Reply With QuoteAre you using the right fuel? 11:1 usually requires a higher octane.
have a pair of dart heads on my chevy 383 stroker engine. The markings on them say SB 250 (maybe 260). I am trying to figure out more about these heads so I can get my setup dialed in.
It is currently in an 85 full size blazer, with 11 to 1 compression pistons, 1.6 roller rockers, a Holley Contender Manifold, and carter AFB 600 carb. The cam is a comp cams 268H. It is still using the stock fuel pump for the 305 chevy. The gears are 3.73's and the tranny is a fresh 700-r4.
Its doesn't seem to be living up to its potential right now. Any advice would be appreciated. Also, I plan to make this into a turbo motor at some point...would these be good heads to use?
How do you test vacuum secondaries to see if they are opening?
I just invested in a FIRST TPI setup with an Electromotive computer...maybe this will make some of my issues go away. Also, my cam is degree'd at zero.
- Keith
Are you using the right fuel? 11:1 usually requires a higher octane.
Carb seems small. Have you tried a 750cfm DP?
GET THE OCTANE BOOST OR PREPARE FOR SOEM REALLY EXPENSIVE FUEL. 11;1 WITH CAST IRON HEADS IS A NIGHT MARE FOR A STREET MOTOR. THE HEADS YOU HAVE A PROBABLY 305 TORQUERS. MY RECCOMENDATION IS THAT YOU CUT YOUR CO,PRESSION BACK. YOU ARE NOT GOING TO BE ABLE TO RUN ENOUGH TIMING ON PUMP GAS TO MAKE THE MOTOR REACH IT POTETIAL.GET THAT COMPRESSION BACK UNDER 10:1 OR GET A SET OF ALUMINUM HEADS. DONMT PUT TOO MUCDH TIMING IN IT RIGHT NOW WITH OUT SOEM REAlly good fuel or youll be consuming pistons. the cam you have is a good choice for a street truck but you could help it out a little by putting a small converter in the truck because its not making any power till about 1800-2000 rpms.You need a converter that wil foot brake to about 2000rpm. this will make a world of difference in performance alone. your small cubic inch motor needs to be able to build some rs to get its power. the convedrter will allow you to do this without changing your gear or hurtinh your fuel economy. you also need to add a corvette servo piuston to you 700 to firm up the shifts a little.Oh and the addition of a tranny cooler will help eliminate excess heat build up from the converter under heavy load.Get that motor with a good carb soem timing and a little fuel, add some converter an d it should be liek driving a different truck. just beware trying to add any timing to it right now without some 104 octane fuel. i cant believe your not hearing soem serious detonation already. i think you will find that soemone has pulled all the timing out of the motor if it has that much compression.otjherwise it wouldnt run on pump gas for very long. Hope i helped
oh and ont quote me on the heads because i thin ki may be wrong about which onresw the yare. the could very well be sr torquers or sportsmans as i am not familiar with the casting numbers on dart heads.
I am familar with your 383 because i blew one up on pump gad with a little timing an 10.25 to 1 compression.Split the cylinder wall. if you heads can handle it add some cam.and if you add a bunch of cam add more converter.
I know the full size Impala's qualify as boats, so I would imagine the Blazer's do too. Just kidding.... that's why this is a great forum, plenty of people to help you out with questions and problems. God knows a lot helped me out with my engine problems!
Does any one have any info about my heads? I contacted Dart...but they have not gotten back to me...it says on the head SB 250...or 260...hard to read their writing
I found out another problem with the setup...see the dist. used to be in my boat...the mechanical advance was removed because I was running turbo's. I had a breakdown one day and put this dist. in the truck...no mech adv. SO, put it all together and you have...slug
This will be changing soon as I will be going to a fuel injected setup with distributerless ignition in the next couple months. Hmm...tuning with out getting dirty...almost seems like a sin against nature.
A few things here,
Are you sure thats SB and not SR? Worls marks alot of their heads as S/R for Street Replacement.
Thats little too much compression for that cam, I could only guess at your cylinder pressure but it has to be up there. Think about blending the bowls and a good thick head gasket. I personally wouldn't try much over 10:1 with only 268* @.005 lift unless I had a narrow lobe center.
A 600 CFM carb would work well for your application. THe smaller venturi promotes good torque at low RPMS.
And finally from someone who knows, don't do the TPI unless you want to replace the whole unit with aftermarket upgrades. Stock TPI units can barely feed a 350 @ 5k rpms. On a 383 they run out of breath by 4500 if not earlier. They were never meant to flow the high numbers that are needed to feed your engine. If your no going to spin the engine past the mid 4k range you'll be happy but the moment you try to outflow that intake the powerband will fall flat.
Its a unit called FIRST, the whole system is huge compared to stock gm...the runners..the plenum...the air door...its a pretty trick system.
- Keith
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