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TBI 350 Heads = decent power??

This is a discussion on TBI 350 Heads = decent power?? within the Performance forums, part of the General Discussion category; How much power is possible out of the 350 TBI from 90-95 trucks while still using the factory heads. Lets ...

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    TBI 350 Heads = decent power??


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    How much power is possible out of the 350 TBI from 90-95 trucks while still using the factory heads.

    Lets just say that the Intake is upgraded, roller cam and lifters installed, high flow TBI unit, and proper tuning.

    I believe these heads have 1.94" intake, and 1.5" exhaust valves along with 76 cc chambers, but don't quote me on that one.

    I have read in a DIY 350 book from S A Designs that 350 hp is possible with factory heads. True or False?
    1995 Chevy Extended Cab 2wd: 14 FF, HSR 406, NV4500, Solid Front Axle

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    Re: TBI 350 Heads = decent power??

    you can make some decent performance while keeping these heads, mainly in improving torque, but in no way can you get 350 HP from stock TBI heads, and even if you could the tbi and the rest of the electionics could never support it.

    1995 K1500, 350, NV4500, 9.5" rear axle
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    Re: TBI 350 Heads = decent power??

    I won't say that it's impossible, but it's damn sure gonna cost a lot of money. For what you'd spend struggling to get 350 hp from the TBI heads, you could probably swap engines, or buy a blower. I mean, if you're gonna invest into a roller cam and all, then why are you so against changing the heads??

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    Re: TBI 350 Heads = decent power??

    im confident that with the right setup, you could have 350 fwhp from stock heads.

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    Re: TBI 350 Heads = decent power??

    Quote Originally Posted by cedjunior
    you can make some decent performance while keeping these heads, mainly in improving torque, but in no way can you get 350 HP from stock TBI heads, and even if you could the tbi and the rest of the electionics could never support it.
    WTF, I don't know where people are getting this dumb idea in their heads that the "electronics could never support xxx HP". I've seen this discussed in at least 3 threads in the past week, never with any factual information to back it up.

    Yes, the Rochester 220 TBI for the 5.7, the heads, the exhaust, the cam and the intake are all restrictions in the TBI system.

    That said, however, the computer (we'll use the 7747 for an example) reacts faster in most instances to changes from sensory inputs (TPS, MAP, CTS, Knock, etc) than the engine can react to. Usually in a matter of milliseconds, depending on programmed variables. Problems stemming from the placement of the injectors (wet flow versus port injection) are not the fault of, or within the control of, the ECU - and the 7747 (if I'm not mistaken) has been used to control TPI-style bank port injection.

    Now, assuming you're too dumb to get your ECU reprogrammed when you start making modifications, then the ECU will be confused and send out rough fuel trim levels in order to correct for the strange conditions it sees. Much like an incorrectly tuned carburetor, you'll never produce your engine's full potential power if all parts aren't working in perfect harmony. The ECU, especially the speed density ones, is capable of compensating for some small changes, but not huge ones.

    The biggest problem that many people have with the older TBI ECM's is the lack of an 8192 baud data port, meaning that you can only datalog information approximately every 1.6 seconds, whereas 8192 baud TBI ECM's can datalog in very close to real time and the accuracy of information within a given data cell is not nearly as questionable. This becomes something of an issue when tuning, however it is far from impossible to tune slow-baudrate TBI ECM's as many on this forum (including myself) have done. With properly adjusted VE tables and other variables, as well as a host of upgrades, 350 HP on a TBI motor is not impossible to do with a reprogrammed factory ECM.

    On another note, you obviously didn't read the full original post, the OP didn't ask how much was possible with bone-stock heads, they asked how much was possible while keeping these heads - implying that things like port matching, porting, polishing are all within possibilities. My speculative side is that he was hypothetically speaking - asking about the possibility of HP production with factory heads, not saying that they had intentions of actually building a motor to produce 350 HP with factory heads, because there are quite a few cheaper and easier head swaps that would put you a lot closer to 350 ponies.
    Last edited by Greenbuggy; 05-03-2005 at 01:54 AM.
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    Re: TBI 350 Heads = decent power??

    Quote Originally Posted by Greenbuggy
    there are quite a few cheaper and easier head swaps that would put you a lot closer to 350 ponies.
    Even with LOTS of head work, the factory TBI heads would still have trouble producing the 350hp. They would make gobs of low speed torque, but the 350 hp number would still be hard to attain. Like i said, it's far from impossible, but these heads have a TERRIBLE combustion chamber, terrible quench, and a VERY, VERY restrictive ramp in the intake runner. The worst thing is that there is hardly andthing you can do to increase the flow characteristics of the intake port. Short of a good gasket macth and smoothing out the very narrow part of the short side radius that isn't covered with the ramp there really isn't much you can do. I would hope that as you said this is merely a theoretical question. Because as i said earlier, if you're willing to go through the hassle and invest the money to switch to a roller valvetrain then why would you be against a head swap, especially when it's probably the most restrictive part of the entire TBI system.

