Sprint,

If you dismantle a TB, you'll see that the housing for the injector itself is bolted to the base of the throttle body. There is a gasket sealing that housing to the main throttle body. One of the mods is to use a second gasket raising the injector housing further out of the TB opening.The hypothesis is that the injector housing impedes the airflow into the venturi area. You should also radius the throat of the venturi as it goes from horizontal to vertical. Part of the effort to optmize airflow. More airflow through the venturi increases mixture velocity and that enhances throttle response and power. The bigger the TB bore, the more you want to direct airflow through the throttle plate and less through the IACs. Make sense?

 

OK I'm with ya now, makes sense too!!

 

Looks like all you have is a small drop due to running an air filter.
But you're getting real close to the magic 'atmospheric pressure' at WOT.
Which shows the intake system is able to supply all the airflow the engine desires.

The injectors sitting right in the middle of the airflow can cause some slight presure drop. They are right in the way.
They remind me of carb venturis. I guess they ARE like venturi's as the fuel is dispersed due to airflow rather than any unique spray pattern.

I've been reading your post here and over on the CrossFire Vault for a couple of years. You've done more with CrossFire than most anybody around.
I see you're running the X-Ram manifold but before you got it you were running the CrossFire induction.


Got a couple of questions for you that, I'm sure, the other 84 guys will want to know about.

1) What did you do with the 'swirl plates'?

2) Did you take them out or thin them down?

3) Where did you get your TB's enlarged? I reside in a fairly large town and there's no one that can do something like that here.

4) What cam are you running with your setup?
There's a couple of GM cams some of the guys run. You know what they are?

5) Did you do the manifold port exit enlargement with other mods?

6) The 1/2 size exit ports cause the air column to accelerate as it squeezes by the small part of the manifold (Bernouli's Principal) just before transistioning into the head port. This gives the CrossFire that fabulous throttle response and low end zip. It also starves the engine at higher RPM.

Will porting the manifold ONLY cause a discernible reduction in low speed torque?

7) What heads are you running?

8) The X-Ram is a Weiand manifold IIRC. Is it a single or dual plane manifold? Seems I recall it being a single plane manifold which is oriented more towards RPM rather than torque.

Yeppers, we need to talk about the CrossFire more here on CF.
Lot's of us have them and there's N-O aftermarket support for'em.
The 84 is a real DIY Vette.

I have the 1.6 rockers on the intake. 1.5's on the exhaust.
Running 'cut back' plugs un-indexed. No cat. Flowmaster 40 Series muffs.
It's a typical CrossFire.
Runs GREAT. 100% reliable. Needs more Power.

 

Surprised EFI-CFI hasnt turned up here

 

Me too. I hope he's O.K. I've not seen a post from him since mid December.

I can answer some of these, if you care to hear from my experience:

1. I eliminated them, then bored and radiused the transition from the TB bore, to the plenum area, by "hogging" the ports in the plenum lid...a lot. There was no discernable loss of drivability at all under any conditions EXCEPT for the first 3-4 minutes of driving immediately following a cold start. Since I live at 7000' in Park City, UT by cold start I mean less than 20* F. After 3-4 minutes driving/throttle response was flawless.

2. Took them out

3. I bored mine to 2.09" myself. I used a "boring bar"; a machine found in motorcycle and snowmobile shops used to bore small engine cylinders. You can also use a simple lathe. Or you can send them to a guy named Dan Plette (sp?). He can be found here or on the CFI vault easily. I would like to add that on a stockish car, boring TB's won't show any gains.

4. I ran a "summit" brand 224/234 @ .050 cam. The cam you're referring to may be the LT4 HOT cam? If so thats a roller cam, not flat tappet.

5. I ported the entire length of the runners in my intake as much as I could. That is the only way to go. Porting JUST the exit of the runners will result in minimal gains, as the rest of the runner is still too small for a 43 CID cylinder. The increase in power is DIRECTLY proportional to the amount of metal you remove from the inside of the runners.

6. No. None. Again, the runners are WAY TOO SMALL, and you'll not hurt low end torque measurable or noticably by porting. The more you port, the more power you'll have, everywhere.

