Paul,

Not looking to pick on you, but this is the kind of dis or mis information that continues to be spread about the Xfire and particularly the 84.
Put the same motor in an 82 and all of a sudden its a "collectable" when in fact the 84 would destroy a late year C3 on any track.
This is what gets people like CFI, Tom and myself really tee'd off.
And we've been trying for some time now, apparently with little success, to straighten out people who really don't know what they're talking about. Go to 3rdGen.org and see what people have done with TBI motors. Should open your eyes a bit.

 

i keep seeing this statement about "if CFI had its intake ports the same size as TPI it wouldve been faster"

somehow, however, when you CFI guys are porting your Xfire intakes, i doubt you call it quits at the stock TPI runner size and opening. id be willing to bet you take it a bit further and at least port match the intake to the heads (which im sure a stock 85' wont have) and claim that "things are equal now"

has anyone ported their intakes to an actual stock size TPI manifold port size and left it at that? thats really the only way you could do an actual comparison between the power output between the 84 and 85

 

this isnt a bad point but i dont think anyone has stated how they have ported thier intakes other then cfi-efi stated he has extensive porting on his. and you may be right about the porting to the head. however i think the main point is with a lil time and effort and little $ spent the cfi intake can perform as well if not better then a stock tpi on the same motor not whos intake is ported the best. meaning the cost of swapping to a stock tpi system is a lil steep for the amount of gain you get from it. obviously a mini ram or super ram or some other aftermarket tpi system at the least should flow better and give better results.

 

TPI motors are also Batch Injected. For anyone unfamiliar with this, the TPI setup fires all four injectors on each bank at the same time, right in front of the intake valve. So basically when #1 cylinder is on it's intake stroke, and the #1 injector fires, so does numbers 3,5&7 injectors, regardless of what position those cylinders are in, leaving the fuel charge to sit there, stagnant, until the intake valve opens. I'm not sure which system is better as far as power is concerned, but at least a CFI system fires the fuel at the throttle body area, allowing the fuel to atomize and gain some velocity through the intake, before it reaches the combustion chamber.
It wasn't until the early 90's, I think, when sequential injection was introduced, firing each injector individually.

 

most CFI people port match to a typical 1204 gasket. Not much better than the TPI port.

 

Dominic,
Your picture shows the obvious reason the CFI is restricted. However, you failed to show, as Paul Harvey used to say..."The rest of the story". Match porting, which may or may not be an advantage over a stock TPI, doesn't solve the problem of the port size from one end to the other, from the head to the plenum. The Fel Pro section in the Summit catalog lists a stock SBC port as 1.23" X 1.99". Here is a cross section of a CFI intake manifold. Not only does it reveal the size of the "peanut" ports, but you can see the limited potential for making them much larger.



As you can see, the CFI port is barely taller than the WIDTH of a stock port, more than 5/8" shorter than stock. The outside of the port casting is only about 1 3/4", less than the height of a stock port.

RACE ON!!!

 

Look at the picture I Just posted, above. The port opening on the ported CFI manifold may be larger than that of a stock TPI manifold, but the runner sizes are still smaller.

It would seem that if the CFI and the TPI manifolds had equal runner sizes and port openings, the TPI should out power the CFI. The logic being the superior (admittedly) port injection. However, I feel the long runner length of the TPI limits the rpm capability, and therefore the horsepower production capabilities, of the TPI.



Yes, I have ported my manifold extensively. But for the non-Crossfire tinkerers, who are until now, unfamiliar with what the manifold looks like, "extensive" has some severe limits. To those that have done some grinding on their own manifolds, a 3 pound coffee can full of grindings may mean more than to the rest. The port matching, which is all most do, is the easy part. "Extensive" applies more to the effort and a somewhat greater amount of metal removal, but as the pic shows, there isn't a whole lot to be removed, in the first place.

RACE ON!!!

 

Unfortunatley, you are MORE wrong than you know or that you post implies. MOST people open JUST the last inch or so of the CFI runner, opening up just the end to the same or similar size as the head. Then they call it quits.

Those people (the vast majority) do not touch or at best, only smooth casting blems in the rest of the runner. CFI-EFI, Myself, and Dom are the only people (that I know of) who have opened up the CFI intake FOR THE ENTIRE RUNNER, enough to make a meaningful difference. Out side dimentions of the runner limit how large you can go to around the same size as a TPI base. So has anyone ported their intakes to an actual stock size TPI manifold port size and left it at that? I doubt it, due to outside dimensions, but CFI, myself, and Dom have sure tried, and we ended up with "TPI" or better power, for nothing but effort. When I was "done" w/my car it was making ~320 hp through the CFI intake and the long block was FAR from ideal.

I thought this thread was done when I said:
....but the poeple who have never had their hands on a CFI intake continue to spew garbage.