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    Re: TBI 350 Heads = decent power??

    greenbuggy, it is nice to see someone that understands what the ecu is doing speak up for it. we all appretiate getting some realistic information to help explain what is going on and i agree with its potential and the importance of a tune.

    however, the "perfect harmony" of the system described just ins't there. it's well known that the lo5 heads (and even the lo3s on the 305s) were the worst designed heads that gm ever produced. they simply cannot flow what would be provided by the high flow tbi, intake etc and the full potential of those upgrades would never be reached.

    350hp possible? maybe, but not realistic. hypothetical or no, i wouldnt believe it until i saw some dyno numbers. i just cant imagine anyone putting the money into those upgrades and not changing the heads also, especially when you can find a used set of l98s that can be a great upgrade for around $100-200. A tbi is capable of great thing but the stock heads are the biggest restriction on the entire system and it is absolutely not worth trying to keep them.
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    Re: TBI 350 Heads = decent power??

    It was a hypothetical question. I know there are many head combos I can use with the TBI set up. I do not believe that switching to a roller valve train would be that difficult as the block was set up for it, but GM just put tappets in. I have been looking at Dart, AFR, Edelbrock, and Newer Vortech heads, but can't seem to make up my mind. My main goal is building a torque monster, but having good HP numbers would be a plus. Oh and I do have the software to do my own custom tune.
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    Re: TBI 350 Heads = decent power??

    yeah, it's not that hard to change to a roller cam, it's just the money involved. roller lifters ain't cheap. then you have to buy the dog bones and spider and etc. Not to mention the cams themselves are usually $200+

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    Re: TBI 350 Heads = decent power??

    Quote Originally Posted by Greenbuggy
    WTF, I don't know where people are getting this dumb idea in their heads that the "electronics could never support xxx HP". I've seen this discussed in at least 3 threads in the past week, never with any factual information to back it up.

    Yes, the Rochester 220 TBI for the 5.7, the heads, the exhaust, the cam and the intake are all restrictions in the TBI system.

    That said, however, the computer (we'll use the 7747 for an example) reacts faster in most instances to changes from sensory inputs (TPS, MAP, CTS, Knock, etc) than the engine can react to. Usually in a matter of milliseconds, depending on programmed variables. Problems stemming from the placement of the injectors (wet flow versus port injection) are not the fault of, or within the control of, the ECU - and the 7747 (if I'm not mistaken) has been used to control TPI-style bank port injection.

    Now, assuming you're too dumb to get your ECU reprogrammed when you start making modifications, then the ECU will be confused and send out rough fuel trim levels in order to correct for the strange conditions it sees. Much like an incorrectly tuned carburetor, you'll never produce your engine's full potential power if all parts aren't working in perfect harmony. The ECU, especially the speed density ones, is capable of compensating for some small changes, but not huge ones.

    The biggest problem that many people have with the older TBI ECM's is the lack of an 8192 baud data port, meaning that you can only datalog information approximately every 1.6 seconds, whereas 8192 baud TBI ECM's can datalog in very close to real time and the accuracy of information within a given data cell is not nearly as questionable. This becomes something of an issue when tuning, however it is far from impossible to tune slow-baudrate TBI ECM's as many on this forum (including myself) have done. With properly adjusted VE tables and other variables, as well as a host of upgrades, 350 HP on a TBI motor is not impossible to do with a reprogrammed factory ECM.

    On another note, you obviously didn't read the full original post, the OP didn't ask how much was possible with bone-stock heads, they asked how much was possible while keeping these heads - implying that things like port matching, porting, polishing are all within possibilities. My speculative side is that he was hypothetically speaking - asking about the possibility of HP production with factory heads, not saying that they had intentions of actually building a motor to produce 350 HP with factory heads, because there are quite a few cheaper and easier head swaps that would put you a lot closer to 350 ponies.

    No matter how many ECM's you reprogram, the computer system on 88-95 trucks would never support 350 hp.

    And yes I did read the whole post, so please don't imply you know better. Posts with that kind or tone make you seem like an ass****. He asked what potential those heads have. Well I guess potentially if you want to grind out the swirl port portion of the head you could possibly get those heads to flow comparable to other heads, but thats completely unrealistic. Have you ever seen inside those heads? There is a big chunk of metal in there, hence the name "Swirl Port" So why even bother?

