Alright I am having a problem w/ my stroker build-up. I am building a 385 stroker, I was planning on running my AFR's but I changed my mind after talking to lloyd and Bret. As soon as I sell them, I was gonna but some Trick Flow 215's, and have Lloyd port them further. My problem is my pistons, I need some good lightweight forged pistons, these heads are 67cc, and I will have then milled to 64cc, I will be running a "0" deck block, its .040 over, and I was told that i want a compression ratio of 11.8-12.0:1, I am having trouble finding pistons that would have that ratio. I was always taught that I would want to run a flat-top piston for better quench, and more complete combustion. However the only pistons I can find that would be what I need are Dome pistons. Does anybody have any suggestions? I really need help w/ this. What would you guys do?

 

Ask Bret, if he's building the motor. The options are a dome or further milling of the head. Either will work and I wouldn't sweat it. Plenty of motors with domed pistons out there running fine.

Rich

 

What size AFR heads are you selling to go with TFS 215's heads?

 

I get 11.8 with a zero net dome, so the only dome would be to offset the valve reliefs. I haven't discussed this with Bret (he's on vacation where it's warm!), but I've seen similar very low domed pistons in the shop.

As Rich said, perhaps the heads will be milled more. Ask the guy who is selling you the heads and pistons for advice. He has a vested interest in having things correct.

 

I had AFR 190's that flowed 275@600 lift that I'm upgrading to the 215 TFS's. I am having the bottom end assembled at a local mahine shop, but I am buying everything. I will be buying the heads from Summit racing, and I already have SRP pistons that I will be returning, and probably have JE do a custom set of pistons for me. Lloyd is doing all the head work, and Bret will be doing sending the valvetrain stuff to Lloyd and Designing the camshaft. Like I said I would run the small domes maybe even a 4cc if everything would be fine, and there is no adverse affects....then I can save the money on haveing the heads milled. I talked to Lloyd last night, he ays the heads sound good as long as I can get the pistons I need to have the static compression ratio about 11.8:1, because the cam Bret is designing will be fairly large and that is were I wanna be compression wise, along w/ 9:1 dynamic compression ratio. Plus Lloyd doesn't think its a necessarily good idea to mill the heads much past 62cc, we don't want intake, and accessory fitment issues. I guess my only way to get the right pistons are cutoms anyway, but I just wanna make sure there aren't adverse issues w/ a small dome.

OldSStroker: Yeah thats why I was thinking a dome would be better than a flat-top w/ no reliefs....that way I could have reliefs and compensate for them w/ a small dome.

 

It sounds like you are on the right track.

 

Hey guys, can you tell me if there are problems w/ running a small dome like that. I have often heard that a dome piston will not promote a complete burn, and that I will have serious detonation problems....First is that true, and second would a small dome of that volume needed(2-4cc) make that much difference over a flat-top? I posted thread like this on another forum, and got hell from a bunch of members saying that I am wanting to much compression, and that I am trying to make a pro-steet engine!! I don't understand, this is what Lloyd said I should have for compression, is that a unheard of thing, or what? Now this is supposed to be something to what Lloyd and Bret do for a LE3 package, so I don't think that is so outrageous!! Now if I don't find that magic number in compression that I am looking for, will I be losing alot of power? I just want this thing to run like a raped ape, and not have to worry about it! Now I thought that if I was told by Lloyd that w/ that compression I will be able to run on pump gas, then I am gonna believe him, why is that a problem for so many people. Am I dumb for thinking that? Oh, and OldSStroker....when is Bret getting back from his vacation, could you have him give me a call when he gets back.....I'm Kyle, he has my cell number.

 

Detaonation resistance is not determined by static CR but by "dynamic CR". This is a function of the static CR and of the cam, specifically the point at which the intake valve closes. If you think about it, compression does not begin until the intake valve closes, which may not be unto 60-70 degrees or more after bottom dead center with a large "street" grind or even later with a race cam. If you do a search on the term "dynamic compression ratio" you can read some rather extensive discussions of this that have occurred here.

As far as the dome goes, I already expressed my opinion. If Bret is doing the cam I am sure he already set the combo up in software and can give you an accurate hp estiamte. So, ask him. But the difference is likely to be small. If you are paying for expert advice, I think you should take it!

Rich

 

Thanks man, that is what I wanted to hear. I have been doing alot of research, and I am gonna get more advice from Bret and Lloyd to see what they say. We didn't plan on a dome piston originally, but Lloyd said that I want 11.8:1, and a dome is the only way I see getting that right on. I was just curious what you guys thought about a dome piston, or if you thought it was a bad idea. I will take their advice once I get it, but until then I just wanted to see what you guys thought. You guys on this board have some badass engines, and thought you wouldn't mind chiming in. Thanks.

 

That's what you get for posting on another forum!

As Rich said, you should design for Dynamic Compression Ratio (DCR) and valve timing. Let's assume a DCR of high 8s to maybe 9.0 just for an example. When the optimum (or nearly so) valve timing is determined based upon all the other engine and vehicle parameters, you "back in" to the static CR you need, evidently high 11s in your case. Getting that SCR is the challenge, balancing combustion chamber size and piston dome. It can be a fine line between good flame travel and detonation problems. If minor detonation is going to be a problem, it will probably be below 3000 rpm or so. If you can't fully load the engine there, due to a 3000+ converter or lots of gear or traction, it's less of a problem.

Remember, you are not looking at Tsunami-like dome sticking .450 or more up from the piston top. It's just a little bump, usually with tapered sides.

Friday, the 18th, BTW.

 

OldSStroker...Thanks for replying, thats what we are shooting for is a Dynamic Compression ratio of 9.0:1, and a static ratio of 11.8:1. That is what I am trying to do is balance everything, and thats why I didn't think a dome that tiny would make that much difference. I just wanted to see what you thought. I run a T56, and while at the strip I will be doing huge clutch dumps to get the engine in its range, no biggie there!! This car is set-up as more of a road-racer or autocrosser, than a drag car. It will def. see the strip though, but 95% is street racing. Its my all-purpose warrior!! I wanna run low 11's on the spray, and keep kickin' *** on the street....And attempt to fight off you fourth gen guys!! I trust Bret and Lloyd so thats not a problem, I know they will steer me in the right direction. thanks guys.

Kyle