57 Engine - 300HP v 250 HP, how can I tell?

[lancemb]

In a previous post, I described how my model 75 has no VIN on the engine, and thus seemingly replaced at one time. 

 

I also have noticed that although the car runs and drives great, it doesn't seem to have the power that my other 57 and 58s have had.

 

I don't know if this is due to a weak transmission, or the engine, and got me to wondering if the engine had been replaced with a 250 HP version.

 

How can I tell, since there is no VIN on it, without tearing the engine apart? 

[SpecialEducation]

Other than the obvious 2bbl/4bbl difference, I don't know how you could tell without a number.  As far as I recall, It's only a difference of 9.5:1 vs 10.0:1 on the compression ratios.  If it seems down on power, I'd probably look at ignition timing.

[old-tank]

Check the compression:  my old Chilton's lists 170 and 185 for 250 and 300 hp respectively. 

[60FlatTop]

Put a weaker spring on the accelerator and see if that helps.

Bernie

[buick man]

…. well one could just add to the length of the speedometer tip :)'

[NTX5467]

If you suspect the engine has been "changed", then you'd need to look at things that might have "come along for the ride" with the replacement engine.  These could include the distributor and carburetor, for example, if the "replacement" engine came from a salvage yard source.  You might also check for the casting date on the cylinder head or cylinder block (sometimes, casting dates will precede the production date of the vehicle by up to six months).  For some Buicks, there can be a "casting letter" visible without removing the valve cover, which the model year's service manual could illustrate (rather than looking for a casting "number" under the valve cover area).  IF the engine was a Buick "service replacement" item, then the carb and distributor numbers should match the model year of the vehicle you have.  If it came from another source, they probably would not, matching the numbers of the donor vehicle instead.

 

In general, to get a 50 horsepower increase, back then, it would have needed a larger carburetor, dual exhaust, and probably a little wilder camshaft and/or larger valves (as the later Chevy 327/250 vs 327/300 did, but with the same camshaft specs).  An increase in mechanical compression ratio (9.5 to 10.0) would NOT have made that much horsepower difference by itself.

 

I'd concur with the ignition timing issue, possibly with an incorrect timing mark (at this stage of the game).  Might also be an issue with a mis-adjusted carb linkage or additional "build thickness" under the floor mat?

 

Bernie might be on to something!

 

NTX5467

[Caballero2]

I have one of each on the floor of the shop.  I will check to see if head castings number is different.

Dan

[lancemb]

Thanks for the input.  As a little more info, the carb is the correct 4 bbl as is everything else on the outside as far as components including dual exhaust, unless there is some way to tell that is not obvious.  I guess if the heads are different that would be good to know (Caballero2 I am interested to know what you find).

 

The timing is worth checking.  I am fairly certain it's not just a matter of thick carpet or throttle travel.  I've driven enough of these cars where I can get a pretty good sense of how much "go" it should have.  It's obvious enough anyway in my opinion; there is a huge difference.

 

The compression would also be interesting to check, but would only be an indicator probably if they were on the high end of the range for the lower version.  If it was much higher than that would give me high confidence that it was indeed the higher HP version.

[High Desert]

On 3/27/2016 at 1:35 PM, lancemb said:

Thanks for the input.  As a little more info, the carb is the correct 4 bbl as is everything else on the outside as far as components including dual exhaust, unless there is some way to tell that is not obvious.  I guess if the heads are different that would be good to know (Caballero2 I am interested to know what you find).

 

The timing is worth checking.  I am fairly certain it's not just a matter of thick carpet or throttle travel.  I've driven enough of these cars where I can get a pretty good sense of how much "go" it should have.  It's obvious enough anyway in my opinion; there is a huge difference.

 

The compression would also be interesting to check, but would only be an indicator probably if they were on the high end of the range for the lower version.  If it was much higher than that would give me high confidence that it was indeed the higher HP version.

These are the heads for my 300hp engine if that helps.

[High Desert]

I looked through the spec book. The only difference listed between the two are the heads. Bore, stroke, crankshaft all seem the same.

[Caballero2]

All four series have the same number; 1172889.

Sorry,

Dan

 

P.S.  Lancemb:

  Single or dual exhaust on you car?

Edited March 28, 2016 by Caballero2
Ask question (see edit history)

[High Desert]

Oops, looks like the camshaft may be different too. So, just the heads and cam.

 

[NTX5467]

I'm wondering when the "lower performance" happens?  Off-idle, part throttle passing, or WOT?  Just curious.  Possibly a muffler that might be a little clogged up from "lower rpm operation"?

 

Thanks for those engine specs, High Desert!!  Quite a bit of difference in the camshafts, but not quite worth 50 horsepower by itself.

 

More things to look at . . . .

 

NTX5467

[High Desert]

1 hour ago, NTX5467 said:

I'm wondering when the "lower performance" happens?  Off-idle, part throttle passing, or WOT?  Just curious.  Possibly a muffler that might be a little clogged up from "lower rpm operation"?

 

Thanks for those engine specs, High Desert!!  Quite a bit of difference in the camshafts, but not quite worth 50 horsepower by itself.

 

More things to look at . . . .

 

NTX5467

I'd love to thank whoever posted those specs originally. I just downloaded them for my own reference. It does seem like Buick went through a great deal of effort to ensure the Special had a weaker performing engine, while keeping it mostly the same. 

[lancemb]

Thanks guys!  Weird that the heads would have same numbers on them if different.

 

I have dual exhaust.  The exhaust was installed by me new 8 years ago.  It did also have duals previously.

