Old Olds Fan

Question: Has anyone figured out the dynamic compression ratio of a 1965 442 stock 400 engine? If so, could you report the results here, and save me a lot of effort.
I have decided that to better understand my 65 442 engine gasoline/octane/timing issues, it would be a good exercise to run dynamic compression calculations using the ‘stock known’ original engine specifications. I need a bit of help as I don’t have adequate Oldsmobile experience in dissembling and measuring, primarily knowing usual stock deck clearance, and, all the specs I’m using here should be double checked and verified. I am not knowledgeable enough to be sure that I’m correct when trying to extrapolate intake valve closing from the specs I’ve found. That’s where I’m hoping all of you will help. I’m sure I might be wrong in any or all of my assumptions. So please be critical.

First; The 65 cam specs: Part# 387484 Duration Int. 278* / Exh. 282*
Valve Lift: Int.0.430 / Exh.0.432 Overlap 52* Bank Angle 54*
Question: at what lift were these specs reported? (.004, .006, .050?) How does it effect things?
Is it correct that Olds rates duration at zero lift, while most cam manufacturers rate duration at .050" lift? How does this effect things? (see below)
I think I’ve worked out the lobe separation to be 228 degrees.
Correct/Not Correct?
I think the intake valve closes at 252* ATDC (72* ABDC) which means it eaten up 70% of the 4’’ stroke (2.8”), which, I figure means that there is 1.2”of true compression stroke post the intake valve closure. Correct/Not Correct? This is the big one!!

Second; I think I have found that the stock ‘A’ heads cc at 77cc’s to 80cc’s?

Third: Maybe usual deck clearance has been reported as .014”?????
Is this what folks actually find?

Fourth; Early 400 motors used dishless pistons, also some 425s, but not all, only high compression 425s. Correct? (10.25 : 1 reported as the Compression Ratio) Correct?

So I know; bore is 4.0” stroke is 3.975” rod length CtoC is 7.00”
Compression Height is 1.615
I believe, the head gasket has 4.125” ID cylinder holes, and compresses to .025”

Using a calculator at: https://www.uempistons.com I put in the left hand values.

Cylinder Head Volume (cc)
Cylinder Head Vol (cubic in.)
4.697
Piston Head Volume (cc)
Piston Head Vol (cubic in.)
0.000
Gasket Thickness (in.)
Swept Volume (cubic in.)
49.951
Gasket Bore (in.)
T.D.C. Volume (cubic in.)
5.219
Cylinder Bore Diameter (in.)
Gasket Volume (cubic in.)
0.334
Deck Clearance (in.)
Note: Neg. nubmer above deck, Pos. number below deck
Deck Volume (cubic in.)
0.188
Stroke (in.)
STATIC COMPRESSION RATIO
10.571
Rod Length (in.)
Adjusted Stroke (in.)
1.633
Intake Closing Point (degrees) ABDC @ 0.050 lift plus 15 degrees
DYNAMIC EFFECTIVE COMPRESSION RATIO
4.932

What do you think?? Please correct me where I’m wrong.
I not sure of the 1.633 adjusted stroke, but my calculations are even worse at 1.2”
If these numbers above are correct I can see that there are significant improvements to be made when rebuilding an engine or for that matter just changing the cam. I understand that an engine with 8 to 8.2 dynamic compression should run well on 89-91 Octane gas. I kind of find it hard to believe that the Olds engineers of the day would have had it this far off. So where did I screw up? Help Please!!

Old Olds Fan

Sorry, the chart from the calculator didn't post well. These are the values I used in "the left column": Cylinder Head Volume (cc) 77 Piston Head Volume (cc) O Gasket Thickness (in.) .025" Gasket Bore (in.) 4.125" Cylinder Bore Diameter (in.) 4.0 Deck Clearance (in.) .015" Stroke (in.) 3.975" Rod Length (in.) 7.0" Intake Closing Point (degrees) ABDC @ 0.050 lift plus 15 degrees 108*(degrees)

oldcutlass

Have you read this? You also have to take into consideration the head gasket .017
http://www.442.com/oldsfaq/ofcrc.htm

Old Olds Fan

Thanks for the link good info. Yes I have included gskt. compressed thickness at.025" I'm looking for the dynamic cop. ratio, it includes the cam profile and where the intake valve closes, which begins real compression some where up the stroke (reduces stroke making compression) That's the best way I can explain it, that's why I looking for guys that know a whole lot more than I do. I think you really have to have a very complete understanding of cams, which I don't.

oldcutlass

I agree valve timing effects compression.

oddball

I've never seen a dynamic ratio calculator. Most of what I've seen in that area is more rule of thumb or experience based discussions. I suspect the real calculations are quite a bit more complicated, and I've absolutely never seen information on how to interpret or use the result. While it would be neat info, it really wouldn't help you in this situation.