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    Re: TBI 350 Heads = decent power??

    Alright lets put a few things to rest.

    As for head flow numbers. With some basic porting these heads can flow decent numbers. In fact numbers well ahead of l98's, 113's etc.

    Valve Lift------Intake Flow---------Exhaust Flow
    .050--------------35.6----------------------31.0
    .100--------------72.4----------------------60.5
    .150-------------105.8---------------------87.3
    .200-------------133.4--------------------124.2
    .250-------------154.1--------------------147.3
    .300-------------180.6--------------------171.5
    .350-------------195.5--------------------184.7
    .400-------------209.3--------------------196.3
    .450-------------217.4--------------------203.7
    .500-------------224.3--------------------215.6

    These were some home ported 193's. 225 cfm at .500. Not too shaby. Im liking the high flowing exhaust. That means use of a single pattern and use of a tighter LSA without increasing overlap. Cam timing like that sounds like a great recipe for more power to me.

    Some Unported head flow numbers

    083 iron L98 head: 202 intake; 141 exh
    113 alum L98 head: 199 intake; 149 exh 2.00/1.55 valves

    Some Ported

    083 iron L98 head: 229 int; 171 exh
    113 alum L98 head: 220 int; 191 exh

    Well Looks like the ported 193's smoked everything else. Shows what someone who knows how to use a grinder and knows head flow can do with a port.

    The thread can be read at

    http://www.thirdgen.org/techbb2/show...hreadid=283217


    Now lets look at the computer. Ok the 7747 is right on par with the early TPI computers as far as computing power. The main difference being Injector drivers. I see lots off TPI camaros breaking over 350 hp. The later more powerful computers shouldnt have a problem of supporting over 350 hp. The computer has absolutely nothing to do with max power. The problem with making big power on a TBI is airflow. You just cant get enough. Id be willing to bet if you used say a 900cfm 4 barrel holley tbi unit with a stock computer controlling it there wouldnt be a problem making 350+ hp on it.

    I think everyone needs to do a little more research before they really start ragging on something and talking about how bad it is. Though Ill admit even Im guilty of not following my own advice sometimes.

    Josh
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    Re: TBI 350 Heads = decent power??

    Quote Originally Posted by badburban
    Alright lets put a few things to rest.

    As for head flow numbers. With some basic porting these heads can flow decent numbers. In fact numbers well ahead of l98's, 113's etc.

    Valve Lift------Intake Flow---------Exhaust Flow
    .050--------------35.6----------------------31.0
    .100--------------72.4----------------------60.5
    .150-------------105.8---------------------87.3
    .200-------------133.4--------------------124.2
    .250-------------154.1--------------------147.3
    .300-------------180.6--------------------171.5
    .350-------------195.5--------------------184.7
    .400-------------209.3--------------------196.3
    .450-------------217.4--------------------203.7
    .500-------------224.3--------------------215.6

    These were some home ported 193's. 225 cfm at .500. Not too shaby. Im liking the high flowing exhaust. That means use of a single pattern and use of a tighter LSA without increasing overlap. Cam timing like that sounds like a great recipe for more power to me.

    Some Unported head flow numbers

    083 iron L98 head: 202 intake; 141 exh
    113 alum L98 head: 199 intake; 149 exh 2.00/1.55 valves

    Some Ported

    083 iron L98 head: 229 int; 171 exh
    113 alum L98 head: 220 int; 191 exh

    Well Looks like the ported 193's smoked everything else. Shows what someone who knows how to use a grinder and knows head flow can do with a port.

    The thread can be read at

    http://www.thirdgen.org/techbb2/show...hreadid=283217


    Now lets look at the computer. Ok the 7747 is right on par with the early TPI computers as far as computing power. The main difference being Injector drivers. I see lots off TPI camaros breaking over 350 hp. The later more powerful computers shouldnt have a problem of supporting over 350 hp. The computer has absolutely nothing to do with max power. The problem with making big power on a TBI is airflow. You just cant get enough. Id be willing to bet if you used say a 900cfm 4 barrel holley tbi unit with a stock computer controlling it there wouldnt be a problem making 350+ hp on it.

    I think everyone needs to do a little more research before they really start ragging on something and talking about how bad it is. Though Ill admit even Im guilty of not following my own advice sometimes.

    Josh

    so where'd yah get those stats josh .

    The computer will handle 350hp, no questions. Josh knows his stuff.
    Last edited by NorCal_z71; 05-03-2005 at 10:04 PM.