7. I was running stock heads for a SBC 400; #881 IIRC

8. X-Ram is a Wieand single plane w/a top. The stock X-fire is also a "single plane". When you are dealing w/EFI, a dual plane is not beneficial or necessary for "low end torque". That design is useful for a carburetor, where velocity through the venturi is essential to draw fuel from the bowl. A non-issue w/EFI. A "single plane" intake is better.

9. I agree. Mine ran awesome all the time. It did need more power (when it was stock), and I "fixed" mine to low 13's and 24 mpg.

 

If you decide go with 1.6 rockers make sure to check the clearance of the slot the pushrod's go through in the head. Some heads clear and others do not. If yours dont you will need to grind the slots wider for clearance. This can be quite a chore if the heads are left on the motor. I ran the CompCams Stamped 1.6 Roller tipped rockers for quite a while before I built my 383. They worked quite nicely. With a ported manifold, and the 1.6 rockers I ran a 14.6 @ 96 mph in the 1/4 and that was with stock TBs. I disagree with opening up the TBs on a stock motor. If you do there will be a significant bog off idle - unless you swap out the ECM to a HAM'd 7747 or 8746 you wont be able to tune it out.

Oh - welcome to the Crossfire Club. Long live the underdog...

 

No, it wasn't. You claimed that:

By my calculations a 350 spinning 5000 RPM at 80% VE requires 405 CFM. Well short of the 572 the stockers deliver.

Furthermore, I have first hand been involved in the boring of TB's on a STOCK long block, heavily ported intake, '84. The difference in well documented 1/4 times before boring and after was ZERO. It made NO difference on a stock Long block & ported intake. Meaning the TB's weren't a restriction after porting. This is real world data backing up the above calculation.

So your post wasn't good information. Boring the TB's isn't worth the effort until you've gotten a heavily modified engine; at least over 300 CSHP.

 

No. I don't like the Xram. All the results I discuss are with a Xfire manifold and diffuser plates.


1) What did you do with the 'swirl plates'? Yes, still have them in

2) Did you take them out or thin them down? Yes. You can see pics on Xfire forum

3) Where did you get your TB's enlarged? I reside in a fairly large town and there's no one that can do something like that here. Dan Plett on Xfire forum

4) What cam are you running with your setup? Custom grind. Matched to heads. 270d @ .006 single pattern/.528" with 108LSA
There's a couple of GM cams some of the guys run. You know what they are? Thought about using Hot cam. I originally started with a CompCams Marine Cam. The one I have now added ~ 30hp. But just as importantly, the cam moved the tq curve from 3800 to 4200rpm and the hp curve from 4800 to 5400rpm

5) Did you do the manifold port exit enlargement with other mods?
Started with port match, then got manifold EH'd

6) The 1/2 size exit ports cause the air column to accelerate as it squeezes by the small part of the manifold (Bernouli's Principal) just before transistioning into the head port. This gives the CrossFire that fabulous throttle response and low end zip. It also starves the engine at higher RPM. Doesn't seem to be doing that on mine anymore. Motor will routinely rev to 6000rpm even tho power drops before that.

Will porting the manifold ONLY cause a discernible reduction in low speed torque? I felt I picked up torque

7) What heads are you running? TFS 23d

8) The X-Ram is a Weiand manifold IIRC. Is it a single or dual plane manifold? Seems I recall it being a single plane manifold which is oriented more towards RPM rather than torque. The Xram is an adapter for a Weind manifold. I don't care for the contorted air path. Others have used it with success.

Yeppers, we need to talk about the CrossFire more here on CF.
Lot's of us have them and there's N-O aftermarket support for'em.
The 84 is a real DIY Vette. Yes it is. But adding a ZF-6, Dana 44, and C5 brakes really take advantage of the additional power and the original Z51 suspension

I have the 1.6 rockers on the intake. 1.5's on the exhaust.
Running 'cut back' plugs un-indexed. No cat. Flowmaster 40 Series muffs.
It's a typical CrossFire.
Runs GREAT. 100% reliable. Needs more Power. Always needs more power. With a 105mph trap, I estimate about 380 hp on a 3500lb car. I ran 2" TB before the major mods with no problems. Once I got the cam and heads, I increased bore size to 2.13"[/QUOTE]

 

Thanks for all you info Dominic, I've also been following yours and Elkabongs and others mods and deciding how to procede.. I've already added the 1.6's and here in Houston my base 1/4 time improved from 15.2@88 to 14.7@92 on my A4 Z51car. My ported intake w/modded swirl plates will be installed Thursday. i'll be heading to the track Friday night or Saturday and also getting a couple pulls on a dyno here on Saturday. I'll let y'all know how it goes. My car runs great, is dead reliable and I don't wanna oull the motor yet so my mods will stop there for a while. I intend to pick up a 2nd small block and do heads cam etc... at that point. Thanks again for your continued help!

