383 TPI Question

[jim_in_dorris]

Well, I finally have the budget to build a new motor for my 87 1/2 4x4. It's only a little each month, but I have a fairly good idea of the parts I want to use. I am going to use Dart SHP heads with an Isky nn257/265 cam and long tubes. I am trying to decide if going TPI will choke the motor at the upper RPM levels. Peak horsepower is at 5000 RPM with this setup, and I have heard that the TPI manifold isn't much good after about 4900 RPM. I have had the truck for 10 years, and have hit 4900 + RPM less than 5 times (I drive like the old man I am) however I really want torque to tow a trailer with. I have towed upwards of 6000 pounds with the stock motor on this truck, but it struggles. So, my question is; Should I stick with TBI, or is TPI worth the extra effort? I know this will start a firestorm of opinions, but lettr rip guys. I have talked about this before, but now I have the money for parts (the bottom end is my christmas present to me).

[dave w]

I see both Pro's and Con's to both TBI and TPI systems.

For simplicity and cost factors, I favor TBI using the 2nd generation TBI PCM, 1619747. I favor using an early version 454 throttle body, with 80 lb injectors and near stock fuel pressure. I favor a modified Edelbrock TBI intake (enlarge the throttle bores to fit the 2" 454 throttle blades). I feel the Edelbrock TBI intake will maintain a better air flow velocity of the air / fuel mixture than a carburetor intake with a TBI adapter plate.

The spreadsheet I use to tune a 16197427 PCM is an excellent tuning tool when combined with WBO2 information in the data log! See attached screen shot.

dave w

[Fast355]

I think everyone knows my intake of preference of the victor jr 2bbl with a late model 454 TBI although in your application I would use a Performer RPM dual plane. I like using the high pressure 46 or 61# injectors that flow ~74 or 105 lb/hr at 30 psi.

[jim_in_dorris]

Sounds like I have two very respected people telling me TBI. I get votes for different manifolds, so I must ask about the BB Carb to tbi adapter that I have. Dave, you said you don't like it. Why? And Fast you must think it's ok. Same why. I don't have a problem staying TBI, the torque curve isn't as flat, but I do have a little higher peak torque that way.

I have a set of 454 injectors (the high flow low pressure ones) as well as a 454 TB and an 8625 PCM, so I have that covered. I need to decide whether an APU1 or a Burn 2 coupled with an Ostrich 2.0 will fit my needs better. I will be diving back into my $0D mask this winter getting ready to use it with the new engine.

[Nasty-Z]

I will cast my vote for a 454 TBI unit on a single plane manifold , the model year of the TBI body itself is incidental , I would use the the early low pressure injectors as they are more tolerant of higher pressures than the later units , I have as well as others ran them at 70+ psi with no adverse effects . To regulate the pressure I would use an external adjustable vacuum referenced regulator and block off the stock unit. To control it I would upgrade to the later '7427 PCM .

The 454 TBI on the single plane manifold will offer the best of both worlds for you , dead on reliability , and it will feed whatever you have planned , and the '7427 will make tuning a relative breeze.

TOM

[Chewy1576]

I'm running a SBC TB with 80# injectors over a 383 with the Edelbrock TBI intake. At 3000+ RPM, the SBC TB doesn't feed enough air and the power fades. In the future I will be boring out the intake to support a BBC TB.

[Nasty-Z]

In a TBI application a dedicated dual plane TBI specific intake is generally a restriction , many times it is more of a restriction that the TBI unit itself (such is the case with the BBC) . A single plane carb intake with an adapter plate or a 2bbl single plane such as the one Fast posted above is a vast improvement in any TBI system.

As most always in the auto industry , designs are made to be a compromise , such is the case with a dual plane manifold , it is a crutch in a carb setup to improve drivability , it acts much the same in a TBI system , it improves drivability / tunability , but since any cylinder can only "see" half of the available air flow , it becomes a restriction pretty quick for a performance engine. Of course there will be opinions , airflow through an intake is fact.

TOM

[1project2many]

For very mild gains one can put a spacer under the TB and reduce the height of the divider. When doing this one will open the coolant crossover passage. Welding the passage closed eliminates the crossover and reduces intake air heating. There are faster and better ways to improve airflow, but this can make a difference.

