Landracing Forum
Tech Information => Technical Discussion => Topic started by: Cajun Kid on June 19, 2008, 09:13:58 PM
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I know on my Fiberglass HotRods with powder coated frames and all the wiring for running on the street getting all electrical components a good ground is very important. My question is on my race car it is a glass body on a new freshly powder coated chassis. The new engine did very well on the dyno... When we fired it up in the car it seemed as if the starter was very slow and then the engine seemed FAT not wanting to rev as crisply as before. We put jumper cables from the battery to the engine block and the starter spun over very strong and fast. but the engine did not seem to rev a crisply.
The motor mounts and trans mounts are urethane,,, can the MSB box with a poor ground and the engine with a poor ground cause this symptom?
We just finished putting new grounds wires from the block to the chassis, the battery to the chassis, the MSD boc the the block.. When I get off work tomorrow am going to the shop and crank it again to see if that fixed it..
Just wondering if we are on the right track ?
Thanks
Charles
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I think you just proved the answer. MSD needs full current flow.
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Never used MSD box before,,, But when I get to shop tomorrow after lunch, I hope to fire her up and see if all the grounds we put on solve the problem.... Car sounded good but the rev's just did not seem sharp and crisp.. I talk to my motor guy he told me about the grounds... Since we are on time crunch to get all the bugs worked out before Maxton, I figured better ask some of you experts...
It has been 17ish years since I piloted a race car or race bike... just want everyting to be right when I unload the car at Maxton nect friday.
Charles
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Charles, we have a lot of faith in you, there is help at the races as well, don't be bashful. Hope your tests go well and you get in a few good runs. :-D
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Thanks Glen.... this is one good group of people...Have a great night.
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I think you are on the right track also. My instructions suggest grounding each head, if you haven't done so already and possiably the distributor. Good luck
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S351 yes I was thinking it would be a good idea to ground them as well. It is going to look like the block, heads and dist are on an EKG machine LOL...
Thanks for the tip
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Ground everything with wire back to the battery. I might use two or three grounding lugs depending on how far apart the electonic units are so there are fewer wires running the length of the car. Race cars should never rely on the chassis for ground.
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Thanks, I am doing just that.
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Ground everything with wire back to the battery. I might use two or three grounding lugs depending on how far apart the electonic units are so there are fewer wires running the length of the car. Race cars should never rely on the chassis for ground.
Ditto, big time.
A zero resistance ground reference is critical to anything that carries a load. Ignition and starters apply. Clean, filtered power is critical to the performance of all electronics; most of these have good internal filters but can't function without a low resistance current path to ground.
Too many builders make sure of good power connections and neglect the grounds. Use wire and connections equal or better than the power connections and never rely on the chassis.
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Cajun,
If you are running a data acquistion system be carefull. If you are, use only one ground point for everthing. I recommend using one wire from each head, one from the ignition, one from everything else to a 1/4-20 stud. If you have more than one ground point you introduce what are called ground loops. The ignition will emit RFI which will radiate to the ground loops which will then mess the data acquistion up. This not a small point, it is very important. Do not use the frame as a return path when you use a data acquistion. We do this on Top Fuel cars and we did it on our lakester and the Racepak data is perfect.
Sorry for being a no-it-all, but it comes with being an engineer.
POPS
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Pops;
Running all ground returns to a single point (a "star" ground) is a good idea at DC. At high frequency the inductance of ground return wires can make them a relatively high impedance and if any EMI/RFI source has significant capacitance to the chassis, you have a ground loop even in a star- ground system. The ideal case would be to create a big ground plane by sheathing the bottom of the car with sheet copper but this isn't practical, of course. When all is said and done, the best compromise is probably a star ground systen like you suggested with heavy gauge wire. Placing RFI filters in the power lead of sensitive systems can also help.
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Hmm I a still a bit confussed but with such good answers from the this group of folks
I am just confussed at much higher level ... LOL
Thanks for the help. It seems as if your suggestions have worked.
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Hmm I am still a bit confussed but with such good answers from the this group of folks
I am just confussed at much higher level ... LOL
Very funny and very true Charles! That is how I always feel with LSR involved. The more I think I understand the more indepth things get and the more confused I get and the less I feel I know and as you said, always on a higher level! LOL
Ask Todd about the circle of knowledge when you see him this weekend. I think the thought was passed on to us by ScottG and it fits the bill!
Deb
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That's a perfect example, and just what Charles is experiencing. The circle of knowledge was shared with me by Joe Timney when both of us were in the middle of my shop and a conversation had us each telling the other hjust ow much we didn't know.... Joe just happens to not know alot more then I do, which made me understadn the circle of knowledge all that much more. :wink:
Lack of knowledge can be a very productive way of not looking at things - and it only takes more knowledge to gain it.
Looking forward to seeing you in a few days Charles.. glad it's coming together for you.
Todd
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Don't be confused. If you are not using a data aquisition system Odoms suggestions are fine. If you are using one do what I suggest and you will be a happy guy, its very simple to implement. If you want you can call me at 714-269-9645.
