Compression ratio and pump gas

460
.030 over
22cc dish
xm278h cam specs here
.040 compressed gasket
edit forgot 0 deck

Currently have d3 heads, found a deal on c8ve-e heads. Putting in calc at 72cc (assuming they need to be decked) puts compression ratio at 10.2:1, 75 cc puts it at 9.93.

Will it be possible to run pump gas with this combination? I've been told it's borderline, but figured someone on here would be able to give me a closer to definite answer.

Application is mud bog racing, but also sees some street time (why I want to stay pump gas friendly).

No issues on 92 IMO. Watch the total timing is all

Captainp4 wrote: I've been told it's borderline, but figured someone on here would be able to give me a closer to definite answer.

application + posted engine specifications = maybe (+/- a yes or no) ...    ...

Dave.

Any other opinions? Do I need to post more info for a better answer? Let me know what else you need.

Keep it cool and stay on top of your tune.

Captainp4 wrote:460
.030 over
22cc dish
xm278h cam specs here
.040 compressed gasket
edit forgot 0 deck

Currently have d3 heads, found a deal on c8ve-e heads. Putting in calc at 72cc (assuming they need to be decked) puts compression ratio at 10.2:1, 75 cc puts it at 9.93.

Will it be possible to run pump gas with this combination? I've been told it's borderline, but figured someone on here would be able to give me a closer to definite answer.

Application is mud bog racing, but also sees some street time (why I want to stay pump gas friendly).

A few areas of the specifications you post could help operating with "pump gas". The camshaft may "bleed off" a bit of cylinder pressure although very little at low engine speed. Another area is your posted .040" quench. This will help to lessen the possibility of detonation. With cast iron cylinder heads, my approach would be to remove a full point (1.0:1) of compression from your build. This can be done several ways, some more efficient than others. The decision will be guided by the expense of the direction you choose. As has been posted, stay on top of your engine's needs, you may get by with the compression ratio's you post. As your post indicates, the application is mud bogging although you elect to operate the vehicle on the street too. Be truthful with yourself about the application. Which part of the vehicle's operation will require more time? If your going to mud bog it, build accordingly otherwise prepare the engine for daily driving and stick it in the mud once in a while! Removing a point of compression from your application may not be noticeable in regard to performance. Allowing the engine to detonate even briefly will eventually upset your day!

Dave.

Currently it is ~9.2:1 with d3 heads. I'm more worried about racing than I am driving it on the street, but don't want to lose that ability. It is a secondary vehicle that I'll take up to the gas station or short drives occasionally (the most it would ever see is an hour drive up to the race track to watch the events when they aren't running the bogs. When I'm competing it gets towed up.) I saw these heads for a reasonable price and figured it'd be a cheap way to make a little more power (they would also be ported by a good friend). I realize I'm butting right up against the limits of "cheap" power, but wanted to see what everyone's thoughts on eeking a little more out of my current build with a little more compression. I'm having a hard time getting past 3rd-4th place in the events and while I have big plans for a stroker, the bank account doesn't agree right now    I'm still learning here, so this may be a stupid question.. is it close enough that dumping octane boost in it would make it "safe"? Or a different head gasket thickness? I know enough to know the word "quench" applies when talking head gasket thickness, but beyond that .. still learning, like I said.

Haven't actually weighed it, but I would guess upwards of 5500 lbs, probably close to 6. 78 Bronco on one ton axles, 40" boggers, full body, roll cage, etc

69F100 wrote:If you go to the track pick a few gallons of good race gas to mix in with pump gas be about as cheap as adding the octane booster

dfree383 wrote:A good tune and 92-93 oct it will be fine. Got to watch lugging it in a heavy truck.

Captainp4 wrote:Haven't actually weighed it, but I would guess upwards of 5500 lbs, probably close to 6. 78 Bronco on one ton axles, 40" boggers, full body, roll cage, etc

Octane booster may damage fuel related soft parts. Lugging and/or a heavy vehicle is an invitation for detonation. I haven't ask, standard or automatic transmission? An automatic may be a bit more forgiving to a detonation issue. As I replied earlier, the compression level you can operate safely (regard to detonation) versus a level that may be marginal will not provide you the assistance you need to move up the finishing ladder. Compression were talking, not the additional work you continue to add to the topic. I'd look elsewhere for application performance unless your engine is stalling and preventing your success at the track.

Dave.

LivermoreDave wrote:

69F100 wrote:If you go to the track pick a few gallons of good race gas to mix in with pump gas be about as cheap as adding the octane booster

dfree383 wrote:A good tune and 92-93 oct it will be fine. Got to watch lugging it in a heavy truck.

Captainp4 wrote:Haven't actually weighed it, but I would guess upwards of 5500 lbs, probably close to 6. 78 Bronco on one ton axles, 40" boggers, full body, roll cage, etc

Octane booster may damage fuel related soft parts. Lugging and/or a heavy vehicle is an invitation for detonation. I haven't ask, standard or automatic transmission? An automatic may be a bit more forgiving to a detonation issue. As I replied earlier, the compression level you can operate safely (regard to detonation) versus a level that may be marginal will not provide you the assistance you need to move up the finishing ladder. Compression were talking, not the additional work you continue to add to the topic. I'd look elsewhere for application performance unless your engine is stalling and preventing your success at the track.

Dave.

It is a c6 automatic with reverse manual valve body.