[sjkonyndyk]

agree with you DD's are not worth .02 but for comparative reasons it backs up what you read adn gives weight to a otherwise weightless statement being that I personally have not swapped cam for cam on a true environementally controlled Dyno.

[oldbogie]

Originally Posted by 91chevyss

Hi everyone, I have a questions for and about my motor in which heads i should use. first of all I have 91 silverado with a 350 tbi its been bored .060 over, a crane cam 114132 with a .440/.454 lift, edelbrock shorty headers, jet performance stage 2 chip, electric water pump, dual electric fans, throttle body spacer and a edelbrock air cleaner. I also have a edelbrock torker intake to use and adapter to use carb intake to tbi. the truck also has 3:73 gears. also approx. how much hp and torque do i have now thanks.

The cam you have is about equivalent to the old 300 horse 327 cam which in a carbed 350 also nets about 300 horse which tell you it under-cams a 350 and probably the 327 as well. However, this alone won't deliver 300 hoses on a 350 with a lot more compression than today's fuels will tolerate not to mention the TBI. Frankly I'm surprised that this combo runs on something as simple as a Jet Performance chip as these only mildly screw around with the operating temperature and mixture in a most general way. This really takes a custom chip such as you find at http://www.tbichips.com .

Electric fans and water pumps save precious little power contrary to their advertisements unless you run at red line all the time. Accessory power consumption is an exponential relation to RPM. The average power loss from fans and pump is in the onesy, twosey horsepower range till the RPMs get up over 5000, at that point the power consumption starts to get serious. But until that point its a little bit of nothing much.

Shorty headers are a scant improvement over cast manifolds. To get power improvements you need to look at full length headers with collectors. These provide serious torque and power improvements that are proportional to the camshaft timing.

Spacers between the TBI of carb and the manifold are really a tuning item, while advertised to do marvelous things to engine power, like so many things sold, these are the results of tests on "ringer" engines. That is they are set up specifically to get these results. Simply bolting this stuff on any engine doesn't assure that engine will see any improvement and perhaps will cause losses. The torquer is a good choice but sandwiched between the TBI and Swirl Port heads, it's hardly making a contribution.

The OEM TBI has a flow potential of about 410 CFM. this certainly is inadequate to feed a 450 horse engine more like a top of maybe 250 if the engine has enough cam and compression. Solutions are found on 454s or at Holley. The 454 TBI and the Holley 502 are rated at 670 CFM using a 2 inch throttle bore instead of the 1-5/8s or 1-11/16s of the SBC. Holley says the 502 can support up to 275 HP, but with 80-90 lbs injectors on a 350 it should support about 340 hp which is beyond the reach of your cam.

Heads, you've said nothing about heads. The stock TBI engines came with Swirl Port heads, these pretty much shut off around 4800 RPM. Plus they have fairly poor combustion chambers. A set of Vortec heads are worth about 40 horses just bolting them on, most of that comes from the greatly improved combustion chamber and some more from better port flow, these will raise the top RPM potential with the cam you have by offering better breathing and much more efficient combustion.

Aside from the heads; the big problem remaining in your engine is the OEM pistons. They use a deep circular dish in the crown to arrive at this engines mild compression ratio. This makes for a lazy squish/quench function which can be thought of as mechanical octane built into the engine. A flat top piston is the best solution toward getting at efficient combustion and optimum detonation management, but this especially with a small chambered head like the Vortec this can lead to more compression than all the mechanical tricks and fuel octane can overcome. The solution lies in the D dish piston where all the dish volume is placed under the valve pocket and the piston presents a flat top to the head's squish/quench deck. This with the proper gasket and or milling the engine block for a zero deck, allows the piston to close to the squish/quench deck at about .040 to .060 inch. This really kicks up both the squish and quench functions which allows you to optimize the compression ratio against the available octane fuel for the best power that can be reasonably extracted. But even with the pistons you have, a set of Vortecs will put enough additional power out the crankshaft that you will feel them working.

A roller cam of the same specification as what you have brings nothing to the table power wise. What a roller cam does is eliminate the wear problems encountered when ZDDP was removed form oils about 25 years ago. Passenger car engines went to roller cams as they tended to use a larger cam and stiffer springs, trucks used a very mild cam and soft springs so scuffing wear between lobe and lifter wasn't considered a problem till 1996 when what little anti-scuff agents remaining were purged from all but diesel rated oils. This is not to be confused with why roller cams are used in full up race engines which is an issue of lift rate, they allow a much faster rate of lift than can be had from a flat tappet once off the initial ramps.


You're off to a good start but need to keep going.
Bogie

[91chevyss]

i found a rebuilt tbi with 50 mm and they said it would support up to 450hp #230571186774 (ebay) it has 700cfm or should i get the trick flow twisted wedge heads i found on ebay with 180cc intake 2.02/1.60 valves and a 63 combustion chamber. also about where would i be at with both as far as hp and tq. thanks.