A couple of corrections on the cam topic. All manufacturers publish both "Advertised" and "@ 0.050" duration numbers. It used to be only Advertised, but the problem is what counts as the start? 0.001? 0.00001? That can make a lot of difference because the ramps generally start VERY slowly. Cue the marketing "interpretation" battles. So the 0.050 is better for comparing cams, while the difference between advertised and 0.050 tells you how steep the initial ramp is.

Lift is almost always reported as "gross lift", which is the maximum lift from the cam considering the stock rocker ratio. e.g., stock Olds rockers are 1.6:1. So if the cam has 1" of lift in it, the valve actually moves 1.6". Most cams have 0.25 to 0.45 lift in the cam. Cams have to fit within the cam bearings and have a pretty big base circle, so lift is always limited.

You've done some research, so you know that the longer the intake valve is open, the lower the dynamic compression. Overlap will also have a major effect because the exhaust valve is likely still open when the piston starts moving back up. That also effects how much exhaust remains in the cylinder which also has a big effect on the whole process.

Gas was pretty different in '65, which makes it difficult to run the engine like it used to. There are several options:
re-work the distributor to have a slower, or reduced, advance curve
modify the engine to reduce static and/or dynamic compression. static = thicker gaskets, larger heads, dished pistons, etc. dynamic = larger cam

The depth of the piston in the hole at TDC varies quite a bit from the factory. So you're only guessing until you actually inspect your engine, which is darn near impossible without removing the heads.

Stock cams generally have low lift, little overlap, and short durations. This gives excellent idle qualities because the cam is pretty ideal there. However, those qualities dramatically limit its ability to move enough air at higher RPMs, hence limiting power. So the stock stuff is always a balance, which is why differences between low performance and high performance (ie, base 455 vs w-30) is mostly in the cam.

Old Olds Fan

Oddball thanks for the reply, you answered the “Advertised/ 0.050 duration” issue for me, I understand “gross lift and the base circle”. What I don’t know is whether I’m deriving intake closing angle, lobe separation, or intake centerline correctly and they affect everything. I’ve been working overtime on this one, but made big time gains last night. I found a dynamic compression calculator on the web. Not at all easy to download but I now have it on my desk top. You can try yourself by going to; http://cochise.uia.net/pkelley2/DynamicCR.html then to the bottom of the page. I used the larger file and after some screwing around got the calculator. (I’m not very computer savvy so maybe it’ll be easier for others.)
I’ll just report the results I got and readers can check the figures from what they know.
PLEASE IF YOU SEE INCORRECT VALUES LET ME KNOW!!
(I’m concerned by the negative overlap and cam advance, not being correct.)

Results from Pat Kelley’s calculator: 3 different processes

1st. Note: Red figures were derived by me, possibly incorrect!
Crank stroke 3.975”
Rod length 7.0”
Advertised intake closing angle 72* (* denotes degrees)

Results
Dynamic Stroke 2.8617
Dist. of piston from BDC

2cd.
Advertised duration
Intake 278*
Exhaust 282*
Lobe separation 228*
Intake lobe centerline 113*

Results
Seat timing Open Close
Intake 26* BTDC 72* ABDC
Exhaust -304* BBDC -202* ATDC
Overlap -176 Total Cam Advance 115*

3rd.
Cylinders 8
Bore 4.0”
Stroke 2.8617 (calculated)
Chamber Vol. 80cc
Head gskt. Thickness .025”
Head gskt, bore 4.125”
Piston to head clear .015”
Flat top piston volume 0cc

Results
Quench distance 0.040”
Displacement 287.6906 c.i.
Calculated Dynamic Compression Ratio 7.65396
Static Compression Ratio 10.2425 (calculated using stock stroke 3.975”)

I ran new calculations changing bore 1ST. overbore 0.030 = DCR 8.164 SCR 10.950
2cd. “ 0.060 = DCR 8.23 SCR 11.088
Real cool tool Should really help with all the different parameters that can be changed when thinking about a build.
I’ve just got to figure out whether I’m getting the numbers correct regarding the cam.

TripDeuces

http://cochise.uia.net/pkelley2/DynamicCR.html

This should answer your questions on DCR

http://www.wallaceracing.com/dynamic-cr.php

DCR calculator

rootney

I think your lobe separation angle is way off. Should be 110 to 112 approx.
This is plainly listed on the cam spec. sheet.

George

MDchanic

I suspect his lobe sep. is 114°.

Nice links, George.

