I am very confused with the internal external balancing. I've searched and still very confused. If I want internal balance, I must provide the flywheel and harmonic balancer when getting balanced. So what happens if I go externally balanced? Just install the internals and slap on the stock flywheel and balancer? I just don't understand what the difference is because to my understanding, both internal and external still needs a balancer and a flywheel that balances the rear.

I'm building a 396ci, can someone tell me what the advantages of both are? I've searched and read that an external can make more hp

 

Internal balance requires a neutrally balanced flywheel and damper. If your stock engine had a flywheel with a balance weight on it and a non-balanced or eccentric damper, you would need to change them to neutrally balanced parts, and they would NOT be needed by the balance shop. The internal engine parts would be balanced, most likely by adding "heavy metal" to the crank. With a 396, this might be impractical due to stroke length and part weights, or just the high cost of the excessive amount of heavy metal required.

External balance requires the flywheel with the balance weight on it and probably the damper, too. These are added to the crank along with the bob weights and the balance performed. Much less (maybe no) heavy metal is needed, again deending on the part weights.

If you want internal balance on your 396, you or your engine balance guy could calculate the bob weights and ask the crank manufacturer if the crank can be internally balanced with that bob weight, and about how much heavy metal will be needed. That should help you make your decision before you buy all the bits and drag them to the balance parlor.

 

All internal combustion engines require a harmonic balancer. They not only help keep the rotating assembly balanced they also cancel out damaging harmonics that could destroy the engine. The natrual harmonics in a engine can hit frequencys so high they can actully crack the block like a opera singer can shatter a glass. I have seen this in tests over the years while making balancers for schwitzer turbos. also if you can afford it Eagle makes great bottom end kits for just about anything and come already balanced whether internal or external. I bought there 383 kit and it came with a card telling what each individual piece weighed and what the static balance of the assembly was.

 

If it's a LT1

The flywheel/flexplate is included in the stock assembly for balance. So if you are keeping the LT1 parts then get the flywheel neutrally balanced and get the rotating assembly neutrally balanced. Then it's internally balanced, and if you euchre a flywheel you don't have to tear down the motor to put a new one on.

I asked Jimlab this a long time ago, but why a LT1 in a RX7? Why not a Northstar, LS1 or SBC?


Bret

 

OK, still very confussed cause either way I still have to bring my parts to get balanced right? I guess all I wanted to do was put the internals together now and worry about balancing later.


SStrokerAce, I guess I would have to answer your question with another question. Why go for an LS1 and not an LT1? Some people have actually done the LS1 and it seems to me that the LT1 is a better fit for the 93+ RX7s. Plus parts are readily available for the LT1s, can't say that about the LS1s, not yet anyway

 

You have to get them all balanced anyways. The thing will shake like a 7.8 quate if you don't get them balanced and probably destroy itself. Are you building the motor or is someone else?

K, but a SBC is cheaper, has more parts out there and any external parts like headers will fit a SBC if they fit a LT1. The LS1 is just a better motor to start with the other parts can be done. I just first work with the best archetecture I can start with.

Bret

 

Perhaps, but an SBC would require an expensive belt-drive timing system and a front-mount distributor, or a coil-per-cylinder setup with a cam sync and crank trigger to work without modification of the fire wall. A rear mount distributor will not work with the clearance available, and the front-mounted Opti-spark solved that problem nicely.

As far as height goes, the LT1 is more compact than an LS1 or an SBC with a typical intake. You could get a TPIS Mini-Ram intake for an SBC, but the point is that you'd still need an LT1-style intake for an SBC to get adequate clearance, unless you liked adding a big cowl to the hood of an otherwise very sleek car.

And where headers are concerned, *nothing* fits perfectly and very little fits period. Custom headers, shorties, or stock cast iron exhaust manifolds are about the only option. There's nothing to be gained by running an LS1 or an SBC where exhaust is concerned. You're starting from a pretty much blank slate regardless.

Northstar... why bother? We're building fast cars here, not trying to find an engine that can easily be covered with sleek looking panels so that everyone will forget that under it all you've got a stock engine with mediocre power in your roadster at the car show...

The LS1 is a larger engine, and not necessarily superior when both are modified. Sometimes less sophisticated architecture is good enough... sometimes fit and engine placement -- and not having to hack the floor up to get to the shifter --- are more important.

 

No problem John. Have your rotating assembly internal balanced and have your short block assembled, then get your clutch neutral balanced later.

 

thanks Jim, I figured that's what I'll do

 

Good points. A crank trigger would be a pain, but depends upon the power you want to do. Intake manifold options on a SBC are much greater and it's not a big deal in the grand sceme of things, at least there are mulitple options. Since all the motors really need a custom exhaust, then they are all equal in that department. In a few months the LS1 with have a huge advantage in the head department with the new AFR castings, and the fact that you can get 440 cubes out of the block. If you want stupid power, better heads and more cubes will get you there. Not ragging on you man, just never thought of all the options a guy has that the LT1 is the first one I would go with.

As for the Northstar, it's a much better looking engine when done up then the LS1 or LT1. When you get down to the bare bones of it, the thing is basically a baby LS1 with 4 valve heads. Look at the intake manifold on one.

