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1badchev
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Discussion Starter · #1 ·
Thoughts from anyone.... i currently have a TBI 350, with the stock cam from a 350 hp 327 sbc, throttle body spacer ajustable fuel pressure regulator and a custom burned prom chip.... 1st off i have a buddy who has the same cam as me in his 350 but he is running a carb (no Fuel injection) and he can run circles around me... 2nd off im really un happy with the 500 hundred dollar Prom Cip that i have all it seems to do is make it idle smoother with no lob from the cam. what can i do to gain more power easliy and cheaply? ive read about guys running 305 heads, what about vortex heads which will benifit more? and what about the edlebrock intake for TBI? is it worth the 300 bucks? or should i just pull the cam and go with a different one?
 

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TBI`s suffer from lack of air flow compared to a carb. Also If the heads came originally on the TBI engine they have the worst ports in small block history, the dreaded swirl port. Gear ratio of each vehicle plays a big role in this as well. TBI really isn`t a performance orientated system, it did well at low RPM but doesn`t have enough airflow for upper RPM performance. The 350 horse 327 cam is a old, outdated design. You would have came out far better by using one of the new computer compatible cams.
 

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Jethrotrc said:
Thoughts from anyone.... i currently have a TBI 350, with the stock cam from a 350 hp 327 sbc, throttle body spacer ajustable fuel pressure regulator and a custom burned prom chip.... 1st off i have a buddy who has the same cam as me in his 350 but he is running a carb (no Fuel injection) and he can run circles around me... 2nd off im really un happy with the 500 hundred dollar Prom Cip that i have all it seems to do is make it idle smoother with no lob from the cam. what can i do to gain more power easliy and cheaply? ive read about guys running 305 heads, what about vortex heads which will benifit more? and what about the edlebrock intake for TBI? is it worth the 300 bucks? or should i just pull the cam and go with a different one?
I concur with Doublevision, the heads have to go. Vortec's would be the most popular answer. That drives you to either the GMPP or Edlebrock intake as the stock TBI intake doesn't have the same bolt patter nor is it able to keep the higher positioned intake ports closed up without leaking air. 305 heads are a lot of work by the time your approaching out of the box Vortec performance you've sunk as much or more into the 305 heads. But with your original swirl port heads it's all in by 4500 RPM where the 350/327 cam wants to come on at least a grand higher, you're probably not getting more than 250 horse at the crankshaft with this set up.

Piston selection is also very important, these days the D dish design is the selection. The dish is sized for the desired static compression ratio all under the valve pocket. The side opposite has a flat surface which closes vary closely to the head's squish/quench deck typically .040 to .060 inch including the piston head clearance to the top of the block and the gasket. This forces the mixture violently into the area by the spark plug, this is squish. It both increases the chance of a burn from the plug and it speeds that burn across the chamber so more power can be had from using less advance which wants to peak the chamber pressures too early which in turn leads to t]power lost trying to turn the engine backwards and increased detonation because the piston can't get away from the excessive pressures and temperatures that occur too early. The second feature of the close closing of these parts is the cooling of the late burn by the great surface area to volume ratio, this is called quench. This helps quell detonation, the features of squish/quench help modern unleaded fuels better operate at high compression ratios. One thing your engine is doing without telling you is if it gets into detonation, there is a sensor that "hears" it and signals the computer to pull the advance back till it stops. Both ways, detonation or pulling the advance back cost power, but this way doesn't also cost the engine.

The TBI itself is too small, you need a unit from a 454 truck or a Holley model 507, both of which flow about 670 CFM against your stock 350 TBI of 400 CFM.

Of course another new chip is needed.

The old 350/327 cam has too much overlap for fuel injected engines. While the lift and duration is nice, modern engines like the Lobe Separation Angle (LSA) opened up from 112 to 116 degrees. This increases manifold vacuum, something Manifold Absolute Pressure sensing EFI likes and EFI engines just don't need as much cam overlap as carbed engines do, though an argument could be made that TBI does and for a bit of flow it probably would but that trade is greater than getting the manifold pressure up. EFI engines are a new technology making the old 350/327 look rather flintstoneish, but to get these moden engines there, you need to understand their unique rocket science.

Bogie
 

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1badchev
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Discussion Starter · #4 ·
Thank you both for your knowlege, so i need to pick up a TBI from a Big block ....what mods need to be done to make this work? and i have seen others drill out the holes on the intake to match the bolt patteren of the vortex heads, yes kinda jerry rigged but it works.... but how much of an advantage is a aftermarket intake going to give me? likei said before is it worth the 300 bucks for one? On to my next question, am i going to see any more power from just going to the big block TBI or should i stick with the TBI i have now and opt for a different cam? I have a set of Vortex heads on hand they need to go to a shop to be cleaned and what not....but down the road i am building a 400 sbc, i have 2 i picked up for a good price....but well discuss the 400 later about what i have heard and what your knowlege says but i want enough out of my 350 to "get by" until the 400 is built (i should say until i have money to build it) also parts that can carry over are a plus like the vortex heads...
 

