iceblue

Simpson,
Your level of enthusiasm is evident from the quality of your craftmanship (photos are pretty good as well).

These Offenhauser manifolds are exact copies of manifolds produced by GM in the late 60's for Z28 Camaro road racing (302 ci I think). They are popular in the Camaro world and there is a lot of good info available about them on the Camaro web sites. Edelbrock made a similar manifold.

The GM 82/84 crossfire manifold is significantly different. I traded-in a '64 (327/365 4-speed) for my '84. The '84 is a much better car but not as fast as the '64 in a straight line. A major difference between the two cars is the '64 loved to rev where as the '84 doesn't. I used to like to demonstrate that shifting in the '64 was purely optional, it could be started from rest in third gear and would easily run to 100 mph before shifting to fourth (but gas mileage was probably less than 15 mpg and it needed high octane leaded). That excitement is missing from the '84. On the other hand, it's always run well and I've never understood this "ceasefire" thing. Believe me, the '64 was much more difficult to tune and needed it way more often.

I've always thought the L83 is strangled by the TBI system so I think what you are doing with the TBs and manifold probably can make a major improvement in engine power and flexibility. What's getting fixed obviously is air flow but what about fuel. Based on very quick calc's (I'm no expert and I didn't consider injector duty cycle) the two 90 lb/hr injectors you mention would be good for 300/350 hp. The stock L83 injectors must be smaller, probably sized for 200/250 hp. If true, then larger injectors are necessary to get much benefit from the manifold/TB porting. How difficult is it to find the larger injectors?

Thanks for your interest. Iceblue

hugie82

Simpson, you have to get a youtube video when that sucker is fired up!!! Oh, I wanted to tell you RockAuto.com has your 90PSI injectors and your right...their not cheap

simpson36

TBI is a low pressure system designed to run at a nominal 11psi.

The injectors are simple fixed orifice solenoid valves and can tollerate up to 30psi which will pass significantly more fuel.

I designed MOATB to run at 23lbs (if I remeber correctly) based on the owners HP goals. I've posted the calcs on the forums somewhere if you want to get the numbers.

Crossfire is much maligned, but I think by people who do not understand how to make it work. It actually works very well and has plenty of capability for a reasonable street car if you know how to get it.

What gives with that whacky setup anyway? I'll give my recollection and maybe sombody can chime in with some historic facts, but basically I think that the new tighter emissions regs of the time were given in grams per mile and the test was a simulated circuit that included hills, decelleration, stops, etc.

Grams per mile is the reason for the 2.7X rear axle ratios. Detroit was not concerned with gas mileage in 1982.

To meet the emissions aggregate, they needed to do things like shut off the fuel during decel (which crossfire does) in order to get the circuit total down enough to meet the regs. Hence ECM controlled injectors.

The only mass production TBI GM had at the time was for the 4 banger, hence Crossfire.

It's an oddball system with an interesting history, but it's fun to play with.

hugie82

Nobody can deny that the Crossfire produced butal low end torque!!! 2400RPMs and almost 300tq American V8 torque. People talk about a stubble because GM used silicon to seal the manifold top plate that always leaked. 10 years later Felpro finally made a nice gasket that takes care of that problem

Desert68

I believe it is STR-10 and the STR stood for Street Tunnel Ram because it could supposedly fit under a stock hood. They made them for several engines.

aussiejohn

Simpson,
Great project. I drive a 1987 four cylinder (GM) Holden Camira d.d. , I think Chevy Cavalier??? is the USA equivalent, and the 21 year old Rochester TBI works flawlessly. There are plenty of them at wrecker's yards and this would make a nice project for one of my V8 cars. I can't wait to see your inline twin four barrel conversion.

I've been thinking of building sometning like that for a few years now, but didn't think that anyone else had done anything like the work you've done. The cross ram does not interest me but a twin four barrel conversion does. How long before we get to see that?

Fianlly, you haven't mentioned anything about the Electronic Control Module that runs this system. What do you use?

Regards from Down Under

aussiejohn
9 months to go

simpson36

I already did a whole thread on the 'Dually' project. I just don't remeber which forum it's on . . LOL!!



I don't think you can use junkyard 4 banger TBs for a dual setup because they probably don't have the balance port needed to syncronize the TBs. Crossfire TBs are plentiful though. I pay no more than $40 for a pair of bases. They cost a little more then that by the time I'm done with them though . . .LOL!

