These are some of the most common questions I field from individuals.
Understand that these are my opinions, based on years of experience with
engineering the parts, testing them, and tearing down the used (or used up)
pieces. Understand that reading my answers here and going to your local
"engine expert" may yield different answers. I do not have all the answers
and I learn something every day in this sport. If they have the experience I do
with this sport, and think I'm wrong, please buy parts from them and don't waste
time sending me a dozen emails about what they say SHOULD work and what
shouldn't. I do not mind calls or emails with questions, but I won't waste
the time arguing about certain items. Understand that things all work
together - if you change something in one area, all things can be affected:
Q:
What camshaft should I run?
A: There is no single answer for this questions. Cam profiles can
be manipulated to fit your individual needs, especially if you get into custom
ground cams and roller profiles. ALWAYS spend money on a decent camshaft
with trusted materials and grinding techniques. ALWAYS buy a camshaft
based on specifications, and NOT names such as "Corvette cam", "R/V cam", "3/4
race cam", etc. Unless you know the specs, these mean very little.
Also, understand that in this sport we have so many configurations of engines,
exhaust, rear gears, track types, etc., that selecting a base cam should be on
the conservative side so it will work in less than ideal conditions, should you
have to run in them. My personal preference for cams is either Comp or
Lunati. They have held up time and time again under heat and load.
That isn't to say I wouldn't use a free Crane or other cheap cam, but if you are
spending the money, buy a Comp or Lunati. There are more expensive cams
out there, such as Isky and Ultradyne that work great also, but for the money
Comp and Lunati are great.
Q: Can you give me a general range for a camshaft to use?
A: For most 350 Chevy engine combinations you are fine with a Comp 268H
grind. They are great all around cams. To compare the specs of a
268H in case you find another alternative, they are 218/218 @ .050 lift, 110 LSA,
and .454 lift. Chrysler 318s with a good gear can run this too, as can the
360's, but if you don't have gears behind your 318, or you have a smaller cube
Chevy (305, 307) you may want to drop down to a 260H with 212/212 @ .050 lift.
For a little bit more hopped up 350 or 360, go with a Lunati Bracket Master II
cam, #00016. The specs are similar, but the BMII has slightly more lift
and seems to like compression a bit better. Not a noticeable difference to
most, but I prefer it. If you are a great engine tuner you can get away
with bigger cams provided you understand the trade offs.
Q: My buddy has a cam out of his race car, can I use it?
A: Again, I need specs to give you an answer. Duration at .050
rates first with me, then lobe separation angle, and lift sort of takes care of
itself unless you are dealing with custom grinds or roller profiles. Don't
confuse lobe separation angle with lobe centerline, which is commonly given.
The lobe separation angle describes the amount of overlap between the intake and
exhaust centerlines in crank degrees. Most cams with duration in the 218
@.050 lift area have 110-112. As the lobe grows with duration, the amount
of overlap increases, which decreases the LSA. The narrower the lsa, the
choppier the idle (this is an over simplification, but accurate for our
purposes. Most circle track cams are ground with around 106 LSA and have a
very choppy idle, which produces better peak power but does not give a wide
smooth powerband). With a custom ground cam, you can get more duration and
therefore overall power (though it moves up in the power band, so you need more
gear and matching components if you choose) and have the LSA ground to
your specs. While I won't talk about my custom grinds much, there is a lot
to be learned in this area
Q: Why should I spend money on your carburetor and distributor?
A: You shouldn't, unless you are ready to make the next step in
performance. Beavis once said "You can't polish a turd," and that
statement is so true. Putting performance parts on a weak base engine is a
waste of time and money. You need to have a sound engine, by that I mean
one that has compression in all 8 cylinders, all cam lobes and valves
operational, and is in a generally good state of repair. I have people who
buy my products and put them on an engine with 4 dead cylinders and wonder why
it won't help it. Remember, you can't polish a turd.
Q: If my engine is good, how do your products help?
A: Carbs are as complicated as cams. There are a ton of variables
that determine the carb requirements. You can find those on the carb page
of my web site. The carbs are built to your particular needs. I can
vary most any aspect of the carb and make it work with your application. I
also offer trade in credit if you buy a carb for your set up now and later build
a different set up and need a different carb. Understand that getting the
fuel in the chamber and firing it can make huge differences in engine heat,
valve/head/piston durability, starting, power, engine stalling, etc. I can
put my parts on an 305 engine, tune it in, and make more power than some "hopped
up" 350's out there because they are using the wrong combination of parts.
Lazy engines with no throttle response are not fun to drive. The fast
response of your engine can mean the difference between taking a side shot in
the door bar or taking it in the axle or A-frame.
Q: Will your carbs work with race fuel?
A: Yes, but DO NOT use race fuel unless your engine is 10.5:1 or higher.
This is one of the most common errors I see. Without getting too complex
(basically trust me on this), the burn rate of fuel is inverse to its octane
rating. 110 octane fuel burns slower than 87 octane. That is fine on
a 12:1 engine where the air fuel mixture is compressed tightly and the piston
has an irregular shape, but on an engine that is 8.5:1 and therefore does not
compress the fuel as tight, it takes longer for the flame to travel across the
cylinder to completely burn the mixture. By the time the full air/fuel
charge is ignited, the piston is already pushing it out of the cylinder into the
exhaust port and exhaust pipes. This is why you see so many cracked
exhaust seats, burned valves, cherry red headers and pipes, etc. with high
octane fuel use. The only time that high octane fuel is an advantage is
under very hot conditions where the engine is trying to ignite the fuel before
the spark plugs fires (detonation). This can be cause by hot spots on the
pistons, head, head gasket, carbon, etc, and can be minimized on a properly
built engine. This is why people think the fuel starts better and runs
better when hot, and it can be true. But, because of the earlier stated
facts, the high octane fuel actually causes the engine to get hot faster with
increased head temps. Ideally, you can solve this two ways: Have two
fuel tanks with a control/diverter valve and run 87 octane most of the race, and
when hot, switch the valve and mix in high octane fuel, OR try our adjustable
timing distributor - advance the engine timing during most of the race with the
race fuel so it can burn completely in the cylinder, then retard when you need
it to start.
