bogus

69427

As an '84 owner, I was appalled at the crappy fuel distribution in the intake manifold. It just looks like such a basic mistake in design. (I believe even McClellen admitted as much in his book.) I'm not using the crossfire manifold design anymore on my turbo 355, but I'm curious what CFI enthusiasts are doing to cure this deficiency.

Dominic Sorresso

69427,

The "design" of the Xfire manifold isn't as much the issue for crappy fuel distribution as is the crappy fuel delivery method. IOW, a significant problem with the fuel distribution is the "in series" fuel line necessitating use of 2 different size injectors accomodating the drop in FP between the front and rear TBs. IMO, even a stock Xfire will benefit from running fuel lines in // and same size injectors in both TBs. This modification allows the motor to run soooo much smoother. Any change like this however, will be "optimized" IF you tune the ECM calibration.
Also, I have never seen a manifold so restricted. The first thing any Xfire owner should and does do is "port" the intake to match the head port.
I currently run 2.13" TBs with 80# injectors at 20psi using an Aeromotive 13301 VAFPR . The EBL ECM allows me to run variable FP based on engine vacuumwhich optimizes Injector Pulse Width for all rpm ranges.
My Xfire manifold has been port matched and Extrude Hone'd. It still has the EGR channel and I still use the diffusers under the TBs. Runs 13.3s on street tires with a 60' of 2.01 and a 102+ trap speed. Gets 24mpg hiway. I think that shows the basic design of the Xfire manifold isn't so crappy and that it can indeed support competitive levels of hp and torque.

elkabong

Gents - Lets not forget at the end of the day we are just talking about air, gas and spark. You can bag on the Crossfire manifold all you want but it works within it's limitations as with all things. I use the XRam because I built a 383. I have tried a siamesed crossfire but I ran into issues with it running lean at higher rpms.... And frankly I did not spend that much time trying to figure out what was going on because I needed to get it on the road and pass emissions. Needless to say I went back to the XRam and I am going to stick with it... It may not best solution but it is the only option available for a 383 in a 84.

Extrude hone is another option and Dom has proved that. I spent a lot of time talking with Extrude Hone Engineering and their thinking was the best they could get out of a Crossfire Manifold was 245 CFM per runner and that would be with the runner walls being 0.05. That was in theory, they would have liked for me to pay the $600 for the EH'ing the manifold and then they wanted me to pay to for them to put it on their flowbench to find out what it flowed. Needless to say I considered this a bad investment the $$$ per hp is not there.

J, take the comments to heart. I understand the position you are in but there is no sense in putting something together if the risk is high that you will not be happy with it. You would be better targeting 300hp. Given flow numbers a nicely ported Crossfire manifold will be able to support that. No offense to your builder and yourself but the science just is not there.... Yes science.. Also, we can't find mechanics to work on these things because not many people understand them. So what makes you think your engine builder does?

Like I said earlier take these comments to heart. We are not baggin on ya we are trying to help ya.... What you are being told just does not add up.

JLeatherman

Why is 245 cfm not enough? That outflows a lot of aftermarket heads at .500 and even .600 lift. Seems to me that that should be plenty. Additionally, the smaller cc of the crossfire runners should promote a higher velocity of A/F charge. I'm not a fan of the Xram because it is a single plane manifold. I'm building a motor for low-end torque and the Xram base seems counter-productive towards that goal. Has anyone ever tried modding the Xram to be a dual plane? I guess I'll just see what numbers I can get from a ported stock manifold for now.

elkabong

I may get nailed for this but here it goes....... First, in theory, 245 CFM will support 377ish hp. Second you missed the point about the wall thickness of the runner being 0.05". No way you can do that by hand. Also, what EH told me is they could not guarantee 245 CFM but they would like for me to pay them so they could find out. There are also many other factors and the biggest being the cam and heads.

I posted this on the Crossfire Forum. It is not the tell all but a indicator as far as flow numbers based on horsepower targets. The 75% column is a approximation of a sine wave that simulates the intake valve opening and closing event. This table is just a crude approximation I used while talking with EH. The calculations are based on information I found on other forums. This is not meant to be the end all to how much flow it takes to produce N hp. There is a lot of stuff not factored in eg runner length, viscosity, temperature, cam duration, valve lift blah blah blah. But it is interesting none the less.

JLeatherman

220 cfm seems like a reasonable goal, and I'm sure to manage over 300 hp on that one. My plan is, next winter when I'm out of college and employed, I'm swapping heads and intake. For now, I guess I'll just live with 300-325hp and see what the stock heads will do. Any comment on the converting Xram to dual plane?

elkabong

Why would you want to convert the XRam to a dual plane? If the cam is selected properly then there is not a need. The biggest issue is getting the manifold to fit under the hood. Have you thought about using a single TB out of a 454 truck?

