I was told and from the way it looks you can not use much cam with a TBI unless there are some tricks you can do to change PROM etc. Comp Cams list computer cams all with 4 degrees advance and 112-114 LSA, but all the better HP cams are listed TPI not for TBI. Crane Cams list a 2050 and they were just talking about Compression ratio's and not sure if that will help as I assume it's vaccum that throws MAP off on a TBI.

Maybe this is a dumb reason, but we wanted a cam that not only ran well but you could tell it had a cam, not a mom's tight idle etc. No offense, since I have know some mom's that ran some impressive big blocks etc, but it's just say the average mom's car.

I looked at XE262 which has a 4 degrees advance built in as most Comp Street cams do and they also have a Marine version with about 2 degress advance built in and wondered if that would effect things much. Is it that hard to get a computer PROM to work with a good HP cam? Using a Roller 4 bolt main block, but presently been trying hydraulic cams, because of cost. There are some hydraulics that have 460-480 lift and with 1.6 rollers would run very well if TBI could be used to run them, 68 injectors and will be about 600 CFM when done on TBI, springs are setup for up to 540 lift.

Lunati offers a few with about 217 duration and 454 Lift 600 RPM Idle and 17 Lbs vaccum. I was told at one time by Turbo City that not to exceed 210 duration and look for a 112-114 LSA on TBI cams. Why are TBI's so touchy compared to a TPI? I ask this because it's very expensive to get a TPI or Command 950 system for 350 even if I like the looks of Holleys Stealth Ram etc, again, there very expensive and about prices of a street supercharger.

Truck's had a lot of work done such as Phatom Grill, Cowl Hood need TBI air cleaner to use right, Rear Fenders cut and molded 4" extended fenders, running 345x55x16s that replace MT 15x29x15, loved Mickey's for looks but it was tight and barely rubbed. Point is truck looks and has setup now for Air Ride all around, but I just don't use it because it's frustrating. It had a 4.3 z motor and now a HP 350, but it does not run like it should. Want more HP and torque and thought well try 350, which will leave option for a 383 later.

Are TBI's that restrictive, or do I need more program knowledge? Is it a waste of time or can it be done? Can seem to get even a 268 duration let alone a 270-280, but I am told TBI's will run or is it because others use a Holley TBI etc? I may see if I can modify Edelbrocks 1000 CFM air cleaner to fit TBI depending on size of air cleaner which would get some cool air from Cowl hood, but cam, I am not sure what's up with that at all. Any ideas? HP TBI's out there? Please let me know what you did if there are any out there?

Presently running a 350 4 bolt main, HYP F.M. Pistons H345NP40's, New cam bearings rebuilt motor, balanced used ARP rod bolts, resized rods of course, comp cam 12-402-4 212-218 444 lift (Maybe could of used more lift Exh?), 1.6 comp rollers, flow master 40 dual outlets front of 345s, single 3" inlet, highflow cat, 4L60E tranys, 3.42 rear end. Have SR 1.94-1.50 76 cc head, told when got them they were torker 2.02s, anyway I pulled heads using a Fel Pro 1094 gasket for better quench/compression. Consider shaving heads but local shop does only about .020 as they are not setup for manifold side work, way in country. Have a set of torker 67cc BARE-Heads which were suppose to rull replacement for Pro's SR, which I may use later when I get valves or kit promised. Need more HP and performance, which compression and changes will help some, but I am looking at other options and trying to figure out this TBI issue. Sorry it's this long, but writing is not a well learn skill for me but trying!

 

I ran a Comp Cam 270 in my 355, and ran mid 13's.

The bigger the cam the more the effort to get it right. And the window for what is right gets smaller.

Work on reprogramming what you have while it's stock, and then when it comes time for the big cam'd motor things will be almost second nature.

