Computers, TBI and CAMS

[ftn96]

I've been reading ,my arse off the past week or 2 and have called the 3 main cam producers adn asked for CAM recommendations, and have gotten different info.
From what I understand, Computers react negatively to excessive duration and lack of lobe seperation.
Quick, review....Im combining a late 70's block with vortec heads, and trying to utilize a stock 90 computer and TBI.
Apparently the TBI can only handle so much flow, for obvious reasons. So this keeps me from going for top end HP, which I dont need anyway...
And the low duration to keep the computer happy is easy to find, but finding one with the right duration and the right lobe seperation is the problem. According to the tech rep at Scoggin Dickies, the smallest amount of lobe seperation I want is 114 degrees. There are not many cams out there with that amount of seperation. But the ones that you do find "usually" have a higher duration which "supposedly" freaks the computer out.....
So with 3 different recomendations, theya all had the same duration requirements, but the lobe seperation is where Im having a conflict. I have lots of options for a 112 lobe seperation as far as lift and duration, but to find one at 114 with the same or even close ball park specs is next to none.

SO, how important is lobe seperation to a computer? with a TBI for that matter???

Serious gear head answers only if that is possible.

Im thinking that the Extreme Energy. XE12-249-H is a good selection....
It fits the duration specs for a computer at 206/212 (actuall, not advertised) highest lift possible for the stock vortec heads without the spring upgrade, and a 112 lobe sep.
Would this be a good choice?

Are there any sites other than cam manufacturers that have good info on CAMS/COMPUTERS/TBI's?????

Still hoping the GOV'T will ban the use of loud stereos with RAP music.

<a target="_blank" href=http://www.mccords.s5.com/myk5/index.htm>NashvilleK5</a>

 

[Stoopalini]

The only input I can offer you, is that after a head and cam replacement on a TBI motor, a replacement chip for the ECM is required.
Some people get away with swapping heads/cam and keeping the stock chip; but most of the people I know have had to get chips burned for their configuration.

Did the companies you called mention anything about getting a chip burned for the configuration you are going for? I don't see why a properly tuned TBI system would freak out because of the cam specs .....

My $.02 ... hope it helps

Thomas.

-- '84 1-Ton Blazer --
When the goin' gets tough,
the tough go 1-Ton

 

[Nrose07]

Manifold vacuum is the biggest problem with cams and tbi units. Lobe angle seperation is a major factor in the manifold vacuum. The speed density system in a tbi has to have a min. amount of vacuum. If you don't meet it the you will have poor performance. There are a few ways to compensate, 1. Don't install your cam straight up. Advance it 4 degrees, and make sure it is, by degreeing in the cam. 2nd, have a custom prom burned, not a generic performance but one tailored to your specs. Hope this helps, Matt.

Displacement, cubes, and did you say you drive a riceburner???

 

[ftn96]

Ok, good info keep it coming....
For some reason I had gotten myself into the mind set of working around getting a chip made. I am however open to it other than the fact that its a little pricy and it may take several times of sending it back and forth to get it right.

I may drop back and just get all TBI spec stuff, like the TBI heads, Ebrock TBI intake, and Ebrock 3702 cam and be down with it, other than an extra point on the compression from the new pistons and the over sized bored.
With all that said and done I think I could get aroun all the computer stuff with easy and still have a motor thats gonna out perform what I have now, which is all I want, Just a little bit more. But never having built a motor before, I can use all the info I can get........

Thanks

Still hoping the GOV'T will ban the use of loud stereos with RAP music.

<a target="_blank" href=http://www.mccords.s5.com/myk5/index.htm>NashvilleK5</a>

 

[Thunder]

Here's what I know about lobe seperation:
The stock cams for chev computer engines range from 114 to 118 degrees seperation. I think you can go down to 112 with the stock chip, any lower and you will loose vacume and it will idle bad.
112 degrees will give you better mid range torque. 114-118 will give more off idle torque.

The stock chip will usually run cams that have under .045 lift. And durations under 214 degrees.

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<font color=blue>Nevada... Where the pavement ends and the west begins

 

[ftn96]

I was just sitting here think dahh. The heads I have on the truck now are the TBI ones. So going to a new set of them wont "really" help me much, other than I will need to have a set ready to swap over on the weekend that i would do this. So that leaves me with finding another set reworked or getting new ones.
So here we go again with more options and pointing me back in the direction of the Vortecs.
Maybe I'll say screw it and convert to TPI......mo money mo money, man the wife aint gonna want to hear that.

Still hoping the GOV'T will ban the use of loud stereos with RAP music.

<a target="_blank" href=http://www.mccords.s5.com/myk5/index.htm>NashvilleK5</a>

 

[dyeager535]

You could also consider running the entire TPI setup, to include the heads, right?

They obviously aren't as good as the Vortec heads, but you can get a complete TPI setup for about $600, minus the heads, and if you are getting that stuff off a complete motor (say, donor car) it shouldn't be that difficult to grab the heads for a "bit" more. Of course, getting "used" heads brings up its own set of problems, and I'm not sure I'd want to bolt a set of used heads up to a block, without at least having the block mating surface of the head checked for "straightness"

But its another option, that may end up being less than going Vortec.

Dorian
My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>www.dorianyeager.com/index2.html</a>
Why insist on counting when the ring gear has the tooth counts stamped in?

