Tuned Port vs Crossfire Injection

[Andy]

Laymans terms, can someone please explain the major differences.

Thanks..

 

[Jim Martley]

Cross-fire is a throttle body injection system. Kind of like a higher tech carburator. You have an air and fuel mixture moving from below the throttle body thru the intake manifold and then into the cylinder .

Tuned Port injection is where the fuel is injected into the airstream in the intake port area of the cylinder head. The manifold just moves air.

 

[Brianjt1987]

A tuned port system is much more efficient. It has a much more even fuel distrbution to all cyls. T/B's tend to have the cyls that are closest to the T/B run richer than the one's that are further away from it. Also there is no fuel puddling in a tunned port system as the intake & runners are not carring any fuel. Overall a much better system & IMO I think the TPI unit is one of the coolest looking engine parts Chevy ever made.

 

[patsnitrovette]

I switched to tpi and ill never go back to carb. again.

http://temp.corvetteforum.net/c3/patsvette/new_pics_466.jpg

 

[OldSkool]

Also, with the TPI cars, the long intake runners (one per cylinder, btw) that they came with from the factory allow these engines to produce great torque at low rpm. Although it hurts top end hp, all that torque makes them alot of fun to drive.

And by changing the runner length, you can move the hp/torque peaks up where you want them.

I had a TPI 350 powered Trans Am, and while the car was a rocket off the line, it ran out of breath at 4500rpm. IIRC, they were rated at 230hp and either 330 or 345 ft. lbs.

IMO, crossfire was just a gimmicky thing, while the TPI is a proven performer that is much more sophisticated.

I was just reading an article in GM High Tech Performance the other day, it was on TPI. This year marks the 20th aniversary of it, and the article talks about how it works and how to mod it. They also mentioned that first real street car with EFI to break into the 11's was TPI powered.

And yeah, TPI looks really cool too.

Mike

 

[geekinavette]

I don't think calling crossfire a "gimmick" is realistic. It is based on the late 60s crossram used on the Z28 302 engines, but uses throttle body injectors instead of carbs. The crossram design is a proven performer...GM just screwed it up with ridiculously small intake runners on the crossfire intake...and a big EGR channel that does terrible things to fuel distribution. If the crossfire intake had full size runners a stock TPI wouldn't stand a chance against it. I have been experimenting with siamesing a crossfire intake...and though I don't have any dyno numbers...from the testing I have been able to do I'd estimate mine is making somewhere just shy of 300HP...with 355CID stock bottom end, a "moderate" flat tappet cam, long tube headers, and stock heads. One downside to crossfire is that there is basically no aftermarket stuff available for it...and since it was only used for two years there isn't a lot of knowledge among mechanics.

What I think a lot of people fail to realize is that the return to the upward climb in Corvette performance started with the crossfire system. It deserves more respect than it gets.



Bill

 

[Andy]

Bill..thanks for the info. I need a bit more education....can u please explain the purpose of the runners and throttle body?

Andy

I don't think calling crossfire a "gimmick" is realistic. It is based on the late 60s crossram used on the Z28 302 engines, but uses throttle body injectors instead of carbs. The crossram design is a proven performer...GM just screwed it up with ridiculously small intake runners on the crossfire intake...and a big EGR channel that does terrible things to fuel distribution. If the crossfire intake had full size runners a stock TPI wouldn't stand a chance against it. I have been experimenting with siamesing a crossfire intake...and though I don't have any dyno numbers...from the testing I have been able to do I'd estimate mine is making somewhere just shy of 300HP...with 355CID stock bottom end, a "moderate" flat tappet cam, long tube headers, and stock heads. One downside to crossfire is that there is basically no aftermarket stuff available for it...and since it was only used for two years there isn't a lot of knowledge among mechanics.

What I think a lot of people fail to realize is that the return to the upward climb in Corvette performance started with the crossfire system. It deserves more respect than it gets.



Bill

 

[patsnitrovette]

The runners just move air from the throttle body,the longer runners make more torque and the shorter the runners ,the rpm's move up the ladder .I dont knock crossfires at all,ive seen a few of them run pretty good.I just prefer the tpi for now.


http://temp.corvetteforum.net/c3/patsvette/new_pics_466.jpg

 

[82X-FireVette]

Andy,

The two systems are very different. The Crossfire system has two large fuel injectors that spray fuel into the throttle bodies where it is mixed with air. The fuel/air mixture travels into the intake manifold, goes down the runner tubes and into the cylinder heads. The left throttle body sends fuel/air to the right side of the engine and the right throttle body sends fuel/air to the left side of the engine, thus the "crossfire" or "cross ram" designation.

The TPI system has one throttle body the air passes through. It goes into a manifold (or plenum) and then into some runners or tubes where it is mixed with the fuel being sprayed by the fuel injectors. There is one fuel injector for each cylinder (8 in total). The mixture travels on into the cylinder heads.

So you see, the fuel is mixed with air before it goes through the throttle bodies in the Crossfire system and it is mixed with air after it goes through the throttle body in the TPI system.

The aftermarket has very limited supplies for Crossfire systems but has many available parts and options for the TPI system.

 

[grumpyvette]

http://www.digitalcorvettes.com/forums/showthread.php?s=&threadid=2264

http://stealthram.com/flowcomparison.html

the basic differance other than that the cross fire intake itself is highly restricted is that the cross fire intake has twin throttle bodys that are similar in function to two computer controled single barrel carbs that flow mixed fuel/air into an open plenum, where the 8 individual runners pull that mix to the cylinders, TPI, is a MPFI system (MULTI PORT FUEL INJECTION) where EACH runner has a dedecated injector at the entrance to the cylinder head mounted in the intake runner, giving much higher level of control over the A/F mix reaching the cylinders as the intake itself only flows AIR

THE STOCK CROSS FIRE intake flows in the 170-180cfm range
the STOCK TPI intake flows in the 190-200cfm range

good aftermarket intakes flow in the 250-310cfm range