Q: I have flat-top pistons, do I need higher octane fuel?
A: Flat-top pistons mean very little. Most flat-top pistons are
merely marketing ploys. A lot of people think they have something when
they say "I put in flat-top pistons, man, and it made a huge difference!".
Wrong. Most of the typical 4 relief flat-tops out there are ground with a
different pin height, or compression height, as it is sometimes referred to.
They actually sit down in the bore about .020 further than the factory dish
piston. While they do boost compression a little, your typical 350
"flat-top" engine with no block decking, an open chamber head (say a 882, 487,
993, or similar casting), and Fel-pro head gaskets with .038 compressed
thickness, will yield around 8.4 to one. Not much better than stock,
really. These pistons are very common in rebuild kits and if they are
produced by Speed-Pro have a 345np part number. If they are SP
hypereutectic, then they are a H345np. If you step up to a true
"flat-top", which in Speed-Pro land is a H631NP, you will gain something and
have compression in the ball park of 8.9 to one. They do cost more money, so be
prepared for that.
Q: What type of piston should I run?
A: I prefer cast pistons. Cast pistons expand less from heat.
Hypereutectic materials are next best, and forged come in last. With a
properly tuned engine (no detonation, hot spots, etc), you don't need the
additional durability that the hypereutectic gives, and you certainly don't need
the forged piston strength. You can keep the bore clearances tighter with
the cast pistons. This brings me to my next point. Don't believe an
engine builder who tells you to put pistons in bores with .010 clearance and
over-gap the rings. THIS HEATS UP AND KILLS ENGINES FASTER THAN STOCK
CLEARANCES. The theory is plausable, but what happens in reality is
completely different. I have much research in this area, and most engine
builders understand my point once explained in derby language. Again, most
shops don't understand the derby environment. Price our engines, and
theirs, and buy from someone with derby experience.
Q: I keep killing my TH350 transmissions, and my buddy that builds them does
them just like yours. They have low gear only because he doesn't hook up
the vacuum advance. Why are they breaking?
A: No, it isn't just like mine. Folks, my TH350 trannies don't
have only low and reverse because I leave the modulator unhooked, or because I
block the governor. THEY HAVE NO SECOND OR THIRD GEAR PERIOD. If you
want to buy one from a shop that says they are building them just like mine,
fine, but they aren't, I'm willing to bet. Even my TH400 trannies aren't
done that way, though they are different due to design characteristics.
Again, there are a lot of copies, but none as good as the original. Also,
see my explanation of tranny cooler design flaws on the transmission page, which
contribute to many tranny failures.
Q: If I buy an engine and trans, can you put it in my car and tune it,
or can I just buy a car from you and come pick up the whole thing.
A: Yes, we will build almost anything you want to suit your needs.
I have had customers drop off their cars and I'll install the engine and
transmission, break them in and tune the engines. Or, you can purchase a
car for them to be installed in from me.
Q: What are the advantages and disadvantages to purchasing a complete turn
key derby car?
A: Several on both sides. First I don't recommend incurring the
cost of a custom built car on your basic cars, such as cars for 77 and newer
derbies. If you can still buy those cars for $0-$200, why worry about the
body getting wasted. However, if you are looking to be competitive in the
old iron classes, spending the money up front for a well built car that you can
take things out of when you are done, including ideas, tips, and a ton of
tricks, then give us a call. I especially recommend trying us when it
comes to Imperials and 71-76 GM wagons. If you have not built one before,
or have had bad luck with them, then try buying one ready to go. Why spend
$500-$1200 on a shell only to have no idea how to build it, and have it
destroyed in one derby? The cost of having it built by someone who knows
what they are doing and will gladly point out how it was built, where its weak
points are, and give you customer support should pay for itself in the initial
car. Then everything you take out of it and place in the next car will be
much less expensive. I have Imperials that regularly win me $3000 before
the body is done. After that, I sell the sub frame, transfer all of the
goodies over to another imp, and go again. With complete turn key
imperials starting around $4200 (Clean 64-73 Imp body, GAS 350EL, GAS TH350 with
tranny cooler, Raptor rear end with gears and shifter, aluminum radiator, fuel
cell, optima battery, ready to derby), after using up one imp body you would be
over %75 percent of the way in paying for everything. By the second one,
you'd be in the black. Plus, breaking things with an Imperial is more
satisfying than with most other cars. One of the drawbacks is building to
your local rules. If you give me a set of rules and tell me to go with it,
I'll build in every gray area I can find. If your officials are strict
with you, you may be in trouble. This can all be worked out before the
down payment is made. Trust me, I won't build a car that won't stand up to
rules or your expectations, and I won't sell you something you can't use.
With the purchase of the complete car comes an explanation of why things are the
way they are. You are paying not so much for labor, but are buying tips
and tricks on a car you may know nothing about. I won't share
anything before the car is paid for, so don't try to play games and pick my
brain. Either you want to pay for an education or you don't. This
isn't high school where it comes for free. You are paying for a 4 year
degree with a complete car.
Gropp Automotive Specialties
Scott Gropp
(402) 450-6351
