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Post by rookie on May 11, 2015 2:07:41 GMT -6
Morning everyone. 1st post here.. so here it goes.. I've been building on my dirt race car since i don't know when, life a responsibilities tend to get in the way. I eventually took it out to see what it could do. (its important to mention in know nothing about driving race cars), and was massively disappointing. Being a complete newbie, rookie...whatever..  , i was expecting allot more. I thought i had it running well, but it didn't do well at all. It started out well but only a few laps in it began missing and backfiring badly. It only seems to happen when the engine reaches operating temperature. The valve lash was the major culprit, i reset it, and it eventually sets out again. The motor is a bone stock 350 TBI converted to a carburetor setup (650 Holley with vacuum secondaries) . Being cautious, the idea was a low powered car and get some seat time. After spending time with the track owner, he very kindly offered tips on where to focus to get it running better. I'm not after a high powered big money car, just learning at the moment. The advise and focus points offered were. 1.) Carburetor is too small 750 DBL pumper will work better. 2.) The valve lash issue is hydraulic lifters warming up, Since they older they not maintaining pressure. I have a 750 carb that can be rebuilt. Figured i may as well change out the cam, while i'm in there. What information is needed to recommend a good cam? I thought going solid lifter would be better, but any suggestions and guidance will be welcome. Last thing, i live in South Africa. So please send suggestions, ill work out what is available here. Thanx for reading. |
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Post by flipflopoo1oo on May 11, 2015 9:12:56 GMT -6
How many rpms are you turning--- Lift has a few issues as to stock part--- We have to run 4412 two barrels in most classes as rules go so carb may not help! Gears -car weight- and all comes in on cam choice and degree installed!!! Most lower classes have vacuum rules and cam's are a large part of that!!! Give us all the info you can to be able to help you more!!!
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Post by rookie on May 12, 2015 1:37:45 GMT -6
Thank you for your response. Before I attempt to answer your questions. I’d like to explain the dirt racing culture and level of experience in South Africa. Maybe it can assist you understand when providing advice. We don’t have track rules, you race what you bring. Just as long as the car is compliant to the safety rules set out. So if I want to bolt a supercharger onto my car, I can run it. No one cares, but I’ll probably be the laughing stock for the night..  Cars are classed by their displacement in Cc’s 1400 1660 2100 V8’s run together. V6’s run with the V8’s. Sprint cars are more exhibition cars in this country. In my 35 years on this green earth, I’ve only seen 4 (1,2,3,4..) on the dirt track circuit. Seeing your World Of Outlaws sprint car series run races would be awesome. So compared to the United States we are in our infancy in the sport. Without offending the gentlemen who run their cars here, I don’t believe for a moment that much thought, if any, is given to the setup of the car itself, suspension, spring rate, shocks, ballast, tyre pressure and so on. Just scratching the surface I know.. I have been reading these forums for a number of years now, while building my car and getting it going. I think I can safely say, if I were to understand and apply just half of the knowledge and experience you guys have to my car, I would dominate races. There are so many factors you guys consider, its hard keep up. To try and answer your questions. (You might laugh a little..) I don’t recall seeing a Tachometer in any of the race cars at the track. Mine doesn’t have one, which means I need one since you asking for it. Gear ratio is 3.23:1, like I said.. bone stock.. Weight is 1,300 KG (2,866 lb) No track rules, I’m basically after an engine that runs well, has more power so I can learn the drive it. Any changes to the car setup, I would be learning as I go along. But getting a car on the track and seat time is my goal right now. Thanx again. |
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Post by flipflopoo1oo on May 12, 2015 9:51:17 GMT -6
Ok -- kind of car and engine -- as far as ratio we don't run drive but first or second asto length of track --1/4 mile circle or 3/8 mile! Degree of banking for setup advice and turning-- running high or low on the track or is it flat? Leaf springs on rear or coils? A ton of cams out there and if no rules the matter of stock heads and springs and lift is limit we won 86 % in four states in 2.5 years with a 450 lift rule and had to pull vacuum 12 at 1200 rpms-- Does the heads have any porting done or bone stock! Do they run trucks  A 305-312 at 450 would be a good start on a cam for stock! We ran a lot bigger and had springs to turn up a bit-- won most at 6400 rpms by staying in the torque range of cam design and degree installed!!! |
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Post by rookie on May 19, 2015 2:41:44 GMT -6
Sorry for the delayed response..
Got busy.
The car falls into the Hobby stock category. Bone stock 350 SBC, TBI (Converted to carburetor)
Heads have not been touched, no flowing done. But i would like to flow them when they out.
Over here, the hobby stock cars are right hand drive.
Track is a 1/4 mile flat oval track.
Coil springs all round. The springs in the front can be set, it has a threaded housing allowing to compress or release.
Only cars and quad bikes run on this track, if that answers the "running trucks" question.
I've been reading up about Hydraulic vs Solid cams. As far as i understand, the performance differs but not by much. Unless you hunting for every horse you can get, is there any value in going solid right now? Getting a good running engine and setting up the car might be time and money better spent? Especially in my case..
Hope it helps..
Thanx.
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Post by flipflopoo1oo on May 19, 2015 6:59:48 GMT -6
Two cams-- the solid lets you adjust cam specs at the rockers to fit your needs-- HYD is a bit stuck other than degree and bleed-off lifters! A lot of good 450 lift cams as to stock valve springs-- RPMs a bit limited until replaced or shimmed for higher revs! 1.6 rockers if push rods clear head guides, adds a 25-30 thousands lift and quickens the ramp speed at the valve! A great place to start-- spring shims and 1.6 rockers--- neither requires pulling the heads!!!
