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#1
08-04-2006, 01:41 PM
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273 cast pistons -are the 4-bbl worth the extra $??
Suppose I'm building a 273 for some performance... For pistons, only cast are readily available. Sealed Power 8.8:1 CR from Summit, etc. for about $290 a set. Or, 10:1 CR from Egge for about $400 a set. When I get the head work done, it won't cost me any extra to have them mill 'em beyond a standard light mill, so I figure I can get to 9.5:1 (maybe more) and save some dough. I'm assuming that the 10:1 cast piston is no stronger than the 8.8:1, so why pay the money? Am I right? OR should I pay good money for some custom forged pistons -see combo I've devised below...
Performance mods and other details will include a nicely balanced '66 273 engine w/forged 318 truck crank and stock rods, Hughes cam that peaks at 6500 (but will rev to 7K easy), solid lifters, Hughes adjustable aluminum rockers, small tube Hooker Super Comp Headers (they don't offer the cheaper Comp one's for a '66 Dart -damn them!), X-pipe, 2.5" duals w/Edelbrock mufflers and pipes out the side ahead of the rear tires, 575 CFM Speed Demon w/mech secs, Edelbrock Perf. RPM intake, MP elec ignition, "302" heads w/comp valve job, 1.88/1.60 valves, bowl blend and mild exh. porting, gasket matched to intake and milled as needed to get between 9:5 and 9:9-1 CR, 8 3/4 3.55 LSD posi, 4-speed w/T-A ratios, manual steering car, no A/C... '66 Tran-Am road race replica that will hopefully run in vintage club races someday, but street for now 
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#2
08-04-2006, 05:14 PM
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Well, it all depends on what comp ratio you want.
If you zero deck it with the dish oem pistons, you might have valve clearence issues. My 273 has the 8 something dish and they are down in the hole some too. I put magnum heads on it and I have about 487 lift and everything clears fine. The 10 something comp pistons are domes, and they had closed chambers too on the commando, or 4 barrel 273.
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#3
08-05-2006, 03:59 AM
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Yup, and to add.
The cast piston will be just fine, forged are more forgiving, and last longer. I have a set of TRW's that have been in two motors now, so you do get what you pay for. To get max power from the heads, a set of custom pistons may be the trick, to match the closed chamber. Get real trick and the 10.5-1 will run nice on 93 octane! NICE! SOme of it comes from the small bore of the 273 too. Your carb is perfect, your manifold is perfect, your head choice and valve size is perfect, I might downsize your exhaust to 2 1/4", if not too late, the 273 isn't a very big engine.
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#4
08-05-2006, 05:23 AM
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only thing i would ask is why use a truck crank when the 273 already has a forged one? after researching stuff for my poly 318 buildup, i have learnt that the truck cranks were often cracked due to 2 things, they had hardened journals, and big heavy flywheels hanging off the back. i have one crank that is in 3 pieces!
my machinist is an old timer and tells me that over half that used to come in out of the trucks were always cracked due to the drivers holding speed down hills by revving the crap out of them and also the hardening of the journals. im using a forged car crank in mine...
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#6
08-05-2006, 04:36 PM
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Quote:
I'd do the Egge pistons and use a gasket to slightly adjust the ratiio. The only thing in the build I should note to watchout for is the use of 1.88 valves in a 273 bore. They don't fit unless you notch the cylinder bore. Otherwise everything else I like.
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#7
08-06-2006, 02:30 AM
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Cageman says the 10 to 1s are domes, if they come out the bore that won't work with the closed chambered heads, 10.5 to 1 is alot for a steel head engine; how much duration you got in that Hughes cam? I like compression, but on 93 octane, better have some duration on that cam!
