I have seen BBF builds where the piston is "proud" of the block's deck 2-5 thousandths, just need a piston with correct compression height and enough dish to give acceptable CR, head gasket thickness would essentially be the quench distance. Lots more options with gaskets than pistons. You can play with cam events to tame a little too high CR, but try to keep dynamic compression ratio around 8 to 1 for street driven vehicles.
I was looking at a set of Speed Pro pistons #H336CP 30's with a compression height of 1.772" which is 0.002 less than stock. It has a PHV of +12.0cc which would net me a 9.8:1 compression but a squish of 0.063 - 0.051 (depending on the head gasket) which is not good. Dropping the deck height would bump the CR to over 10.3:1 which is not where I want to be. Not sure on the dynamic compression tho. I'm just confuzzled that there is not an "easy button" as in I can't believe I am the only guy that is building a stock ish 30 over 351. It can't be this hard. Cheers, Doc
Are you talking about the cam that's 269/296? Lunati doesn't have a 270/300. Either way, Racetec makes an affordable forged piston in the Autotec line that has a 22cc dish which at zero deck would give you about 9.1-9.2 C.R. with your heads. Probably not much more than those hypereutectic slugs, and a WAY better piston. I imagine you know that the cam you're looking at needs a 2500 converter. Looks like fun to me.
Cam timing and the cam "events" will dictate what your dynamic compression ratio will be, a "big" cam will bleed off combustion pressure due to overlap and/or when intake valve closes. You can get it to run 10.3 CR but in order to do so you may need to install a camshaft that is too radical for your wants or needs just to allow the engine to "live" on pump gas. Having a .030" over-bore already gives a bump in compression. Try this link http://www.wallaceracing.com/Calculators.htm and go to CID-engine calculators, about halfway down the page on LH side, lots of good tools to help nail down the details. Hope it helps
@pmrphil this is the cam I was looking at https://www.lunatipower.com/bootlegger-retro-fit-hydraulic-roller-cam-ford-v8-351w-276-300.html I think a bit lumpier than I would have initially picked but I like the dual lobe profile. I don't have a TQ for the AOD so I have to buy one anyway. Do you have a link for those Racetec Autotec slugs? I need to clear the cache on my browser as it keeps giving me the same results and Summit is a PITA to do comparisons. AQL Thank you as always you manage to find the best info out there!!! The up side is I haven't spent any money on the project yet other than the machining and my machinist says he can generally beat most prices on the web. Cheers, Doc
My oops, I didn't know you were speaking about a hyd. roller. With the aftermarket heads, personally I wouldn't have so much extra exhaust duration, probably around 228 or 230. My internet skills kinda suck, I have no link to Racetec, but the piston I was looking at (in the catalog) was a shelf piece, not a custom.
I'm a little confused about the "retro -fit" thing as the 95' block is a roller block. I did find the "perfect" piston on the Racetec side of the house for $118.60 EACH!!! 1.794 compression ht and 22.6cc dish (although they list it as -22.6 and have the comp ratio at 9.4:1 but in a calculator it would come out to 17.5:1 but by making it positive it's 9.6:1 so I'm thinking the -22.6cc is how big the dish is from flat. The flow data on the heads is better than stock but not by much @.5 lift I get 231 cfm on intake and 157 on exhaust so I was looking for a bit more duration. You wouldn't happen to have a catalog or two that shows a compression height of near 1.79x" with a dish that's a little less spendy? Cheers, Doc
I'm getting the impression that I'm going to have to have the block or the heads decked to equal 0.020 to 0.030" which just opens up a whole world of combinations that keeps me in my 9.5 ish CR and the squish/quench ~0.040" with 1.770-1.774" pistons. I can find Cometic Head gaskets that compress to 0.027" but that will still net me a squish /quench of 0.050"+ with the stock block which is not preferred and quite possibly why the original motor was such a dog and I could never get the timing right on it. I have to wait on the machinist to tell me what my final numbers will be once he gets done boring it 30 over. Mebby take 20 off the block and 10 off the heads and use standard 0.040" head gaskets. My head hurts especially knowing I have to pick a cam after that gets sorted out. Cheers, Doc
Okay, let's start with the retro thing. If the block is machined for hydraulic roller lifters already, you don't use a retro cam. The base circle is incorrect, you would use a cam made for a 5.0 with the 351 firing order (same as the later mass air 5.0) and use stock hydraulic roller lifters with the factory spider retainer. The Racetec pistons are a different forging made for racing. NOT what you need or want. The number is Autotec 1000473 and I can order them if you need, or your machinist can if he has an account. And I don't have a price sheet in front of me, but I'd bet that they're less than half of that. And flow-wise your target should be around 70% exhaust flow as compared to the intake, so you're right where you should be, there. It won't need any more than 4-6 degrees extra on the exhaust side.
@pmrphil I digging what you are laying down but doing the calc for squish and quench I will still need to have some knocked off the deck or the heads to get it right. Yeah I was reading about the small base circles and such but didn't know how to translate that to a roller block 5.8L. Thank you. If you could be so kind as to make a recommendation for a cam? I'd like it a bit lumpy at the light but the car is not a drag monster it is more of a cruiser and I'd like to take advantage of the power in the middle as opposed to the high end or grunt at the low end, that said I'd like to get off the line respectably. It's a 6000 lb car, I'm only gonna launch so hard. I already know I need new valve springs for whatever cam as these are for a flat tappet and seals as I found bits of them allover the heads. The heads were supposed to be port matched to both the motor and intake but I find no evidence of that happening so given gaskets and a Du-More tool I will make it so. Any and all input is desired and appreciated more than you know. Cheers, Doc
6000 pounds? Are you sure? I may still have Babe's Washington registration, and I'm sure that it said her curb weight is 3800 or so from the factory. I'd expect a '70s loaded Caddy to be around 6000 pounds.
If your machinist is able to accurately measure the deck height (many places don't have the tooling/means) I can have Autotec alter the pin height on the pistons (for an extra charge, of course) to keep you from having to deck the block. Keep in mind, though, all the measurements come into play, stroke tolerance, actual rod length (as compared to advertised length, etc. to get this thing close to zero deck. Plus or minus .005 really won't make any operational difference in the real world.
GVWR is Gross Vehicle Weight Rating, or the maximum load it will carry. You'll be looking for Curb weight, which is the vehicle weight. One easy way to measure it is at a truck scale or your local dump/recycling center scale.
I think I like that option better than a deck job as it will also bump my CR up from about 9.2:1. Looks like I have some serious measuring to do. Stroke should be interesting to perform w/o pistons, mebby can use the original slugs wrapped in tape. I'm pretty sure the machinist and I discussed getting all the measurements and he didn't seem to bat an eyelash. I get off early on Fridays so mebby this week I'll either get some answers or the block and crank back or both. On another note I was finally able to get Midnight up in the air via 18" worth of pavers. Even at the max height of my jack I was never able to get under the trans but now her nose is even with my nose. Cheers, Doc
I got you, didn't know that and will need the real number for cam specs Thank You! A quick search yielded ~4020. So I'm thinking that's fair. 3 tons did seem a bit heavy. Cheers, Doc
This is mine with my fat azz and 1/2 tank of fuel.5.o-AOD with a lot of aloomanum parts.Might add 300# for cast iron 351w..
In Washington State, the original vehicle weight when built is printed on the registration. I think Babe's was 3816 pounds or some such.
