68Tom

OK, so I'm getting pretty close to rebuilding the original engine in my '68 442. It's numbers matching, so I'm going to keep it close to stock. However, in order to make it more driveable with the weak gasoline readily availble, I am considering dropping the compression to 9:1. However, I'm worried about power loss.

From what I've been told, running 10.25:1 compression on lower octane (than necessary) will obviously sap power, so the 9:1 ratio might actually not make much difference in terms of losing power.

I guess my question is, what would you recommend in terms of the rebuild that will not only maintain, but also possibly increase performance, while maintaining a stock appearance and not breaking my bank? I'd like it to be at least the original 350hp (it's a 4-speed), if not higher than this.

I just want to go in prepared to informatively discuss the rebuild with my engine man. Thanks.

Olds64

I wouldn't drop the compression. If you are driving it now on mid-grade or premium then why shoot yourself in the foot during the rebuild?

68Tom

I'm not driving it at the moment. I have no idea how it should perform in stock form, as its had a blown head gasket due to way too much compression since I've owned the vehicle. Hence why I was asking for advice.

Oldsmaniac

If it is stock now leave it stock. If an overbore is required you will need new pistons and I would go with stock compression ratio. I drive a 66 Sfire with a stock rebuilt 425. I use premium fuel. It performs well and timing is about stock specs. If I were to run regular fuel with lower octane the fuel itself would not make much of a difference in performance. I may need to retard the timing from factory specs due to pinging and then performance may drop off some. My car is driven on occasion to cruises and for fun. I did not have hardened valve seats installed as recommended by some for unleaded fuel. Every once in a while I add some lead substitute to the tank just because and do not know if it really is required. Compression would need to be very high to blow a head gasket. Mostly they fail due to age. You want to have the heads checked for cracks if you suspect a head gasket problem but have not pinpointed the exact cause

68Tom

Yep, it's stock now. Fairly certain the engine has never been out of the car. I'm guessing (and it's only a guess) that it will need a re-bore. Everything will definitely be checked.

joe_padavano

First, octane by itself does not make power. The higher octane fuel is actually more difficult to burn, resulting in marginally lower mileage and an infinitesimal reduction in power as compared to regular. The advantage of higher octane fuel is that the detonation resistance allows other horsepower-increasing measures, such as higher compression or increased spark timing. Looking at this another way, if you must back off on the spark timing to run lower octane fuel, that will reduce power.

Having said that, if you replace your factory steel shim head gaskets with the thicker FelPro blue gaskets, that will reduce the CR a little. The actual reduction will depend on the measured bore, stroke, and combustion chamber volume, but expect between a 0.25 and 0.5 point drop just from that change. Of course, if you have the heads done while they are off the engine and the machine shop surfaces them, you may negate any CR reduction from the gaskets.

68Tom

So would you recommend I stay at the same compression, Joe? What other tips would you recommend I do to the '68 400 engine?

J-(Chicago)

If that head gasket has been blown for a while, moisture in the air could be eating up your block and head surfaces. I'd have the surfaces redone anyway to make sure everything is trued up correctly. Blown head gaskets from my experience usually happen when someone operates the car at really high coolant temperatures causing warping.

citcapp

Stay with the same compression and work with the timing to insure it runs correctly. I run preminum in my Olds 10.1 compression 480+hp runs great.
No worries.

64Rocket

If it does have a blown head gasket, one, it may have sitting for some time and the factory steel shim head gaskets rust out. Then when it is started again they tend to blow thru. Two, if it is blown and has been sitting for some time, the water in the cyl may have caused damage to the cyl wall, which means an overbore for sure, let alone the rust to the valves in that cyl. Third, you will have a hard time finding pistons for that engine. If you do get some, I'm sure they will only be cast. You will have to take measurements to find for sure your compression. You will have to consider the piston below the deck, the head CC will be 80 to 84 CC's and the CC's of the cup in the piston you get. Plus the thickness of the new head gasket you use.
Lots of fun.

Gene

68Tom

The car, in fact had been sitting for some time. As far as I can tell, it was last registered in 1992. So, I'm fairly certain what you have described is what has happened. In fact, initially upon starting, you could tell one of the pistons wasn't even firing. I'm fairly certain an overbore will be required, hence new pistons.

The guy I'm taking my engine to primarily works on Olds engines. He has a few sets of pistons he had made, one set at standard bore and one at .060 over, that I believe he said are 9:1 compression, hence my asking the original question.

88 coupe

'68 Olds 400.
OEM equivalent.
9.0 and 10.5 CR.
Std, .020", .040", .060", and .080".
$381.11 a set.

http://www.egge.com

Norm

68Tom

Well that definitely solves some problems. Thanks!

442scotty

dont make the mistake of cheaping out and using the .060 pistons...get the good stuff...you might only need .030

88 coupe

Or .020"

Norm