 

I notice the lack of power when accelerating from a stop or at low speeds.  There is no other issue that I notice; it starts right up, choke seems to operate fine, no hesitation, and idles and accelerates very smoothly - just not with much power compared to all other 57 and 58 Buicks I've owned (all big series).

 

Indeed it seems like they went through a lot of effort to make the Specials have 50 less horsepower!

Could the combination of the cam, heads, and dual exhaust be good for 50 HP?  I would think the exhaust would be worth 10 HP if part of that figure.

[old-tank]

The car may have a different axle ratio.  It would be real hard to check the gears, but you can get a general idea:  install a tach  temporarily on each car; drive 60 mph with a GPS and see if there is difference in the rpm.

[High Desert]

12 hours ago, lancemb said:

Thanks guys!  Weird that the heads would have same numbers on them if different.

 

I have dual exhaust.  The exhaust was installed by me new 8 years ago.  It did also have duals previously.

 

I notice the lack of power when accelerating from a stop or at low speeds.  There is no other issue that I notice; it starts right up, choke seems to operate fine, no hesitation, and idles and accelerates very smoothly - just not with much power compared to all other 57 and 58 Buicks I've owned (all big series).

 

Indeed it seems like they went through a lot of effort to make the Specials have 50 less horsepower!

Could the combination of the cam, heads, and dual exhaust be good for 50 HP?  I would think the exhaust would be worth 10 HP if part of that figure.

12 hours ago, lancemb said:

Thanks guys!  Weird that the heads would have same numbers on them if different.

 

I have dual exhaust.  The exhaust was installed by me new 8 years ago.  It did also have duals previously.

 

I notice the lack of power when accelerating from a stop or at low speeds.  There is no other issue that I notice; it starts right up, choke seems to operate fine, no hesitation, and idles and accelerates very smoothly - just not with much power compared to all other 57 and 58 Buicks I've owned (all big series).

 

Indeed it seems like they went through a lot of effort to make the Specials have 50 less horsepower!

Could the combination of the cam, heads, and dual exhaust be good for 50 HP?  I would think the exhaust would be worth 10 HP if part of that figure.

I don't know. It seems like they tuned the engine to match the 2bbl carb. Is it possible that an engine designed to maximize the cfm of a 2bbl, would actually run worse with a 4bbl? 

 

[buick man]

…. we believe the exhaust manifold header exit ports should tell the real story.  1-1/2-inch for Specials with 250 nailhead & 2-0 - inch for 300 nailhead …  Buick later in the run attempted to "lower" throttle exhaust noise complaints by having dealers perform an overall pipe O.D. reduction procedure targeting the exiting exhaust pipe coming out of the rear resonators for any jobs coming back with sound complaints.  This procedure sized down the original pipe to 1-1/2 - inch I.D. from a previous full flowing 2-0" I.D. system on Century, Super and R.M.'s.

 

Edit: btw: be weary today when purchasing an exhaust system as most if not all will sell you a ready to go overall 1-1/2-inch I.D. system instead of the factory correct 2- inch I.D. system.

Edited March 30, 2016 by buick man (see edit history)

[lancemb]

18 hours ago, buick man said:

…. we believe the exhaust manifold header exit ports should tell the real story.  1-1/2-inch for Specials with 250 nailhead & 2-0 - inch for 300 nailhead …  Buick later in the run attempted to "lower" throttle exhaust noise complaints by having dealers perform an overall pipe O.D. reduction procedure targeting the exiting exhaust pipe coming out of the rear resonators for any jobs coming back with sound complaints.  This procedure sized down the original pipe to 1-1/2 - inch I.D. from a previous full flowing 2-0" I.D. system on Century, Super and R.M.'s.

 

Edit: btw: be weary today when purchasing an exhaust system as most if not all will sell you a ready to go overall 1-1/2-inch I.D. system instead of the factory correct 2- inch I.D. system.

Buick Man the driver side exhaust manifold is different between single and dual exhaust only.  Mineis dual.  Are you saying there is a difference in the exhaust ports on the head though? 

[lancemb]

On Monday, March 28, 2016 at 3:30 PM, High Desert said:

Oops, looks like the camshaft may be different too. So, just the heads and cam.

 

Ok after reviewing all suggestions this seems to be the most surefire and easiest way to determine.  According to this the valves are open significantly longer on the 300HP version.  Hence, I think all I have to do is remove a valve cover, turn the engine until a valve just starts to open, mark the crank, turn it until valve fully closes, mark crank again, measure degrees movement of the crank, and compare to this chart.

 

Does this make sense? 

[buick man]

4 hours ago, lancemb said:

Buick Man the driver side exhaust manifold is different between single and dual exhaust only.  Mineis dual.  Are you saying there is a difference in the exhaust ports on the head though? 

… yeah, but we would just measure the header port with a tape measure or a popsicle stick.   btw, the cam is different on the Special as well.  The 300 h.p. has a higher duration lobe and when listening to the exhaust has a noted wallop in the idle as well.

4 hours ago, lancemb said:

Buick Man the driver side exhaust manifold is different between single and dual exhaust only.  Mineis dual.  Are you saying there is a difference in the exhaust ports on the head though? 

No what I mean is the header pipe I.D.  is/was sized the same as with the rest of the exhaust system when stock.  Regarding the head exhaust port, then yes the port would be milled less than the 300 h.p. head because what would the advantage be of just adding a larger I.D. pipe with a narrower head port and a taller cam ? 

 

I would give Russ a call regarding these specific questions. He is the crowned nailhead king.   Here is his Nailhead site :  http://nailheadbuick.com