[oldbogie]

Originally Posted by 91chevyss

i found a rebuilt tbi with 50 mm and they said it would support up to 450hp #230571186774 (ebay) it has 700cfm or should i get the trick flow twisted wedge heads i found on ebay with 180cc intake 2.02/1.60 valves and a 63 combustion chamber. also about where would i be at with both as far as hp and tq. thanks.

That would be right at the edge of the biggest 90 gallon per hour injectors you can get.

The heads are fundamental to getting to 400 plus hp. But Twisted Wedge heads take a unique valve gear arraignment, if that isn't included they are no deal as the rocker mechanism for these heads is really pricey.

Bogie

[dromero5]

Okay i have built 2 TBI engines and let me tell you what the bottlenecks are. The first one was a 350 with 9.7:1 compression with the 12-256-4 cam with 175cc Trickflow 87-95 heads. I used a factory TBI manifold bored to 50mm and 454 injectors. I had Brian at TBI chips tune the chips almost got 18mpg and it dynoed close to 285hp and 418 ft/lbs of torque. It ran out of breath at 5000 because intake was restrictive even with the 50mm TBI from xtremefi.com. Second motor is a 383 with Trick flow 195cc heads with 9.5:1 compression with 12-365-4 cam with the Edelbrock 3704 intake bored to 48 mm with 50mm TBI unit with 454 injectors. Ran 1.6:1 rockers on both setups. This one wasn't dynoed but estimate it is around 320 hp and 450ft/lbs of torque based on similar builds. Once again this one is torquey but top end falls off around 5200. The biggest bottleneck seems to be the 2 barrel TBI intakes. I think i may swap in a 4bbl carb intake like an Edelbrock and use TBI adapters and have EGR tuned out of chip. 450 hp is almost impossible with two barrel TBI, on an aftermarket 4bbl TBI it is doable.

[91chevyss]

the id number on ebay for the heads are 110632908863 take a look and let me know and i wanted bigger cam for sound and all i really wanted a lope but my stock tbi heads want hold but like a .480 lift i think, whats a good cam i could get but not to pricey and one that would help to get around the 400 450 hp you know so i wouldnt have to buy anotherone i wish i wouldnt have got the one from summit (the crane cam) its like 225 now. what should be my first step. appreciate the help.

[dromero5]

Well I hate to say it but you are limited with cams with TBI and if you want one to sound "lopey" your 7747 computer is going to hate it due to the overlap. You have to look at cams under 268 advertised duration or under 225 degrees@.050. You can run big lift of over .5 but it is important to keep the LSA above 112 degrees. As far as heads go I would at least entertain vortec heads that are machined to accept more than .470 of lift and ditch the stock swirl ports. Stay away from World Product Sportsman II heads have had nothing but oil consumption with those unless you have them completely gone through with a machinist. AFR heads simply can not be beat but like the Trickflow heads they basically outflow the potention of the restrictrive two barrel TBI intakes. With a 383 your really pushing the limits of TBI past 350 hp. Dyno, or in person tuning is a must.

[91chevyss]

to dromero5 and i guess to everybody I was going to buy the adapter for the two barrel tbi to my edelbrock torker intake but haven't yet but i do have edelbrock 1407 which is a 750cfm that needs to be rebuilt i had the kit but took it back because i needed the money but im scared to carb it because i not sure how hard it is to get it running also the carb has a minor crack on the bottom i took it to a mechanic and he said it could be fixed okay should i switch it to carb and change the heads because i would save money from not buying the 50 mm tbi therefore i could get heads. also if those 2 engines you built if they had a 4bbl carb how much power would they have. i also brought a mechanical fuel pump a while back for the swap but i backed out thanks yall for the replies

[dromero5]

I have had good luck with the 1405 and 1407 Edelbrock carbs in a pickup with the #1465 off road kit in them. They are easy to tune and have charts in the back of the owner's manual to get you jetted or real close. I have also ran the Torquer Intake manifolds but was happier with the Edelbrock performer for better low end and midrange power. Had i not went with TBI the first 350 should have made around 330-340 hp and I just read a buildup of a 383 with similar compression using 7 different Comp Cams. The 12-256-4 cam made 402 hp and the 12-262-4 made like 419 hp. The 12-365-4, which i ran in the 383, is in between so i assume you could pull 410 hp with a 750 cfm with 9:1 compression ratio with a good .040 quench. i sacrificed hp for driveability as i live at high altitude and cold winters and don't like off camber carb sputters when i am rock crawling. I may have made more with the trick flow heads because i think these were tested with Patriot 180 cc heads.

