v80z Posted March 29, 2006 Share Posted March 29, 2006 Well I have been out on the interstate and have completed several drives with no major mishaps. First Impressions.BLur. Remember when you first saw hans Solo and Luke make that first jump to hyperspace and all the stars instantly got trails converging out from the center of their vision? HAHAHA. In my 42 years have never had a car that could rip the tires 1st and 2nd. That is so much fun. Normal medium lauches produce alot of squeal BUT NO BLACK MARKS. HMMM. Car is too light? Now on to the tuning. Config: 1970 10.25:1 CR 350 SBC .030 over Stock heads med. performance Intakes are the 1.94 not 2.02. Exhaust 1.60 stock bottom pistons have pressed rods with Hypertectic pistons heads have new valves, fresh cuts, fresh stem seals, press ins removed and replace with screw in. Crane race roller rockers Cam Solid circle track Cam I picked for upper end power not drivability Solid Lifter Cam specs Valve adjustment Hot .030 Gross valve Lift .508 Lobe Lift .339 Duration at .020 tappet lift Intake 298 exhaust 294 Duration at .050 tappet lift Intake 251 exhaust 248 Valve timing at .050 intake Open 23.0 BTDC Closed 47.5 ABDC exhaust 54.0 14.0 Edlebrock air gap peformer intake edlebrock 750cfm carb HEI shell connected to a crane CD ignition and crane PS2 coil Vaccuum adavnce is hooked up In the current config with the dizzy set for no advance , in the stcok position. I have fair accelleration from idle to 5000 rpm. After that it starts to break up? Carburation? Timing? Advance? What are the basic steps I need to go through. Quote Link to comment Share on other sites More sharing options...
John Scott Posted March 29, 2006 Share Posted March 29, 2006 I'll bite on a few. Start with your ignition, then go to carburetion. Initial with a cam that big should be around 18-20 degrees. A good rule of thumb is to set the timing at 3000 rpm, either with retard light, or degreed balancer, to 34-36, then see what your initial is. At least at this point you have the proper full advance set. Starting with the initial, you might find that you have way too much total, ususally the case, causing predetonation. Get the right bushings stops, what ever and get into the advance mechanism of the distributor and make sure your total then is limited to around 34-36 at full advance, find a spring combination that starts your ignition curve 100-200 rpm above idle, all in by 2500. Again, you can use a touch more if you are up in the clouds, I run 38-40. Locked out is ok for some, but not as nice starting or street manners. I swear by BG's advice for initial timing: 10-12 for cams less than 220@ .050, 14-16 cams less than 240, 18-20 cams less than 260. I'm using 19 right now with my 244, but add a touch for altitude. Amazing how many people with a big cam bitch about the performance, and don't run enough initial, or take the time to get the distributor curve right. At low speed high overlap, low cylinder pressures take longer to burn need more advance. Vacuum advance can be touchy, most don't even connect it on a performance engine.If you do, limit to around 8-10 degrees at idle from manifold source only. If you are using locked out advance disconnect it. Its only for part throttle response and slightly better mpg.The old ported theory doesn't work well with performance engines. Usually makes pinging at part throttle. Most of the guys I know don't run it. Your solid cam should wind out till it blows, so cutting out after 5000 might indicate weak springs, (new?) , poor ignition system, timing, jetting? I'd guess your hp peak to be close to 5800-6000? Guessing the rpm range should be around 3000-7000. You didn't mention the lsa, but Circle track cams usally are around 108-110. Nice tight power band. HEIs with the right parts can rock! IMO, with a nasty cam like that, streetablity and mpgs aren't a big concern, I'd pony up and get a Holley double pumper and pick up a little more hp. Edlebrock is a great street carb, but Vic jr himself admits they are not intended for really hot set ups, and you can gain hp with the Holley. With wideband afr tuning, wide open should be around 12.8-13.1. Best for drag only 12.5-12.9. Without a wide band, holley stock jetting is really close at sea level. Subtract 1 jet for every 2000'. Primary side I tune for clean cruising w/o lean surge. If you feel lean surge go back up a couple. Access to a track? go for best MPH indicating hp in the secondary side. Then you can go back to timing and add a touch up or down and see if anything picks up. Better heads would really wake up the combination, as the small valves and stock floww are a roadblock to the potential of the cam. You results may vary! I bet the .030 lash makes a nice mechanical noise. Isky? Mine is .028, no hiding a solid! Quote Link to comment Share on other sites More sharing options...
