therealmark

Stock '89 350 truck TBI Swirl port heads. First off, I KNOW they suck so please don't waste paragraphs trying to convince me you're right.

I've been searching trying to figure out what the maximum lift I can get out of them without machining anything, but I haven't really come up with any solid answers. I believe fast355 had a post that mentioned he was over .500 on exhaust but beyond that all I can find is a buncha heated opinions.

I intend to change the springs anyways and I'll even buck up for retainers but I want to accomplish this without removing heads from the block so machining is out. The cam I'm intending has .465 lift, so corrected the 1.6 is .496, at least according this calculator I found online- http://www.wallaceracing.com/rockercalc.php

I'd imagine I'm at about the edge of what I can get away with there. Anyone have a solid answer?

Thanks!

M.

kdrolt

I don't think the 1.6s will work. IIRC the valve seal boss (around the valve stem) on the L31/LT1(iron)/L05/L03 is the same in terms of dimensions, and going above, or near, 0.480 valve lift on the LT1 (iron) is risky due to the mech interference. So I think the same "rule" applies for the L05.

Searching for Fast355's posts is a good idea. HTH.

ShiftyCapone

iTrader: (7)

.480" is about as far as you can go. There are slight dimensional differences from head to head but the norm is around that number. My 187 heads (305 TBI heads) had that limit exactly (baseline before I cut the guides). Even if you could hit your goal on stock heads you would risk pulling out the pressed in studs. To run that lift you will at a minimun have the pressed in studs removed for screw in units. Having a shop cut the guides at that point is another $20 or so. Fast has run some high lift cams on stock pressed in studs but I don't think he made it very far without them working loose.

350BENZ

I realize this is an old thread. It is very pertainent to what I am preparing to do. My question is how much lift will the pressed in studs tolerate before any problems occur?

I built a 350 from a l31 shortblock, cam and all, with mildly ported 187 heads, tbi factory prom for the 193 heads, short headers into single 3"exhaust, no cat to power my camper truck. Its not for performance. It can rev 4500-5000 but will mostly stay under 3000. I have a manual tranny in it and i just want to get a little more bottom end and power around 2000 to 2500. That will keep me in high gear on the highway at speed without having to downshift. Better on fuel.

I bought a set of 1.6 roller tipped self aligning comp cams rockers. they will put me up to .43x intake and .45x exhaust on the factory L31 cam. LCA is nearly perfect at 106.25 for valve to displacement ratio: according to Vizard. The extra rocker ratio will make it seem like 105.5 which is still acceptable. overlap will be just over 40* which is in the high range for hauling and low range for street. Basically I expect to get a bit more torque with the extra lift but keep the power curve in the lower range with relatively low overlap. I know overlap will be more than with the stock rockers but should be acceptible.

My concern is this. what is the maximum lift tolerable for pressed in studs with factory springs keeping in mind that this is a mild cammed engine turning low rpm? Should i need to put screw in ones for only .455lift? I dont want to take the heads off again.

alvanwie

I would not think pulling out studs with stock valve springs should be an issue.

UnderCover89TBI

iTrader: (25)

But if you change to aftermarket springs thier could be a problem? I was going to do valve seals, pop in new springs, retainers etc while there and do 1.6 RR on it.

JeepYJv8

Im glad i found this today. im running l05 tbi with swirl port heads in a jeep (cause i love the torque). also 12-249-4 cam with upgraded springs. I was just going to buy some 1.6's and slap them in there. I take it this wont be good?