 

i have decided on comp cams 268-4 224/230@ .05. 114 LSA. 5800 rpms. with this i think i need diff gears. will go 3.55, since now at cruise speeds(72mph/ 5th gear ) i am tach at about 2000 rpms and that may result in surge during the cru9se mode. i experience that now in 5th at about 1600 rpms or 55 mph. if i experience any surging at idle i may disable closed loop and try open and tune A/F with my wide band 02 and or smell. i think this may be max cam i can run with my limited tuning experience. others may have run larger cams with success. that cam should compliment my other mods and make it a balanced package. i think the issue with TBI may be the map sensor rather than TBI in general. i dont know much about MS other than seems GM has one and only and we all use same.
Air cleaner? the one i found to fit is the edelbrock oval.

 

Pretty health cam as 270 cam is 224 @ .050 mentioned by Grumpy if it's the one I think he's referring to from Comp.

Even 218-224 with 112 or 114 LSA and 2-4 advance built in would work from Comp as 270 magnum should be and sound health in a 350, not sure about 383-I would of been happy with that.

Summit even had a 282 114 CL cam that seem interesting and more lift, not sure who makes their cams. Lunati Bracket Cams seem cool!

It sounds like XE268H is what you are using, nice lift of 477-480 with 1.5 rockers. Once you get it worked out, it should cook and closer to what I use to use, know small blocks will have a little less duration then 290-295's that I ran in big block, but 260s seem way to low with less HP gains unless setup wrong or issues with MAP. I was told a different MAP from another year may work (Buick forget though), but it's a patch like trying an adjustable MAP.

Problem I had was vaccum with cam I had only a 212-218 @ .050, but I had hoped Pro's new heads would change things 67 cc, bummer no valve or valve kit. Checking on milling heads .020 (76cc'x) and Fel Pro 1094, .015 gasket vs .041, just checking on if there will be an issue with intake surface and trying to find a Manifold Gasket for Aluminum Manifold WITHOUT exhaust crossovers. Good luck and guess I will have to get a cable (ALDL/Computer) once done and see what I get if winALDL will read ecm (Service # 16168625) and consider Tunercat etc. Thanks and good luck!

 

With big cam tbi's it gets hard to get smooth accelleration under big loads, at low rpms. The AE stuff in the prom has been the hardest for me to nail down, at low rpms.

 

same here but not a big cam. i attribute it to design of xram and atomization issues. i added more AE at 10% increments and it helped. cool weather was also an issue. with my changes 4/04 i should be improving that. that cam i am considering will possibly also need 3.55 gears to help acceleration with AE pump shot.

 

added sig

 

Too much air filter can make things even worse.
I wound up running best with a 2.25 or 3" max 14" filter.
When I ran a 4" I built a little ring that sat on top of the throttle body and extended up an 1.75". So that the gap from the ring to the air filter lid was the same as if I was running the 2.25 air filter. But, I got the benefit of the greater filtering area.
It was just .030 brass sheet stock, and then some 1/4" chicken wire on the top of it that fit against the housing lid, to keep it in place.

Ever notice that *ring* on some GM air filter housing?. It's a clever little deal. It gets the air organized above the *venturis*.
That way the air goes past the butterflies in a more predictable manner.

the thing about air flow is that it's easy to get caught in the if a littles good, too much should be just enough, and it don't work that way all the time.

 

The longer the spacer the more harm you are doing to total mass air flow. Raise it up too much and the injector pod takes up more space resulting in more pressure drop at high load high engine speed. I have a datalog somewhere around that shows a 3kpa drop difference and that was with the stock ring vs no ring and with the Holley 670 with the small injector pod. 3kpa is very little but with my engine and a GM pod I bet that number would have been higher.

 

How do explain dropping .2s?.
You can look at individual elements, and analyse them, but it's the total package the matters.

The intake tract is all about little tweaks, and finding out what works. By dampening the air flow and using less AE, the car was quicker, .2 is a worth while amount. It may or may not help anyone else, but for 50 cents worth of brass it's worth trying.

 

That's impressive. Do you have lockers data for those runs?