JLeatherman

I've heard of the 454 TB stuff, but does that manifold really flow any better than a ported crossfire manifold? Also, should I get a 7747/8625 ECM, or get an ECM from the same vehicle as the 454 TB system?

CFI-EFI

Do you know the difference between a single plane and a dual plane manifold? Take a look at one of each, and I think you'll be able to answer your own question.

Good luck getting a 454 big block manifold bolted on to a small block engine.

RACE ON!!!

JLeatherman

By "converting" the Xram to dual plane, I meant taking a performer dual plane intake manifold and cutting it down the same way the Xram uses a Weiand manifold. Can the Xram top plate be made to fit a Performer dual plane manifold.

As for the 454 TB, what manifold do you use with that? I know the original one doesn't fit, I'm not an idiot.

69427

We may or may not be talking the same thing here, so I don't know if we're agreeing or disagreeing. My complaint is that the manifold runners are configured so that each cylinder bank takes its air and fuel from the opposite side of the manifold, which is not a big deal for the air, but the fuel is a problem. Correct me if I'm wrong, but it's my understanding that the injectors fire alternately (under non-WOT conditions), so there is a left, right, left, etc, firing of the injectors, but not a L,R,L intake of air, as the sbc is not a 180* firing pulse per bank engine. If both injectors were centrally located then this would not be a problem. I've often wondered if a two barrel TBI mounted centrally on a CFI manifold would have much better fuel distribution. When I pulled my stock engine to drop in the turbo engine I was astounded at the variation in exhaust port carbon build up.
As I said before, I'm just curious what CFI tuners are doing to address this issue.

bogus

The reason that the Xram people used the Weiland intake is so it would still fit under the hood. My real problem with the CFI intake is that it is iron... heat retention and weight SUCK.

Let me try this one on for you: The basic architecture of the Xfire is now 20+ years old. It was a stop gap even then*. It can be made to perform very well (an otherwise stock L83 can be made to put out 300hp with the right bolt on mods), however, because the computer is so slow (15 instructions per second!), the ability to fine tune simply isn't there. In short, CFI has it's limitations.

Have you considered other induction methods? The Mini Ram with the FAST computer? One of the Holley EFI conversions? Or even the DFI systems from Accel? Sure, they are expensive, but the performance potential is insane. Sequential injection is the bom, yo. MPG and MPH! All in one, infinitetly adjustable package. All you need is a laptop.

Going to carb is so damned backwards, I would stay CFI first, cause at least it adjusts. Carbs are a fixed analog device. As such, they required the extra barrels to create additional fuel delivery options. A two barrel can flow like a 4 barrel, no question, but it's drivability will suffer tremendiously, because it will either work well low or work well high, it will never work perfectly in both environments. Think about those massive 1 barrel Flying Toilet carbs... drag race only... dump lotsa fuel all the time.

CFI is an improvment, it will adjust flow as needed. Properly tuned and built, it will work well. Consider upgrading the ECU to a later truck model. It will operate the Xfire just fine (with minor wiring upgrades) and will do so at 150 operations per second - better on the fly fine tuning!

I am pretty sure the 454 TBI injectors will fit the CFI intake.

OEM TPI is a pig. I don't like it. Sure, tons of torque, but it's a bitch to get power from. I agree with CFI-EFI that power potential with CFI is not that far behind TPI. However, the basic architecture of TPI is better. It has much better fuel delivery potential, it just needs a better intake.

I hope this starts to help solve your problem here... Remember - it's all about the air flow!!!

* GM had license to use Bosch injection at that time, but thanks to an exclusive use clause, only Cadillac could use it. That clause was removed and Corvette got TPI in 1985.

bogus

from my observations (and they are limited) the CFI TBs seem to spray fuel all the time. You are thinking of the batch fire injection used from 1985-1993... with CFI, I suspect fuel pooling is a greater problem.

The cross ram intake isn't a new idea... Mopar had some seriously sick intakes back in the day... the Golden Ram was a monster with 2 huge 4bbls mounted across from each other!

comp

and they made Torque

js292

If he goes with a 7747 ecm Speedtronics makes a HAM so there would be no need to cut a splice the harness.

But, before that I think he needs to come up with a game plan and some realistic goals.