- Eric

Old Olds Fan

Thanks Trip I'll study the information. I agree I'm off, and I now remember J. Mondello saying lob separation will be between 106 and 114, usually 110-112 he also mentioning dual patterns, so intake and exhaust have different lobe centers, not sure how that plays into lobe separation, but for sure the way I was figuring it is way off, back to school, I only might be correct on intake center line, but that seems to work for the other calculations.
Where can I find those specs, Lobe separation, and intake center line, for this stock (Olds part # 387484) 65 442 Cam?

Old Olds Fan

Trip that sites very helpful, good to get the cranking PSI figure, that allow someone to get a better understanding of stock engine condition to begin with, that and a leak down. Then I guess put 93 octane in, check total mechanical advance, dial a little out of the vacuum advance and hope for the best, keeping your ears tuned for ping.

cutlassefi

The intake is on a 113 intake centerline. (278/2-26) Not sure your exhaust numbers are correct, don't understand 304 BBDC and 202 ATDC. That would mean the exhaust has an overall duration of 686*.

Most of the stock stuff is on wide lobe seps to keep overlap to a minimum.

Old Olds Fan

Thank cutlassefi I'll use 113 as the intake center line. I also agree that I'm off on the exhaust numbers. So the question remains; is there an archive some where that will list cam specs, which will also have lobe separation and the value openings and closings for the old stock cams?? I know this information would be on the cam card but Ive never seen a card for a stock cam. All I can find is duration, lift and overlap, I'm guessing any other numbers and don't have it right, obviously.

cutlassefi

If you get the opening and closing info for the intake and exhaust we can figure the lobe sep from that.

olds 307 and 403

I used the Wallace racing calculator just now. I didn't degree my cam due to cheapness and wanting my car running. If my cam is advanced 2 cam degrees, 4 crank according my Cloyes timing set, my cranking pressure should be 142 psi, 140 in the straight postion. My compression test pressure was 140-142 psi. 1635 ft is my track altitude for my track. If I bump it to 9.5 to 1, it should be 182 with same cam. I plan on doing just that. Just curious what octane will be needed with 180 psi? I plan on turning the vacuum advance way back on my Mallory 42 series. Seems accurate to me.

Old Olds Fan

What was the dynamic compression ratio, 180psi probably is about 8.2 :1 that'll require 93 octane at least, your vacuum advance is not in play when straight line racing, only at part throttle cruise. Altitude effects fuel mixture,air's less dense

olds 307 and 403

Actually higher, if it is accurate. I know it only functions part throttle, this also a fun cruising car, pinging to death around town is no good. If I have to run premium, so be it. I believe Shell 92? Premium is the highest in town. It is not a daily driver and want 9's flat in the 1/8. If I can get money together for the heads someone is selling, their current chamber CC would give 9.5 to 1 with shim gaskets and out flow my #8's. I will curious to see where my final compression ends up. My point was it hit my current compression dead on, will see with the higher compression ratio.

Old Olds Fan

O.K. fellows, I found the cam specs on the “400/425 Cam Choice”thread, including the value opening and closing. The valve event timing will help figure out the lobe separation and intake centerline. I had previously used advertised duration, (what’s on the thread is @ .050”), but never could check valve event. I’ve used advertised duration for the dynamic compression calculators, and played with lobe separation and intake centerline to get as close to the valve events as I can. The results are below;
Dynamic stroke Cam timing/ Overlap
Input, Input
Stroke 3.975” Adv. Int. duration 278* Adv. Ex. Duration 282*
Rod length 7.0” lobe seper. 117* Int. centerline 116*
Adv. Int. close 59*( degree)

Results Results
Dynamic Stroke 3.22” Intake Exhaust Dist. Piston from BDC 0.7533” Opens 23*BTDC 75*ABDC
Closes 79* 23*ATDC

As you can see I didn’t get all the valve events to come in correctly, I do have the intake opening and exhaust closing correct to specs. I felt this was good enough to get dynamic compression results. (below)

# of cyl. 8
Bore 4.0”
C/C vol. 80cc
Head gst. Thick 0.025
“ “ Bore 4.125”
Deck clear. 0.015
Flate top 0.0cc

Results
Quench 0.04”
Dis 323.87cu.in.
DYNAMIC COMPRESSION RATIO
8.49079
This high a dynamic compression ratio would certainly require the very highest octane gasoline available today (93) and probably would have detention issues at stock timing settings. Taking 4 degrees out of timing for every 1 octane point missing from the recommended high octane (96-98)gas would soon leave you with no initial advance and a very lazy motor. IMO at the minimum one needs to think of recamming a stock 1960’s engine in order to get decent performance without detonation issues