Langdon's Stovebolt Engine Co.

VACUUM ADVANCE AND WHY YOU WANT IT FOR YOUR CAR

An often-asked question from many callers relates to whether they really need a vacuum advance mechanism on their distributor. I think this question stems from their observation that many “high performance” distributors do not incorporate vacuum advance and the resulting implication is that it is not desirable or necessary for a “good” ignition. There are a handful of applications where vacuum advance is not of significant benefit:

1) Pure racing engines
2) Severe duty very large trucks
3) Constant speed and load applications (airplanes, generators, pumps)

Other than the above, for normal automotive applications the vacuum advance will benefit the engine as follows.

1) Improved idle cooling
2) Improved idle quality
3) Improved fuel economy
4) Improved throttle response
5) Improved drivability
6) Enables improved spark knock control under full throttle accelerations
7) Enables leaner fuel jetting at light load to further improve fuel economy.

The basic reason for all these improvements is that the vacuum advance mechanism allows the distributor to supply a more optimum spark timing proportional to the load and speed output. Without the vacuum advance the distributor can only vary spark timing in proportion to speed and ignores its need for approximately 20 additional degrees of spark timing (“advance”) at light loads: (idle and cruise conditions)

The basic reason for the change in optimum timing at light loads is that when operating at light loads, the mixture is leaner for fuel economy and less dense because of light load. These conditions cause the charge to burn slower, and thus, to reach peak pressure at optimum point in the cycle, the spark must be initiated earlier. Failure to do this will result in “retarded” spark timing and all the aforementioned losses.

All engines are different, and have different spark timing requirements, but they are all the same in that as load is decreased, additional spark timing is required for optimum combustion.

Do yourself a favor – 1) make sure your distributor has a vacuum spark system and 2) experiment to find out what your engine “likes” for timing at idle, light load, and heavy load. Then change the vacuum can to achieve a result closer to the optimum.

TH350-400-700R4-200 4R and PG to early Chevrolet & GMC 6 cylinder engines

With the advent of the Stovebolt Transmission Adapter the installation of the GM TH350, 200 4R and 700R4 is made possible. This requires an “open” driveline and cannot retain the torque tube. In addition to the rear axle, the installation of a transmission cooler, shifter, and T.V. cable mounting make this a project not intended for the novice.

We strongly encourage the use of a 200 4R in combination with a 3.73 or 4.10 axle ratio so your efforts will result in a satisfying combination of low speed performance and highway cruising at modern speeds up to 70 MPH. The THM 350 could be used at a substantial loss in low speed and highway cruising (both). The use of the Powerglide is strongly discouraged.

The original design of our transmission adapter used measurements from 25 engines and 50 bellhousings. We found that GM was off as much as .020″ from centerline on many manual shift engines, and even on some matched set Hydro-Matic engines. We then took the average to build our adapter. In occasional cases of too much run out (.012″), the use of eccentric dowels will be required. Currently, however, both dowel pin location specifications are the exact factory blueprint dimensions machined exactly by CNC technology and assured on every adapter by assembly and dial indicator. Checking on your block and with your transmission is recommended.

To start, unbolt the four bolts that hold the factory transmission to the bell housing, and pull out the transmission. Remove the throwout bearing, the pressure plate, and the clutch disc.

We are now down to the flywheel which must be removed before the bell housing. The flywheel is held on by bolts that are retained by a flat metal strip that has tabs that are bent over to prevent the bolts from turning. Use a chisel to flatten the ears before removal. After the bolts are out, carefully remove the flywheel. Now you are ready to remove the bell housing. Remove the 6 retaining bolts and now remove the bell housing. Clean the grease and dirt off the back of the block and install the adapter plate.

Our kit comes complete with a spacer for the crank and a flexplate that has been re-drilled to Chevrolet 6 cylinder bolt pattern. Remove the 3 dowels from the crankshaft and install the spacer then the new flexplate using the special washers provided.

Set the transmission on a transmission jack and strap it down. Carefully install the converter to the transmission turning it with light pressure to insure it slips into the pump. Lift the transmission into place and install mounting bolts. Now turn the converter to line it up with the flexplate and slip it forward. Install the mounting bolts. It’s a good idea to use Loc Tight on these.

This kit requires the use of a 250 Chev 6 starter (part # Delco 323-236). It may be necessary to make a slight notch in the starter housing for clearance to the flywheel teeth. We strongly recommend purchase of this starter from Langdon’s Stovebolt to assure proper engagement, shimming and clearancing.

