TBI camshaft?

[spudz]

I am building a motor for a TBI truck... Its a 30 over 350 with factory flattops. I am looking for a good camshaft for it... I want something I can hear but isn't gonna mess with the computer. Anybody done a cam swap with a TBI motor?? I was looking at the cams on the Comp cams website and it looks like reguardless I am going to need an chip.. What one do I need?

[wicked_sky_gazer]

Originally Posted by spudz

I am building a motor for a TBI truck... Its a 30 over 350 with factory flattops. I am looking for a good camshaft for it... I want something I can hear but isn't gonna mess with the computer. Anybody done a cam swap with a TBI motor?? I was looking at the cams on the Comp cams website and it looks like reguardless I am going to need an chip.. What one do I need?

Dunno if its along the same lines but before i use a chip i would look at a hypertech system, you can re-program them for different ranges and uses, i used one in my '99 tahoe with the vortec 350 and it was amazing to the point that i am updating my elec and control system to 99 so i can still use it.

[rfmaster]

spudz

Before a camshaft can be be recommended you need to supply a bit more information.

Truck weight, 2x or 4x4
Engine static compression (if known, estimate)
SBC - flat tappet or roller?
Intake manifold - stock TBI, after market TBI, or carbed with adapter plate?
Heads - stock, reworked, after market??
Exhaust system
Transmission, converter stall speed
Rear end ratio, tire size.
Cruise RPM range for 65 MPH
Daily driver or weekend warrior
Emissions testing in your area or MPG goals

It is too easy to recommend a cam, but a right one requires some thought and careful consideration...

//RF

[Pyrotechnic]

There's not a whole lot you can do without a reprogram. I've heard of some success with the Edelbrock Performer grind. Sometimes if it's just a mild cam without a bunch of overlap you can experiment with raising the fuel pressure slightly to get things right.

If you want a radical cam with a lumpy idle....forget it without a reprogram.

I wouldn't buy a chip that someone made without even seeing your vehicle. Sure they can do some calculations and get close, but it's not going to be optimal.

[jeffspower]

No programmers for TBI- chip has to be burned. Unless you swing the bucks for Tunercat (or similar) that you use on a laptop to create your own chip, stay with a cam just over stock with a smooth idle. Anything with a noticable lope & a stock chip can't run it worth a darn. And IMO, purchased custom chips for custom engines are a waste of money, and can be worse than stock.

[spudz]

ok its for a 89 2500 LD 2wd. the truck is all stock. The motor should be around 8:1 I guessing and is gonna be flat tappet. Heads are stock with a fresh 3 angle valve job. Don't care about MPG and we dont have emmisions testing or inspection or whatever. I just want a decent pulling motor that sounds great.. I guess if I gotta take it to a shop to get a custom chip burnt I will. Oh the truck is gonna have long tubes and true duals. BTW I want to get the whole kit with springs etc.. And whatever ratio RR they recomend.

[Billla]

I talked with a friend of mine that does a lot of EFI swaps - his advice was either to drop it in unmodified or give it a miss. It's possible to upgrade the socket for programmability and/or have a new chip burned - but it's not trivial and it's not cheap. The last very custom tuning and burn that he did was over $1,500 in time and materials (!?) "Generic" tunes go for around $250 and as jeffspower noted they sometimes aren't very effective.

Just one opinion - not my area of expertise but I do completely trust my source

Note that the later model ('94-up) OBD I and II stuff is a different deal entirely. There are a ton of tools out there for tuning and many good tuning shops.

[Pyrotechnic]

It's actually more cost effective to buy or build a Megasquirt. The biggest reason is that it interfaces directly with a standard PC. The software is 100% free. No ridiculous or outrageously priced licenses, no BS. You plug it into your computer and start programming. You can do trial and error tuning on the street, or go buy some dyno time and tune it there.

It can control nearly any injector configuration, from TBI to true multiport.

It can also control a 7 pin HEI distributor to give you a computerized timing curve just like the stock GM system.

[Ol'Rover]

if your going to change the cam, you will have to change computer settings unfortunatly.

[spudz]

I am really second guessing myself now... I may call the junk yard an get me a low miles junk yard motor...

[rfmaster]

Hey spudz

An ECM EPROM reprogramming is required if volumetric efficiency of the modified engine is outside ECM fueling adjustment range. An internal combustion engine is an air pump which happens to burn fuel to operate. Changing camshaft, exhaust system, heads, intake manifold, etc causes changes in its volumetric efficiency (VE).

As it happens to be TBI system used by GM in our trucks is rather adaptable, given that you do not exceed adjustment range limits built into ECM firmware. With that said lets take a close look at your combo, which is aside from a free flowing exhaust is close to stock. A stock '89 ECM has (probably) service number 1227747 with EPROM having broadcast code similar ASDU or ASDZ or equivalent. These combos are very common and well know to TBI tuners. In your case, you have a heavy duty truck that needs the low end torque to get things moving, and not high end HP (F-body or Y-Body). Truck TBI setup uses MAP sensor to determine a better part fueling strategy. The biggest issue with after market cams in TBI setup is excessive cam duration, overlap and LSA. Large duration cams sounds very loppy and have lousy idle qualities due to low vacuum. For example a stock TBI will idle around 600 RPM (in gear) and have about 17 to 20 inch-Hg. Larger duration cam will have 800+RPM idle and about 10 to 12 inch at idle (on a good day). Such cam will not work with TBI nor will it work with your low compression motor (no low end power). Which brings us to overlap and LSA. Overlap should be kept relatively low and LSA should be above 112 degrees for cam to work with a stock TBI EPROM. Stock TBI cams are puny - in a stock 350 (LO5) TBI truck engine has 8.3:1 compression and was rated 210 HP. Camshaft has a small duration (I/E @0.050) 194/202 and lift of only 0.385"/0.403" with LSA 112degrees. A stock ECM has an ability to adjust fueling if it is able to enter close loop operation provided that VE of your engine is not too far off programed parameters.

As far as cam recommendations (finally)
I have seen good performance reports about couple of Comp Cams

1) 12-231-2 grind #X4250H with duration @"0.050 206/214, lift 0.432/0.453 and LSA 111deg
2) 12-388-4 grind # 252AH-12 with duration @"0.050 206/212, Lift 0.425/0.440 and LSA 112deg

Both of these cams can be (according to posts) used without resorting to EPROM reprogramming, but for best results a custom EPROM should be burned.

MAIL ORDER CHIPS DO NOT WORK - at best it is a guess work. No two engines are the same.

If you are willing to learn (and please do not pay $250 to a snake oil salesman) - you can burn your own chips (not as expensive as you may think), but that is a subject for another post all together.

//RF

[BLE 'BURBAN]

Check out www.tbichips.com

[Pyrotechnic]

This cam should work too:

http://store.summitracing.com/partde...2&autoview=sku

Has very similar specs to the ones posted about...maybe a little bit smaller. I read a post somewhere on hear stating good luck with it.

I also have a friend who swapped in a GMPP 330HP crate motor into his 94 TBI truck with no computer mods and it runs and drives just fine.

[Billla]

I'm learning a lot here - thanks, guys! As noted, this definitely isn't my area of expertise.

[spudz]

thanks guys this is pretty cool info