[dave w]

I feel intake runner design and intake plenum volume are very important factors for performance. There is a compromise, so the intended use of the engine is an important decision. My experience, without the aid of a dynometer, has shown a vehicle of about 5000 lbs that is used for daily driving (95% of the time @ less than 3500 RPM's) and occasional towing responds well to an intake design with long runners and a moderate size plenum. I feel the Edelbrock TBI intake is slightly better intake than a dual plane 4 barrel intake with a TBI adapter plate for the following reasons:
The Edelbrock TBI intake has slightly longer runners than a dual plane 4 barrel intake.
The Edelbrock TBI intake plenum has a slightly smaller volume than the dual plane 4 barrel intake. The smaller plenum will help maintain a high velocity of the fuel air mixture at lower engine speeds (less than 3500 RPM's).

dave w

[jim_in_dorris]

Sorry I have been busy with work. I really appreciate the advice. I am now pondering how much I need between 3500 and 5000. I really don't want to choke the engine too much on the chance that I will need some of the top end. I like the idea of a single plane, however I chose the heads because they would support EGR (I do still live in CA). Weiand used to make a single plane manifold with EGR, but they have disappeared. If anyone knows of a single plane manifold with EGR, let me know. I like that the Edelbrock TBI intake has EGR, is there room to bore it to accept the 454 bore size? I will definitely use my 454 TBI with the 454 injectors so that I don't have fueling issues. (Yes I know that it doesn't have a carb eo #, but it still would have an operating EGR) It looks like a stock TBI manifold, what are the differences? Does it make enough difference over the stock manifold to justify the cost? This is something I am curious about. I am going to have to get my truck on a lift to see if I have a cracked flex plate, or if what I hear is the end of the lifespan for the existing 350. (It has over 200K miles on it) I also need to have my son finish replacing the heater core in my wife's 2002 blazer so we have something to drive if my truck dies. It's kind of slow right now at the dealership where he works, he got 1 1/2 hours of customer pay today, and two PDI's yesterday. Prior the those 2 days, he had 40 hours the first 4 days of the pay period. I am hoping that with the slowdown he can pull the wife's blazer into a stall and get the heater core done. I may have to drop in a little 283 we have sitting in the yard into my truck for a short time. I would have to replace the cam if I do, it has a giant cam that wouldn't be any fun in my truck. I guess the priority for my rebuild is getting greater.

[1project2many]

I haven't looked at an Edelbrock TBI intake years but when I last saw it the only advantage was larger plenum volume. It had stock size throttle bores and of course, no need for large runners. But it had EGR and the coolant connections and accessory brackets were all there. I usually opt for a different manifold.

GM sells a dual plane intake for L31 heads that works pretty well. under part no 12496820. It has no EGR though. There were some cars that used external EGR adapters... I believe they were equipped with 60 degree V6 engines. I've seen those used creatively to add EGR to an engine. Holley makes some interesting manifolds. Part no. 300-66 is a TBI manifold for early heads and it has EGR. Although it only has two bores and three bolt holes, it's clearly built using a 4bbl casting made for a carburetor manifold. There's also 2 and 4 bbl carb spacers that have EGR attachments found on older Ford vehicles. There are a few 4bbl versions on Ebay right now in the $20 - $40 range. Pontiac also used carb spacers with EGR valves in both 2 and 4 bbl versions on the 301 engine. The 2bbl version bolts to a 4bbl manifold.

[jim_in_dorris]

If i go to external egr, I would use vortec heads instead of the Dart SHP heads. Then I would have to add egr to the exhaust which I don't really want to do. I don't have annual smog where I live, and can probably get away with dropping EGR. That opens up more manifold options, so a single plane manifold would then be possible. I looked at the Victor Jr. but I am not sure how the TBI is adapted to fit it. So I am back to dual plane vs single plane pros and cons. Keep it coming.

[dave w]

So maybe the topic has drifted from simplicity / low cost option to other intake and head options?

dave w

[Hog]

Well, I finally have the budget to build a new motor for my 87 1/2 4x4. It's only a little each month, but I have a fairly good idea of the parts I want to use. I am going to use Dart SHP heads with an Isky nn257/265 cam and long tubes. I am trying to decide if going TPI will choke the motor at the upper RPM levels. Peak horsepower is at 5000 RPM with this setup, and I have heard that the TPI manifold isn't much good after about 4900 RPM. I have had the truck for 10 years, and have hit 4900 + RPM less than 5 times (I drive like the old man I am) however I really want torque to tow a trailer with. I have towed upwards of 6000 pounds with the stock motor on this truck, but it struggles. So, my question is; Should I stick with TBI, or is TPI worth the extra effort? I know this will start a firestorm of opinions, but lettr rip guys. I have talked about this before, but now I have the money for parts (the bottom end is my christmas present to me).

There was a guy on another forum who did a TBI to TPI swap in a Chev truck, specifically for towing use. He was disappointed as the TPI torque is made in the mid rpm, while the TBI's torque peak is more in the low rpm area.

peace
Hog

[Fast355]

There was a guy on another forum who did a TBI to TPI swap in a Chev truck, specifically for towing use. He was disappointed as the TPI torque is made in the mid rpm, while the TBI's torque peak is more in the low rpm area.

peace
Hog

Experienced this myself years ago with my G-van TPI swap as well. Only in a very narrow RPM range in the midrange did the TPI do better than the TBI.

I once ran TBI heads with a Performer RPM and a Holley Projection adapter. The engine was stronger everywhere above 1,500 rpm than with the TBI performer.