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    Re: TBI 350 Heads = decent power??

    Quote Originally Posted by cedjunior
    Well I guess potentially if you want to grind out the swirl port portion of the head you could possibly get those heads to flow comparable to other heads, but thats completely unrealistic. Have you ever seen inside those heads? There is a big chunk of metal in there, hence the name "Swirl Port" So why even bother?
    The ramp connot be grinded completely out...you'd create a hole

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    Re: TBI 350 Heads = decent power??

    Also, if you read on you'll find that those heads were flowed using backcut, swirl polished, stainless valves treated with a 5 angle valve job...that if FAR from a stock valve. worth well over 10 cfm easy Still pretty good numbers though
    Last edited by InProgressC1500; 05-04-2005 at 04:03 PM.

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    Re: TBI 350 Heads = decent power??

    Quote Originally Posted by InProgressC1500
    The ramp connot be grinded completely out...you'd create a hole
    Thats what I'm saying, it wouldnt be realistic.

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    Re: TBI 350 Heads = decent power??

    Quote Originally Posted by cedjunior
    No matter how many ECM's you reprogram, the computer system on 88-95 trucks would never support 350 hp.
    Where exactly are you getting this information? As noted above, plenty of guys thirdgen with early TPI ECM's are easily breaking the 350 HP barrier. If you think that a TBI computer can't do more than 350 HP, do you think that the guys running MFI could never break more than 200 with NO COMPUTER? Obviously 350 HP out of a TBI is going to take a big TBI with some machining, a built bottom end, good heads, good intake, good exhaust, descent cam, FPR, and plenty of cash - but as far as delivering the correct amount of fuel - I think 350 HP with a proper tune is not only doable but within the realm of someone with a descent amount of money, a datalogger and some tuning knowledge.

    An issue you could take up with me if you so chose to would be 350 HP crank vs 350 RWHP...I don't think its impossible to get 400 RWHP out of a TBI motor but I do think that it is a much stiffer challenge than 350 RWHP


    A guy just posted up a cool little device on the GMECM mailing list that can take the bank driver outputs from an early TPI/TBI ECM, runs them thru a microprocessor and outputs sequential injection to turn a TPI/LT1 setup into sequential port injection. I don't think sequential injection is worth *that* much more power, but pretty cheap at around $379.

    http://www.bakengineering.com/page5.html

    And yes I did read the whole post, so please don't imply you know better. Posts with that kind or tone make you seem like an ass****. He asked what potential those heads have. Well I guess potentially if you want to grind out the swirl port portion of the head you could possibly get those heads to flow comparable to other heads, but thats completely unrealistic. Have you ever seen inside those heads? There is a big chunk of metal in there, hence the name "Swirl Port" So why even bother?
    He asked a hypothetical question, he wants an answer. Practicality plays little to no part in hypothetical questions - if he wanted a practical answer he'd be asking "whats the cheapest way to get to 350 HP on my TBI motor" and he'd get a completely different set of answers.
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    Re: TBI 350 Heads = decent power??

    On the flow numbers.

    Yes backcutting valves can be worth 10 cfm. Yes he is using backcut valves anyone with a steady hand, a grinder, and some patience can backcut their valves. Swirl polished means nothing in terms of performance. Its mere a marketing skeem to sell more. The 5 angle seats mean nothing as well. There is no clear cut advantage to the 5 angle vs a good 3 angle. So long as the bowl blends smoothly into the seats thats all that matters. And if you really want to get into the nitty gritty of it. Vizards ported heads, which are where some of those ported head flow numbers come from, have backcut valves for the obvious benefit of it.

    If you really want to pick up some exhaust flow radius the face of the exhaust valve. Backcutting is worth a cfm or two but radius the face can easily pick up 10 cfm.

    I am by no means saying these are the next hot ticket for hot rodding. But what I am saying is that with a little bit of work they could be a killer truck head with a good cam choice. Keep that LSA down to a 108 for a 350 and run a single pattern cam since the I/E ratio is so good. When well tuned I think it would surprise a few people.

    Greenbuggy

    Thanks for the link. Sounds kinda cool.

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    Re: TBI 350 Heads = decent power??

    Josh extracted all that info from my post(s) on Thirdgen, and I got the swirl data from Fast355's original post.

    The 193 heads don't flow well in bone stock condition, but neither do the 083 (iron L98) heads -- unlike what the "experts" over at TGO have been saying (with no proof) for years. The 193s flow better on the exhaust, and the 083s flow better on the intake. BOTH respond well to porting. Period. And yes the aluminum L98 heads (113 casting) outflow them both in stock form, but they are more costly and arguably not as durable when you really port them and run them for high power (according to Vizard).