 

I'll add my bit to the TB size discussion....
I have run a 12.48 ET at about 112mph with 2.00" TB's.
I have since made a 2.20" pair, but it has not yet run any quicker.

I have a few new parts coming (3.45 Dana44, better converter and a bigger cam) and hope to slice another couple of tenths off.. Biggest hurdle will be finding the extra fuel, not air!

 

Damn it ben..... Now I gotta do a cam swap.

 

xrcrx,

Glad to see you are showing very positive results. Several of us on this forum are just trying to show that the Xfire isn't the "dog" others want to make it out to be. It responds to mods just like any other SBC because that's what it is. I always laugh when members here drool all over an 82 but mention the 84 and they snicker. Go figure!

Jim,

What are the specs on your cam?

 

The transformation has started.I've decided against using the diffusers , it's never really cold here.The EGR passage has been removed, the ports opened and gasket matched. I should have dyno and track results by Saturday night if all goes well.

 

I'll be looking for your dyno results, but you need to grind WAY more than just port matching. The power increase is directly proportional to the amount of metal you remove from the intake.

-Tom

 

Thanks for the input. Luckily I've read and appreciated ya'lls help here and at the CFI forums. The runners have been opened up at bothends and the EGR hump is gone now. I used pics from the CFI forum as a guide. It's a work of art ! After reading thru many previous threads the decision was made to delete the diffusers. I will post results as soon as I get them.

 

218/224 @ 0.05 - .528/.534 with 1.6 rockers lsa=112.

I am thinking of something around 230/230 - .550/.550 with 1.6 rockers. I have good flowing TFS heads so I am thinking that a single pattern cam would be best. I also don't need to worry about emissions anymore which means truel dual's are in my future. The air pump is coming off to make room for my Aeromotive VFPR and parallel plumbing of the TBs.

 

The intake bolts weren't even finger tight. The bracket to the A/C-and tensioner has a bolk broken at the water pump, I had just replaced the power stearing lines, it looks like the reservoir itself leaks! All kinds of bad discoveries so far. Yet the car has run great and been dead reliable!

 

Well if you're using the same heads I have, you could use a single pattern cam. Not sure the extra lift will help since the flow numbers I have seen looks like the TFS heads stall at around .500" lift.
I think the question will be what overlap? With a 383, it can be greater. And for that you need the adv. duration and LSA. I'm using a .528" lift with 1.6s. Vizard says that flow is optimized when lift equals at least 25% of the valve diameter. So 2.02" valves...
At that point the valve is pretty much out of the way of the airflow so port efficiency actually increases. I was playing it safe with piston to valve clearance.

 

Tom, when you 'port match' a CrossFire manifold you HAVE removed a L-O-T of metal. A WHOLE LOT.
The stock manifold exits at the transition to the head ports are HALF SIZE on the CrossFire Manifold.
Port matching them will leave a pound or two of metal on the ground.
(Maybe not THAT much but not far from it).
ONE HALF of the intake port is closed off on a CrossFire manifold.

Now I know YOU already know all this but would you mind an awful lot if I post it for everybody ELSE?

Got a question for you since it seems every post I make gives you somewhat of a case of heartburn.
This question hasn't got a thing to do with Fuel Injection.
Here it is:
Will changing from a 2 barrel carb. to a 4 barrel carb have any effect on the dynamic compression of an engine?
For sake of discussion let's say the carb ports are 2.0" in both cases.
So in one case there is a total of 4.0" and in the other 8.0". I can convert those to Square Inches but for sake of discussion that doesn't matter.

DOM, your answers to those questions SHOULD be a sticky on CrossFire modding. Great info

 

It would depend on what is down stream of the carb (engine combo). If the 2 bbl carb was a limiting factor on that combo, then going to a 4 bbl should increase dynamic compression at the engines tq peak. If there are factors after the carb that are the limiting factor, then increasing carb size isnt' going to change anything, except perhaps less low wnd torque and worse throttle response.