 

[BARRAZA]

The Vortec heads will not bolt up to the TBI intake. There is a new TPI intake that uses the Vortec bolt pattern but it's pretty pricey. BTW, the vortec heads are MUCH better than any other factory iron heads and better than many aftermarket aluminum heads, and they're cheap.

 

[BARRAZA]

Another thought, the vortecs are as much as 40 hp stronger than the 882 or pre LT1 aluminum corvette head using streetable cams, so you could probably take 5 to 10 degrees of duration out of the cam in equivalent motors and have the same power as the TBI heads with the bigger cam.

 

[CaptCrunch]

Boss and I are discussing this quite a bit in pm's right now too. Nrose is right... it is all about Vaccum for the most part as the TBI system is a speed density type system. 112 is the aftermarket recomendation for the most part. I would choose the cam guys you trust most and follow their tech advice to the T. There are adjustments that can be made to modify the computer's reading of the vaccum. Turbo city sells an adjustable Map sensor, but when I tried to get info on it from their tech email service the dude really didn't answer any questions or tell me exactly how much it will let you play. You could try talking to a place like fastchips.com about the issue as well, but again you will be at some mercy as to what mods could be done.

GM Perf parts does make an Intake for TBI to Vortecs... I believe Edelbrock does as well now. TPI is also an option. SD chev says with the vortech heads and their adapter manifold w/ a otherwise stock tpi unit, ecm, and chip it will make 300 hp, but then again I wasn't thrilled with their online tech either. They had a couple motors they said would make 300 or 330 hp with the stock TBI unit, ecm, and chip but I found that hard, if not impossible to believe. I asked a good friend who is the head of a GM parts counter about it and he laughed his tail off. He knows performance stuff too and all the crate SBC's he said are tested with either a 650 or 750 carb... the stock TBI uynit is rated at like 500 cfm. Holley does make a replacent TBI unit w/ 80 lb injectors and will flow 670 or so cfm. The word out there is they run rich on a lot of stuff that isn't modified and when i called them the reported it should handle a mild BBC, 383, or 400 motor just fine. It may need some fine tuning chip wise for injector width, but he also recommended playing with fuel pressure w/ a regulaor to lean or richen it first. I would make some PHONE CALLS or walk in to the head GM Performance parts dealer if it is nearby. Also I have found Pace to be the best IMO for dealing with performance needs such as this one. They seem very knowledgable especially on the vortec head swaps.

-Mikey
1987 Chevy K5 Blazer- 350 TBI
<a target="_blank" href=http://coloradok5.com/gallery/captcrunch>http://coloradok5.com/gallery/captcrunch</a>

 

[ftn96]

I've talked to 2 people that said they have the Ebrock 3702 cam working with TBI and it works great. I think I have all this dont to a T now, other than figuring out which path has the best output for the price.
If I decide to go with the TBI heads, what could I do to them for a limited amount of money to make them flow better? Basic port and polish job?

Still hoping the GOV'T will ban the use of loud stereos with RAP music.

<a target="_blank" href=http://www.mccords.s5.com/myk5/index.htm>NashvilleK5</a>

 

[Thunder]

I'm using one of turbocitys adjustable map sensors. Its the 3 position electrialy switched one. It does work as clamed. I am also using some of their other TBI mods and have been pretty happy with them.
When modifing a TBI motor you really need a scanner or lap top with software that you can get real time readouts from the diagonstic port so you know what the computer is seeing. Then make adjustments accordingly. I dont think there is any sure fire way to use the adjustable stuff without one.
That is how to make the adjustable Map sensors and fuel pressure regulator work the best.
I have talked to turbocity on the phone. On some things they have been real good on. but on others they have been kind of non comittal because of ths many varibles in engines. And I think they dont want to be accused of making false claims. Or violate smog laws( they are in Calif). Kind of like yeah we sell it but you have to figgure out how to use it kind of thing.
As for the flow thing. 500 CFM seems small but the TBI is a lot more efficient than a carb. Even a stock 350 TBI engine puts out around 20+ more hp than a stock carbed 350. So unless you are building a total race engine looking for high RPM power the stock TBI will work pretty good if modified a little.
There is some info on modifing TBIs on this page form Blazer pics

<font color=blue>Nevada... Where the pavement ends and the west begins

 

[CaptCrunch]

Thanks for the input thunder... My main question was how much can you veer from the stock like vacuum parameters with the adj. MAP. Kinda hard to choose a cam without knowing. So what cam did you change to?

And as much as you have praised the stock TBI... I won't buy it. It is a good system but it definetly has some things that could be much improved. Holley has addressed some of the problems in the tbody design with their new casting. Plus once you start modifying you will easily out class your injectors and run lean. Everyone makes a big deal about running lean on nitrious... well it isn't any nicer on a non-nitrious motor. Which ever post was talking about 383's on TBI taking a dump after 30 or 40k... well this is why.

I like a couple of Turbocity's product... the piece for the stock air cleaner assembly and the INJECTOR spacers are decent mods that have been proven power makers on the dyno. The TBI spacers are really iffy. Actually I have never seen a spacer similar in design to those make much more power. Spacers with a crossover passage on carbs I have seen make a difference on some motors.... and not do a thing on others... It really depends on the vehicle.

-Mikey
1987 Chevy K5 Blazer- 350 TBI
<a target="_blank" href=http://coloradok5.com/gallery/captcrunch>http://coloradok5.com/gallery/captcrunch</a>