TBIThrottle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.
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i was thinking of doing a head job on my 91 tbi 305.
i was planning on professional PORT and POLISH job according to the specs of my mild comp cam 08-500-8, along with putting slightly bigger intake valves 1.84 to 1.94 but i have heard that they are not worth porting. WHY?!?!?!?
the reason why i dont want to go with the older style heads is because i already have roller tip rocker arms, push rods, and springs for the tbi heads.
will the head job not do me ANY good.....Im probably willing to be happy for some.
any advice?
Theirs a ramp cast into the bowl under the intake valve that restricts flow to the cylinder but makes the air fuel mix "swirl" into the cylinder which makes for better fuel economy, or so i'm told, basically it's an economy head not a performance head. best off going with pre centerbolt head, tpi head or vortec head from a 305.
I have unsuccessfully tried giving away 350 TBI heads, people wont even take them for free. But of course you'd see gains opening up heads, in any aspect.
I port and polished my heads in my garage with a standard abrasives kit and pneumatic grinder. It's a relatively mild engine, still retains the TBI heads , and pulls HARD on up to 5200 RPM. Just perfect for a street cruiser IMHO.
If you're handy with the grinder, give it a whirl. You'll need a couple of long shank mandrels as well. DIY saves money.
The heads get a bad rap because people don't understand them. No stock 3rd gen head was a "performance" head. In fact the TBI heads outflow TPI heads on the exhaust and lag slightly on intake. A little port work does go a long way to be able to support 250 to 300hp with ease. Just ask Fast355 what he has done with swirl port heads. At the end of the day it comes down to proper cam selection combined with DIY chip tuning. People often skip tuning and then blame the heads because it parallels the TBI naysayer tabloids.
The heads get a bad rap because people don't understand them. No stock 3rd gen head was a "performance" head. In fact the TBI heads outflow TPI heads on the exhaust and lag slightly on intake. A little port work does go a long way to be able to support 250 to 300hp with ease. Just ask Fast355 what he has done with swirl port heads. At the end of the day it comes down to proper cam selection combined with DIY chip tuning. People often skip tuning and then blame the heads because it parallels the TBI naysayer tabloids.
The heads get a bad rap because people don't understand them. No stock 3rd gen head was a "performance" head. In fact the TBI heads outflow TPI heads on the exhaust and lag slightly on intake. A little port work does go a long way to be able to support 250 to 300hp with ease. Just ask Fast355 what he has done with swirl port heads. At the end of the day it comes down to proper cam selection combined with DIY chip tuning. People often skip tuning and then blame the heads because it parallels the TBI naysayer tabloids.
TBI heads, even stock will make more HP and more TQ than most other heads below 4,500 rpm. Gobs of torque can be fun on the street.
I have unsuccessfully tried giving away 350 TBI heads, people wont even take them for free. But of course you'd see gains opening up heads, in any aspect.
I'm guess this is because not many people on this board own 350 TBI's, just my guess...
Back to the topic, so shifty, you're saying that you could do other mods (mainly being what? Cam and tuning?) and get 255+ hp from this motor without swapping the heads? Just porting?
Yeah, I think torque is awesome too.
Another quick question, how far up would you guys recommend taking the stock 305 tbi motor up to before shifting? Personally I don't take mine higher than 4500 or 5000, otherwise it doesn't really feel like it's accelerating anymore, the other day (I dunno whether this is a problem with the motor or just valve float or some other inhibitor) but I revved up to like 5000 in like second and it almost started slowing down, it stopped accelerating, is there a problem there?
The heads get a bad rap because people don't understand them. No stock 3rd gen head was a "performance" head. In fact the TBI heads outflow TPI heads on the exhaust and lag slightly on intake. A little port work does go a long way to be able to support 250 to 300hp with ease. Just ask Fast355 what he has done with swirl port heads. At the end of the day it comes down to proper cam selection combined with DIY chip tuning. People often skip tuning and then blame the heads because it parallels the TBI naysayer tabloids.
thats what i was thinking espcially since you said it...no third gen STOCK head is performace to begin with. thanks for the help guys. i know that porting out a set of older style heads would maybe be better but, i should be able to make up on that with ecm tuning.
The heads get a bad rap because people don't understand them. No stock 3rd gen head was a "performance" head. In fact the TBI heads outflow TPI heads on the exhaust and lag slightly on intake. A little port work does go a long way to be able to support 250 to 300hp with ease. Just ask Fast355 what he has done with swirl port heads. At the end of the day it comes down to proper cam selection combined with DIY chip tuning. People often skip tuning and then blame the heads because it parallels the TBI naysayer tabloids.
I would tend to believe the 187's and 193's flow numbers would fall behind heads like the 416's after 4000-4500 rpm though.
shifty and fast355 know about these heads they post about them all the time. they are a decent street head - lots of torque but wont do much over 4500 rpm.
im still going back and forth about using them, but my issue is do i want to spend the money on a valve job, new stainless steel valves, screw in studs and the time to polish the exhaust - i think the intakes need to be a little rough - smooth but rough for the swirl, or spendd that time on some better performing heads.
the really nice thing about this is the good low rpm torque and you can use late model 3rd gen intakes - well up to 96 on the 305 but nothing from the lt or ls.
I know this is quite an old thread, but I thought I'd post what I've done so far. I'm building a TBI-fueled 383 for my '92 Sierra, and to save some money I decided to stick with the 193s for now (Vortecs are kind of pricey around here, plus the Vortec-specific intake, and I have emissions testing so an EGR is required). This is my first time porting, so I'm sure there are others who have done prettier jobs. What I've done so far is with a Dremel and flex attachment. I have to get some stones with longer shanks if I'm going to be able to finish the runner though. This is basically far as I can go on the intake currently. I haven't touched the exhaust yet, but that will probably just be some smoothing as opposed to shaping. You can also see other pictures in the link.
Funny thing is I've had several people tell me they're going to choke the motor up like crazy... it's not like I'm just taking a bone stock set and putting them on...
Nah you should be fine. Alot of people out there talk mad trash on swirlies mainly b/c they're ignorant and too lazy to learn for themselves that these are actually a very good stock casting. Now if you compare them to like AFR's or even the heads from the later style LS engines then yeah maybe both of the latter are better. I also ported and polished my 193 swirlies and on my 360" they make a ton of torque and pull hard from idle to 5K rpm.