jt1 Posted March 29, 2006 Share Posted March 29, 2006 Get the initial timing, total, and advance curve right, John covered that very well. Ditch the vacumn advance. Rig up a fuel pressure guage and make sure you've got adequate fuel pressure, like 4-5 psi @ WOT Take it to a chassis dyno w/wideband O2, or use a LM-1, to get the mixture right. Check with the cam manufacturer and be certain you're running valve springs that are adequate for your cam. This should probably be step #1. jt Quote Link to comment Share on other sites More sharing options...
v80z Posted March 30, 2006 Author Share Posted March 30, 2006 Thanks guys. That is alot of info and some I will have to ask more questions about. Let me do some work and more research before getting back to you. The cam comes from a store on ebay called Racers Outlet http://stores.ebay.com/Racers-Outlet I bought springs enough to handle the 508 lift Which is not a tremendous lift. John and jt1 hang with me on this thread as I work through all the issues you have given me. It is very much appreciated. Man this is fun. John when you say locked out do you mean that the advance is fixed at 34-36 with no mechanical advance? I guess you would use some sort of electronic retard to get started? Who is BG? "If you are using locked out advance disconnect it. Its only for part throttle response and slightly better mpg." I dont know what a locked out advance is. I dont think it is as my timing marks seem to advance when revving from idle. Lobe Seperation is 106 they suggested .030 for lash but I am running close to .020. Yeah when I start it you can see the spectator's inquisitive looks. Which Holley? What other carb brands? Quote Link to comment Share on other sites More sharing options...
Mike C Posted March 30, 2006 Share Posted March 30, 2006 If you are going to run a GM HEI, you need the vacuum advance to get sufficient total advance without running excessive initital advance. If you want to dive in, you can modify the advance mechanism to get more mechanical advance and lock-out the vacuum canister. This is a trial and error process. Do a google search on modifying distributor for more mechanical advance. As far as total advance, you will have to experiment for your motor. With GM iron heads, I would expect to see low 40's optimum. I run 41 on mine now, and it just picks up power the more you turn it up. I have 16 initital. I run MSD small cap distributors which have adjustable mechanical advance and on a performance app, lock out the vacuum. The only Holley to get is the 750 double pumper IMO. This is the carb most start with when modifying for more flow. The HP version has choke tower already removed and four corner idle which would be my recommendation. BG is Barry Grant. Quote Link to comment Share on other sites More sharing options...
jt1 Posted March 30, 2006 Share Posted March 30, 2006 IMO locking out the advance- meaning the mechanical and vacumn advance don't function, the timing stays where you set it, all the time- is a race only mod. Most people who do this use a timing retard to crank the motor, or wire the starter and ignition separately so they can get the motor spinning, then turn on the ignition. I think this would get old real quick on a street/track car. "If you are using locked out advance disconnect it. Its only for part throttle response and slightly better mpg." I'm pretty sure John mistyped this, meaning "vacumn" instead of "locked out". Right now, since you've just got the car running, I wouldn't throw any parts at it, I would tune what you've got so you can drive the car and enjoy the fruits of your labor. Total timing at 36deg; get the initial to 16-18deg, working with the slots or bushings, however you do it with an HEI; get total advance in between 2500-3000 rpm, working with the springs and weights. Spend half a day on a chassis dyno and get the carb tuned correctly. You'll need a tuning kit for the 750, and spend some time on Edelbrock's site, there's good info there on tuning their carbs. You'll know how much power and torque you're making, and probably pick up a good bit. There's simply no way to tune a carb as good by seat of the pants as you can do with a wide band O2. jt Quote Link to comment Share on other sites More sharing options...
Oldestzguy Posted March 30, 2006 Share Posted March 30, 2006 It is when I read threads like this, I realize I don't know jack#### !! Quote Link to comment Share on other sites More sharing options...