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#10
08-09-2006, 01:54 PM
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Hey all,
Sorry for not tuning in, but I didn't get an e-mail telling me that there were more replies... I need to look into that... Anywho, thanks for the replies. Let's see, where do I start. Much of what is on my combo is a wishlist, so I'm glad I haven't made any more purchases. I don't have a new crank yet. Car was originally a 2-barrel 273, -will it still have a forged crank? Didn't know the valves wouldn't clear, so thanks for the heads up there. That will have to be done as 1.88s are definite. As for the 10.5 pistons hitting the closed chamber heads, don't know on that one and don't know if the 273 4-barrel heads were closed or not. Of course, that would be good to know. Leaning toward the 8.8 pistons and getting the compression to 9.5 to 9.9 by ccing and milling the heads the right amount. Intake duration @ .050 lift is 237 degrees. I'm looking at the smallest solid cam Hughes offers... I will likely contact them for a possible custom grind since I'll be road racing and may benefit from a slightly different cam than their stock spec ones... JP
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#11
08-09-2006, 07:09 PM
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I faintly remember taking my heads off my 273-4bbl and they were out of the hole about a hair, domed with 2 valve reliefs. Much less than the gasket and the gasket was a .020 steel shim, Man its been years..The heads were closed, like a heart shape. The 302 heads would be a great head for that motor. Mine was a tight rapping motor for sure, all stock solid cam motor. The replacement 68 318 short block was faster though with all the 273 parts on it, upgraded Cam was a Herbert stage 2, Changed the single plane 4bbl intake to a Edel Performer, probably helped the low end considerably. Too bad the oil pump expired....I would still be running it.
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#12
08-09-2006, 11:38 PM
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mechanical cam and hydraulic cam duration, I don't believe are the same, due to lash, but ask Hughes, and he'll tell you what is the diff, and tell me if I am wrong! 237 is not too much at all, would work at 9.5 to 1 on 93, light weight car, get minamum .035 - .040" piston to head clearance. oh, I remember reading about the 66 Trans Am Dart, Bob Somebody (started with a T, Tiluis? ) how many did it win that year? I know it did good. I did a thread on here about headers by Doug on A body, Kamstra wrote in that a friend has them on a mid sixties Valaint, altho Dougs doesn't really list it for the pre 67 a body,(correct me if I'm wrong!) but they fit in his friends, and there are pictures so you can see how it fit. that was just a couple weeks ago, you can see it. Good luck, sounds like fun, and what part of Il is New Lenox in?
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#13
08-10-2006, 10:32 AM
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pishta -Sorry your oil pump spoiled your fun with the 318!
re: the T-A Darts, yes, Bob Tullius as well as Tony Adamowicz were among the Dart T-A racers. Here's an address to Tony's very cool site where you can learn more of the '66 Dart and first year of Trans Am: http://www.a2zracer.com/index.html Famed NASCAR racer David Pearson also ran a '66 Dart in T-A... Not sure which car I'll replicate... I'm leaning toward the Tullius car since I have the most photos of that one -but the lack of photos of the Pearson car kinda makes me want to do that one too (Mopar mentality I guess, unique is better...)! Yes, I don't think you can compare duration of mech. and solid cams... The spec I gave was right out of the Hughes catalog. Again, it's the smallest solid that they list. Reason why I may contact them for a custom grind is that I'm guessing we can come up with a better spec for road racing -or maybe I just go with one of their hot street hyd. cams and run 1.6 roller rockers since the rules allow it. Thanks for the tip on the Doug headers. The Hooker Super Comps are $522+ freight a set, but made for the application -so I'm sure it's worth it. I'm guessing I'd spend as much or more on Doug's or any other application specific jobs. New Lenox, IL, my friend, is just east of Chicagoland Speedway / Route 66 Raceway in Joliet. I'm about 5-6 miles from the grounds, and can here 'em run regularly (major drags, NASCAR, Indy, Petty Driving Experience, testing, local bracket racers, etc.) -especially when there's a good wind out of the west / southwest (which is most of the time!). Haven't had much time to get there with 2 young boys (1 & 4), but got clearance from the tower (wife) to drag everyone out for the Mopar event coming up 8-25 - 27. We'll probably just check out the car corral and swap area, and just give the wife and my 4-year-old a taste of the drags since neither have seen it before!! By now, you might be wondering how the heck I'll campaign a vintage T-A car if I can't even get to the (very) local drags that much. It's a long term plan you see... Trans Am just celebrated 40 years, and my goal is to get my car ready over the next several years, sorting it out on the street and in autocross events, and then running a full season with the SVRA during the 50th anniversary of T-A (and beyond if possible). Thanks for tuning in to all, JP
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#14
08-11-2006, 02:34 AM
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Are the Hookers 1 3/4"? That might be a bit much for a 273, it would go like hell, once wound up, might miss the low end, course I don't know low you would run it, rpm wise. 4 speeds help that (need one, gotta 66 to 70 a body one,) course the ticket for yours would be in alum case. I would look at all the other 64 to 66 a bodys at the show you're going to, and see what their headers are, how they fit, all that. I was born in Elgin,Ill. Lived 9 years in Fox River Grove, up by Barrinton, still got a brother teaching at Dekalb. Cubs are having a rough one, but are doing better, course, Sox might do it again, time for the Bears! So maybe you can't do it all now, but you have a goal, and you gotta have goals, so it oughta work out for you, gotta eat, gotta have clothes, heck my wife and I just bought a bigger better house, might slow my car stuff down, but it'll work out. nice to have have you been to the big track yet? That's Blues Brother area!