Trying to install a new motor when you already had gremlins in your system is going to be a battle. You should have diagnosed all you sensor and misc. issues prior to pulling the motor so that way you could work on just tuning your new setup. Now you have to fix all your pre-existing issues and tune a new setup

qws

J's goals have changed to a 325hp motor, which is a little more realistic. But I do agree with you.
Hell he would be money ahead if he went with the 290hp ($1600) or 330 hp ($2300) crate engine, then he'd have enough extra money left over for the X-ram and some RR's or whatever else he may want. I would think it would be a much easier build up for the future.

Tom400CFI

That says little to nothing about fuel distribution. Carbon build up in teh exhaust port could easily and more likely be a result of oil burning...especially in an old stock engine. What did I do to address this issue? Not much. I ditched the restrictive "Swirl plates" under each of the TB's. That should have worsened a fuel distribution issue, but it didn't. My plugs read fine, and 24 mpg highway isn't bad w/a 400 CID small block.


That's misinformation. The CFI intake is aluminum. I would know, as I ground a bunch of it out. It weighs about 10 lbs and actually transfers heat faster than iron.


What does your LT1 get for gas milage? I doubt much better than what CFI owners (who are at least somewhat in the know) get. As I said above, I was getting 24 mpg w/400 CID, and a 3.45 rear gear.

What it boils down to is this:
*Ported intake is good to about 320 hp from what we've seen. Though I wish we could put CFI-EFI's intake on another long block because he ported his intake WAY further than anyone else has.
*There are other options besides X-Ram if you want more than ~320 hp; The Edelbrock SY-1, and Offenhauser Cross ram intake, w/a custom aluminum lid (could make that w/a jig-saw and a drill) and stock TB's.
*Stock-bore TB's aren't hurting power at all until you get to at least 280-300 hp. Putting other TB's on and boring the stockers is wasted effort; it should be done "last".
*Any TBI injector from GM will fit in the CFI housing. From the 2.8 liter V-6 to the TBI 454 truck and "marine" motors. Most of us are using the injectors "for" the 454 TBI truck motor, which are rated at 90 pounds per hor (PPH)
*You don't need a "dual plane" intake with EFI, as you needn't worry about velocity through the throttle bores like you do with a carb.

IMO the original poster should port the stocker as far as he dares in order to save money. He should shoot for 320 hp and he should get it w/the set up mentioned and a ported intake. When he has more money, he can get heads, and then step on on the intake to a SY-1, Offy, or X-Ram, and go looking for 400+ hp w/a stock looking CFI.

-Tom

CFI-EFI

There is so much wrong with this post that the moderators ought to just delete it. First, a Crossfire manifold is NOT made from the same cast iron as bogus information's head. The Crossfire manifold is all aluminum.



"The basic architecture of the Xfire is" is a lot older than 20 years. Have you you forgot the DZ302? What about the picture you posted and mis-captioned?



More ignorance. A "Flying Toilet" IS fuel injection. It is not a "1 barrel carb"



Very unclear. The "454 TBI injectors" will fit into the Crossfire TBs. But because the 454 TBs are 2 barrels, they won't bolt onto the L83 intake manifold, in place of the 1 barrel TBs.



The fuel delivery isn't a problem with either system. Just ram an open fuel line into the intake and both will receive more fuel than they can handle.



I thought it was, "fuel delivery potential", as in the previous quote.





I don't dare say it never existed, but *I* never saw a Power Ram Inducted, 383. The ones we played with, way back when, were 413s. Have you forgotten the woeds to the song, Shut Down? It happened on the strip, where the road is wide...

RACE ON!!!

69427

You're comparing apples to oranges here, and no, I'm not thinking about any PFI systems.
The throttle bodies don't spray all the time, otherwise you couldn't control the mixture ratio. They alternate and vary their pulse width. Big difference from a carb.
Chrysler knew what they were doing with their fueling. Re-read my second post, and you'll understand my point. Chrysler used a carb for each bank. Each time a cylinder inducted air, there was a supply of fuel on that same intake runner. Chrysler didn't try to fuel the left bank occasionally from a carb that supplied the right bank. Try to envision what's happening in the interior of the CFI manifold. The injectors alternate left and right, but the air flow pulses in the manifold don't alternate in a steady left-right pattern, as I'm sure you're familiar with on a sbc. Sometimes the TBI injector above the intake runner injects fuel for the cylinder, on other cylinders the injector that's firing is located on the opposite side from the port entrance. Two very different paths for the fuel. It's not a problem if there is perfect mixing in the large plenum area, but those swirl rings under the throttle blades just look like a poor bandaid attempt to cure this problem. This is my continuing question. What are tuners doing to correct this uneven fuel distribution?