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#1
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72cc alum round port combo?
I originally intended to build a +.065 400 using Speedmaster 72cc round port heads. I have been told the ports are really too large for this application.
My question is, what engine size combo would best use “as cast” 72cc heads? If I went to a 488 stroker wouldn’t the piston dish size become an issue? How many cubes are needed to make best use of these heads? What would be an effective combo to build somewhat easily? I don’t have car in mind yet but for conversation let’s say a 3600-4000 lbs fun driver that will run 11.50’s A streetable gear or an OD transmission & stiffer gear if required by engine size. Any thoughts would be welcome! Murf Sent from my iPhone using Tapatalk Pro |
#2
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First off do you have heads yet and how many cid motor do your want to build?
A nice balance between running in the mid 11s with a car with your weight and hooking it up easy enough to run those mid 11 times is a 440 cid motor which can buzz easily to 7K . A motor like this can make a easy 600 hp with a aftermarket head flowing only 290 Intake cfm and live forever with a factory block ! I much prefer to run a small chamber head on a build and use a dish piston to keep the compression within range for pump gas usage as the shallow small chamber unshrouds the Intake valve faster with less lift and in turn makes more power.
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
#3
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72cc alum round port combo?
Yes, I own the heads already. I thought a 4” stroke would make sense but I don’t really know anything.
Does anyone offer a 3” main 4” stoke crank anymore? I have Pontiac length Eagle rods already & a 400 block. I see the 4” stroker kits available are long rod set ups. I guess I could sell what I have & just buy a “kit”. How large of dish would I want for a 91 octane driver type engine? ETA, No real preference on CID. I had originally planned on building it as a 412 but have received feedback that this wouldn’t be the greatest set up. Thanks for your input! Murf Sent from my iPhone using Tapatalk Pro |
#4
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I just built a 428 and could not find a aftermarket 4in stroke crank with a pontiac J and 3in mainTom
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#5
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Who told you the ports are too big for your app? They have the same runner volume as a E-Head, which work fine on 400s.
The 'typical' E-Head package from any of the Pontiac vendors is usually 310cfm or so, which is still more than the SpeedMaster out of box. The KRE D port generally is setup for 295cfm. Remember too, that in 'general', you shoot for about an additional 1 point more static CR for aluminum heads. That puts you roughly in the 10.5 SCR range. (many go more) If you're building a 400 block-based engine, the cost difference between building a 400, and say a 461+ stroker, is nominal. And you know what they say about 'displacement'. Stroker rotating assemblies usually can be ordered with pistons that target your desired target SCR, and no additional cost. In other words, if you're building an engine from scratch, it makes total sense to build a stroker. Even if you're not shooting for a max-effort build, having a larger displacement engine means you will be on the low-end of the duty-cycle, and that means it will last longer. .
__________________
. 1970 GTO Judge Tribute Pro-Tour Project 535 IA2 http://forums.maxperformanceinc.com/...d.php?t=760624 1971 Trans Am 463, 315cfm E-head Sniper XFlow EFI, TKO600 extreme, 9", GW suspension, Baer brakes, pro tour car https://forums.maxperformanceinc.com...ght=procharger Theme Song: http://www.youtube.com/watch?v=7zKAS...ature=youtu.be |
#6
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Quote:
It has been stated on the forum a few times. I don’t recall who but it seemed to be supported by more than one member. I have the 400 block, crank, Eagle Pontiac size rods & +.065 400 pistons on hand. It would be nice to use what I have. It would probably save me at least a grand. That would be nice as I am an old retired fart with limited income. But like you said CID helps. If you were in my situation, would you just go ahead & build a 400 & gear the future car to take advantage of the combo? Sent from my iPhone using Tapatalk Pro |
#7
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Thanks Tom. I hadn’t be able to find any but thought I might be missing something. Sent from my iPhone using Tapatalk Pro |
#8
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An option if you can tolerate the higher power-band. Larger cam and higher converter stall etc. Ballpark peak power 6300 RPM plus.
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#9
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If you have a rotating assembly, yeah, would probably have the assembly prepped and balanced. But contrary to what many say, OE cranks are a crap-shoot, have seen many with stress cracks that 'reveal' themselves under use. Or during magnaflux.
If the crank doesn't check out, you may have to re-evaluate your direction forward, guess you can wait 'til that happens before you decide, but you will still owe for the machine work, etc. New cranks are like $325, which still need machine work. Remember, even new rods need to be at least checked, if not sized. You probably should balance the assembly too. That stuff adds up. Rotating assemblies are usually ready to install, with all machine work already done. Maybe price it out, see what the difference is, it might help with the process. Is the block prepped? Bore & hone for your pistons? Align bore checked? Decks checked/prepped? Nothing wrong with a 400, and yes, gear it properly and it will be nice, but in general, by gearing it 'right', you will probably want an overdrive. You generally don't have to gear a longer stroke engine as much, and can be made move livable with slightly more 'highway' gears. And still perform well. .