I wouldn't call a 450hp NA 4.6L slow, and it can spin to 8K without much of a hitch. Add on that it's shorter which will help your weight distributon and it's much lighter than any of the other motors mentioned here. It has awesomely strong internal parts, and yes it does have it's draw backs too, but he new longitudinal block will solve that problem.

Now if you want big power like you have Jim, take that 450hp NA Northstar, throw 2 small Garret Turbos on that thing and you have 650-700hp and it's a completely driveable.

The motors also have heads that the Modular Ford guys would love, and when they are ported you easily outflow a 4.6L Mod Ford head by 30-50cfm, (which is 15-25% Easy).

So you have a Aluminum Block, a Small package, 4 valves a cylinder, a composite low intake, low weight, and a pretty good amount of power. These things make some awesome power when hot rodded. http://www.chrfab.com/

Maybe it's me but something that looks like a Hemi under the hood of a RX7 would be kind of cool
http://www.chrfab.com/images/CHRF%20Images/MVC-880S.JPG

Just my thoughts.

Man how the hell did this turn from balancing to Northstars?

BTW JL did you get that motor yet? You gotta be like a kid in a candy store to thing that thing is on it's way.

Bret

 

Well Bret, keep in mind that when I started my 396 build-up, there was no such thing as a 440+ CID LS1.

Seriously, at that time, you either got a very expensive ($4,000+) rotating assembly to get 382 cubes from your LS1, or you went bigger with an LT1 for less money. You have to remember that technology has passed me by while I've been waiting on my engine, thanks in large part to Mark Montalvo.

John, coincidentally, has many of the parts that I bought to build the 396 I was originally planning on before I went off the deep end, which should net him somewhere around 550-600 horsepower with the right heads. Once you have the parts in hand, it's really easy to want the better technology that's become available, but a lot harder to justify dumping what you've already paid for to make the jump.

In our application, the LS1 has to sit farther forward and lower in the engine bay to clear its relatively bulky manifold, which means less ground clearance and hacking up the transmission tunnel to get at the shifter. In a car that was 50/50 balanced from the factory, where the engine sits is a big deal, even if the block happens to be lighter, if you're going to try to preserve the balance of the car. The LT1 sits farther back and more than low enough in the chassis while maintaining stock ground clearance, and while the T56 is shorter than the OEM RX-7 5-speed, it lines up perfectly with the shifter hole, which tells you something about the engine placement. Believe me, I put a lot of thought into this before deciding on the LT1.

http://home.earthlink.net/~jimlab/pi..._side_view.jpg
http://home.earthlink.net/~jimlab/pi...hifter_loc.jpg

Any LT1 will power a ~2,700 lb. car with no problems, obviously, and any advantage the LS1 might have in the cubic inch and head department these days costs so much that you might as well start with an aluminum Motown block, go straight to 454 CID, and use SB2 or 15-degree SBC heads.

Bottom line, not everyone has the option of jumping to a different engine platform as technology advances, especially if they already have a sizable investment in "older" technology. People always ask "Why an RX-7, why not just start with a Camaro?" Curb weight, for one. Weight distribution, for another. Handling for a third. But one of the most important reasons is that some of us already had RX-7s in need of new engines and really liked the car, (if not the often finicky original power source) so why go out and buy a Camaro if you have a good platform with a lot of advantages to build upon already?

It finally showed up... almost untouched since the dyno session in April of '02, and missing quite a few parts, not to mention an aluminum flywheel Street Twin that magically changed into the steel flywheel version... but it looks good.

http://www.rx7club.com/attachment.php?s=&postid=2207471
http://www.rx7club.com/attachment.php?s=&postid=2207479

 

Hey Jim if you have room for those breathers, how come you didnt have wilson build a taller intake?

 

Jim,

Thank god you have it now.

Does the missing clutch and flywheel suprise you after $35K+ later and this amount of time.

As for those breathers, drop those things anyway. You might as well make a crankcase evaq system with some braided hose and AN fittings. It's going to work better and look better.

I guess back when you started this deal the tables were turned. But I like your idea of a aluminum SBC with a set of 15* or SB2 heads on it.

I think the RX7 is a good looking car, so yeah it's a good platform to build off of, especially if you have one. For me why do the F-body when you can do a C5. I'll just never understand AutoXing a 4th gen f-body, a C5 will walk all over it.

Bret

 

I don't have room for those breathers, which is yet another thing that was supposed to be resolved over the last year or so... and wasn't.

The main clearance problem is at the front of the intake. My throttle body is angled down slightly and my intake (Hogan's) is about 1/2" shorter than an LT1 intake in overall height to resolve that.

 

Not really, but you can always hope that people will turn out to be more honorable than you expect them to be.

You mean with a vacuum pump? I don't plan to run one, but I do plan to have valve covers made with spring oilers and AN fittings for a remote breather system.

If I'd known that I was going to end up with aftermarket engine management and an aftermarket coil-per-cylinder ignition, I sure wouldn't have started with an LT1. But still, the most common solution for a big stroker at that point was an Olds rocket block. I don't think the Motown block had been released yet (early '01) and the aluminum version definitely hadn't.