Cruise range on the stock L98 cam is probably ~1500 give or take 100 rpm.

The engine makes peak torque at 3200 rpm, but you know it's going to make >300 lb-ft very low in the curve. My short runner 427 small block makes over 350lb-ft of torque at the REAR wheels at 2000 rpm.

The TPI setup would be great for a truck motor, because they can make really unwieldy amounts of low end torque.

All that said, I have an 83 F-250 with a 460. I'd probably never stick a Chevy motor in there out of laziness. If I had one with a 400, I'm sure I could find a way to tune it up to make some really nice torque down low.

I agree with the others to stick with a Ford motor, but merely because I think you can get to a good place with far less effort.

If the OP does decide to go TPI though, I'd be more than willing to help with questions on the setup.


*edit*
FYI, I found this web page, pretty cool: http://www3.telus.net/cbradley/Engin...fications.html

149hp@3200 rpm, 300 lbft @ 1400 rpm.

*edit2*

Also dug up a dyno curve for an L98:

http://dl.dropbox.com/u/721726/Power.jpg

Bottom graph shows torque, 325 rwtq @ 2600 rpm. Probably doesn't have as much punch off idle as the 400, but I think it would still make a very solid truck engine.

 

Thats what I have found. I could try the other port however

You are right, it is a C6 transmission, C4 is the lighter duty trans. My mistake

 

Yeah, you want "ported" vacuum for the advance, and it's the higher port, over near the ear with the carb model number stamped into it.
Manifold vacuum should not be used on the vacuum advance, since it works exactly opposite the way the advance is designed to work.

 

Not exactly correct. You are correct that most Fords use the ported vacuum advance. But really all the ported vacuum does is lock out any advance at idle. Once you open the throttle to go, the advance works just like it would if it were hooked to the manifold vacuum.

If you want to think of the vacuum advance as a "vacuum retard" mechanism, that's not that far off from a correct description. The vacuum advance will try to advance the timing any chance it can, and when you lose vacuum(when any load is placed on the engine) it's going to relax and the timing will be retarded back.

 

Making sure

So having it hooked to the port or the full time advance, all that does is change idle vacuum that the distributor sees?

Port- no vacuum= distributor is going to advance itself at idle
Full Time- vacuum= at idle there is going to be less timing

When cruising or part throttle the vacuum is the same between ports.

So why would the ford engine need more timing at idle? does it run better that way? My mitsubishi idled at 5 degrees but thats a 4 valve high flowing cylinder head.

The 400ci engine idles just fine actually. The Rhoads lifters make it idle perfectly. It does take a couple of seconds for the Rhoads lifters to collapse so once in a while there is a lope in the idle.

When the engine was built I am thinking the idea was that the Rhoads lifters would act kind of like a v tec system. Good idle and I think what they were going for was when cruising that the Rhoads lifters would still be partly collapsed and you would get good towing. Unfortunately I don't think it works well. I think they are fully expanded and they are following the cam profile (which is a pretty radical cam)

WOW! I have never ran this engine yet. I am looking forward to what ever project I find for this. (Maybe find a chevy truck...) That is much better then a TBI system. It is a wonder why they didn't put that in the truck motor more (except for expense)

 

The easy way to remember it is that Venturi (ported) vacuum is always above the throttle plate while manifold vacuum is below the throttle plate. Manifold vacuum (unless otherwise specified by the carb manufacturer) pulls vacuum at idle. Ported vacuum only pulls vacuum when under throttle.

What Rogue is saying is that the way you have it hooked up now, you are pulling vacuum on the distributor at idle and you would want to pull it only during throttle. At least that's the way it was explained to me...

