Sleeper-Z Posted January 3, 2005 Share Posted January 3, 2005 started her again last night and she won't idle. the only way is with a rag over the carb (makeshift choke). either than that there is no hope for an idle under 1800rpm. here's the basic setup: 60 over 9:1 pistons (9:1 with 72cc heads) 72cc dart pro1 200 heads (mild port) victor jr. intake (fully ported) 248/248 solid flat tappet cam 850cfm (probably flows around 860cfm) holley hp carb oh well, that's what i get for upgrading everything except for the pistons/rods/crank... hopefully in the next couple of month's ill build a 12:1 383 or maybe a 427 sbc. i have video but i need to find a way to get in on the computer and then find someone to host it for me... it does sound pretty wicked. thanks, steven m. Quote Link to comment Share on other sites More sharing options...
Tim240z Posted January 3, 2005 Share Posted January 3, 2005 850 carb is way to big. 700 will do nicely, maybe a 750 at most. Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted January 3, 2005 Share Posted January 3, 2005 sounds like a vacuum leak. carb base, intake, vacuum line, vacuum ports, check it all over good. Quote Link to comment Share on other sites More sharing options...
Sleeper-Z Posted January 4, 2005 Author Share Posted January 4, 2005 i thought at first it was a vacuum leak but... replaced intake, billet base plate, metering blocks, gaskets, etc. i'll troubleshoot some more... although a full forged setup 383 sounds good to me, but i'll need about 3 months of pay since i'm a full-time student. Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted January 4, 2005 Share Posted January 4, 2005 started her again last night and she won't idle. the only way is with a rag over the carb (makeshift choke). either than that there is no hope for an idle under 1800rpm. here's the basic setup: 60 over 9:1 pistons (9:1 with 72cc heads) 72cc dart pro1 200 heads (mild port) victor jr. intake (fully ported) 248/248 solid flat tappet cam 850cfm (probably flows around 860cfm) holley hp carb..' date=' steven m.[/quote'] I'm assuming we are talking about a 350 SBC? Based on your statement that you are thinking about upgrading to a 383/427 implies to me we are talking about a 350 SBC (?), yes/no? Your confusion w/this engine build is about the only issue I have w/the hot rod magazines. They are great at giving engine builds - yet they are poor at explaining airflow velocity basics; as in how to choose the proper DCR to SCR relationship as well as how to match your Cam Profile and Cylinder Heads with your choice of DCR to SCR - nothing against you Sleeper Z. I'm sorry you have wasted your time to get an engine that doesnt perform the way you envisioned. I relaize the engine sounds good - but it wont perform well because of the mismatched engine components. These are the hard lessons learned (wasted time and wasted money) that the hot rod magazines dont touch. If we are talking about a 350 SBC, then I'd say the title to your thread should be "Over Carbed AND Under Compressioned". If we are talking about a 350 SBC then your engine doesnt know if it is a race engine or a street engine due to the mismatched components. It is confused: unfortunately for you - airflow velocity (port pressure or the lack thereof) will be the final determining factor. I would like to know if your 248 cam is the @ .050" duration or the Advertised Duration. If it is the @ .050" duration then your engine is severly under compressioned if said engine is going to be a race engine. If it is a street engine then your cam/cylinder heads (assuming a 350 SBC) are too large for pump gas. Regarding the cyl.heads: is the "200" indicative of 200cc's for the Intake Port volume? If the 200 represents the Intake Port Volume in a cc measurement and your cam's duration is using the @ .050" listing - then your engine combination is a race engine: with a street engine's compression ratio. The result is a mismached power band to a poorly breathing engine. The engine's power will suffer throughout the entire rpm. Even if the compression ratio was appropriate, your redline would be in the 7000-7500rpm range which usually comes with a 900-1200rpm idle. If this is a street engine, how many times will you actually be rev'g your engine to the 7000-7500rpm range? Since you have a 9.1 SCR, your engine is further hindered in its breathing = even a higher power band, in the 8000-8500 rpm range. You need to do one of two things: 1)first decide if this is going to be a race engine to be ran on race gas or is it going to be a pump engine to be ran on pump gas. 2)Decide on a deplacement 3) If you are going to go with a pump gas 350 SBC then you need to get a smaller carb, get some cylinder heads w/smaller Intake Ports and get a smaller duration cam to bring your airflow velocity up (better port pressure = better cylinder pressure) and to bring your peak power band down from the 7000-8500 range to the 5500-6000rpm range If you are planning a 383/427 - then the 200cc Cylinder Heads will work fine as a street engine on pump gas. If you go w/the larger 383/427 you wont need 12.1 SCR unless it is going to be a race only engine. If it is a street engine then you need to rethink your desired SCR as pump gas doesnt usually like 12.1 SCR's. Just something to think about. Kevin, Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted January 4, 2005 Share Posted January 4, 2005 10-11 to 1 compression is as high as you need to go especially for a street car. Mike Quote Link to comment Share on other sites More sharing options...
HICKL Posted January 4, 2005 Share Posted January 4, 2005 you sure your idle circuit in your carb didn't just get gummed up from sitting? Maybe that cowl hood is the problem, I'll come by and pick it up. Quote Link to comment Share on other sites More sharing options...
Sleeper-Z Posted January 7, 2005 Author Share Posted January 7, 2005 Kevin, Although i'm sure you were trying to help... I already knew all that. And I made this thread to say what I have done wrong and how i was going to fix it. no offense taken. i planned for the 900-ish rpm idle and the 7500~ rpm redline. basically my goal was a 9-10 second car that is still "streetable". hel*, i even planned for the car not to idle and knew the parts were incompatible because the compression would be too low. just to eager to "get er' done!" BTW 350 block 248 at .050 200cc intake port "race" engine the truck is my daily driver and the trailer was coming it's okay though, i'm in texas, where 010 blocks go for $50. just have to get some drivetrain parts and i'm rolling. just not sure what direction i am going to do. complete the car and race, or give it up. kind of hard to do each, but school and money will be the defining factor. Quote Link to comment Share on other sites More sharing options...
Michael Posted January 7, 2005 Share Posted January 7, 2005 To add to the discussion... Some people believe that guys who haven’t actually successfully built a well-running engine either don’t understand basic engine theory, or can’t make up their minds on what parts to use. That’s like saying that if you’re not street-smart, you can’t be book-smart either. Well, in fact it’s entire possible to have a robust understanding of the internal combustion engine, and nevertheless to still end up with a poorly-idling, fuel-puking, clanking heap that gets 8 mpg and makes 90 hp at the crank. How? Well, start with a 350 V8 core, do everything 100% right on buying correctly-matched parts, get all the tolerances right, assemble everything right, then screw up ignition timing by 20 degrees, and bingo, you’ve got 8 mpg and 90 hp. Or, forget to add oil to that brand new crate engine, and now you’ve got 0 hp. Meanwhile, your neighbor, who thinks turbulent separation is a kind of divorce and natural frequency is a rock band, has a smoothly running engine making 200 hp, because he remembered to add oil and his dad taught him how to set the timing by rotating the distributor while listening to the engine. Quote Link to comment Share on other sites More sharing options...
Sleeper-Z Posted January 7, 2005 Author Share Posted January 7, 2005 forgot to say thanks for the replies guys! Quote Link to comment Share on other sites More sharing options...
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