    On the 193 heads, the intake swirl ramp is not as much of a restriction as almost everyone at TGO (and here) says it is -- the data on three different swirl port heads before/after porting prove that. The combustion chamber shape is VERY good -- it's almost the same as used on the L31 Vortec heads. It has a projected nose central location for the spark plug, so it's all designed for fast-burn. GM even marketed the head design as a fast-burn head back in the late 80s. Hell HRM even ported a set of v6 swirl port heads and got decent results, and over 300 fwhp naturally aspirated. I added that info in my TGO post.

    Swirl polished valves: a marketing description

    Multi-angle valve seats: sometiems helpful but not the holy grail of headflow

    Backcut valves: a proven flow gain at very low lift; older heads lose some low-lift cfm because they didn't have backcut valves.

    What is the restriction to power on the TBI 350 (LO5)? In stock form, almost everything because GM designed it that way. Of course, all of that can be corrected to any degree you choose (or are willing to pay for). If I were modding a C/K truck I'd port the heads REALLY well and I'd keep the stock cam. I'd add stamped steel 1.6 rockers. I'd use the valve seals, springs, retainers and locks from a 94-96 Bcar (fresh springs, lighter valve components with no heavy rotators on the exh). I';d do something to the exhausta nd air filtration. I'd probably burn my own chip. The engine would retain it's manners at all speeds, I'd lose no torque anywhere and it would still run with a lot more power at high speeds. It would also cost me very little to do the above other than my time and my elbow grease. FWIW.
    Last edited by kdrolt; 05-10-2005 at 11:11 AM. Reason: minor corrections

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    Re: TBI 350 Heads = decent power??

    Ok so Factory ported heads flow better than stock L98 heads, but ported L98 heads out flow ported factory heads??

    Ok so how much would a "good" port job cost on a set of factory heads?

    Heres My planned motor:

    Factory bottom end,balanced (this wil be a crate short block)
    Replace factory cam with a Crane 2030
    Swap factory heads with a set of L98s
    Have the L98s rebuilt (please someone tell me what all that would be othewr than like valve guides) with a 3 way angle and clean up the combustion chamber
    Use the L98s intkae manifold
    Do a clean up/Port match and polish everything
    Free mods done to the TB
    Headers,TBi spacer,injector spacer, dual exhaust and a custom chip
    What do yal think?

    Since this a 4X4 I want alot of torque but my ponies would be nice.I already have the TB/injector spacer, duals, and TBIchips custom chip and I will ge another chip from him.
    02 1/2 ton 4X4
    6in Superlift w/ 315/75 toyo open countrys
    16X10 Classic II rims
    All stock other than that, but thats about to change.

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    Re: TBI 350 Heads = decent power??

    Quote Originally Posted by Chevy_Mudder6
    Ok so Factory ported heads flow better than stock L98 heads, but ported L98 heads out flow ported factory heads??
    Did you read the thread at TGO? The answer is no the ported L98 heads did not outflow the ported (193) heads, but I leave it to you to find out why. And when you say "ported factory heads" you are being too general ---- my post concerned the swirl port heads used on 305s (187 casting) and 350s (193 casting , and maybe the 191 casting as well).

    Ok so how much would a "good" port job cost on a set of factory heads?
    You can search this forum, as well as TGO to see what people paid, but it might make more sense to call the shops near you to find out what they charge. Most people who go that far don't go that route -- they just learn to port their own to save money and get almost the same performance as spending $500 to $1000 on new heads.

    Heres My planned motor:

    Factory bottom end,balanced (this wil be a crate short block)
    Replace factory cam with a Crane 2030
    Swap factory heads with a set of L98s
    Have the L98s rebuilt (please someone tell me what all that would be othewr than like valve guides) with a 3 way angle and clean up the combustion chamber
    Use the L98s intkae manifold
    Do a clean up/Port match and polish everything
    Free mods done to the TB
    Headers,TBi spacer,injector spacer, dual exhaust and a custom chip
    What do yal think?

    Since this a 4X4 I want alot of torque but my ponies would be nice.I already have the TB/injector spacer, duals, and TBIchips custom chip and I will ge another chip from him.
    The L98 intake is a TPI intake, so it doesn't use a throttle body with (2) injectors --- it uses 8 port injectors fed into a lower intake manifold base, and then it uses an upper plenum connected to the lower intake by individual runner tubes. I think you need to do some more reading before you become seriously separated with your money.

 

 
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