__________________
. 1970 GTO Judge Tribute Pro-Tour Project 535 IA2 http://forums.maxperformanceinc.com/...d.php?t=760624 1971 Trans Am 463, 315cfm E-head Sniper XFlow EFI, TKO600 extreme, 9", GW suspension, Baer brakes, pro tour car https://forums.maxperformanceinc.com...ght=procharger Theme Song: http://www.youtube.com/watch?v=7zKAS...ature=youtu.be |
#10
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"No replacement for displacement!" GTOAA--https://www.gtoaa.org/ |
#11
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Since this is the street section, I am going to tell you to stick as close as possible to 400 CI in order to keep your swept volume and CR to a manageable 10.5:1. There are all sorts of interpretations of a what constitutes a street driven car. A high compression engine requiring race gas, crutched by a huge x long camshaft, high stall speed convertor, limited spark lead and low gears driven on the is really just a detuned race car. Unless they are selling race gas on every corner where you live, keep your eye on the 10.0-10.:5 CR prize.
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Triple Black 1971 GTO |
#12
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4.25 stroke cranks and rotating assemblies are at least $50 less than the 3.75 stroke ones, FYI.
The rotating assemblies come with custom Ross pistons, and as stated, you can call and have them made with a dish to meet your desired SCR. 72cc heads are a common volume so the required pistons are readily available, and usually in stock. Stroker kits are $1800, add up what it costs to have your on-hand parts prepped and compare. It's really that no-brainer. And you can always sell your parts to offset costs. In some cases, vendors will even accept some parts for a credit. .
__________________
. 1970 GTO Judge Tribute Pro-Tour Project 535 IA2 http://forums.maxperformanceinc.com/...d.php?t=760624 1971 Trans Am 463, 315cfm E-head Sniper XFlow EFI, TKO600 extreme, 9", GW suspension, Baer brakes, pro tour car https://forums.maxperformanceinc.com...ght=procharger Theme Song: http://www.youtube.com/watch?v=7zKAS...ature=youtu.be |
#13
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"Piston Selection- Based on your desired compression ratio, our techs work closely with Ross Racing to design a custom piston for your application. Many sellers limit you to only a few piston options, Butler Performance working in conjunction with Ross Racing can design thousands of different pistons for almost any application."
__________________
. 1970 GTO Judge Tribute Pro-Tour Project 535 IA2 http://forums.maxperformanceinc.com/...d.php?t=760624 1971 Trans Am 463, 315cfm E-head Sniper XFlow EFI, TKO600 extreme, 9", GW suspension, Baer brakes, pro tour car https://forums.maxperformanceinc.com...ght=procharger Theme Song: http://www.youtube.com/watch?v=7zKAS...ature=youtu.be |
#14
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A forged rotating assembly will be closer to $2300-2600. I would not use an off shore cast crank with a 280 cfm round port unless it was a really mild build.
We have a couple 3.25” N cranks turned down for 3” engines. I kept with 2.25” journals. It was pretty economical, we used an Olds thrust bearing and a spacer cut with our plasma table. I had to turn the oil seal surface down on our lathe, the crank grinder didn’t have a narrow enough stone. I spent another $80 to grind the mains down over a standard crank job. Better than an off shore cast, weaker than an off shore forged. One of the guys up here does quite a few 3” engines like that. His personal car is about 600 hp plus an occasional 200 hp NOS hit. The strength of the N crank depends on how it is prepped, and the previous service life. A 455 2bbl has a different service life than coming from someone’s 20 years of abuse in a 600 hp bracket combo. It depends on what you can find. I know of a 406 with 72 cc round port E heads with ram air manifolds and a full exhuast it made a little over 350 hp on a wheel dyno. It had a comp HR mutha thumper cam. That would be around 420-430 hp at the flywheel. Kind of a crappy cam pick with the RA manifolds imho, headers might have been worth another 30-40 hp with that cam. Wouldn’t have taken much to get that engine well into the 11s. Similar combo to a 400 with speedmasters. A well picked HR cam paired up with a great converter 11.50s would be pretty doable with the 400. Last edited by Jay S; 09-11-2020 at 03:54 PM. Reason: Error |
#15
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I run a 4.120 bore 400, 4.3 gears with a 275/60/15 on the street, it's unbelievably fun with a good converter. I'm putting together a 4L80e for it now so I can do long highway trips (Aussie version of drag week called drag challenge). Pure street car, not the lightest by any means. Consistent 120mph through a full exhaust. Can't wait to hit it with a 100 shot when I get the suspension fixed.
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'71 Holden HQ Monaro - 3850lbs race weight, 400c/i - 11.4 @ 120 '66 Pontiac GTO - 389, 4 speed street cruiser |
#16
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#17
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Murf, Those heads wouldn't scare me a bit on a 400. The intake runner size isn't all that big. Technically it's SBC size. When you consider the 100's of thousands of engines built with this runner size that are much smaller than a 400 and how well they run, both aftermarket and OEM stuff, there is no reason to be hesitant. If a 400 is what you want to build, I'd go for it.
If a stroker is in the budget, I'd certainly go in that direction. I like cubes and what that brings to the table. Either way sounds like a cool project. |
#18
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Hey Larry, thanks for the reply. Don’t know what I’ll do yet. I’m leaning towards a 400 cause that’s what I have. Us seniors have to watch our money! The wife wants me to do some work on her convert over the winter, so who knows when I’ll build a motor. Hell, maybe I’ll win the lottery by then. Take care Murf Sent from my iPhone using Tapatalk Pro |
#19
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I'm still trying on the lottery too. |
#20
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__________________
1977 Black Trans Am 180 HP Auto, essentially base model T/A. I'm the original owner, purchased May 7, 1977. Shut it off Shut it off Buddy, I just shut your Prius down... |
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