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#15
08-11-2006, 02:50 AM
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my bad they are 1 5/8, fine for 273
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#16
08-11-2006, 09:50 AM
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Yep, 1 5/8 w 2.5 outlets and 43" tubes -should rock on the 273! Glad you agree it's good to have goals. I'm good on the 4-speed, but thanks for askin'. btw, aluminum isn't allowed as it was not available on a 66 from the factory, which is goofy since aluminum drive shaft is ok... Ah, racing rules.
Anywho, yes I've been to the track some (a couple of NASCAR races(my company gets pit passes!) some bracket racing, and the first Mopar event a little while back... Nice to have nearby, and hoping they make a real road course there someday. They were supposed to have the World Superbikes run there years ago, but it was a joke. They basically plotted out a course using the strip and the parking lot a la an autocross event! The racers showed up for testing and qualifying and said NFW -totally unsafe. I was bummed... Yep, Cubs not so good, Sox not bad. Go Bears!! Blues Bros territory indeed. Gotta go... I'm on a mission from God  Oh, one more thing... I made the comment about going to a hydraulic cam with 1.6 rockers since rules allow, which was kinda dumb after I thought about it since it would be even better to do the 1.6 with a solid cam. I was planning on running the Hughes roller rockers for added accuracy anyway, so I might as well take advantage of using a higher revving mechanical cam as long as I'm going to be checking tolerances anyway. Since the practical limit for the cast pistons (not to mention my intake) is 6500 RPM, it should enable me to run a really nice solid with enough low-end to come off corners nicely while still having pretty good top-end. May even spring for forged pistons. Ross quoted around $750 a set -or another $350 more than I was planning to spend. It's probably worth it to wait, save for the forged, and be able to take it to 7000 or so when I need it on tracks with long straightaways. JP
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#18
08-12-2006, 10:51 PM
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roadrace, I just looked at the Trans Am pictures, from the pictures, sure looks like the racing Mustangs didn't handle so well then! Plymouth actually beat Ford to the Ponycar, Barracuda came out first, it it probably out handled it too! What is the wheelbase on your Dart, 106? It said on there that the photaghraphers could get alot closer then, thats a fact! and the courses now are lots safer. I read about the '70 Trams Am attempts, I guess they got around the corner good, but engine failure! But it says something about people running 10,000 rpm, I'm guessing they didn't have the benifit of the lightweight Ross or JE pistons we now have!
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#19
08-12-2006, 10:54 PM
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CAGEMAN, speaking of pistons, if Ross says my +.060" 318 pistons are 615 grams, that is pin weight included, right? They are comp height 1.807, Chevy pin. Is that pretty light for them?
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#20
08-14-2006, 05:21 AM
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The solid cams in the 273's were pretty tame, wether a two barrell or a four barrell. It would run way better with a 340 hydraulic cam. Both the 2 and 4 barrell had the same heads, they are closed chambers up to 1968. Like in all mopars, the factory CR ratings may not be even close to the reality. Measure things first, only after that check what you need to achieve the CR you want.
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#21
08-14-2006, 11:07 AM
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Quote:
Back to the handling, etc. The Mopars, Darts in particular, were noted for their handling. I believe the Darts had a longer WB at 111, which is a plus for high-speed stability needed on tracks with long straights... Whew, 10-grand! Yikes!! Of course, that was when the factories were involved (=big budget compared to a would be private club racer like me). I'm thinking I won't go past 7000 RPM unless my financial situation changes greatly and I can afford to drop in new engines whenever I need... JP
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#22
08-14-2006, 11:08 PM
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I know the 67 a bodys where 111 inch, unless it was a Barracuda or Valiant, they were 108. I'm not sure on the 4 door darts, or Valiants, seems like 112 for the 4 door Dart. I think I read 106 for the early a body, and a bit lighter than the wider 67s. You can use the good t bars, got a size picked out? Yeah, 10,000 rpm is alot NOW, they had Keith Black building them, they woulda done better if they backed that down a bit! you are better off staying 7 and under, with the small bore engine.
