That perspective is the major problem, or source of confusion w/this thread. It isn't really a CFI vs. TPI thread....at least I don't consider it to be. What it is, is a (And it's been said multiple times, but here goes again)...

It's a "Don't waste money coverting to stock TPI, because the gains aren't worth the money or effort" -thread. To wit (and I quoted this before):The problem (again) is that people repeatedly say that since you "start out 25 hp ahead" w/TPI, everything you do from then on, you're "25 hp ahead", and that just ain't true. Especially when money is involved -and it always is. Again the only reason why TPI starts out 20-25 hp ahead (long blocks being equal) -and it does and no one has denied that, is because it has full sized port cross section. The CFI as cast, does not, and there is your 20-25 hp.

 

Thank you.

 

 

I love this thread. here are some pix of a verry rare crossfire.
its a 83. I bet you dont have one.





notice how it has the 82 style air cleaner? thats because this car was a 83 pre production model, that gm showed the guys at mattel so they could make the hotwheels version. the base of the car is copyrited 1982 and the car is genericly labeled 80's corvette

just thought id share. I picked it up at a thrift store for $1.25
long live the crossfire !

 

also noticed on the matchbox car it looks to have t tops rather then a targa top.

 

My car was built in June of 1983. Doesn't that make it an "83?

RACE ON!!!

 

Naw, the glass top's just cracked.

 

Well thanks for clearing that up. Either way, I wouldn't complain. TPI or CFI, you'll make good pulling power with either. And I do agree, the CFI seems to have some thrift saver type modifications you can apply. I actually am very interested in learning more about the CFI system.

Use to have a friend who squeezed 300+ hp out of one in his 84 but I guess when he took delivery of a 383 LT1, he didn't think twice about plucking the cross fire out of the engine bay. No doubt, the 84's get a bad rep from an engine that will be a reliable daily driver and good performer with the write homework and effort.

I don't know if anyone else has ever listened in on an actual conversation about CFI but I had the pleasure (or lack of) to hear one at a Corvette repair shop by some guy who had been bitten by the speed bug apparently. He just kept going on and on about how 205 hp just wasn't cutting it and he had to get in something faster. He just kept going on and on about how lacking the engine was. He ended up leaving and the mechanic he talked to just shook his head and told me he gets that kind of talk about the CFI all the time.

By the way, loved that nitrous set up for that CFI in that picture! I also didn't know the CFI manifold port could allow 5500 rpm area gains in the engine. All this CFI talk makes me want one so I can see how much I can work out of it. Personally, if you do these right, they really are the ultimate sleeper engines of the Corvette world.

 

I'll sell ya a ported CFI intake for 200.00+shipping. I gained 4/10's in the quarter. That's a definative hp gain. usable rpm's climbed by 400.

 

"(long blocks being equal)". The only difference in the 1984 and the 1985 long blocks is the camshaft. Other than the "stick" they are identical.

Any one that has pulled the intake off of a Crossfire, with an eye on modifying it, knows what you've said, Tom, but I don't think I have ever seen it written, expressed, or posted in those words before. Excellent job!

Additionally, it is too bad they didn't put more meat in the casting when they designed it. With a little bit of material to work with, that manifold would have the potential to be a screamer.

RACE ON!!!

 

I got that Hot Wheels Vette too lol My mom got if for me in 1985ish. Its sweet

 

There really isn't much to learn. There are hundreds of thousands of 350 CID (and 305s), 2 bbl TBIs running around. That is basically what the Crossfire is, except the two barrels have been separated and moved to the opposite sides of the engine. It is a big mystery and black magic, until you think about it and break it down to the basics. No big deal.

RACE ON!!!

 

Even the Cams were the same.403/415 lift. The only difference in the 84-85 long blocks was that GM used TRW forged flattops in the 84's,that were leftover from an earlier program .Not all the 85'sgot them.

 

Quote from my April 1989 GM "1984 - 1989 Chevrolet "Y" Parts amd Illustration Catelog.

"Group .0519 CAMSHAFT, Engine:
84........Y (5.7-8)....14088843 CAMSHAFT.
85-86...Y (5.7-8)....14094728 CAMSHAFT.

Group 0.629 PISTON, Engine.
84-85...Y (5.7-8)....474190 8 PISTON, (STD) 3.9980-3.9990 DIA."

1984 to 1985: Different camshafts; same pistons. If the pistons changed during the 1985 model year, it isn't indicated in the parts book. The '86 used two different pistons. One for iron heads and one for aluminum. Neither was the same as the '84-'85. Both were cast.

RACE ON!!!

 

For those of you that never pulled a Xfire manifold, here's how it was handicapped by GM. Like a NASCAR restrictor plate.
Port matched runner vs Stock.

 

It really isn't just a matter of manfold port size that accounts for the 25 HP. CFI sprays the fuel on the throttle plates, like a carb. TPI sprays the fuel into the intake ports at a higher pressure. This is why ultimately TPI can produce more HP, even if it cost $$.

 

Whaaaa???!

What some of us here are trying to demonstrate is that the stated difference in hp between the 84 Xfire and the 85 TPI motor basically comes down to the reduced cross section found in the stock Xfire manifold. Although I would agree with you regarding the superiority of TPI v TBI, in this discussion the point is not relevant. In contrast to your point, the TPI motor with superior fuel delivery manages to produce only 25hp more than a motor utilizing an inferior fuel delivery system and significantly restricted runner size.
I suspect GM used TPI primarily due to emissions and not power considerations. If you read Car Craft, everybody makes more power using a carb instead of EFI on similar motors.

 

Had a guy challenge me in my '84, he in his new S600 V-12 Mercedes. He won't try that again! (It was just a short race. I'm sure I'd loose on the Autobahn!) Talk about the most bang for your buck!!!

 

That is so wrong I can't belive that you typed it (or think it). Go back to automotive school, before you spread more mis-information.

 

That is absolutely, 100%, totally WRONG! 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. But that isn't the way it worked between the 1984 and the 1985 Corvettes. The difference in the power is 99% air flow not fuel flow or distribution. If what you say were true, porting the Crossfire still wouldn't, and couldn't, allow the Crossfire to keep up with any TPI. There are too many ported intake Crossfires running around out there proving you wrong. If GM built the CFI with the same size ports as they did the TPI, they wouldn't have been able to sell a TPI until years later, with aluminum heads, higher compression, roller cams and more advanced electronic controls. For a professional claiming to know all Corvettes, you sure missed on that one.

RACE ON!!!