The Official Hot Rod Thread - Part 2: No Replacement For Displacement

[RustyHornet]

Gonna drive the Venti tomorrow morning to breakfast. Forecast says like 20 degrees and snow. Should be fun. What’s the over/under on how long it will take to get it started?

Get it running, hold 2500 rpm for about 30 secs. Should be fine then. That carb and intake set up isn’t gonna like the cold. It will be snotty. I’ve got a factory manifold for you, add a properly set up q-jet and all your problems will be solved.

 

[RustyHornet]

Mine started right up a few years back when it was -12.

 

[ChristianPatriot]

Get it running, hold 2500 rpm for about 30 secs. Should be fine then. That carb and intake set up isn’t gonna like the cold. It will be snotty. I’ve got a factory manifold for you, add a properly set up q-jet and all your problems will be solved.

You know my address. Send it on.

 

[churchmouse]

Get it running, hold 2500 rpm for about 30 secs. Should be fine then. That carb and intake set up isn’t gonna like the cold. It will be snotty. I’ve got a factory manifold for you, add a properly set up q-jet and all your problems will be solved.

"WINNER"

 

[RustyHornet]

You know my address. Send it on.

It’s gonna cost ya. About $4000 should cover it.

 

[ChristianPatriot]

It’s gonna cost ya. About $4000 should cover it.

Dude that’s a steal. Why so cheap?

 

[RustyHornet]

Dude that’s a steal. Why so cheap?

I’ve got a couple of them. Just trying to pass on a deal.

 

[ChristianPatriot]

I’ve got a couple of them. Just trying to pass on a deal.

#whataguy

 

[churchmouse]

I have a list. PM inbound soon.

 

[RustyHornet]

I hate decisions....

 

[churchmouse]

I hate decisions....

I hate living with them.
Decisions can be easy. The results of the decision can be rough.

 

[ChristianPatriot]

 

[bobzilla]

Damn it man.

Meh. I knew it was coming. Just thought I had more time.

 

[churchmouse]

Meh. I knew it was coming. Just thought I had more time.

The clock starts with the turn of the key.....Tic-Toc.

 

[ChristianPatriot]

Alright, so here’s an engine theory question for ya. Is it better to obtain your desired compression ratio by way of domed pistons or by having a smaller combustion chamber? Or does it really matter? Is one better for low-rpm and the other better for high-rpm?

Example #1: 76cc head with a 6cc dome with a 10.98:1 CR
Example #2: 64cc Head with a 6cc dish with a 10.96:1 CR

 

[KJQ6945]

I'll be curious to hear the more knowledgeable on this. My guess is, it's just cheaper to mill the heads than replace the cans. A thousand ways to skin a cat.

Good Question CP!

 

[ChristianPatriot]

I would tend to lean towards small chamber with a little bit of dish, but I haven’t been around half as long as some of these guys

 

[churchmouse]

You can achieve static CR many ways. Trim the heads...deck the block...play with chambers etc.

The advantage of an "Open" chamber head is solid performance all they way to the top of the cams ability to feed the engine. The larger "Open" cambers will do this.

While the smaller chambers allow high static CR numbers they do tend to fall off towards the top of the power band in their ability to feed the beast.
They come on hard and fast.

Both ways work but how you will drive the thing is the key.

My stroker has true flat tops in it. The heads are the small chamber world (Merlin) offerings. When I rebuilt the engine after a few seasons of it running in my buddys car I squared up everything cause thats how we roll. Set deck height and took just a bit off the heads. This put the chambers at 62cc's. With the cometic gasket the static CR is 11.2 to 1. Higher than my target for this engine. I will have to run a mix of racing fuel and pump.

 

[thunderchicken]

CM makes good points here. The big key is how it will actually be driven. Our deal has __cc chamber "wedge" heads and flat top pistons with minor valve reliefs it has @ 14.5:1cr. She brings the power in and just keeps making steam up to 7700rpm then it starts to gradually fall off ( very slightly) up to 8000rpm. We won't push her any harder than 8k. Now here is another important thing to keep in mind. Regardless what pistons you run when you open the box..finish them. Smooth out any sharp machined edges around valve reliefs or domes. Those edges can craleate hot spots and can lead to detonation and hurt parts. Especially if you run a power adder.

 

[ChristianPatriot]

Seems like I’ve heard a smaller chamber promotes better mixture of the fuel and air, but yeah I can see the bigger chamber being better up in the higher rev range.