If you were to switch the 4.9liter over to carberation to avoid the computer problems, you obviously loose some drivability (ie: mileage, throttle response etc..)But what about the HP and Torque #'s how do they suffer or improve ?? And is it worth it to avoid the computer problems ?? How hard is the computer issue on the 4.9 liter conversions ??

I heard today that if you convert an EFI car to run on LPG you don't need an ECM. Not sure about the accuracy but an engine builder had a few of them on the road and running fine.

------------------

My Old Fiero | Accessories

The performance of the carb'd version of the 4.9 depends on which one you use. If you mate the carb well, you should get about the same numbers as the 4.9's injected brother.

If the engine is over carburated (too rich), or too lean, or has the wrong jets, or needs rebuilt, or - - - , then the numbers will be less

I will be using a freshly rebuilt 350CFM 2 bbl from an early 350 on the Challenge car, will let the forum know how that goes.

G

[This message has been edited by cadero2dmax (edited 03-21-2002).]

All the old-timers that I talk to recommend using a 400-500cfm 2 barrel, or a 350cfm 4-barrel for that size motor. The motor has plenty of off-idle torque, so it would follow that this motor has a bit of room to play in either direction

I've got a line on a nice, cheap, rebuilt holley 500cfm 2bbl. I can take it back if it's too big... I'll let everyone know how THAT goes, too!

One question that begs asking: I'm a little worried about fuel pooling on the PFI intake... I'm thinking I should steal a 4.5 TBI intake manifold instead?

pooling is normal even the Pfi will pool by intake valves as long as it is not TOOO MUCH
the only motors that do not do that are direct in to clynder diesels

------------------
Question wonder and be wierd

quote Originally posted by ray b: pooling is normal even the Pfi will pool by intake valves as long as it is not TOOO MUCH the only motors that do not do that are direct in to clynder diesels

Thanks ray! Do you know perchance how I would be able to detect excessive pooling? Would that be normal plugs on *most* cylinders, with one or two fouled plugs (or extremely sooty deposits?) ?

I read the other post on carb sizes and while I agree with the formula presented I'm kinda lost based on my experinces.
I've seen lots of sb 350's with 600-650cfm carbs on them, my 460 has a 750cfm currently and I should be easily be able to go to an 850dp(and plan on it, it only revs to 4900 at the moment)
How can you expect to get any performance with a 350cfm carb on a motor thats 4.9 L?
I would think that a minumum would be a 500 cfm and if its got any cam/head work then you can go from there. Are the cam/intake/heads on the 4.9 that wimpy?
Again I'm far from an expert and I agree that too big is really bad but it sounds too small to me. I'd start with a Holley 500cfm minimum.

quote Originally posted by 85GToronto: [B] How can you expect to get any performance with a 350cfm carb on a motor thats 4.9 L? I would think that a minumum would be a 500 cfm and if its got any cam/head work then you can go from there. Are the cam/intake/heads on the 4.9 that wimpy? B]

The 2bbl I am using on the Challenge car CAME from a 350, with more hp than the 4.9, and almost as much torque. Take a wild guess what the size of the TB on the Caddy is? The 350 carb actually has more flow than that "wimpy" TB.

Yes, the cam/intake/heads are "wimpy" in a 4.x Cadillac motor. Maybe it was designed that way for a purpose?? Maybe they wanted to move a large car down the road respectably, yet have good mileage. It is called torque.

Remember, this engine is a square bore engine, that in itself limits this engine For those of you that understand the difference in torque and horsepower, that is how this engine develops that torque -with "wimpy" breathing. This engine drives more like a diesel than any other gasoline engine I have ever driven. Lots of low end pull, limited RPM, good performance with excellent mileage (but this one sounds better than a 302 Ford doing it!)

Mess with cams/intake/heads on the 4.x Cadillac, and you will lose that torque. Lose that torque, and - yes, Virginia - you WILL have a "wimpy" motor.

Sure wish all you people would quit trying to theoretically improve an engine which you know so little about, have never driven or even ridden in, and for most never even seen before. Go beef up your SBC's and leave us little guys alone!!

See you at the 1/8 mile at Ed's swap meet.

G

"Horsepower sells cars, torque wins races"

Cadillac 4.9 with an Allante intake

[This message has been edited by cadero2dmax (edited 03-21-2002).]

I was not really looking for a carb size of CFM rating to use...... I was kind of looking to see if anyone had actualy used a carb. and gotten back some dyno numbers ?? even desktop dyno #'s would be okay... I would like to see if it is a reasonable swap of HP and ease, for mileage and drivability...
Balancing air flow CFM with the engines real needs should be just a matter of some involved math (and I suck at this math)....
Really just wanted some realistic HP and Torque numbers for a Carb'd 4.9 liter engine.
Thanks to all who have replied thouugh, every bit of information is helpful !!

