Hi all, I will try to keep my question short.

I swapped in a 1990 police 5.7 with the matching TBI. It run fine, but isn't as big a performance boost from my built 305 as I hoped. I have been looking at FiTech throttle bodies.

My question is about replacing the TBI manifold for a 4 barrel manifold such as the Edelbrock 2104 along with the FI change. What, if any, performance gains could I expect from this? I read lots of "you could do this or that", but nothing from someone who has made a similar swap.

Anyone?

Thanks

 

I'm going to go out on a limb and "assume" (yeah we know what we get when we break that word down into its component parts) that you're working on a L03 Camaro or Firebird.

You should expect few if any gains.

The way you make a motor run better is to find THE ONE THING that MOST limits its performance at any given moment, and address it in a way consistent with the rest of what you have, and your goals. It is NOT to unbolt the big easy-to-get-to parts sitting right up on top and putting on KROME or whatever. Find The Bottleneck, open it up, expose The Next Bottleneck, fix it, and so forth. If you work on something that isn't The Bottleneck, you won't be able to tell that you did anything, because The Bottleneck is still in control.

In the case of TBI, the things most limiting its performance are, the exhaust (every single piece all the way from the heads to the street), the heads, and the cam. In that order. Then AND ONLY THEN will replacing the intake make ANY difference AT ALL.

Another thing to plant firmly in your mind is that often the thing that most limits the performance of THE CAR isn't THE ENGINE in the first place. In the case of your TBI car, you might consider a converter and gears. Maybe even before you dink with the engine at all.

 

Pretty much all accurate except the stock cam will restrict the engine LONG before the heads will. I have proven the stock swirl ports to be capable of over 250 hp at the wheels with nothing more exotic than a production LT4 cam and 1.6 rockers and 275 hp to the tires with a GM846 cam. Even at 180 cfm the stock 350 swirl ports are capable of over 350 hp at the crank. Most small block heads are more restrictive at the exhaust ports than the intake and the swirlies flow better than the average small block head there even better than Vortecs to the point I run single pattern cams with them.

 

I'm watching.. I have an L98 with a bored GM TBI intake I'm soon to put in my car along with headers and hopefully a 46mm TBI unit or atleast a modded stocker with 14psi spring or 68lb injectors.

 

Thanks for all the replies and sorry for not responding sooner. I was rushed in my original post and regret not going into detail. I think I left a confusing and misleading question that is hard to answer.

My engine is a 1990 police 350 with roller cam. The cam is the same as went into the Corvette engine. It also has flat top pistons. It specs out at 190hp, but I am sure it is closer to 200 with no smog equipment on it.

No disrespect to anyone... I know all the arguments on heads and I don't disagree with anyone. I made the decision to stick with swirl ports when I rebuilt the engine last summer, mainly because I don't have the money for better heads.

I just performed a mod that leaves me room if I want to install a surge/swirl tank with an internal Bosch 044 pump. Since my external pump is starting to cut out I figure I need to replace it soon. Having a pump with more pressure would be needed if I were to switch to a different EFI system. So with that lining up as a cost effective option I thought I should take a look at the possibility of a different intake and higher flowing EFI. The Police TBI flows around 490ish CFM. The FiTech flows 850.

I am wondering if the swirl port heads will flow well enough warrant the upgrade, For example, if it might net another 50hp it would be totally worth it, if it were worth 20hp probably not. It it would provide no gain at all then I would not even consider it.

 

190 HP isn't very impressive. That's about what a stock LB9 TPI 305 puts out. Given that's the spec on the motor you dropped in - do gears and torque converter first. That's going to net you more than any engine modifications at the moment. Also do exhaust - headers, etc. Then see where you are at. Even with ALL that my LB9 isn't what we would call fast. Thus the 350 Vortec on my engine stand.....

GD

 

Yep done all that.

 

If you have done all that then changing the intake won't yield much that you couldn't get on the stock TBI with tuning. The cam and heads are your bottleneck.

GD

 

CAM 90-91 L98 10111773 In/Exh Dur@.050" 202'/207' Lift (w/1.5) .413"/.428" LobSep 114.5'

Not saying I couldn't do better, but any more would take considerable tuning work.

So consensus seems to be that better manifold and larger throttle body won't help with replacing heads and cam?

 

I agree that cam isn't bad for a lower rpm engine. Its actually a good fit. I do wonder how much better the 083 heads are over the 193s and if it would make any difference in HP? I see them up for sale sometimes, you might could get a set cheap and use your intake on them.

