Are any of you savvy engine builders running 10:1 to 10.5:1 compression in a 454 on pump gas. I have heard the age-old advice that you can't run more that 9.5 to 9.8:1 compression unless you buy aluminum heads. Well, I have also heard many in different forums and people at local car show say I'm running 10.:1 and as much as 10.5:1 compression on 91 to 93 octane in my car, and it runs just fine. most of these are street cars with big loopy cams. So, what say you! I have a 70's 454 block #361959 with an original forged LS6 crankshaft and a set of 10141279 100cc vortex heads 2.19 intake valves, 1.88 exhaust valves. A ZZ502 cam, a set of Scat I beam connecting rods and a set of -10.5 domed hypereutectic pistons. roller lifters, roller rockers yada, yada, yada. according to the local online compression calculators it should put me at about 10.5:1 compression. I'm sure there are cars running around out there with higher than 9.5:1 compression on pump gas. So, what is your secrets, I'd like to know. I have a 1973 Corvette T top coupe with a 454 8.2:1 compression 275 hp in it now. The only rubber it will burn is the fan belts when they squeal. Future upgrades include a 5 or 6 speed manual transmission, 3.73 gears in the rear, stronger U joints, larger 3" axle tubes, and some 275/60-15 tires. Any and all experience, advise, and wisdom would be appreciated.

 

Can you do it, yes. Will you need to be careful with your ignition timing curve. Yes.

 

Both of my big blocks are in the 10:1 static range and run fine on 93 pump gas. The '72 454 was 8.5:1 factory and I put in domed pistons to get to 10; the '67 427 was rebuilt to the factory spec of 10.25:1. Neither has a lope-y camshaft. They have the original cast iron heads with the '67's being the small closed chamber design with steel shim gaskets (~0.20" compressed height). The only upgrade/modernization are the roller-tip rockers in the '72.

 

Keep the quech tight is what I would advise. .040" is a safe target. Juggle the deck height, head gasket and pin height to make that happen.

The dynamic compression ratio is the other tool to use here. You play with different intake valve closing points to determine the DCR. Calculators are out there.

Then it's timing curve.

I'm running 10.7 C/R on pump gas in my iron headed SBC and have no issues but It's built with a tight quench and a careful DCR. It can be done.

 

I have a 1968 C3 with a 427 and several years ago I rebuilt my 427 into an L88 engine. I have the full compression that GM used in the L88's cars and and other than the cast iron heads I am using the engine was built just like the L88. It was built by a professional engine builder and is a work of "art".

My BB engine can run 12.25-1 compression and runs fine on high octane (93) pump gas. Today the 12.25-1 is not that high as they use higher compression in the newer engines. GM said the L88 was 12.5-1 but they rounded it off to the next highest number, hence the 12.5 claimed is really 12.25-1 even on the L88 engines.

The best reason I can explain to you why I can run all day on 12.25-1 is that the L88 cars came equipped with the best cold air induction system that pushes cooler ambient air into the engine. My engine uses the L88 hood air box assembly as did the factory L88's and it can do great work. The faster you go the more cool air gets rammed down the throat of the engine. I have also insulated my fuel lines to protect them from heating up my fuel and then I brought the fuel lines in over the bell housing to the rear of the throttle bodies fuel inlet thus preventing the fuel from being heated up prior to being consumed. Cool Fuel and Cool Air makes power....

The cylinder heads are another BIG factor. In 1968 and earlier they used a Closed Chamber Cylinder head and in 1969 they switched to an Open Chamber cylinder heads. After reading about the differences it seems that the 1968 Closed Chamber heads are very hesitant to detonate where the open chamber heads will ping very easily. I have the head and piston combination that is matched and they are using L88 pistons. With the piston at TDC without the heads on my pistons stick out the top of the engine block by more than 1/2" giving me the L88 Compression.

You do not "need" aluminum heads with a high compression Big block. You will need a good effective cooling system to be able to get rid of the extra heat you will be generating. I run an extra level of protection in my engine using something called EVANS NPG Coolant. The NPG coolant will not let your engine knock or detonate as it controls the heat more effectively. They claim it stops hot spots from forming and it really works well to keep the engine happy. I have not had any detonation since I have been using it.

I will be honest and tell you that I was worried about the extra heat being made. The 1968 BB has a smaller radiator than BB of later years and this is an issue to contend with. I have a Water/Methanol injection system that cools down the intake tract very quickly and gives the engine the equivalent of 115 octane fuel when the injection pump is running. This system has not been used very often as the engine does not get that HOT and under load very often if I can avoid it.

The extra compression of the L88 engine make any 427 a radical machine and most fun to drive. There is little as nice as hearing the four barrel open up and the 427 starts whining through it's chambered exhaust on a lonesome highway....

The extra compression will work fine with your cast iron heads. If you need to on a hot day you can do what I have done and installed a Timing retard box that pulls timing with 4 switches under my dash. Each switch pulls 2 degrees of timing to allow me to fine tune the engine if needed on the road. My MSD ignition system keeps the spark hot while running and the compression is a non-issue for the most part.

I just love the extra power that a higher compression engine can make. There is a lot of difference in the way the 427 will wake up... My C3 will Burn it's tires past the 1/8th mile mark and only stops when you let off the throttle.

 

It is defiantely a CR vs IVC trade-off.
That is why big cams can easily run more compression.

Use the Wallace Racing DCR calculator.
Keep the DCR below 8.2. even 8.0 for iron heads.
And that is IF you have good quench.

Why push it?