 

You guys are wound way too tight. First you tell me I'm 100% wrong and then you go on to agree with me. "a more controllable system for better emissions, milage and power" That's what I'm saying. I said it isn't JUST about airflow, got it? You guys start to sound like a bunch of consiracy kooks. Yea, GM held back the TBI so they could force TPI on an unsuspecting public!
The idea that a ported TBI couldn't keep up with a TPI is nonsense as you've proven. You guys must not be aware of the simple fact that an L98, even with fullsized ports, didn't flow very well, that's why there are aftermarket manifolds. As CFI-EFI says and I agree is that having 8 injectors instead of 2 is ultimately better on all counts and that's all I'm saying.
Look I've been working on cars for a living since before these cars were new. TBI was an inexpensive way of controlling emissions which was the biggest concern at the time. TPI requires more computing power which is why it came later. Ultimately everything is a compromise between emissions, power and milage and TPI does a better job.

 

I don't think that anyone is "wound too tight"
That is true, but that is NOT "all that you were saying". You said:...and that statement was just flat out wrong. Whether you actually thought that, or maybe that's just how it got typed out, the above quote is wrong, and that is why you got a bunch of reaction.

 

Paul,

In that case, you would know that TBI has been used by GM well into the 90's. As for the "computing power" necessary to drive TPI, the early TPI ECMs weren't any different in capability than the TBI ECMs.
The C3 ECMs primarily used 4k bins. They just had drivers for 8 instead of 2 injectors. That's why the early TPI systems were "batch fire". Each side was treated like one TBI injector. And GM flip flopped between MAF and SD systems for a few years. The most sophisticated motor GM had ever used, the the LT-5, is an SD motor just like the Xfire.

No one argues your final statement here. But your initial premise was wrong. Just admit it and us 'wackos" will leave you alone.


Tom,

For purposes of accuracy, I did the port match, cut back the top of the runners about 3/4" and had the runners Extrude Hone'd.
At 3450lbs w/driver and a 104.6mph trap speed, that works out to about 310 rwhp. Not too shabby even for the small xsection.

 

I am going to have to start using shorter, easier to understand words or more sentences to explain concepts to those with comprehension problems. People keep reading into my posts, things I haven't said.

But it is. You are wound backward. Your statement IS wrong, and I didn't go on to agree with you. You said, "It really isn't just a matter of manfold port size that accounts for the 25 HP.". That is where you are wrong. I won't repeat all the descriptions and pictures of the ports. But the ports ARE exactly the reason for the difference in power. Fuel hitting the throttle plates isn't killing a lot of power.

When you quoted me you left out one VERY important word. You said that I said, "a more controllable system for better emissions, milage(sic, nor a direct quote) and power". What I really said was, "There is no question that an injector in every port is a superior, more sophisticated, efficient, and ultimately a more controllable system for better emissions, mileage and power.". You chose to start your quote of my statement after the word ULTIMATELY which was italicized in my original statement, to emphasize it's importance. Yet you chose to omit it. As my statement, taken in it's entirety, says, the TPI is a better design. ULTIMATELY, down the road (from 1985) it has the POTENTIAL for better emissions, mileage and power. As presented, the early TPIs had little performance to offer over the CFI.



That IS nonsence. Who said that??? The fact that a ported CFI (TBI) can keep up with and surpass a TPI is the proof of my point. You seem comfortable admitting it. Now who is agreeing with whom?



Apparently you didn't read or you have dismissed what I wrote in post #147. "It would seem that if the CFI and the TPI manifolds had equal runner sizes and port openings, the TPI should out power the CFI. The logic being the superior (admittedly) port injection. However, I feel the long runner length of the TPI limits the rpm capability, and therefore the horsepower production capabilities, of the TPI."



Ultimately, TPI has (had) the potential to do everything better. In early production, it didn't. I don't think anyone is arguing that 8 injectors, one in each port, isn't a better idea. But, to blame the 25 HP difference between an'84 and an '85 on fuel distribution, is ludicrous. Even YOU said, "The idea that a ported TBI couldn't keep up with a TPI is nonsense as you've proven.". Since porting the CFI manifold allows TBI to keep up with TPI, doesn't that ALONE prove where the weakness is in the Crossfire system?

RACE ON!!!

 

OK, I'll explain my point, that its not just port size. Let's look at the numbers. 84-205hp @4000rpm, 85-230hp @4300rpm. I believe these are correct. Notice there is only 300rpm difference in peak hp rpm. If you looked at the hp graph of the 85, I'm sure it would produce more hp at 4000rpm than the 84. I don't have the info, but I'm sure this is correct. So if you have 2 same size engines making different hp at the same rpm there must be a reason. At the same rpm they are pumping the same amount of air, so the difference must be in the fuel injection system. As another case in point, compare a L98 to a LT1. Here you have 2 engines with basically the same type of injection, but the LT1 produces 300hp @ 5500rpm(I think). In this case the difference really is airflow, because the LT1 produces more hp a higher rpm(flowing more air). The LT1 intake, heads and exhaust flow much better than an L98. I'm saying if the 85 flowed so much better than the 84 there would be a greater difference in peak hp rpm. I don't think an 85 intake flows all that much better than an 84, do to its long runner length.
Maybe I'm 100% wrong or need to go to automotive school, because I think TBI sprays fuel on the throttle plate. I'm sure you guys can tell me why I'm wrong.

