What was done: 305 and T5 swapped w/ new 350 (w/ .030 bore) and Tremec 3550/TKO, AFPR, new fuel pump, new T.O. bearing.

I'm now in the "break-in" period, and will take the car back to the shop in a few days for some adjustments, etc. However, I'd like to have an understanding of what's going wrong with the car before taking it into the shop. Below are a list of problems I've been having in the 85+ miles of stop and go driving.

Problems:

1) At cruising speeds the car "jolts" (almost like if you try to start outta 3rd gear). This is solved by giving it gas, or downshifting into a lower gear (but at 50mph dropping down into 3rd gear results in some really high RPMs). This is the biggest problem, as it's not limited to in-between-gear jolting. I've had it do this at 65mph in 5th gear, at 30mph in 3rd gear, at 45mph in 4th gear, etc. I have no idea what's causing this jolting. Fuel pressure?

2) At idle the oil pressure is normal, but while driving, it's buried past 60.

3) Gas mileage is horrible. And the AFPR is open all the way for minimum pressure, but it's still at ~40PSI! (Note: I'm using the stock 305 injectors)

4) There's a squeak coming from the clutch. If I tap the pedal, or engage the clutch, the squeak stops. It only squeaks when car is idle or driving, not when clutch is depressed.

5) Difficulty starting. Instead of the usual turn key starts, it's bogging down, almost as if it had a bad battery or starter. The starter is less than a year old and the battery is practically new (plus the volts are fine). Could this be that I'm using the 305 starter and a bigger spark is needed for the larger engine?

6) Lack of power. For a 350 w/ an overbore (is this technically a 383 even though it doesn't have the turned down crank?) it seems awfully sluggish off the line and the top end is lacking, too (esp. with the jolting)

Most likely when I take the car back to the shop, we're going to set it up with a new PROM. I imagine that will fix some of the problems (oil pressure, fuel pressure, shift lights), but will this cure all (clutch squeak aside, obviously) of the problems, or will more adjustments be necessary?

Thanks!

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Maverick
1989 Formula 350 TPI
5spd Tremec 3550/TKO
several suspension mods

 

The jolting is likely a vacuum leak or else you're running very lean on fuel at high manifold vacuum pressures.

Oil pressure is no problem. It just signifies that you have a high pressure oil pump.

40 psi of operating pressure on the fuel rail of a TPI system is normal. As soon as you get your problems solved you're also going to realize your injectors are too small. Increase your injector size to match your horsepower output.

Bad gas mileage, difficulty starting, and poor power output all suggest that your timing is way off. Check not only initial timing but also full timing and advance rate, including vacuum advance. The 305 starter is a different design then the 350 starter and actually puts out more torque. You've got the right one.

Pull the tranny and make sure you installed it properly. Did you install a pilot bearing in the block for the tranny input shaft?

A 350 with an over-bore of 0.030-inch is a 355. A 383 is a 350 that uses a longer stroke crankshaft from a 400 small block instead of the regular 350 crankshaft. Basically, you still have a 350. A 383 is a different animal.

 

Ooh, you bring up another Quick question.....these "383 kits" they sell...do they require an overbore on the 350 block?

 

I just spoke with the mechanic today. He seems to think it's the fuel filter that's causing the jolting (since it's always around the same RPM, and there are no codes indicating anything else). I'll let you know what they find out when I bring the car in later this week.

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Maverick
1989 Formula 350 TPI
5spd Tremec 3550/TKO
several suspension mods

 

383 is just a generic name for one of the options for a stroked 350 motor. I think the 383 size is based on a 0.06-inch cylinder overbore (don't quote me on that). Using a stock 4.00-inch bore will give you something like a 377 (again, don't quote me on that). They are all considered a "383 stroker". Little differences like how much you overbore the motor are just a matter of what needs to be done to recondition the motor. It's not a performance issue. When you order any engine kit, such as a 383, you have to specify a couple parameters when you order so it will fit with your block.

The first is cylinder bore. The kit will come with pistons and you need to tell the kit supplier how much, if any, that you're cylinders are overbored. You specifiy what you want including a stock block with no overbore at all. Common options are 0.03-, 0.04-, and 0.06-inch overbore. My particular motor was brand new and there was no overbore, so I ordered pistons for a stock 4.0-inch bore.

The second is crank journal size. Often times a kit will be made up of used equipment. As part of the reconditioning process, the crank journals (centerline of the crank on which the crank actually spins) may be machined down a bit to get a good new machined surface. Common options are to get a new crank with no undersize of the journel (no material machined away), 0.01-inch undersize, or 0.02-inch undersize. The problem now is that you took away some metal and the crank will be sloppy when installed in the block so what you do is order oversized bearings for the crank to sit on. The oversized bearing is thicker than normal and takes up the slop from the crank being machined down. You order bearings in the same fashion as the crank was machined down: stock, 0.01 oversized, 0.02 oversized, etc.

The third option is connecting rod length. There is only so much room between the crankshaft and piston so if you order a "long rod" kit (rods longer than the stock 5.7-inches in length) then you need a complimentary set of pistons to use the rods. Basically, what they do to accomodate the longer rod is move the mounting point between the rod and the piston higher up the piston to make room for the longer rod. If you don't do this, the longer rod will push a normal piston out the top of the motor. Hence, the custom made piston.

The fourth basic option you can go for is crankshaft stroke. A 383 kit is simply a 350 motor assembly with a longer crankshaft stroke than a normal 350. A 327 kit would have a shorter stroke than a normal 350 kit. Either way, you must have special pistons so you don't push them out of the block or sink them way down into the block. It's the same concept as the long rod motor. There's only so much space and if you make the stroke longer then you will push the piston out of the cylinder. The fix is to adjust the mounting point on the piston to move it back down into the motor. It's just a matter of making parts fit right.

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'89 Firebird RED!!!
B&M blown 468 big block
Tremec TKO 5-speed
Strange 12-bolt
Kenny Brown Competition Suspension

 

What effect does rod length have on performance?

 

Rod length has an effect on the dynamics of piston travel. Imagine for a moment the crankshaft is turning and the rod is VERY short. What is the piston doing? It's spending most its time traveling up and down and quickly snapping through TDC and BDC (top dead center and bottom dead center). Now imagine the same thing with a very long rod. What is the piston doing here? It's spending most its time hovering around TDC and BDC and quickly snapping to and from TDC and BDC. This plays an important role in power production.

Producing power from a motor boils down to one major issue: cylinder pressure. If you can build more pressure, then there is going to be more force pushing the piston down which translates to more force turning your tires. With a long rod motor, the piston dwells longer than normal at TDC and BDC. Your spark plugs fire off as your piston approaches TDC and the gas starts to burn. The gas doesn't burn up instantly though. It actually starts to burn up as the piston is coming up to TDC and continues to burn until the piston is already well on its way back down the cylinder. With a long rod motor the piston will dwell longer at TDC which allows the burning gas more time to build pressure in the cylinder. More pressure is more power.

Okay, in short why does a long rod motor make more power? Becuase the motion of the piston with a longer rod is such that the piston spends more time dwelling at TDC. This allows more gas to burn up while the piston is near TDC which in turn builds more cylinder pressure... making more POWER!!! And we all like power!

Feel free to ask any more questions... might as well because I'm on a roll!