Compression and cam timing

Hi all. My 347 is being built for a road car (65 Mustang). My question is, can I run hi compression and keep the cam timing mild to make it nice and drivable? Was think the hi compression would help make hp, mild cam timing would keep it drivable.

Thoughts please.

Thanks, Dave

What do you consider high compression?

With aluminum heads, a cam with the right timing events, and a small quench (.035-.040 or so) you can get 11:1 to run on 93, or maybe even 91 octane. Much above that and it can be a crap shoot. Iron heads will be a compression point or so less.

Don't expect just any cam with (in your words) "mild" timing to work in this situation. Cam timing events are very, very important, and although there are some off the shelf cams that can work just fine, it often takes an experienced person to give a good cam recommendation.

If you wanted a mild engine, you should not have went with a 347. Those things are monster power makers.

Keep your compression under 11.00 to 1 and you will be able to run on cheaper gas 89 octain, and only loose maybe 20 HP tops at the top end.

If you want to have a monster motor, but have pleasent street mannors, then put a 600 - 650 Vacuum Carb on it. That will keep it on the calmer side then a bigger carb.

Rear gears, and Automatic or Standard will also be big factors.

You CANNOT run 11 to one compression on 89 octane, under ANY circunstances. 10.5 to one with 91 octane will work OK. To get a mild driver camshaft, just spread the lobe centers out to 112 or 114. This will tame it down alot. By the way, flat top pistons on a 347 will give you around 10.5 to one, which is very good.

JOE SHERMAN RACING ENGINES

Thanks guys. I forgot to mention its a Boss style motor. 2V Cleveland heads 12.5 : 1 forged TRW's. I'm looking for ways to lower compression as well. Thick copper head gaskets? Not sure if the closed chamber heads can be opened enough.

Thanks

Originally Posted by 4Lowie

Hi all. My 347 is being built for a road car (65 Mustang). My question is, can I run hi compression and keep the cam timing mild to make it nice and drivable? Was think the hi compression would help make hp, mild cam timing would keep it drivable.

Thoughts please.

Thanks, Dave

Dave,
The cam timing can effect the compression. As you probably alread know most cams are ground with +4 advance based on TDC. This is to make the cam more drivable, Idleable.... If you retard the cam to true zero, it can increase the "Static" compression and take some drivability out of it. It's all based on the intake valve closing position and how much intake charge is allowed to excape. It's call the Volume/pressure index and requires a large slide ruler to calculate. Good Luck.

Jeff

Originally Posted by BIGJOE

You CANNOT run 11 to one compression on 89 octane, under ANY circunstances. 10.5 to one with 91 octane will work OK. To get a mild driver camshaft, just spread the lobe centers out to 112 or 114. This will tame it down alot. By the way, flat top pistons on a 347 will give you around 10.5 to one, which is very good.

JOE SHERMAN RACING ENGINES

When I play with my desk-top dyno and decrease the duratinon on the intake side,making it open later it changes the lobe center from say 110 to 114. This changes shows a good 10-15 hp gain. Does this actualy work in manner or does it make the ramp rates to steep?

What do you know about ramp rates ? I have been an engine builder all my life, and I dont know anything about them. The way people talk about camshafts.you would think it is easy for everybody to be a camshaft expert. What I do know about cams, learning from experiance is worth a lot. It is not that you know what works the best, BUT you know what DOES NOT WORK AT ALL. About cams in general, closer lobe centers work best for most engines. As the engine makes more HP per cubic inch, the wider centers, begine to look better. !08 is a very good lobe center for most engines

JOE SHERMAN RACING ENGINES

Originally Posted by BIGJOE

What do you know about ramp rates ? I have been an engine builder all my life, and I dont know anything about them. The way people talk about camshafts.you would think it is easy for everybody to be a camshaft expert. What I do know about cams, learning from experiance is worth a lot. It is not that you know what works the best, BUT you know what DOES NOT WORK AT ALL. About cams in general, closer lobe centers work best for most engines. As the engine makes more HP per cubic inch, the wider centers, begine to look better. !08 is a very good lobe center for most engines

JOE SHERMAN RACING ENGINES

I realy dont know a damn thing, I am guessing that if the cam lobe is the same lift but it opens in 8 deg instead of 20 deg it would have to be much steeper and I think that the rate that a cam lobe goes from the base circle to full open is called the "ramp rate". Further more I was not making a statement I was asking a QUESTION!!!! I am not an expert, I'm just some dumbass playing with numbers on a computer program trying to see what makes more power but I am smart enough to know that just because it "looks good on paper" does not mean it will work in the real world/real engine.

Originally Posted by BIGJOE

What do you know about ramp rates ? I have been an engine builder all my life, and I dont know anything about them. The way people talk about camshafts.you would think it is easy for everybody to be a camshaft expert. What I do know about cams, learning from experiance is worth a lot. It is not that you know what works the best, BUT you know what DOES NOT WORK AT ALL. About cams in general, closer lobe centers work best for most engines. As the engine makes more HP per cubic inch, the wider centers, begine to look better. !08 is a very good lobe center for most engines

JOE SHERMAN RACING ENGINES

Thanks for your knowledge!