What would you do.

[JimNolan]

I'm building a 390 105 block that is bored .030 over. I'm using stock rods and 9.5 pistons with a @ .023 deck height. I plan on using the Fel Pro .038 gaskets also. I'm using a 570cfm Avenger carb and "S" code intake. The rocker ratio is 1.73. The cam is a 268H comp cam and it's set on 106 ICL. With stock C1AE heads and FPA headers it looks like I could get about 315 HP out of it. My question is. While the heads are being rebuilt should I put 2.087" intake and 1.652" exhaust valves in it. Will it help me that much with this low of a HP 390. Thanks guys. 

[blykins]

You probably won't notice much difference.  If the current valves are in good shape, I wouldn't bother.  If you need to replace the valves and need a valve job anyway, probably wouldn't hurt anything.

What will help the driveability and the health of the motor the most would be to get a thinner gasket or have the decks cut.  Having over .060" of quench distance is not conducive to a happy engine.

[JimNolan]

What will help the driveability and the health of the motor the most would be to get a thinner gasket or have the decks cut.  Having over .060" of quench distance is not conducive to a happy engine.

You know, you're right. I just got through figuring how much more money in gas it would cost me a year to go from a 7.8 DCR to a 8.2 DCR. About $150 dollars a year. What the hell was I thinking. I'm going to call the guy doing my heads and tell him to put the big valves in the C1AE heads and I'll go with the .020 shim gaskets I already have laying on the shelf. I've run a .020 gasket on my 406 for 3 years now and not had any trouble with them. That'll give me a @ .044 quench and 8.2 DCR at 10.0 - 1 compression. Thanks for waking me up.

[blykins]

Personally, Jim, I think you'll be on the ragged edge of being able to run high octane pump gas with that combo.  If I were building this engine, I would shoot for around 9.5-9.7 SCR and eyeball the DCR so that it doesn't get over 8. 

I haven't ran your numbers, but maybe you can manipulate the specs and cam timing to give it a good quench distance but not be on the fence as far as compression.  The difference in hp from 9.5 to 10 is going to be negligible, but if it's on the edge and likes to ping you'll be glad you went conservative on the numbers.

[JimNolan]

Personally, Jim, I think you'll be on the ragged edge of being able to run high octane pump gas with that combo.  If I were building this engine, I would shoot for around 9.5-9.7 SCR and eyeball the DCR so that it doesn't get over 8. 

I'm living proof that quench does make a difference. I use forged pistons in my 63 Galaxie engine that gives me a .009" measured deck height using C3AE Heads. I used .020 steel shim gaskets on it. When the weather is cool up here in Indiana I use 87 octane gas with no knock whatsoever. I use 89 octane most of the time. I went to a 61 overlap cam to get the DCR down to 8.06, CR is 10.7.  Now, I've put at least 25K miles on this engine with no problems. But, I don't race it very often either. My cam lift is just .500/.500 but, how many people do you know that's running a .029 quench. 

[My427stang]

I think that's a bad example for people to use Jim.  If it works for you, certainly run it, but he benefits of  tight quench don't increase past about .040 IMO, and at .029, if you pulled any RPM my guess is the pistons would kiss the quench pads.  May not cause damage at that level, but you are running a little tighter than you need to, I'd hate to see other people start cutting things to try to get that tight

Tight quench is just one component, bore size, piston design, cam timing, chamber shape, mixture, ignition timing, temp, fuel, fuel mixture, and a host of other things all lend themselves to octane resistance.  FWIW, I run 10.7:1 in my 489 and have since 2006, my quench is about .048, it'll run any swill I put in it on the street. 

One last comment, I know you know how to calculate DCR because you do it often, but overlap doesn't affect DCR, although the diluted mixture from overlap could reduce detonation at low RPM I suppose.  Did you mean you swapped to a intake closing point of 61 degrees?  61 degrees of overlap for the RPM you run would be a relatively healthy cam.

[JimNolan]

One last comment, I know you know how to calculate DCR because you do it often, but overlap doesn't affect DCR, although the diluted mixture from overlap could reduce detonation at low RPM I suppose.  Did you mean you swapped to a intake closing point of 61 degrees?  61 degrees of overlap for the RPM you run would be a relatively healthy cam.

Ross,
 61 is the degrees my intake and exhaust is open at the same time. 71 degrees is my intake closing angle. I had designed the engine to go into a 63 Galaxie Boxtop to resemble a "B" code 63. I found most of the components before I found the car. I was just going to drag race it. When I changed my mind about drag racing it I needed a different cam. Lunati designed this one for me so I could run on pump gas. 282/296, 214/224 @50, 114/110, .500/.500 lift. It was a 1.73 ratio and 0.00 lash designed cam.

[My427stang]

Cool, sort of like a slow ramp CJ cam, likely a nice street grind in that car and what you have is exactly how Ford made big static compression numbers, heavy valvetrain and old spring design work on the street.   Needless to say that overlap isn't lowering your DCR, it's the late intake timing and long ramps.

I think you'll find that tight quench falls under the law of diminishing returns, in something like an FE with a decent sized quench pad, .040-.045 does all you need IMHO. 

The Gal sounds like a very cool car

[JimNolan]

I think you'll find that tight quench falls under the law of diminishing returns, in something like an FE with a decent sized quench pad, .040-.045 does all you need IMHO. 

The Gal sounds like a very cool car

Ross,
 This 390 I'm putting together is set on 110/106 installation giving me a 8.23 DCR with a .044 quench. If I find I have trouble with engine knock I can always bump the ICL to 108 or 110 and still have good bottom end torque. Truth be known I should take the timing chain cover off now while I can change it easily and set it on 108.

[My427stang]

I think having a little lead to the cam is almost always beneficial, and with a good mixture and cooling system, 8.23 is absolutely fine, maybe even close to optimum (if there is such a thing in DCR)

As long as you have the timing curve right, the power valve to come in soon enough and jetting in the ball park, you'll be fine, don't give up the vacuum and drivability to hit a number that depends on so much more

Quench - good
DCR - good
SCR - good
Cam appropriate for use - good

That leaves

Jetting
Enrichment timing (power valve)
Ignition timing
Engine temp

Sometimes we get too focused on DCR as a number and forget the other variables.  FYI, the 10.7:1 489 I run is 8.33 DCR, it's the other little things that make those numbers work

[JimNolan]

I need to apologize to you guys for starting a post when I didn't know what I was talking about. The engine I thought I had isn't the engine I've got now. After cleaning up everything and measuring it I think I'll still be OK using .020 head gaskets.
What I've got. A 105 block in which the level of the deck is within .001 using a Starrett straight edge ruler mounted on a indicator base (magnetic).
 H395P +.030 pistons ( 9 cc dish from what I can find information on) which set .030 below the deck.
C1AE heads that should cc out to 71-74cc's of dish (heads are still at machinist).
From all measurements taken I should end up with a .050" quench, 9.57 - 9.85 SCR, 7.9 - 8.1 DCR.
 I also spoke to Stan Johnson about the FPA headers I have fitting the C1AE heads, he said it would. Now I've just got to confirm the "S" code 390 intake will seal on the C1AE heads. Thanks for your patience.

[My427stang]

Should be no issues with the S code intake, just use low riser gaskets.

The rest of the stuff looks good for a mild 390, get 'er done!