When I do the heads for 250s we remove the post and plug but use a countersunk hex head bolt below. Last one I did was 2000 so I forgot where my customer got his bolt from. He is also a mechanic (I did all the machining) and we didnt second gues each other. On the flow bench the lump or floor plates as I call them were worth a huge improvement. I did them first in plasticine for the flow test. He made the ruff plates as I asked and installed them with JB weld filler and I did all the porting after. I was surprised how well it would flow when we added the floor plates. Engine is still running and apparently well. Now known as FourAmerica vintage stock car (35 Chev) and last I heard it was running in Florida somewhere. Headstuff all applys even though it is a 250. Re pistons. Probably buying a set of those trick pistons would be the cheapest improvement you could make in the long run. A couple of extra hundred bucks for never having a problem is often a real bargin especially if you dont have your own machine shop and engine building stuff. As much as it might be a pain it is probably money well spent in the long run. (Which means you will never wake up in the next 7 or 8 years saying I wish I hadnt have spent the money. The pain will only be for a second or so right now and then will be nothing but a forgoten memory. ) BTW I applaude you refforts. Six cylinders are really fun to work with and race. All the best on you roject Don
Something else to think about, those piston you now have installed will never have a squish area. The small lip around the outer edge is the only squish area you have, you can deck the block to a zero deck hight and still not have the .050" or less squish due to the dish. Joe
On the other side of the coin here is a pic of my 292 piston its got good squish but pump gas is a no-no
I have heard of JB weld lumps but wouldn't those possibly seperate or crack over time? Or were your lumps made out of metal and you just used the JB weld to attach them? Thanks for your input on the pistons. I'm pretty sure that I will buy those in the next couple months. Just have to let the bank account build back up! Thanks for the picture for reference! What are the specs for your build? What compression are you getting?
Well I just went ahead and ordered the bolt in standard lump kit from 12bolt.com. I called the machine shop and told them to hold off on the bolt boss removal until I get the lump kit in and bring it to them to show them before they do anything. They said they wouldn't be able to get to it until next week anyway. The kit was cheaper than I thought it was, $100 or more, but it was $65 with shipping so not too bad.
Its a 292 80 thou over with 366 3 ring pistons milled to 0 deck 11.9 -1 comp lump port heads big valves a lumpy smith cam(I don't know the specs) 650 double pump carb
What is stock compression height supposed to be? I see replacement pistons have a 2.010 height. At this point, my pistons are .020 overbore and the machinist said they did a .050 cut on the head and just a .005 on the stock deck as of monday and my chambers are around 67cc now. Does that sound about right? He tells me that I will have 8.13:1 ratio. I found summit racings compression calculator and i'm fooling around with that. I found the LPG pistons that I could switch to here http://www.summitracing.com/parts/slp-980p20 I will call summit and see if they can get me info on the dish volume. For now, if I assume that they are 15cc then that gets me a 9.24:1 ratio. That should be nice for my street motor and cam right? Would I run mid grade gas? I have been looking to run off mid grade at least in order to help avoid engine pinging as well as squeezing more power out with the cam I chose. Is it not possible to get your forged pistons in .020 overbore size? oh and I watched your youtube videos. thanks for those! That sounds like a lot more fun than I can afford right now but very cool
Well I talked to a guy a ross pistons and he wasn't much help. He told me to call Heckt power products since he saw the banner in a photo on Tom lowe's website . I have been trying to get in contact with Tom Lowe to figure out my piston solution but Bob at Heckt said that he might be on vacation right now. In the meantime I have been calculating and it looks like If I stick with the .030 MLS head gasket I ordered and then get a set of forged ross pistons at 3.895 bore then I get my quench area to .045 without doing any additional machining. That is assuming that the ross pistons have the .015 piston to deck clearance that Tom's says his have though. Using a compression calculator with the numbers I have shows that I would get about 9 to 1 comp ratio. What do y'all think of that for solving my quench and compression problem? How do I check my valve clearance? I would think it is still okay since these ross pistons have the dish in them.
My pistons have a 2.043 CH. With the next batch I order. Could order a .020 set. It may be this winter. I also highly recommend the use of a tq plate for honing. The bores go square around the head bolts 1" deep into the cylinder when the head bolts are tightened.