Rear support for your transmission

Chassis Engineering in West Branch, Iowa (319-643-2655) makes a good selection of kits for supporting the transmission at the rear mount. This will work well if your engine is side mounted but will not be adequate if you are using the front mounting plate typical of 1937-1951 cars and ’37-’54 trucks. In these cases it will be necessary to fabricate mounts similar to the original bell housing type mounts typical of ’55-’57 Chevy passenger cars.

(revised 7-24-06)

Guide To Proper Cam Selection

Taking it away from stock isn’t a hard job but one that’s going to take a little time for thought. You have to ask yourself just what you want to accomplish: Are you building for the street, the strip or towing? If your build up calls for 2×1; 3×1; 2×2; or 4 barrel carb (keep in the 390-500 CFM range,) then the following chart should help. This information is a compilation of input from Stovebolt and Clifford Performance.

Performance & Economy

Stage 0 Tuning

For absolute best idle quality and torque below 3000 RPM the factory cam is the best. Improved intake is recommended and will result in improved performance throughout the RPM range. When installing improved intake, make sure either exhaust heat or water heat is provided to the floor of the manifold. This may be your best choice for heavy duty towing.

——————————————————————————–

Stage 1 Tuning

Good mileage can be retained by using a camshaft of 254 ° to 264° of duration. These camshafts will idle well and produce very smooth low R.P.M. torque but represent a slight loss of torque below 3000 for a very significant power gain above 3000 RPM. We usually suggest using a hydraulic cam when possible in this type of application. Stick or automatic transmissions OK. Improved intake highly recommended to fully complement the camshaft. When installing improved intake, make sure either exhaust heat or water heat is provided to the floor of the manifold.

——————————————————————————–

Stage 2 Tuning

A good overall combination of performance and mileage is attained by using a cam of 260° to 272° of duration. We recommend using exhaust headers and an improved intake system. Hydraulic grinds are best. Stick or automatic transmissions as noted. Agressive axle ratioand 5 speed.
Camshafts 280° of duration and larger are considered high RPM cams and require a correct combination of modifications to perform properly. Manual transmissions only. This is not for street use and should not be used for 235 and 261 street engines.

——————————————————————————–

Stage 3 Tuning

1) Oval Track
All 1/5, 1/4 and 3/8 mile short flat tracks with engines that have limited carburetion (i.e. 1,2 or 4 barrel carburetion) and have less then 250 cid should use camshaft grinds of 270°-280° or 280°-290°. The larger engines 290 cid and more can use grinds of 280°-290° or 290°-300° depending on track and carburetion used. Headers and head work a must!
All 1/2 to 5/8 mile large fast tracks with engine displacements of 250 or more can use 290°-300° or 300°-310° grinds. Carburetion of large 2 or 4 barrel or multi-carburetion is best. Headers and head work a must!
2) Drag Racing
All limited carburetion engines with 4 barrel carbs should use moderate grinds of 290 to 310 duration. Automatic transmissions can be used ONLY if stall speed is increased to 2800-3000 RPM.
All unlimited carbureted engines with multi-carburetion (Webers, 4 barrels, etc.) can use large cams. Most engines of 250 id or more work best with 320°-330° dual pattern grinds. Lighter chassis cars of 1500 lbs. or less can use 330°-340° grinds. Headers and full head work a must!

——————————————————————————–

A big thanks to Clifford for the use of this information!
If you need further help give us a call at 1-586-739-9601.
We would be glad to sit down and help you with your cam spec.

One of the simplest methods of improving the overall performance of 1937-51 Chevrolet passenger and trucks is with the installation of a ’55-’63 Chevy 235 or 261 six. Not only does the increased displacement enhance performance, but the later engines are a far better design! The 235-cubic-inch inliner made its debut in trucks in 1941 and in passenger cars in 1950 (available only in Powerglide automatic equipped deluxe model cars). The 235 offered improved performance over its 216-cubic inch predecessor, but it still had a number of shortcomings; namely the splash oiling system used to lubricate the rod bearings.

For 1953, Chevrolet introduced an improved version of its venerable six again in Powerglide-equipped cars and featured pressure-lubricated rod bearings. Beginning in 1954, all Chevrolets featured full pressure oiling; this significant change improved the inline engine dramatically. Obviously, swapping one of these engines into an earlier car is a desirable retrofit. But ’53 Powerglide and ’54 full pressure aren’t as easy to come by as they once were, making the more plentiful ’55-’62 engines an excellent choice for such swaps. With the same basic dimensions as the splash system the later engine is a simple and effective up date.

——————————————————————————–

A simple swap for ’37-51′s
The ’37-51 cars all used the same basic engine mounts, which are the rubber biscuit type. Two are used, one on each side of the front motor plate. These mounts are also used on the 1935 Master,’36 Master and Standard, as well as all 1937-51 passenger cars and sedan deliveries. The first step toward improving performance and reliability for these early cars is yanking the original 216 or 15 bolt-head 235 out of the engine compartment.