John Scott Posted March 30, 2006 Share Posted March 30, 2006 Really..REALLY, you don't need the vacuum advance with a HEI or any other distributor. Its not going to give you more advance at wot when your vacuum is 0 anyway. I haven't used it on my last four motors. Don't know anyone who does. Only for part throttle response and slightly better mpgs. You can tune it to tame a bigger cam, but need to use it with discretion and manifold vacuum only. I'll dig up the article later by David Vizard, He likes it when its used correctly. With my procahrged motor, I modified my HEI to have 18 initial and 4 more mechanical for 22 total. Made my own stops on the advance. Took of the rotor, made a bushing that fit in the advance slot, checked with timing light and filed a couple of times, done. No big deal. No I'd never recommend using a locked out advance, I thought that's what you meant by "no advance". Have friends that do, but mostly drag cars with plates. Almost every NA chev V8 will use around, 36 total. Cam and compression will determine initial. BG= Barry Grant. Here it is By David Vizard reviewing the Crane Distributor: Cylinder Pressure: The Number One Influence The reason an engine requires an ignition advance curve is that the speed of combustion varies greatly with the prevailing circumstances. As rpm increases, there is less time for the charge to burn. This, for optimum results, calls for the combustion process to be started earlier. Countering this is the effect of mixture agitation, which increases with rpm. These two factors leave us with the basic advance curve concept. In essence, the timing has to advance as rpm goes up but this levels off as the effect on increased mixture agitation speeds the rate of combustion. The overriding influence on ignition timing requirements at the prevailing rpm is the cylinder compression pressure. To get a handle on what might be needed for an advance curve in a normally-aspirated engine, we need only look at the two biggest factors affecting the compression pressure. These are the compression ratio and the cam timing, and here's how they affect the burn rate. The higher the pressure of compression, the faster the charge burns. Higher burn rates produce optimum results with less advance. The primary factor influencing compression pressure is the engine's static compression ratio. The influence the compression ratio has is also closely allied to the cam duration, or more accurately, the point of intake valve closure (Fig. 1). If the compression ratio goes up while all else remains constant, the amount of advance for maximum output will come down at all points in the rpm range. If a short cam is used, increased compression can have a substantial effect on the advance curve at low speed. If the compression ratio is increased and the engine uses a short duration cam then the initial advance needs to come on much slower as well as total advance being less. If the cam's duration is increased the compression pressure will drop. This slows the burn, so calling for more advance is the preferred move (until pressure wave and ram filling of the cylinder at higher rpm cause the compression pressure to increase). The effect of the longer cam is to bring about the need for the initial advance to come on quicker but total advance may not change that much. Vacuum Advance All the aforementioned applies to an engine operating at wide open throttle (WOT) with the advance curve being totally rpm related. (That's what we would have called mechanical or centrifugal in a regular distributor.) At less than WOT (idle, cruise etc.), the amount of air entering the cylinder is reduced which in turn reduces the compression pressure. As manifold vacuum increases the amount of advance needs to increase. At idle and low-speed operation, the amount of advance required to most effectively utilize the air and fuel entering the engine can be as much as 50 to 55 degrees. This is handled by the vacuum advance; a function many hot rodders believe is not needed because their favorite drag racer does not use it. Now is the time to listen up and listen up good. A functional vacuum advance is the single most effective camshaft tamer you can get. By taking the time to hook up the vacuum advance to a manifold vacuum source you can get a big cam to idle as if it were about 20 degrees less than it really is. Conversely, if you are looking for a decent idle the use of vacuum advance will allow you to use a cam of, at the very least, 5 degrees more duration/overlap than would otherwise be the case. ...so if you are convinced to use the vacuum advance make sure you have a way to limit how much it will advance. Old style distributors usually have too much. Drill and pin the actuating arm so it has a positive stop. I was inspired by the article and gave it a try. Mallory vacuum canister adjust 1 full turn for every 2 degress. 8 degrees additional vaccum at idle, Conclusion? Slightly perkier part throttle tip in. Car is too loud to know if any part throttle detonation. Really don't see a big difference. Your choice. John Quote Link to comment Share on other sites More sharing options...
John Scott Posted March 30, 2006 Share Posted March 30, 2006 It is when I read threads like this, I realize I don't know jack#### !! Wow, just saw your signature Z 30 years ago. WOW...I guess I said that already. John Quote Link to comment Share on other sites More sharing options...
v80z Posted March 31, 2006 Author Share Posted March 31, 2006 John an jt Thanks a lot. I am on nights now. Vwry anxiouss to get started with what you have told me. JT1 I left the thread yesterday looking for a new carb and thinking UUUHHHH where can I steal another $250 - $500 for a holley dominator. but now with your note today. You are right for now tune what I got. Edlebrock's site said the carb I have will support cams up to 240 duration so while mine is higher than that I should be able to put a better tune on it than what I got. I wanted to test drive it tonight because I realized that I had the crane cd box rev limiter set at 5500 rpm asa well aas the shift light. So I think that was the break up at the upper end. I put the shift light at 6700 and the limiter at 7200. Wanted to spin it up but decided to come to work in comfort tonight. I will get on it. Had to work late yesterday and did not sleep much today. As far as a kit for tuning the carb. What do you think is needed JT1. Would buying one of the edelbrock tuning kits do it? When I buy dyno time I would like to be ready. Quote Link to comment Share on other sites More sharing options...