I wish I had known about the square bore issue before my block had been machined. How bad is it? A couple thousandths? Too much for a street motor? They didn't do that from the factory did they? I will ask my machine shop if they used one. It would be great if you could do the .020 bore in your next batch for me. Would that keep the price at $600 for a set? Do I want press fit or the lock rings? The lock ring wrist pins mean that it would be easy for me to install the pistons by myself correct? I can definitely wait until Christmas and then they would be an awesome present to myself! Posted using the Full Custom H.A.M.B. App!
I have the honing info on my website. It is about .004 bulge at every head bolt 1" down in the block. It is serious. He did not use a tq plate. There are very few of the around. I do rent them.
So most every rebuilt 230-292 suffers from square bores? I'm thinking most shops rebuilding a stock one would never consider a torque plate on a low performance 6 cylinder .You think GM used a plate? There was millions of those engines...
How much is it to rent? That's what I was thinking. It doesn't seem like it would be a big problem for my 200 hp street engine.
Very interesting and informative thread...in a number of ways. Compression, squish area, dish configuration, torque plates, milling, holding your machinist's feet to the fire and all the rest. Lots of you guys know your shit. I'm aware of and understand most of this stuff, but it's good to learn something new and refresh too. Sometimes the Hamb kicks ass. jesdude, good luck with your 292.
Thanks Rickbop! I hope I can get it going soon. Here are the cam specs for the cam the machine shop ordered for me. He seemed to think this one would be my best choice. Any input on this? Great for natural aspiration? What kind of idle RPM should I be able to have? Is it good for when I turbo later?
Here is where we are with lump port, 9-1 compression and headers. The bright colored, higher lines are with the cam installed at 110 Lobe center, that means you will need a 4 degree retard key, the darker line is with 106 ICL. Stock manifolds will cost about 25 HP. Idle will be good. Not the best cam for turbo.
I was thinking about using the factory exhaust manifold and installing one of those split manifold flanges to dual it out. Do you think that would be sufficient? What should I change on the cam for turbo? keeping it at 5-6 psi of boost.
This is about as wild as you will want to go, maybe a little less, say 216/224 216/218 makes about 287 HP in the sim 212/212 what you have now, about 265
So in the previous graph, I make a little over 200 hp with my current cam and naturally aspirated? and this graph shows 265 hp with 6 psi boost with the same cam, correct? Also, does that simulator take the valve sizes into account? I talked to the comp cams tech line yesterday in order to retrieve the cam card info from them directly since I don't know where the hard copy is right now. I asked him if the cam I have is turbo friendly and he told me it was good to go With the idle i'm just asking if I will be able to have it around 600-700 rpm idle speed? (naturally aspirated)
yes, I show it making 265 @ 6psi and will have a good idle but it will have some "cam sound" in it. I think the 292 inch will settle it down some compared to a 250. If you are running an automatic then it will probably work well with a small turbo. That is with the cam in at an ICL of 112. At 106 it's down about 15 HP. So you might try playing with the cam advance using an offset key to find the sweet spot of idle and power.
wow that torque looks nice! and that is still with my current camshaft? I would be really happy with that kind of power. The keys are just standard offset keys that i can buy anywhere? I plan on running a 700r4 which will definitely be beefed up by my builder. I am looking at t6racing's turbo manifolds but I don't know much about all the different turbo's out there or what size i need. I know that his manifold uses a t04 type flange and I found a turbonetics for around $800 brand new. I was kinda hoping to find a turbo in decent used condition to start with.
That was modeled with a 53mm GT3071R (PN 700177-23) and a .82 AR. Remember these models assume you get the tune sorted out, timing curve, turbo sorted etc. it may take some work but that's part of the fun. Get a good suppler when it comes time for the turbo, it's easy to get that wrong. Even in the model it took me awhile to get the turbo dialed in. Read this http://www.hotrod.com/techarticles/engine/hrdp_1205_how_to_buy_your_first_turbo/viewall.html
Thanks a lot hoop. That link is very helpful. I picked up the engine the other day and I'm going to take a break for a bit and save up some funds and come back to it in a month or so when I'm ready to swap the pistons.
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