 

The "ported" (or venturi) vacuum varies as the throttle plates are opened. So the advance doesn't see full vacuum as soon as the throttle is opened slightly. The more air flowing thru the carb venturi's, the higher the amount of vacuum created.
Manifold vacuum operates the opposite way, highest when the throttle is closed, and drops as it is opened further. Using this as sourse for the vacuum advance, it will go to full advance when the throttle is closed, and less advance as it is opened, thereby retarding the timing just as it really needs to be advancing. Of course, there's also a mechanical advance in the dist, and the 2 items are working against each other.

Having the advance hooked to a ported source helps improve the throttle response and part throttle driveability of the engine, and generally leads to better MPG and power.

 

I don't think these carbs have venturi vacuum. I believe it's like the previous poster described, the port is above the throttle plate, so the throttle plate "hides" the engine vacuum at idle, and when you start to open the throttle, the blade exposes the port to the engine vacuum.

You can run your engine whichever way it runs best, there is no rule, especially when it's got a lot of non-stock equipment on it. Through experimentation I have found a engine with a automatic tranny seems to work best with the ported vacuum. I have found with full manifold vacuum, this raises the idle speed, so adjustments are necessary to bring the idle down to normal. Then when you put the auto tranny in drive, the torque convertor will put a load on the engine, which seems to lower the engine vacuum, which retards the timing a little bit, and it wants to stall.

So then you usually set the parking brake and tune the carb and the idle speed with it in drive and the wheels blocked. But then when you put it in park, the engine revs high, and then it slams when you put it in drive again.

This has been my experience with running full manifold vacuum. Like I said different engines may work differently, and a manual tranny might work fine with full manifold vacuum on the dist.

 

The best way to test is to purchase a $20 dollar vacuum gauge at the auto parts and plug it up to each of the ports while the truck is at idle. If you are pulling a vacuum (15 to 20") and it drops when you rev the motor, you have manifold vacuum on that port. If you are not pulling a vacuum and the vacuum level increases when you rev the motor, you have ported vacuum.

Set your timing while the vacuum advance line from the dizzy is unplugged, then plug it into the ported vacuum port. Go for a drive and see if there is any difference.

 

The ported vacuum isn't exactly exposed to engine vacuum as the throttle is opened, since the manifold vacuum actually drops by opening the throttle plates. Throttle plates create resistance to airflow, which produces the manifold vacuum. Reducing the resistance, reduces the vacuum.
Ported, or venturi, vacuum is created by the air rushing past the orifice, much like a paint gun sucks the paint out of the cup by air rushing past the orifice in the tube. The more air that rushes past the orifice, the greater the "pull" inside the orifice.
It is actually possible to have greater vacuum created at the ported location than what the same engine can create for manifold vacuum, especially when said engine has a very radical camshaft installed.

 

Update, switch vacuum lines from non ported to ported

Not much of a difference as I thought there was going to be...

Actually there isn't any difference from what I can tell

Maybe my advance is bad in the distributor? or would that cause bigger problems?

 

Looking at the picture of your engine, I don't think you will ever be happy! It appears that the engine was semi-built for higher rpms with little thought of matching components to intended usage.

Problems I see and read:
Single plane intake
750 cfm carb
Rhoads lifters (used to tame down the idle of and overcammed engine)
"Wild" camshaft
Exhaust Manifolds (instead of headers which I would have expected if going for RPM).

Though I hate the company, you might check out an Edelbrock Perforner cam and intake manifold set. This will give you a dual plane manifold with a matching camshaft and you could get away with the same carb for a while.

If you want to go mostly bolt on, open the exhaust to 2.5 (min 2.25) y pipe to a 3 inch single exhaust. Get a dual plane intake manifold (Edelbrock Performer, Weiand Street Action, Summitt stage 1...stay away from the old Edelbrock SP2P toilet!) with a 1 inch 4 hole spacer. Call Crower cams with your details and desires and they will suggest the best cam for you (4x, weight, gears ratio, engine, trans (auto/stick), rpms at cruise). Install it all making sure the timing is correct and you should be quite happy in what it will do. It will never be a powerhouse but should be a capable implement.

Kenny