard to screw up a forward facing hood scoop, but having it too low, too small or too far back from the front of the car can hurt. The cowl hood is not nearly as forgiving. Some of the things to watch are the height of the front of the car and how closely the cowl comes to the windshield. Want to get trick? Do what the big guys do, use a manometer to find the combination that gives the highest pressure.
(9) Weak Valve Springs - Are you installing a bigger cam, higher ratio rockers or revving the engine harder? Think you’ll make more power? Maybe not if you don’t address the valve springs. If your engine goes flat at upper RPMs or during teardown you notice the valve’s keeper grooves are beaten up, you may need more spring pressure. Of course you could always rent some Spin-Tron time and find out for sure, but I’m sure that fits most racers budgets. Many of the cam designers and valve spring manufactures have this testing device. Find out which do and take their advice.
(10) Misadjusted Lash - The proper lash for your cam is dictated by the cam design. The cam designer is basically trying to get the valve to open and close as quickly as possible without bouncing on the seat when it closes. A balance between these two desires is where the most power is made. With the amount of time I’ve spent Spin-Tron testing and now that I’m getting older and less aggressive, I’ve become a real fan of tighter lash. If you don’t need that last couple of horsepower, keep the lash at the cam designers spec or tighter – your valvetrain components will thank you.
1.) Check spark plugs - This is the first thing I tell
people to do if they think they've got a problem. Pull
all your plugs out and take a look - it will be obvious
if one cylinder is having a problem.
2.) Do a leak-down test - If you think your engine is
down on horsepower a leak-down test may help you locate
the problem. It will find blown head gaskets; broken or
stuck valves; and bent or burned valves. If you're
missing a lot of power you'll need to see over 20%
3.) Inspect oil filter - Same as your weekly
maintenance. If bearing problems are caught early by
checking the filter, you may save thousand of dollars
in repairs. A spun bearing will give little warning -
if you think there is a problem, check the filter (it
will be obvious).
4.) Check drain plug - If you're at the track and don't
have a way to inspect your filter, the next best thing
to do is check the magnetic drain plug (You do have
5.) Inspect valvetrain - Check the valve spring
pressure; valve lash; look for broken coils on inner or
outer springs; broken rocker arms; missing lash caps
or; broken or bent pushrods.