Have a good one, Paul

 

Now they aren't. They aren't because of the PORT SIZE. If they were pumping "the same amount of air" they'd be making the same amount of tq at that RPM (the RPM that you picked -4000)


Similar types of injection (multiport, but the LT1 (after '92) is sequential, not batchfire), but not similar INDUCTION...not at all. And that is where the HP increase is for the LT1; air flow. Just like the ported out CFI.

That's because you're not taking into account the runner length and tuned resonance of the TPI which hurts it above 3200 RPM



Well for one thing, when you're talking about max hp or tq, guess which position the throttle plate is in? Hint (WOT). How much fuel "hits" the throttle plate at WOT. You know how many carbed cars there are that make HUGE hp and tq? Fuel in a carb needs to pass the throttle plates too. Never hurt a carb much. The only time "fuel hitting the throttle plates" COULD matter, is at low throttle angles. And the fuel DOES hit the plates. Then it runs down the plates, and off the edges in to the plenum. The COULD affect throttle response, but doesn't seem to in the real world, and probably because programming "covers" that (w/a richer mix).

 

Nope. Not the fuel's fault. Unless you have a MAF unit actually measuring the airflow into each engine, you cannot make the claim that equal displacement engines can/will/do pump equal amounts of air. Two identical displacement engines can have widely different VE numbers depending on the differences in the induction system.

 

You are starting out with one foot in the grave. You are basing your point on a false premise. The '84 L83 is rated at 205 HP at 4300 RPMs the same speed you say the '85 L98 is rated.



That is where you start to err. IF they flowed the same amount of air their power outputs would be close to identical. When you port the CFI, they CAN ingest similar amounts of air and the CFI keeps up with (at a minimum) the TPI. The proof of the problem lies in the success of the cure. If the problem with the Crossfire was gasoline dribbling into the throttle plates, porting the manifold would have little effect. The point and the proof is in the success of the porting.

The comparison between the L98 and the Gen II engines is a poor one and moot. The L98 and the LTx engines are waaay different; heads, compression, cooling, cams, and even the manifolds. With the '84 L83 and the '85 L98, it is ALL about the intake manifolds... Nothing else. The comparison is a direct one on one with no other outside variables.



I agree with that. The '85 manifold doesn't flow all that much better than the '84. Only about 25 horsepower better. All the more reason NOT to swap a TPI on to an engine where A CFI once resided, which WAS the subject of this thread, 8 1/2 pages eariler.



One of the few points you've made that I can't argue.

RACE ON!!!

 

I could refute some of your points one by one, but I'm convinced that would be pointless. If you all want to believe that the only reason TPI makes more HP an torque than a TBI is the size of the ports go ahead.

 

Part numbers are changed many times over at GM for the same piece. The cams did not change.

1984-1986 403/415 lift 202/206 duration 114.5 LSA

1987 A roller but: 403/415 lift 202/206 duration 114.5 LSA

1988-89 415/430 lift 207/213 duration 117 LSA

1990-91 413/428 lift 202/207 duration 114.5 LSA

These are the cam specs for all 92 C4's. Part numbers are know to be superceded when there are changes in delivery, manufacturing, or any of a number of reasons not relating to the actual part and its specs.

1984 C4's used forged pistons. I know this to be fact since my L83 is now disassembled. Replacement parts may very well not be forged. They really weren't necessary.

 

I agree that part numbers change. However, they never go from being the same as something else, to being different. I have the 1984 and the different 1985 part numbers. Possibly YOU are looking at and citing specs for a superseding part number, but the numbers I provided are from the same page of the same publication. In fact the 1985 camshaft is shown directly below the 1984. It wouldn't surprise me to find out that the 1984 and the 1985 camshaft part numbers became consolidated into one part number, down the road. As further evidence, the '84 and '85 cams are different, my FSM lists the lobe lifts of the 1984, L83 camshaft as .2733 intake, and .2820 exhaust. Lobe lift multiplied by the 1.5:1 rocker ratio gives the valve lifts as 0.40995 (call it 0.410) intake lift and 0.423 exhaust lift. If the cams are the same, why are the lifts different?



Agreed. Your information reflects exactly that. Part numbers can become consolidated, as you show. They don't become divided as the parts book shows.



Again, I agree. The 1984 pistons were forged. The 1985, as my parts book shows, used the same part number forged pistons as the 1984.

RACE ON!!!

 

Your reasoning HAS been disputed, point by point, by several different persons. You have admitted to the truth of some of the points that prove you wrong. You deny the logic that has been presented against your position by multiple sources. It is obvious, due to your blanket, unsupported denials, that, clearly your mind is made up, and you refuse to be swayed by facts. Due to that mind set, further attempts to help you see the light, would be futile. Enjoy fantasyland.

RACE ON!!!