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You can get Vortec heads and a Vortec intake, then use a carb to TBI adapter which lets you bolt on a 2 hole adapter on the intake meant for a carb. since you wish to keep the TBI this would likely be your easiest way out. If you drill the heads to set it up on the old 12 bolt pattern the ports will be out of alignment since Vortec ports are taller and sit at a slant.
I knew this could be done and thought about doing it to my 4.3 but later decided I`m going to dump the TBI and go with a carb. I`m not sure of the TBI mods you`ve done, but when I built my 4.3, I ported the swirl port heads very mildly, added necked down ferrea valves with 30 degree back cut, flat top pistons, .044 quench distance, balanced the bottom end, Isky hydraulic computer compatible roller cam, double roller timing set, Edelbrock TBI intake.
I took the TBI off and did a full port job, thinning down the throttle shafts and smoothing the top and air entries. I also added a adjustable fuel pressure regulator with vacuum compensator, fuel pressure bung to check the pressure, Venom high flow injectors and a TBI injector spacer. The engine has about 10:1 compression, runs great on pump gas, has killer torque. The downfall is, due to the heads the power falls off at 4000 RPM. If you haven`t did any of the TBI mods I`ve done you won`t get no where near the full potential out of the system. You have to play with the fuel pressure to find out which setting it likes best. The Venom injectors made the biggest difference of all, swapping out the original half clogged injectors to venoms made it feel like the truck pickup up 30 horses. Since Vortecs flow far better, it`s going to want more air and fuel. and I hate to say also, you`ll have to get another chip burned.
 

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Jethrotrc said:
Thank you both for your knowlege, so i need to pick up a TBI from a Big block ....what mods need to be done to make this work? and i have seen others drill out the holes on the intake to match the bolt patteren of the vortex heads, yes kinda jerry rigged but it works.... but how much of an advantage is a aftermarket intake going to give me? likei said before is it worth the 300 bucks for one? On to my next question, am i going to see any more power from just going to the big block TBI or should i stick with the TBI i have now and opt for a different cam? I have a set of Vortex heads on hand they need to go to a shop to be cleaned and what not....but down the road i am building a 400 sbc, i have 2 i picked up for a good price....but well discuss the 400 later about what i have heard and what your knowlege says but i want enough out of my 350 to "get by" until the 400 is built (i should say until i have money to build it) also parts that can carry over are a plus like the vortex heads...
The Vortec head lifts the entire port up about a tenth inch. This has a similar effect on flow as rolling the valve angle as is done with 18 and 15 degree heads, but this keeps the original 23 degrees while easing the short side turn. Using an intake that doesn't match, does not take full advantage of this feature, leaving some performance on the table. Now I'm going to torque a number of people off with what I'm about to say. That is in this column and in the popular press you will see a lot of people who emphasize, correctly, the need to shape the valve guide and pocket properly for flow. These same people then step off into a place where they really don't know about, which is the intake to head port interface and they go off and say that working this area has little to no benefit. This claim comes from spending too much time on a flow bench with a head that is not breathing thru the manifold it will be joined to. There is a significant difference in flow when a port is connected to the manifold that will feed it and there are good reasons to work the head's ports and the intake passages to improve the flow of the assembly. A high flowing port, shaped without benefit of the manifold does not flow anywhere near the free measured flow. Addressing how the intake sets the flow up as it enters the head port can greatly improve overall flow os the system. Which is to say that idealizing the elements of a system independently does not guaranty that those elements when brought together will continue to be optimized as a system.

I would recommend you get some books on EFI and read up how it works so you have a better understanding of how to modify these things here's one suggestion http://books.google.com/books?id=9w...snum=8&ved=0CB0Q6AEwBzgK#v=onepage&q=&f=false

It is possible to do your own tuning with programs on your computer.But before you do that I'd recommend you get some books on EFI and read up on how it works so you have a better understanding of how to modify these things here's one suggestion http://books.google.com/books?id=9w...snum=8&ved=0CB0Q6AEwBzgK#v=onepage&q=&f=false

Down the road you can get the software and hardware to make your own chips, the equipment is really not any more expensive than a chip or two.
Lots of places to look, here's one:
http://www.pcmperformance.com/index.html

Bogie
 
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