Once the engine is out ( a process made much easier by removing the sheet metal from the firewall forward), remove the motor mount plate from the block. To do this, the vibration damper must first be taken off the end of the crankshaft.

Next, remove the oil pan and the two screws from behind the front main cap that secure the timing cover from the inside. Now remove the four bolts and two studs from the rocker assembly and lift it off as a unit. Older models have the oiling tube attached with a screw-on fitting, so loosen it. Later models fit the tubing into a hole in the head. Set the assembly into an overturned valve cover so the springs don’t push the rocker arms off the shaft. Punch 12 holes into a cardboard box and number them 1-12. Remove the pushrods and put them in the cardboard in order. Use an egg carton to hold the lifters in the same manner.

The crankshaft can now be turned, either by prying against the teeth on the flywheel or turning it with a special socket that fits over the end of the crankshaft, until the two holes in the camshaft timing gear line up with the two screws in the retainer. These screws are best removed by an impact driver. Pull the cam gear forward and remove the shaft. With the camshaft out, three flathead screws will be visible. Remove the screws and the remaining hex-head screws that retain the plate with the impact driver used earlier. (If the engine is a 37-41, the crankshaft gear must also be removed to get the plate off.) Tap the plate lightly to separate it from the block.

Use the identical procedure to remove the motor plate from the 235/261 to be installed. Install the mounting plate from the old engine on the new one. For high performance application (ease of changing the cam) we suggest at this time you drill the tapped 5/16-inch holes in the timing cover all the way through and tap thread to 3/8 coarse, then install studs. Now you can get the timing cover off without removing the pan!

Install a new seal in the timing cover and slide into place, using the crankshaft socket to center the seal on the shaft then tighten the attaching screws and nuts on the new studs. If you plan to use the wide V-belt, the 216 vibration damper and pulley may be used. Remove the pulley from the 216 water pump and press it on the late pump until the belt groove lines up with those in the vibration damper and generator (this operation requires a 10 ton press), then cut off the excess shaft. To make things easy, the Stovebolt Engine Company has these modified pumps in stock. Install the original generator or the wide groove pulley on an alternator. Cast and polished alternator brackets are also available from the Stovebolt Engine Company.

If the late narrow belt is desired, use the vibration damper off the later engine with the water pump pulley from the 53-54 Chevy. Stovebolt also has pumps available for this combination. Use an adapter in the late model head’s temperature sender so the early temperature gauge capillary tube can be installed. Install the flywheel and bell housing from the old engine, along with the original starter and clutch. Now the engine is ready to go back in the car. If a 261 is being installed, make sure an oil filter is used. The 261 is a full flow system on the later models, and no oil pressure will be the result if the oil line to the filter is disconnected.

——————————————————————————–

Jimmies for early Chevys
Interestingly, the procedure outlined can be used to install a GMC 228-248-270-302 in a ’36 Master or Standard passenger car by using a ’37-51 passenger car motor mount plate. Use the water pump and the vibration damper from a ’37-40 Chevrolet, along with the bell housing, transmission and starter from a ’37-39 Chevy car. When using a GMC with a 4 bolt crankshaft flange, use a ’37-39 Chevy truck flywheel for the 9 bolt heavy duty clutch. For the late GMC’s with a 6 bolt crank flanges, use the GMC flywheel with a heavy duty passenger car clutch. NOTE: The ’37-39 bell housings will only accommodate a 10-inch clutch.

——————————————————————————–

Late Sixes for ’52-54 Chevys

To install a late 235-261 in a ’52-54 Chevrolet passenger car, there are two methods to consider. The first is to locate the holes for the late front motor mount in the IFS cross member (still called knee action by Chevrolet until 1954 ). The holes have to be drilled in the correct places. On the 1952 models, there are flat spots in the right place, but on the 53-54 models there are no indications of where they should be, so you will have to get the measurements from a 49-51 and copy them. Then install a 37-51 passenger car front plate on the late 235-261 engine.

The second way to accomplish this swap is to buy custom mounts from Stovebolt Engine Company. The kits come with frame and engine mounts and are a bolt on. The stock ’52-54 motor mount towers are riveted to the frame and have to be cut off, as they will obstruct our frame brackets. Once engine mounts are attached, lower engine into position and bolt down the transmission rear mount. Then locate the frame brackets. Drill frame holes at this time and bolt into place. The Stovebolt Engine Company motor mount kit is also of value when installing a Stovebolt automatic transmission adapter behind a 235-261 because it shortens the spread to the tail shaft of the transmission.