The best computer to use is the EBL setup. The inventor supports it thur the ThirdGen (Camaro/Firebird) forum.

hugie82

Simpson, I thought the balance was done by the first TB having no fuel pressure regulator and the 2nd doing all the regulating with its regulator??? Also I would like to see that set up with the truck dual TB. That would be almost a 1000 CFM out of the box. Maybe if a relay type setup was used to fire all 4 injectors so you don't get a voltage drop splicing wires. Just a throwing out ideas because it looks like your the man when it come to fabbing up a nice TB system

simpson36

Hugie82

We have a symnatics thing here.

"Balancing" is the the same thing as "Syncronizing" multiple carb (or TB) setups.

This refers to the process by which you achieve equal air flow thru each Carb/TB. Factory multiple carb setups have a built in provision for doing this critical adjustment.

Very sensitive ports are exposed to the the air FLOW (note: NOT manifold vacuum) and an equally sensitive device is used to sense the tiny vac signal generated by the port. The port is located such that it is effected by the intitial throttle openning so that the multiple carbs can all be set to the same flow rate.

The ports are simply called balance ports or sync ports and the device is called a manometer. Manometers can be inexpensively made

http://www.thecubestudio.com/Crossfi...tManometer.htm

or purchased in single or multiple tube versions. There are also digital manometers now, but they would need an extremely high sample rate and reaction time to really be useful in tuning.

On any multi carb setup, the accuracy of the linkage is very important. A sloppy linkage will not hold the balance when the throttle plates move and the system will immediately go out of balance. This is what causes the infamose 'Crossfire Stumble"

Speaking of Crossfire, the fuel is actually regulated by the rear TB. In the frint TB there is a 'compensator' which merely smooths out the pulses created by the froint injector opening and closing so that the rear TB injector gets something approaching even pressure.

Driving 4 injectors is a question of electrical power. The stock ECM does not have the juice to drive 4 injectors, but that IS an option with the EBL setup.

The problem I forsee with using a pair of 2bbl TBs is the same as junkyard single barrel 4 banger TBs . . namely no balance port.

If you are looking for big flow, my MOATB setup is 1,100 CFM using a pair of 2.375" Crossfire TBs . . WITH balance ports.

There are those who claim they can balance by feeling the drag on a slip of paper between the throttle plate than the throat wall, and making that the same for each TB. However, this is not anywhere near the accuracy required for a proper balance.

Tom400CFI

Were there ever any results from all this awesome work?

-Tom

simpson36

Hi everyone,

I'm out here plugging along but am just too busy these days to post in forums. I also don't have time to follow up on every project, although I would like to.

I do get a lot of e-mails from customers who let me know how things went with their swaps and I have encouraged people to do their own threads. I provided all of the finished photos to the owner of the Dually project for example, but He was not interested in writing an article and I just don't have time.

What I did was just take my next customer report, asked for permission to post and put in on my crossfire web site. This is fairly typical of the feedback I get and can be read here:http://www.crossfireinjected.com/Cro...mailDenver.htm

I did promise an article on porting the crossfire manifold, so I will definately be doing that, but I can't say for sure when that will be.

Tom400CFI

Well thanks for the post and update. I'm looking forward to the article. The craftsmanship of your efforts is superb!

jseremba

I own a 1984 Crossfire four plus three.
Please do not laugh or yell at me. I have one or two really dumb questions to ask.
1) has anyone ever tried just bolting two truck tbis to the crossfire manifold, just asking. It looks like the bolt patterns are the same. And the truck tbi has two injectors. Sorry just had to ask.
2) I really want to keep the crossfire. So I am thinking of rebuilding my TBIs and using higher pph injectors, I ported the stock manifold. So how much do you charge to port the TBIs. Remember the car is stock and will stay stock. maybe some roller lifters and a new VERY mild cam, new timing chain. Most probably the heads will always be the stock heads.
Really just looking to get the most out of the stock motor.
Thank you for you input.

hugie82

If you read back a few post Simpson37 explains the ECM doesn't have the electrical power to drive 4 injectors if you used 2 truck TB. But he did list and others have listed companies that do cross fire TB modification
Most people get away with an ECM prom/chip and an 85 corvette fuel pump will usually support a mild street build.