jt1 Posted March 31, 2006 Share Posted March 31, 2006 I'm glad you found the cause of the 5500 rpm skip, I was worried about your valve springs. Valve float is a bad thing. 7200 is pretty high on a stockish bottom IMO, but it's your motor. The edelbrock tuning kit is what you want. It's got several different jets and rods, you use them to get the mixture right at cruise and WOT, then use the step up springs to adjust when the transition takes place. Ebrock's site covers this pretty good. The kit is 35 -40$ IIRC. One nice thing about an ebrock is you can change stuff without dumping gas everywhere. The ebrock's are really good street carbs, they just don't quite make the power a holley will. For timing, I usually run all the initial I can with the car still cranking fine with the motor really hot. Generally with a big cam, the more initial means cleaner idling and better throttle response. Get the advance in as quick as possible with no detonation. Tune total for max power on the dyno, with the motor really hot, again watching for detonation. I really can't advise you much on the HEI, most of my experience is with MSD's. The reason I keep yapping about detonation is because with 10.25:1 with iron heads & pump gas, you're on the ragged edge. The big cam's late IVC is reducing the dynamic compression and you'll probably be OK, but it bears watching carefully. If you have problems, reduce timing, and a little colder plug may help. Since you're planning on some track events, you will be running the motor hot at WOT for extended periods, and that is where detonation is at it's worst and will do the most damage. jt Quote Link to comment Share on other sites More sharing options...
Mike C Posted April 1, 2006 Share Posted April 1, 2006 GM specs PORTED vac for the HEI advance. If you run 20 degrees initial, you don't have to have it and can get 34 degrees total with the average GM distributor. But if you are setting timing according to GM's instructions, With 8 degrees initial, about 14 in the distributor, the vac advance +10 gets you up around 32 total. One of the shortfalls of the HEI is the same as most OEM distributors. NOT enough mechanical advance for a performance application, you have to jack the initial advance way up. I don't run the vac advance on my MSD distributor, it would just not run a stable enough advance at higher RPM's, but with the interchangeable bushings, you can set the amount of mechanical advance you want. Currently, I run 24 degrees mechanical advance witha 16 degree initial for 40 total. Quote Link to comment Share on other sites More sharing options...
v80z Posted April 2, 2006 Author Share Posted April 2, 2006 Mike C what is your cam configuration? Quote Link to comment Share on other sites More sharing options...
Mike C Posted April 2, 2006 Share Posted April 2, 2006 My motor is 355 ci, 9.75:1 with GM ported 492 and a Comp mechanical street roller. 236@.050 and .550 gross lift. The iron heads really eat the total advance up. Quote Link to comment Share on other sites More sharing options...
v80z Posted April 3, 2006 Author Share Posted April 3, 2006 Man what a sound loved it. Got the high rpm oil fluctuation. Time for a better oil pan. Quote Link to comment Share on other sites More sharing options...
Mike C Posted April 3, 2006 Share Posted April 3, 2006 Great, what all did you do? Quote Link to comment Share on other sites More sharing options...
v80z Posted April 4, 2006 Author Share Posted April 4, 2006 I havent got into all the steps that youlaid out so well. The rev limiter was set on 5000 rpm on the crane cd box. turned it up. I have been on a long work week and about to get off for 6 days. I will have more time to fine tune. I have read many posts about road racing oil pans. Do you have a suggestion for a chevy racing oil pan? I have seen good pans listed by grumpy for under $100.00. I have seen drag pans for $150.00 and up. And I have seen what is adverised as road racing pans. Do you have a suggestion 7qt Windage tray trap door setup for side to side as well as heavy accel and decel. thanks Quote Link to comment Share on other sites More sharing options...
jt1 Posted April 4, 2006 Share Posted April 4, 2006 When are you seeing the oil pressure bounce? Winging it in the garage or driving around? jt Quote Link to comment Share on other sites More sharing options...
Mike C Posted April 4, 2006 Share Posted April 4, 2006 I like this one: http://store.summitracing.com/partdetail.asp?autofilter=1&part=MIL%2D31505&N=400380+308674+115&autoview=sku Comes with a windage tray which is probably the most important addition for a street/strip car. Quote Link to comment Share on other sites More sharing options...
v80z Posted April 4, 2006 Author Share Posted April 4, 2006 only on the road at sustained rpm for at least 3-5 sec under accell. Blips in the garage dont produce the effect Quote Link to comment Share on other sites More sharing options...
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