I run a 283 cid engine with a 650cfm 4 barrel Edlebrock with vacuum secondaries.
I have run an Approx. 350cfm 2 barrel Holley on the same engine.
The 2 barrel had better low end torque and response but didn't have much for top end. Felt starved for fuel.
Put on the 4 barrel and didn't loose much on the bottom end but had a much better mid and higher end rpm power and response. The 4 barrel appeared better at gas station stops but I really never checked the figures against one another for fuel milage. I am running at present and with the 2 barrel, a stock replacement cam for that engine but have had much better performance and fuel milage with a split durated performance cam from Competition Cams. Long story why I run the less desirable cam now but basically I'm bidding my time till I can get the 350 in the car. The performance cam seem to fit the 4.10 gear better and put the engine in a better operating rpm range for it.

Forgot to mention, I had rather try a carb with manuel secondaries on a 4 barrel. The wieghted vacuum secondaries perform strange when cornering hard.

Sorry I don't have a lot of numbers you can cipher on but I knows what feels better out of the things I've tried.

Hope this helps.

------------------

[This message has been edited by Butter (edited 03-21-2002).]

Hey I wasn't trying to start anything! hehe You're right I don't know alot about the 4.x series of motors. I do know however that the cylinders want to take a given amount of air/fuel in no matter what kind of motor it is, thats just based on cubic inches/rpm nothing else. Of course one can get different levels of performance using different carbs, to me it just sounds a little small for a performance engine. If the caddy doesn't like to rev then thats likely the difference. My BB doesn't either but it sure makes a @%$#load of torque!
Will the caddy rev to 6000 without blowing itself to bits?

the 4.9 doesn't seem to a performance engine..... its that it is in a performance application, given the minimal weight of a fiero.
I am not trying to warm up the 4.9..... Only to ease the engine conversion.
You guys are great !!

This was done on desktop 2000 with ever thing stock on a 4.9L
350 CFM 2 Barrel 10hp @ 13 torq drop
500cfm 2 barrel 1hp increase & 6 torq drop
over the stock PFI

MODIFIE, how would a 500 cfm 4bbl carb work?

[This message has been edited by Wade87GT (edited 05-09-2002).]

[QUOTE]Originally posted by Wade87GT:
MODIFIE, how would a 500 cfm 4bbl carb work?

[This message has been edited by Wade87GT (edited 05-09-2002).][/QUOTE

I will check it and let you know, but it want be no were close to right becouse they don't make a 4 barrel intake for the 4.9 and you would have to run adapter to make the 4 barrel work but then you are defting the purpes the carb will move more air then the intake can handle

[QUOTE]Originally posted by Wade87GT:
[B]MODIFIE, how would a 500 cfm 4bbl carb work?

The 500cfm 4bbl carb gave

20HP and 11 torque over stock

I gotta tell ya, whomever is stating that bigger size carbs will benefit the 4.x series Cad hasn't seen the intake ports on the 4.9!! The two ports are the exact same diameter as the 2 throats on the 350CFM Rochester 2bbl (taken from a Chevy 350) that I took to the swap meet.

This discussion was held at Ed's, with carb in hand and the intake manifold sitting right there.

The numbers being figured do not take into account the way the fuel/air mixture from the carb is getting to the engine (the intake manifold). The 283 with the 650CFM carb and the BB mentioned above had an intake manifold that could get that extra fuel/air mixture into the heads. The 4.9 doesn't, and none are available. The only way to carb the 4.9 is to build an adapter to get the mixture from the carb throats to the existing fuel injection manifold.

Somebody was talking about porting the 4.9, and that is well and good. But I doubt very much that you could take those two holes out to the size necessary to handle the mixture from a 500 or 650cfm carb (at least not all the way to the head)- even if you could machine an adapter that would give you optimum flow from one of the bigger performance carburators in the first place!

G

[This message has been edited by cadero2dmax (edited 05-10-2002).]

Thanks all for the info. I asked about the 500 cfm 4bbl because I have one on the shelf and the 4.9 is my swap of choice. Guess I'll be looking for a 2bbl instead.

quote Originally posted by Wade87GT: Thanks all for the info. I asked about the 500 cfm 4bbl because I have one on the shelf and the 4.9 is my swap of choice. Guess I'll be looking for a 2bbl instead.

Actually, if it is jetted right, the 500cfm 4bbl carb you have will not hurt a thing. You certainly won't lose performance, you just won't gain anything. When you build your adapter, leave it open to the intake ports, and just narrow it to their overall size to minimize pooling - a cut-away would look something like this: \ /.

You might lose a MPG or two to the 2bbl, but your 500 would work just fine.

My posts were to those that were arguing that the 350cfm is too small. Their thoughts
were that they would get more performance simply by throwing a bigger carb on the 4.9.

My rebuttal is that a bigger carb won't make a bit of difference in performance, not that it won't work, or work as well.

G