Sort of a beginner question here and I just need to double check what I think I need to. do on this... I'm now installing a 8BA with a T5 transmission in my Model A and in the process of finding the placement of my transmission mount in preparation of welding that in place. I have finished up my suspension setup and have a small tire rake with bigger rears and smaller fronts. My understanding is that I should setup my drivetrain angle so that my carburetor mount base is level with the ground so I am placing an angle meter on top of that base to see the angle relative to the flat ground. Is the basic approach I outlined here correct? If so how level does that carb base need to be? Should it be as flat as possible or is there some play in either direction? The reason I ask is that as I adjust the angle my transmission mount crossmember is at the bottom of my frame rails and I'm still off by 5 degrees so either I'll need to modify that so I can adjust further or there is something off in my approach for determining the correct angle. This is my first time doing this so I am unsure of exactly how things should look like.
Forget making the carb level. What if you buy an aftermarket intake? All those are flat to the engine. If your carb is always going downhill, the car should be faster. I’ve never seen a car that ran faster uphill than downhill. Just give the engine a half to one degree slope down in the back and be happy. Most fit best like that.
The angle of most engines is around three to five degrees. And yes, the usual goal is to get the carburetor mounting surface pretty close to level. But it's not absolutely critical. You can't be far off in your positioning cuz most transmission cross members have a big drop in the middle so I can go under the transmission mount. Looks like your cross member is straight? As far as up down positioning, I get the transmission and shifter in what I think is a good position relative to the floor. And that basically dictates the up down position of the engine.
Don’t really care about the carb angle. Crank centerline, drive shaft and rear axle angles do a search on driveline angles here.
Thanks for the replies. I had always assumed that the stock carb intake was level with the engine plane so I will try measurements based on the base where the intake manifold sits. I do plan to switch out the stock carb and intake manifold for some performance ones in the future and I’ll design my setup towards that. Hopefully that and not going to full level will allow for the transmission mount that I am using still work for what I’m doing here. As seen here the crossmember is indeed flat and I would need to modify that in some fashion if I needed to drop the bar to a position that would be lower relative to the frame.
Torque tube/banjo rear flatheads lay pretty level in the chassis, with the carb flanges parallel (flat) to the crank shaft, while the later ('49-up) open drive/hypoid rear cars had the carb bases angled forward to level the carbs because the engines/transmissions angled down in the rear. Best to get the engine/trans installed with proper driveline/U-joint angles and deal with the carb issues later using an early style intake, angled carb spacer etc. As an example, my flathead/T-5 '32 has the engine/trans angled down in the rear, but the chassis is high in rear/ low in front, resulting in a 1-2 degree carb angle using an early flat style intake.
Like Bob said, the engines in this era were originally flat to the frame rails, so tilting them back much more will look goofy. One degree or so shouldn’t look dumb, but five sure will. Then you put a five degree rake on the whole kabootal with some large rear tars…forget trying to make the carbs flat for sure.
You mentioned tire rake. I can't tell from the picture, are the tires on the chassis? If not, is the frame positioned to approximate the rake angle? Also, how much weight is on the suspension? If not much have you used rachet straps to compress the springs?
none of this matters, all that matters really is PINION ANGLE . and it it often confusing and probably should be called something else ,, you have a open u joint style driveshaft , the angles at the u joints need to match in degrees (albeit opposite) so that they cancel each others harmonics and you get no vibration ,, all of your other concerns are basically non players , if you have a driveshaft install it, if you don't get a piece of pvc and cut tape mock one , pinion angle is called that because normally you can only adjust the pinion end via shims (parallel leafs) or adjustments in ladder bars etc,, and its easier to adjust it from the pinion end ,,, THESE MEASUREMENTS ARE IN THE UJOINTS YOKES THEMSELVES and has nothing to do with the ground ,frame angle,, tire size ,, you want approximate rear ride height because that changes u joint angles ,, just MOCK the engine mounting to where you like the way it looks and have clearance here and there then move on to pinion angle (with the car on the ground and weight on the springs) and see if you can get what you need ... then blaze away and call it a happy day ,, fabricator john miss you dad
I read somewhere that the stk carb on a flathead should be level (0 degrees), so that’s what I aimed for with my build mated to a T5. Of course, will need to keep the input pinion to the rear driveshaft at the same angle as well.
I put an 8CM flathead (like an 8BA but Merc) in my '41 Merc. Original engine was level....was I gonna re-engineer the car to swap engines? Hell no. I put the new flattie in level as the car and running gear was designed for, and angle milled the carb pad to sit level since it leaned forward and looked awful. Perfect!
Use the oil pan rail if you want a level look not the carb base. There are opinions all over the place on this subject but I prefer to have the engine sitting level with the frame. It is just a look I like. I had a guy at the Portland Transmission Show this year walk up and tell me he wished his was leveled in the frame rather than being tipped back in (high in the front). I suppose there are a lot of personal choices when it comes to your question. What you can't argue with is the u joint working angles, that's like arguing about gravity, it just is. 2-3 degrees down on the transmission yoke, and the same 2-3 up (opposite) on the rear end pinion so the U joints are happy. Remember that this U joint/pinion angle stuff has to be set with the car assembled (at weight) and on all 4s (at ride height) or you get to do it over again after you finish building so you can correct your error you made by rushing. This is an old pic of my roadster, the 8BA is sitting very close to level on the frame. Of course, there is a substantial rubber rake and frame rake so the engine is actually 3 degrees up. The QC is mounted with ladders so I can make adjustments to the pinion on this car. In the pic is 3 degrees down. After assembly I had to adjust that pinion angle a couple of times in order to maintain that balance. As weight (the body, gas, interior, etc) brings down the rear end of the car the pinion angle changes (flattens out).
Thanks again for all the input. It looks like the consensus is to focus on the drive shaft angle relative to the transmission and differential first and then adapt your carb setup based on that. I have stepped the rear as part of the process of getting the stance I was looking for. It seems for my situation that my rear differential will have its yoke shaft parallel to the frame as aside from the crossmember lift the spring and related perches are more or less in the stock configuration. I will double check and measure that to be sure. That said if the best practice is to have both your axle and transmission yokes parallel to each other to maintain the same offset angle on both ends and the axle yoke is parallel to the frame then I will need to ensure that my transmission yoke shaft is parallel to the frame as well. It also looks like making that angle as small as possible is also desireable which would result in me possibily needing to move the engine up or down (more likely) accordingly. Right now my motor mounts are flush with the top of the frame but I could remake (or flip) those to lower my engine position. After I do all of that then my drive train placement should be sorted out for the better and then I can turn my attention to any carb angle concerns. I would tackle this by adjusting the number of springs in my front/rear leaf packs as necessary, finding some sort of angle spacers for the carb, reducing my tire rake, etc., and I would do these corrective actions either individually or in combination with each other.
The working angles of the u-joints are what's important, and should be around 3 degrees or less, within 1 degree of each other. The chassis should be at a desired ride height to establish correct u-joint angles.
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