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#23
08-15-2006, 01:21 AM
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A-biodies came with three wheel bases; the pre '67 valiants and barracudas had 106", in '67 they grew to 108". Darts, except those based on a plymouth platform, were all 111". Pre '67 STW darts were 106", and Demons & Dart Sports 108". To make things even more complicated, all plymouth scamps and '74 & up valiants were built on the Dodge body with 111" wheelbase.
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#24
08-16-2006, 06:42 AM
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You may hate me for this, but I just got lucky. I picked up a HP273 that appeared to have been rebuilt and then not run for very long. It had the correct closed chamber heads and domed pistons so I bought it. Talked the guy down a $25 so it cost me all of $225. Well, I tore it down last night and it's been gone through all right. Back in around 1980 by the date code on the rod bearings. Best part is the +.030" pistons are forged. One thing about the engine worries me and that's water in the oil pan. The crank and bearings all look very good, but there is this goopy sludge that looks like nasty runny pudding. I think it may be from running cold and sitting. The block and heads are going to the machinist to be cleaned and crack checked. If everything is ok it all goes back together as it was except the Crower 256-H cam is being replaced by a 230 degree duration @ .050" lift solid. HP273s shouldn't have a juice lifter cam. That short duration Crower cam and high compression ratio is no good for pump gas anyway.
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#25
08-16-2006, 10:53 AM
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Not at all, I'd be glad for you and hope it checks out okay. The more research I do for the race club I'm looking at, a hot 273 probably won't be enough anyway. I really need to figure out the best way to come up with a 5.0 L Mopar engine that I can afford and that will hold up to racing... I've done posts on this before, so I have a good start on the info. that I need -it's just that I haven't liked the dollars it would run. That's why I started this thread to get some thoughts on what folks thought of the high-compression cast pistons. A few more people here and that I've talked to outside of the chat all agree that I should just keep saving until I can make a legal stroker or sleeved down deal that will serve me well. I'd really hate to get everything else right only to get burned on HP. It's really only about the money, and I have time so that's not as big a deal... The only thing that sucks is that I'll be throwing a ton of money at something that could easily get burned by larger cube street cars that have a lot less money in them -so maybe I just get a house with a bigger garage and buy the convertable my wife wants and build a big bad street engine in that!! It's all about time and money...
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#26
08-17-2006, 08:16 AM
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Well, having gone road racing and spent way too much money to do so I quit. Spending thousands for a little BS trophy wasn't all that fun. It also takes a huge amount of time to build and maintain a race car. Never mind constantly working out bugs and developing the car. If you can buy a good car similar to one you'd build then do it. You'll be money and hundreds of hours ahead of building it yourself. Also, bigger cars may be faster, but they use more fuel, use more expensive tires, take up more space, require a heavier tow vehicle, etc, etc. They are also faster only in a straight line. A Formula Vee can corner as fast as a GT1 car.
The 273 is actually going into a brand X sports car with a cage so I can go do open track days, autocross and such. I'm doing it fairly cheap and without any regard to rules other than safety. I'll be thrown into some catch-all class for weird and overprepared cars where I have no chance of winning. I'm just in it for fun.
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#27
08-17-2006, 09:40 AM
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Yep, I know what I'm up against on the cost of it all. And, I hear ya on finding a car that's already race-prepped -I'll jump on one if the price is right... Since I'm planning a replica racer, I'll still have to do a bit of work to get it right so I've always kept finding a prepped car as my starting point.
I admire your attitude about racing for fun -good luck with that! JP
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#29
08-19-2006, 03:43 AM
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Dart is right
from DartGT66: "Like in all mopars, the factory CR ratings may not be even close to the reality."
And how far were they off? Well, the supposedly-stock-replacement 8.8:1 273 pistons I am using in my Barracuda calculate out to an actual 7.2:1 with stock heads  BTW my unmodified, 2V, '65 273 heads are 69cc.
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#30
08-21-2006, 11:37 AM
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Quote:
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