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Post by rookie on May 19, 2015 15:00:29 GMT -6
Okay, so solid is the way to go.
Has the information provided assisted in working out the cam that would perform best?
Replacing the valve springs isnt too expensive, and probably should be done anyways. Will i be able to keep the rockers?
How do you work out the best fit? Or is it an experience thing?
Thanx for your help so far.
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Post by flipflopoo1oo on May 19, 2015 16:45:58 GMT -6
IF NO RULES -- A 305-312 WITH 110 LOBE SEPERATION UP TO 600 LIFT WITH SPRINGS TO MATCH LIFT BUT YOU WILL NEED PUSH RODS AND ROCKERS WITH 600 LIFT TO HANDLE THE STRESS! 525 LIFT AND 600 LIFT SPRINGS SHOULD WORK! 120 POUNDS ON STOCK SIZE SPRINGS!
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Post by flipflopoo1oo on May 19, 2015 16:47:40 GMT -6
IF NO RULES -- A 305-312 WITH 110 LOBE SEPERATION UP TO 600 LIFT WITH SPRINGS TO MATCH LIFT BUT YOU WILL NEED PUSH RODS AND ROCKERS WITH 600 LIFT TO HANDLE THE STRESS! 525 LIFT AND 600 LIFT SPRINGS SHOULD WORK! 120 POUNDS ON STOCK SIZE SPRINGS!
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Post by rookie on May 19, 2015 21:39:39 GMT -6
How does altitude factor into the selection?
Thinking duration and lobe separation.
Im 1,709 meters (5,697 ft) above sea level. Logically in my mind, i would think that duration would be more and lobe seperation would be less to increase overlap. .
Or am i on the wrong track?
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Post by flipflopoo1oo on May 20, 2015 19:16:26 GMT -6
Dirt is the only track here! Over lap is cause for reversion and that's always a horse killer! Vacuum to vaporize fuel to cause refrigeration of air to get more in while increasing velocity to give a colder mix to have more expansion to aide compression in the blast! A hotter burn with more air -- on low compression the timing is higher to build longer to get the pounds of thrust but it needs a lot of fuel to go with that much air-- fast burning low octane fuel!!! Not high that burns slower and longer!
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Post by flipflopoo1oo on May 20, 2015 19:35:46 GMT -6
One valve closing and one opening-- different sides of the lobes-- more LS is less overlap-- actual flow happens at about .050 valve opening -- depending on valve size -- cubic draw and temps-- a lot more but this is enough to see the change-- degree-ing the exhaust closing to stroke is key to horses and so many factors in getting intake correct most forget that fact!!! More LS close it sooner and still lets you get close to a 108 in. center line-- !.6 rockers and push rod length along with valve splits on a solid cam lets you play a bit to find that happy horse spot!!! Most don't know how but by the specs and then can't see the need of .002 difference in tuning per cylinder with temp issues to factor in-- even on indexing the plugs and setting gaps different to get a few more!!! They are there hiding where most grass is greener if you go that far! Tune is key on anything!!!
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rickd39
Fourth Place
www.duricaracing.com
Posts: 54 
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Post by rickd39 on May 28, 2015 11:14:47 GMT -6
And so it begins...
I am assuming you have a small block Chevrolet engine
You shouldn't go more then .480 gross lift on stock valve springs ( maybe .500 if you are careful)
With higher lift then .500 your stock rockers probably won't work, unless they are "long slot rockers"
With higher lift cam, matching springs, and matching rocker arms, your stock pressed in studs will probably start pulling out, so you will have to either pin them or replace them with screw in studs
A decent 650 carb should work for any Small block chevy with stock heads and valves, a 750 carb will probably be too much at lower RPM's
I would enjoy seeing some pictures of your racetrack and race cars in action if you have a chance
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Post by rookie on Jun 1, 2015 19:10:04 GMT -6
Hello again.
I havent had much time to look around for the reccomended cam yet.
Rickd, thanx for the information. I found 2 video's of the track ive been around. The name is Randfontein, about 40 minutes west of Johannesburg. Check them out, ill take some pictures when im there again.
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Post by rookie on Jun 1, 2015 19:33:13 GMT -6
Can we talk about car setup a little? Specifically around springs. As i said before my car has coils all round. Front being settable. Perhaps i should start a new thread on this? ?
To recap, the car weighs 2,866lb.
Ive been reading about the recomended starting point tech tips. Based on the total weight of the car, the recomended spring rates are.
Lf 900 lb
Rf 1100 lb
Lb 250 lb
Rb 225 lb
Now i dont know if the guys round here are working on spring rates and spending time on car setup as much. But if they are, they aint sharing.
To calculate the spring rates without a rater, i found a site basing the calculation on
Tortion modulus (which for steel is the same)
Wire diameter
Active coils
Coil diameter
And a constant that must be included.
I have it in an image file, bit im using a mobile device at the moment, im not sure how attach using the mobile device. Ill load it up when get near a computer.
Point is, is all this making sense? And can you explain more on depth, understanding what you doing is better than just following instructions.
Thanx again.
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, i was expecting allot more. I thought i had it running well, but it didn't do well at all. It started out well but only a few laps in it began missing and backfiring badly. It only seems to happen when the engine reaches operating temperature. The valve lash was the major culprit, i reset it, and it eventually sets out again.
A 305-312 at 450 would be a good start on a cam for stock! We ran a lot bigger and had springs to turn up a bit-- won most at 6400 rpms by staying in the torque range of cam design and degree installed!!!