[oldbogie]

Originally Posted by dromero5

Okay i have built 2 TBI engines and let me tell you what the bottlenecks are. The first one was a 350 with 9.7:1 compression with the 12-256-4 cam with 175cc Trickflow 87-95 heads. I used a factory TBI manifold bored to 50mm and 454 injectors. I had Brian at TBI chips tune the chips almost got 18mpg and it dynoed close to 285hp and 418 ft/lbs of torque. It ran out of breath at 5000 because intake was restrictive even with the 50mm TBI from xtremefi.com. Second motor is a 383 with Trick flow 195cc heads with 9.5:1 compression with 12-365-4 cam with the Edelbrock 3704 intake bored to 48 mm with 50mm TBI unit with 454 injectors. Ran 1.6:1 rockers on both setups. This one wasn't dynoed but estimate it is around 320 hp and 450ft/lbs of torque based on similar builds. Once again this one is torquey but top end falls off around 5200. The biggest bottleneck seems to be the 2 barrel TBI intakes. I think i may swap in a 4bbl carb intake like an Edelbrock and use TBI adapters and have EGR tuned out of chip. 450 hp is almost impossible with two barrel TBI, on an aftermarket 4bbl TBI it is doable.

I would agree, 330 hp is the best I've gotten one of these things to dyno with the GM computer and have to SMOG. The cam is the big problem, it's just hard to put in enough cam and still get the computer to understand what's going on. A cam much bigger than 210-220 degrees and about .47 inch lift at the valve pushes the vacuum down to where the sensors don't have enough sensitivity to discriminate the extremely small changes in vacuum that occur with what becomes large throttle position changes since you're starting out with very little vacuum. This can be pushed further with the Holley computer that doesn't monitor the relation of vacuum to RPM and throttle position, just the latter 2. The GM computer will not let you go that far because of the need for strong vacuum sensing, i.e. more than 10 inches at idle, that makes sense to the RPMs and throttle position sensors.

I agree on manifolds, the TBI is a low riser that just doesn't feed the ports all that well. Most any decent 4 bbl manifold with a TBI adapter is a better solution.

Contrary to the salesmanship on Ebay, Holley feels that 275 horse is the limit on the 502. You can push it further but you start to use up the duty cycle cushion doing that so the injectors don't live as long. The 4bbl TBI gets you around that problem by spreading the fuel flow over four injectors.


Bogie

[91chevyss]

if i was just to switch it to the 750 cfm edelbrock carb and the edelbrock torker intake how much hp and tq gain would i get and where would i possibly stand at with my engine mods. also if i switch it to carb could i get a bigger cam

[91chevyss]

if i use the edelbrock 1407 the trick flow 180cc twisted wedge heads and a cam 488-509 LIFT, ADVERTISED DURATION 303/313º AND 234-244º @ 0.50 lift DURATION, 110º LOBE SEP. could i possibly be at the 400-450 hp and tq range. thanks

[oldbogie]

Originally Posted by 91chevyss

if i use the edelbrock 1407 the trick flow 180cc twisted wedge heads and a cam 488-509 LIFT, ADVERTISED DURATION 303/313? AND 234-244? @ 0.50 lift DURATION, 110? LOBE SEP. could i possibly be at the 400-450 hp and tq range. thanks

Yes but it would be more reliable on the top end with a Holley or Demon 750. These do a better job of high RPM metering than the Carter or the Q-Jet both of which tend to go way rich and it's hard to get them back while not leaning the mixture too much every where else.

Like I said before used Twisted Wedge heads are only a deal if they come with the valve train. The configuration of these things vary quite a bit production lot to production lot such that valve train parts that fit earlier versions don't work on later versions and vise versa. These are very hard heads on which to get the valve to piston clearances set up when you start talking a big cam you also get piston to valve interference potentials, you have to haul out the old degree wheel and Play Dough and do a mock up assembly to check this stuff out.

For my money when you start talking over 400 horse from a 350 or 383 the best heads to support that don't take trick parts are the AFRs. Here you'll need a larger port than 180ccs to get there, but get there they do. They'll easily pump out 420 hp with a cam no wilder than say a Comp 272 and about 9.25 to 1 compression. With a bigger cam and attention to the piston crown shape and static compression around 10 to 1 these will take a 350 to 450 horse if the rods are up to it. This kind of power is on the upper limit of production rods.

Bogie

[91chevyss]

well i have the edelbrock 750 and torker intake on the engine now and i put a .488 lift cam in it but now im having problems with trans lol if any body has some good sbc heads for sale other than tbi heads let me know

[cool rockin daddy]

Go back, sit down, and write down what you want to achieve. Take a look at the parts you have and see if they are compatible with everything everybody is telling you. Right now, you're just piecing this thing together with parts you happen to have on hand. Not the way to do it if you want a reliable 450 hp engine which isn't going to happen with those heads. I see no mention of the type of transmission you are running and if you expect to run power brakes. SLOW DOWN and do some planning.