POPS
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Interesting post.
For anyone who is building or rewiring a car from scratch, I suggest picking up the Bosch Automotive handbook. There's but 2 pages on proper electrical systems design for cars that carry sensitive electronics, those two pages alone are worth 10x the price of the book in my opinion.
One thing that's not covered in the replies to this thread, that should be, is the phenomenon of power coupled noise. There's a good diagram that shows what Bosch recommends for powering and grounding various systems in an electronically-managed engine (which applies to datalogging systems even on carb'd engines), after looking at it and then taking a look at a brand new Chevy pickup, I changed how i wire cars and have yet to encounter a noise issue with any of my electronics installs.
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This is just an awesome site and great group of folks. My problem seems resolved... I do not have any fancy electronics, Just a battery, a dist. a coil and a MSD box (other than lights and guages etc..) The ground suggestions seemed to solve the weak ignition problem and fully solved the slow starter turnover.
Well going back in the shop to figure out how to make some door handles and bleed the brakes again.
See you all this weekend.
Charles
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I don't know much about electrical stuff, but I have been told that with an MSD you should run an alternator to matain enough voltage for the unit to properly operate. You might wnat to check that out with someone who knows what he is talking about.
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Rich,
I heard the same thing!
You are right about MSD units needing enough voltage. I think performance starts dropping off below 13.5V. You can get by at Maxton and El Mirage if you have a good and fully charged battery, use push vehicle electrical to help start the race engine, and only make a few runs.
I put a small alternator on our car for Bonneville and it worked great.
Tom
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We run 2 group 24 deep cycle batts (80 amp hours,650 cc amps) a 12 watt,3/4 amp solar panel mounted on the rear package tray and no alternator. We most of the time keep a 6 amp charger on in the pitts. There is a volt meter in the car and it has never dropped below 13 volts even on a 5 mile pass. The ing. is a MSD 7AL with a crank trigger. This system seems to work well for us. We never started it after WF until May right before we pulled the engine to inspect. Never had a charger on it all winter just solar sitting in the shop under a skylight and it still fired right up showing about 12.5 volts.
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I do have a small Denso style Power Master alternator.. I like the solar power option to help keep a charge,,, for the June event in the heat at Maxton that may be a good idea to keep the battery charged and allow a small fan in the cockpit so I don't bake while in line all suited up.
Thanks for one tip that leads me to another door of speculation LOL
Charles
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You might want to note for maintainence that virtualy all failures on a car or bike that once worked fine is a ground wire that is corroded, almost never a + lead of any voltage. I have often wondered if bolting on a sacrificial anode like on a saltwater boat might fix a lot of things.
Dave
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Dave, good Idea.
Well got the new car down the track for two runs. Not bad for it's debut. No ignition problems, the better grounds did the Job...
Thanks to all who gave me greats ideas and solutions.
Charles
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Charles - I was the old fart wrenching the red #906 C/GMR this weekend past; sorry I did not have a chance to stop by and introduce myself. I wire race cars and hot rods for (part of) a living, and I'm nearby in Salisbury; I'd be happy to help you with any problems and/or questions. I would have posted on this earlier but I was overwhelmed with car prep! vic
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Vic, thanks for the kind offer, I do understand how busy you must have been leading up to this past weekend and also while there,,, we have been the same way..
I live in Midway just outside of Winston Salem, but also have an office in Salisbury on Jake Alexander..
Like to meet you sometime,,,
Charles
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Charles - My schedule is somewhat flexible as I work from my home shop; sometime when you're down on Jake Alexander give me a call and we'll get together for coffee, a drink, a meal, or whatever. Or come on down to the shop, I'm probably 8 miles south of you (just north of 152 between China Grove and Rockwell. 704/798-5421. vic
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Put the negative lead of your Digital Volt-Ohmeter on the battery ground post (with meter set on DC Volts), then put the positive post anywhere you've a questionable ground. Power up and see how much voltage you read....should be very very small (less than .1). It may look good on a resistance check, be be no good under actual load. (NOTE: During starter cranking you could see .5 volt but not really have a big problem....depends on wire size and length)
To check a circuit under load, for example the wire to the coil + terminal, use this test.
1. Disconnect terminal wire and connect it to the probe end of your 12V test light.
2. Connect the clip of your test light to good ground or battery negative post.
3. With voltmeter on DC volts, put the negative DVOM probe on the battery positive post, and the positive DVOM probe at the test light probe (BEFORE the bulb).
4. Read the "voltage drop" on the voltmeter. Again, this should be very small. If it's reading more than a .1-.2, you have resistance in the circuit UNDER LOAD, even if your ohmeter says NO resistance. The ohmeter doesn't push enough amps through the circuit to identify corroded copper or broken strands.
Hope this helps....the salt sure tears up our wiring!
Regards, JimL
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Vic, good job with the 906 at Maxton...now get offline and get that car prepped! Just kidding, I hear you have a schedule conflict for August??? Hans