Engine Choice 383/TH350 or 454/TH400

[mr402]

Just check my handle. Even though my trucks only have 402s you just can't beat them for bottom end torque. With these trucks as heavy as they are torque is definitely king.

[kenm78]

What type of set-up do you all run with your bbc, I.E. cam, intake trans rear gears. Never delt too much with BB what size cam is too big for power brakes? Or what is some of the things I should do or look at before I build a BB. I understand it costs a little more but everything is $$$ now adays. Just looking for honest feedback. No matter what engine I pick I want AWSOME take off and overall impressive power over the entire power band. I usually drive everything the same I quite freq go to 5000-5800 RPMs becouse I like to really get into it makes me feel good!!! What is your opinions or do's and don'ts?

[mnunn454]

Originally Posted by kenm78

What type of set-up do you all run with your bbc, I.E. cam, intake trans rear gears. Never delt too much with BB what size cam is too big for power brakes? Or what is some of the things I should do or look at before I build a BB. I understand it costs a little more but everything is $$$ now adays. Just looking for honest feedback. No matter what engine I pick I want AWSOME take off and overall impressive power over the entire power band. I usually drive everything the same I quite freq go to 5000-5800 RPMs becouse I like to really get into it makes me feel good!!! What is your opinions or do's and don'ts?

First questions is what's your budget?

Regarding cam/power brakes, it depends mostly on the brake booster type and specs. The more the better, but the minimum for a stock booster would probably be around 11 or 12" of vacuum, but you'll want an expert opinion. Vacuum tanks can be added rather inexpensively. They can help if your system is borderline. There are systems that run off your power steering pump and that care less about engine vacuum, but they're much more expensive.

Regarding engine specs, I'm running Edelbrock's Performer heads and their RPM manifold on my 454. They flow great. 9.5:1 compression, a 750 Holley DP carb, a Comp Magnum series cam (286H) that has .550" lift and 236 duration @ .050 lift. I have a stock torque converter/TH400 and 12-bolt posi rear with 3.73 gears. Headers, HEI, etc. I pull about 10" of vacuum at idle, making the power brakes feel more like manual brakes at a stoplight. I love the way it sounds. It has the guts I want, when I want it. It gets 10 MPG, but I only drive it 10-20 miles once a week on average, so the fuel bill is still reasonable for me. I plan to visit a chassis dyno soon, but my estimated HP is around 450 and torque about 500 ftlbs I think. I have to eat my words. Just ran a cam modeling comparison using my engine's parameters. A dyno run would prove it for sure, but the s/w says it's 545 HP and 557 ftlbs!

I had a 68 Camaro 25 years ago with a modified 327. Mainly due to the rear gearing and Powerglide trans, it never quite delivered the kind of performance I wanted. This time around I was determined to go BBC, just so I wouldn't have to make the engine scream in order to get pushed back into my seat.

Regarding "awesome takeoff and power and overall impressive power over the entire power band" I have 2 thoughts. Awesome takeoff requires lots of torque. High stall Torque converters are made for this, but they have their limits before they start impacting driveability. Generally 2500 stall is a reasonable number. If considering a manual tranny, then getting fairly low 1st gear ratios are important. This is best achieved with one of the later model 5-6 speed transmissions, but be sure they'll handle the torque you're going to be putting out.

Regarding "overall impressive power", I think what you're describing here is best delivered by an engine that deliveres lots of torque over the average power band up to 5800 RPMs. Your planned 383 can do that, and probably well. But to get there, plan on spending $5000 to $7000 if you're starting from scratch. (see Popular Hot Rodding, Super Chevy and Chevy High Performance mags. They're loaded with engine build-up examples) By comparison, I only have about $4500 in my 454.

Also, if I wanted, I can get another 100 horses from my setup just by changing carb, cam and my exhaust. A 450 HP 383 is pretty much at the peak of it's output potential unless you add a lot of exotic and expensive parts. Adding Nitrous can give that same amount of extra power fairly inexpensively. Adding it to a 454 that can routinely handle 600 horses on the stock bottom end, requires little/nothing extra. Adding it to a 450 horse 383 could spell disaster unless the bottom end has been built for it.

One final thing. It's the "wow" factor. For me, when I go to a car show or cruise night and the car I'm looking at (if it's a modified, and not a stocker) has a 383, I'm impressed, but not overly so. Sort of a 5 on a scale of 1-10. The same car with a 454 or above gets more of my attention because of its innate potential to perform. The same is true in reverse. When I'm driving or showing my truck people see the 454 badges and instantly respect it. When I take off and from a rolling start spin both of the 10" wide tires through all of 1st and half of 2nd gear onlooker impression goes up.

Bottom line here (IMO) is the 383 is a great option, particularly with all the latest cam and head technology available. Having now had both SBCs and BBCs and being a firm believer that "there's no replacement for displacement", I just think that if you did it with a 454 [with decent heads and induction] you get closer to the results you seek and wouldn't have to be on the hairy edge of the engine's performance and longivity curve to experience it.

My opinion and perspective here only. I'm sure hundreds of you see it differently. This is just food for thought.

[novajess1972]

No replacement for displacement!!! Had a 383/TH400 in my 67 El Camino, but the 468 in my truck just rules....even with the built TH350 I have behind it!!

Just my opinion.

