Vortec Headed 350

[jjewett444]

To anyone who has built a 350 stock or modded with the l31 906 or 062 vortec heads please help. i just rebuilt a 75 350 out of a gmc c2500 with the 3970010 block. had it rebored .030 over, crank polished, rods reconditionedand i put it together with supplied bearings and gaskets and all that good stuff. however i had a set of vortec heads reconditioned (not milled) but valve job to throw on. pistons are stock style dish .041 head gasket i had a comp he268 cam and matching springs and timing set, a vortec type edelbrock performer rpm intake, edelbrock 1405 carb(relatively new) stock manifolds and true duals 2.25 in with glasspack mufflers. stock distributor and timing set to 10 deg. btdc. basically it sounds more powerfull but feels like a gutless turd when accelerated past half throttle. first 2 days with truck was able to break tires loose now it just sounds mean but doesnt move fast , about the same as the ****** 350 with smog heads i pulled out of the c10. i know it should have more power because i drove a 86 f150 with a bone stock but fresh rebuilt 351w with hei proform dizzy and holley carb and took off loke a rocket with the secondaries wtf... someone plz offer some info, thanks, jim

 

[1987 GMC Jimmy]

So it was running great, and then it just kinda fell apart? I would have said timing chain off a tooth, but it would have been a dog immediately instead of later. Did you get a cold snap up there because we got one all the way down here in New Orleans. Reason I ask is because when it first got really cold this winter in Mississippi, my distributor moved a little clockwise and lost timing. When I checked the base timing to reset it, it was running 4* ATDC, and that's not at all what it was when I set the timing in the summer. Needless to say, it was 105% gutless. Or maybe it just wasn't right enough. I don't know. I'd say that's worth going back to check.

 

[Daveo91Burb]

maybe a lobe or two on the cam went flat? What was your break-in procedure? What type of oil you running? Were the heads magnafluxed? Vortecs are great heads, but have a tendency to crack, especially around the middle cylinder exhaust seats.

I have 062 vortecs on my 76 vette and I'm putting a set of 062s on a 383 I'm building for my burb now. Love 'em but definitely some vortec idiosyncrasies to deal with. (e.g. shaving the casting bumps off on my vette's rams horn manifolds so the valve covers would fit.)

 

[jjewett444]

i have checked and moved timing from about 14 degrees btdc to 10 deg for the past 3 days, tried gapping plugs to .045 and would hardly run. put the back to .060 btw they were all pretty black except for cylinder #1 which was more white. heads were mag'd no coolant being burned but will preform compression test later today after work. the tach i have doesnt work so i guesstamated about 2500 rpm while breaking in cam for 15-20 min however i didnt remove inner spring on the comp 981 springs. i used penzoil conv 10w30 with stp additive zddp and cam was slathered in comp moly grease. it goes ok at part throtte and revving up in park but under load at heavy throttle it just sounds fast but doesnt pick up good. no backfiring or anything so not too sure about a flat cam or anything like that. what if i messed aroung with mechanical advance weights?

 

[75gmck25]

Have you checked the carburetor linkage and transmission kickdown to make sure you are really getting the secondaries to open? You had to use aftermarket brackets and adapters to get the Edelbrock to work, and most of them adjust in multiple directions. If you didn't go through the adjustment process correctly you may not be getting any secondaries.

What cam did you have before the HE268? With 224/230 duration that cam needs some RPM to get going and you might find you need a high stall converter or lower gears to get the power out if it and vortec heads.

And does the transmission (TH350?) kick down when you floor the accelerator?

I would also expect initial timing of about 14-18 degrees BTDC to work best, and total timing should be about 34 degrees by 2500-3000 RPM.

Bruce

 

[Green79Scottsdale]

Did you check your valvetrain components? That much lift with Vortecs needs to be checked and confirmed for proper clearances. Usually it seems machining the spring pockets is needed when going above .460 lift.

 

[jjewett444]

Did you check your valvetrain components? That much lift with Vortecs needs to be checked and confirmed for proper clearances. Usually it seems machining the spring pockets is needed when going above .460 lift.

Lift is at .454 with stock self aligning rockers from 99 suburban which is leff that 1.5 ratio or so ive heard

 

[Green79Scottsdale]

Stock L31 lift is .414/.428
HE268 lift is .456/.456

Most people to check clearances around .480 lift, but I have heard from a couple personal friends that had issues with as little as .450 lift. You may not have a problem, but I would check it to rule it out concretely. With the valve cover off check and make sure a lobe isn't wiped out. Those new springs could have done it in.

 

[jjewett444]

thanks, just got out of work, truck wouldnt stay running at lunch time to leave so i waited till now and got it to stay runnung by adjusting the idle mixture screws counter clockwise about a turn and a half. however it wanted to keep stalling everytime once put into gear so i had to play the game of neutral,drive,nuetral drive etc... gonna run a compression test in a few and double check timing, so as 75gmck25 said initial should be higher that 10 btdc static? also had someone crank it over with v/c's off and it didnt look like a rounded lobe, looked normal to me anyways.