 

I am not looking for RPM so I agree the 193's are fine for how I drive. There are lots of things I could do if money were available. I won't debate that for sure. I actually built a wish list a while back that came out around $4.5k, but I can't put that much money into my project. I was only interested in finding someone who did what I was asking about and what they felt was gained or lost.

 

083s would trade torque under 4,500 rpm for about 15 hp in the 5,000-5,500 rpm range.

The 1990 9C1 9.8:1 L05 was rated at 195 HP and 290 TQ. With revisions to the exhaust and 68 lb/hr injectors in place of the 65 lb/hr injectors in the 1990 the same long block in 1992 was rated 205 hp and 300 tq. I also feel the stock exhaust system choked the caprice engines as heavily as the L03 F-cars. The full size vans and trucks with the 9.3:1 350 and smaller 194/203 @ .050 flat tappet cam were rated 210 HP and 310 TQ.

 

Thanks for the the additional info. I had oreviously read that the 1990 engine was 190 ho and went up to 195 in 1991. Close enough.

I did the ultimate TBI mods. The existing exhaust is not as good as it could be but better than stock. I would not be surprised if I were pushing 215.

What would make me happy would be to improve pulls from 60 mph in the 2500 to 3500 rpm range without sacrificing the lower RPM stats.

 

I pulled the power ratings from inofrmation on GM Heritage website.

With the stock long block save for 1.6 rockers I got an 8.75:1 1-ton 350 crate engine to 200 hp and 300 tq at the wheels in my 1983 G20 van. Edelbrock performer TBI intake that was gasket matched to the heads, bored to 2", 454 TBI unit, 1" open center spacer, thorley tri-y headers and 2.5" dual exhaust with a X-pipe. Swapped in a LT4 roller cam and got 250 rwhp. Swapped on ported Vortecs with 2.02/1.60 valves and an edelbrock performer Vortec carb intake and made 300 rwhp. Factory 1996 LT4 Vette cam, worked over Vortecs and the carb intake were worth 100 hp at the tires.

 

Truck L05s were "rated" at 210 HP.

Sounds to me like all that "Corvette" crap needs to go IN THE TRASH, along with the 193 heads.

I can't believe anybody would be bold enough to claim that 193s will make more power, or torque, or anything else, than 083s. Maybe below 2000 RPM but not anywhere above that. That's fantasy land. Never seen a head with a GINORMOUS restriction stuck in the intake port that could make more ANYTHING than a free-flowing one. Not even just more noise. The very idea is ridiculous, flies in the face of all known laws of physics.

Best thing you can do with that TBI turd is EXACTLY what I said. In EXACTLY the order I said it. For the chassis, converter and gears; you can, and probably should, do that before you even start on the motor. For the engine, exhaust, EVERY SINGLE PIECE from the heads to the bumper... just to keep it simple and a bolt-up, a set of GOOD QUALITY headers that are SPECIFIC TO THE CHASSIS (Not "universal") for something OTHER THAN a TBI car with a 3" outlet (about a 89 L98 would be a good application to look up), a good high-flow cat, and the 3" cat-back of your choice. Heads, I'd suggest Vortec (96-2000 truck), casting 906 or 062. A set of LS6 valve springs and Comp 787 retainers. A Comp XE262 cam or the Lunati VooDoo that's about the same size. If you go with a roller cam, the Comp "304" grind. A Performer RPM 4-bbl intake manifold AFTER all those other things, with a TBI adapter that puts the TB in the same place... there's at least one popular one that moves the TB either to the front or to the rear, can't recall which, but it makes the linkages and cables and fuel lines and everything else not fit.

 

I am not the only one with those same results.

Dewey316 did a head swap on his cammed 305 TBI with a weiand single plane intake on it at the time. The 187 TBI heads made more TQ and HP at ALL points below 4500 rpm than the ported 416s he put on the car did.

Fact remains call it garbage if you want but the factory LT4 Vette cam added 50 RWHP to a 350 TBI with external bolts ons and factory 810 casting swirl ports. It had a perfect idle at 550 rpm. It pulled great vacuum and had very good fuel mileage. It also went through smog like a dream in the carbureted 305 emissions numbers allowed for the 83 G20 Van. The heads are one of the last things that need to be replaced.

One other thing that worked very well with the later model 7427 PCM was the Edelbrock MPFI conversion. I put one on a TBI 350 with bolt ons that was making 280 RWTQ and 190 RWHP. Went to 310 RWTQ and 210 RWHP. Swapping out the clutch fan for electrics took it to 320 RWTQ and 215 RWHP. That 95 Tahoe ran noticeably better than a vortec and had never had anything other than the valve covers and intake off it.