Stock tbi issues (cam related?)

A friend of mine has been running a stock tbi setup on his 383 suburban for a while now. About a month ago he blew a head gasket and opted for a delta cam.

That cam rounded itself out, delta looked at it and said it was their fault. To make it right they have him a new cam that was slightly more aggressive. Now it barely runs and we think the cam is at fault (very lopey idle).

We checked the basics. Compression is about 180 dry on all cyls, good spark, getting fuel, but needs lots of advance (+20 deg static) to get it to barely idle. We havent tried to move it yet.

So my question becomes: is 220 duration @ .050" and .453 lift too much for a stock tbi feeding a 383? and if it is, what can we do to make this streetable (preferably without swapping cams again)

Thanks guys (types from my phone, sorry if it's choppy)

Bump to catch the monday traffic

From what I have read, that is right on or slightly past the edge of what TBI seems to generally be able to handle. that said, I don't know if my information is true or not. LSA can have a decent impact too - lower the DCR too much and you will need a lot of base timing to make it idle. IIRC the TBI works better with a larger LSA (112 degrees or so).

That's kind of what I was thinking too... (on the edge or slightly over what it could handle), unfortunately I have no idea what the LSA is on this cam It's a Delta Cam 274 Grind # 268 if someone might have better luck finding specs than I did.

I sent an e-mail to TBIChips as well. We'll see if they can come back with something.

Thanks!

No helps input, but Brian at tbi chips is very helpful.

Nothing to add, but this is the setup (383 on TBI) I want to put in my truck someday. Watching with interest.

Got news back from Brian (and he didn't disappoint)

Brian @ TBIChips.com said: yeah, too much camshaft for TBI. I likely would not have recommended the next smaller cam in a suburban either. not building a race car. 6500lb suburban needs all the low rpm torque you can get which is why most do build a 383 but way too much camshaft for a heavy suburban. I would have recommended the GMPP HT383 roller cam as you dont have to worry about that cam lobe wear with roller cams and the powerband of 1000-4200 rpms is very similar to stock powerband for strong low rpm torque and I would have recommended the vortec heads to clone a GMPP HT383 crate engine. Which makes good horsepower and great torque. FAR better than the stock 180hp 265 torque 350 TBI motor. But stock 350 TBI heads if that is what is on this 383 is going to make close to 75hp less power and 40lbs less torque than the vortec heads. but trying to run a 6000 rpm 220 duration camshaft is just going to be miserable. Cam wont make enough vacuum below 2000 rpms for TBI to control the fuel properly and the low vacuum at idle will cause the TBI system to have stalling issues as well as the fuel control issues at idle and NO ONE should have recommended to this friend to put this much camshaft in a suburban or in any TBI fuel injected vehicle.

Thanks guys, and good times

Yup. That's Brian. Brutally honest.

Just saw this but thought the same. Why? TBI's make their power down low, where a 383 can augment it. Putting that cam in was a bad idear

Here's some more on the subject from Brian (just for thoroughness). I asked if the owner were to opt for the HT383 cam, if Brian offered a tune that would compliment it:

Brian @ TBIChips.com said: depends on the rest of the build. compression ratio is always a concern when downsizing cams. If the motor was properly built for the bigger cams then it could be too high for the milder duration HT383 cam. have to be real careful on that especially with obsolete iron head technology. aluminum heads much more forgiving on that compression ratio. But once all the details are ironed out, should be able to do a chip with no problems. If the motor has roller cam provisions then i certainly recommend going roller. flat tappet cams are obsolete as well and they are technology that should be allowed to die. I hate the things and that was before oil companies removed zinc phosphate from modern motor oil. Roller cam parts http://www.summitracing.com/parts/NAL-12371042/ http://www.summitracing.com/parts/NAL-12371043/ with pushrods http://www.summitracing.com/parts/hrs-95201 for cam the 3 I recommend running all the time are http://www.summitracing.com/parts/nal-14097395 http://www.summitracing.com/parts/cca-08-409-8 http://summitracing.com/parts/lun-20080660 but in a heavy suburban, that GM HT383 cam really does well. Brian Harris Performance, LLC

I owe this guy a beer.

and one more follow up:

Brian @ TBIChips.com said: I like the HT383 cam but I would have ditched the stock heads for http://www.summitracing.com/parts/sum-162108/overview/ which would be capable of 340hp and 440lbs of STRONG low rpm torque.