Jesse

[kenm78]

I started pulling the 454/TH400 out of the Winnie this moring then the sleet started again so I'm on pause but I am going to pull it and take a look at the set up try to determine if it has the peanut heads or not I imagine it should be a pretty good engine being it is coming out of a 32 foot RV. Any one have any info on RV 454's????

[corn]

Whats really so bad about the peanut port heads? I was always told they were a good street head with small chambers... I dont have any, so Im not just sticking up for myself, its just what Ive heard...

[mnunn454]

Originally Posted by cornfed63

Whats really so bad about the peanut port heads? I was always told they were a good street head with small chambers... I dont have any, so Im not just sticking up for myself, its just what Ive heard...

Quoting from the Mortec paragraph above:
If you are building a motor for pulling or towing on the street, the small oval port heads will make their power at low and mid range rpms, but run out of breath at rpms over 4500. If you are building a strong street performer or a bracket racer, the large oval port heads are the ticket up to about 6500 rpm if you do some bowl porting and add the 2.19"/1.88" valves.

So, what's so bad?

Nothing I guess as long as you never need performance above 4500 RPMs. But since hosepower is an output that's the direct result of torque times rpms, don't expect to get anywhere near the horsepower potential of a better breathing 454.

[kevenj]

My .02 worth:

Whichever engine you decide (both have their pro's and cons) I'd seriously consider going with a 700R4 trans over either of the 3 speeds. A good tranny guy can build a 700 to be plenty strong enough, and you'll have a significantly lower first gear plus a .7:1 overdrive. Just don't try to bolt in a stock one from the wrecking yard or something 'cuz it won't live.

[kenm78]

any one know the demensions of the port size between small peanut oval port and the other oval port???

[bowtiedude]

No question in my mind I would go with 383. There actually are 2 replacements for displacement.


1. Nitrous

2. Aluminum lung say maybe a 6-71

I was never a big block fan, unless you are towing.
But its not my truck.
I'm actually thinking about a Duramax with a stick in my 4x4.

[mnunn454]

Originally Posted by kenm78

any one know the demensions of the port size between small peanut oval port and the other oval port???

Ken,

From the Chevelles.com quote above:
All dimensions are darn close if not right on, it's from memory. Rectangle is 2.125" tall x 1.240" wide, Oval is 1.900" tall x 1.065" wide, Square (peanut) is 1.065" tall x 1.065 wide. All refer to intake port configuration, not plug thread/jacket types used.

[kenm78]

Thanks 454, Im working around the weather here but hopefully within the next week I will have the winnies engine pulled??? Im keeping my fingers crossed....

[kenm78]

Will the engine mounting brackets I used on the SBC work on the BBC???

[mnunn454]

Originally Posted by mnunn454

Ken,

From the Chevelles.com quote above:
All dimensions are darn close if not right on, it's from memory. Rectangle is 2.125" tall x 1.240" wide, Oval is 1.900" tall x 1.065" wide, Square (peanut) is 1.065" tall x 1.065 wide. All refer to intake port configuration, not plug thread/jacket types used.

Ken,

Not to belabor the point (don't meant to), but take a quick look at the big contrast in these port sizes. Rectangle is 2.635 square inches, Ovals are a little under 2 square inches (because of the radiused corners), and the peanut ports are 1.13 square inches.

There's lots of "science" behind port shape/flow etc. [I don't pretend to know much more than the very basics in this area.] Looking at the Ovals, you'll see their intake port area is almost twice as big as for the Peanut ports. The Rectangle ports are about 30% bigger than the Ovals.

But [contrary to what we were told in the past] size isn't everything.

Velocity is an equally important factor to consider. If it's too high (air rushing in trying to fill the cylinder) then there's lots of friction, slowing the velocity, and the cyl only gets partially filled. On the flip side, if the port is huge, the cylinder gets filled easily, but at lower RPMs the incoming air flow stops and starts every time the valve opens. This causes poor fuel distribution, poor combustion and therefore low torque at low RPMs.

The Rectangle port heads are great for WOT applications because they can get lots of air into the cylinder, increasing volumetric efficiency (VE). However they're horrible on the lower end where torque is so vital to streetability.

Oval port heads (particularly the GM 049, and 781 heads, and most aftermarket heads) are a decent compromise and are well matched to balance intake charge velocity (FPM) and volume (CFM), yielding streetability and performance up to 6K RPM or more.

Peanuts are just the opposite of the Rectangles. Great for low RPM high torque operation only. If you want/need to minimize your initial overall costs, they'll work for now, until you can locate some better flowing ones down the road.

One final thing...Open or Closed chambered heads.

Generally the closed chambered ones are preferred because they provide smaller combustion chambers and greater "squash" area (the flat area between the head and the piston at TDC) and therefore greater turbulence inside the combustion chamber, thus reducing the tendency for detonation. However, you can't have small chambers, lots of "squash" and unshrouded large valves all in the same combustion chamber. Making/buying that combination is expensive, so most people opt for the better flowing open chambered heads with less squash and then increase the piston dome size a little to maintain a decent compression ratio. For most moderate to wild normally aspirated performance engines, the larger piston dome required by the larger chamber and the reduced squash area of Open chambered heads is a less important factor than getting good/great VE.

Didn't mean to run on. Just thought I'd share a little of the logic behind my encouragement to swap the Peanuts for Ovals if/when you can (IF you don't end up going 383 that is).

Who knows. Maybe you'll luck out and find the Winnie has Ovals in it!! That'd save some bucks.

Best/
Mike