Author Topic: '78 T/A lots of good advice looking for some clarity for Torque and HP upgrades  (Read 7856 times)

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Offline 72blackbird

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The pistons and rods are cast but are all new from Keith Black and are silicon treated. He said he believes if I made the request upon ordering they could probably get forged ones for me instead.

The cam they use is an Elgin E980P with specs of
Lift: .444/.466
Duration: 288/298
Duration @ .050": 214/224
Lobe Separation: 112 LC

They have other options upon request, not sure if those would be ideal specs for looking to use the 455 and maintain a certain level of street ability. Thought you guys might have thoughts about that.

I would forget about using KB hypereutectic pistons- their durability when facing detonation is marginal at best and the $100-125 cost savings vs. using a forged Sealed Power piston isn't worth the trade off.

I had a customer insist on using KB hypers on his 389 build to save time (I won't build any engine without forged rods, so a set of 5140 I-beams did go into the engine). This engine was capped with a set of no. 11's, so SCR was a mild 8.7:1, and the cam used was a Crower 60240. I did tell him this engine should be fed 89-91 octane, but he tried to run it on 87 and had the timing set to 34-36 degrees total- the results were predictable. Not only did the engine ping violently to the poor fuel, but two pistons cracked due to the detonation, the debris wedged between the piston and a cylinder wall and cracked the block. We were able to reuse the crank, rods, and heads from the damaged 389, but the piston choice cost him a new block and a rebuild- tragic considering this 389 only had less than 5000 miles on it. If my customer had listened to me the first time and ran forged pistons, he would have only had to build his 389 once.

I would also spend the extra money on upgrades like zero decking and dynamic balancing for the rotating assembly- the decking will help your engine against detonation and the balancing promotes longer bearing life. Your cam choice would depend on the heads used on your 455 build- clearily a different cam should be used if you're building a 9-9.4:1 vs. a 8-8.5:1 455. The cam you chose should run well in a 8:1 455.

Offline Angelo

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I don't think anyone makes cast replacement rods, so more than likely they reused the factory cast rods, which are at least 30 years old.

I remember googling "KB hypereutectic pistons", you will find the same story 72blackbird just told, it seems to be an unreliable piston for a lot of different engine families.

Once you factor in all your upgrades for this motor, you may be surprised to find it's close to the same price as what was quoted to you by the other Pontiac engine builders. Plus a Pontiac engine builder is going to include other top end stuff and the little details that are special to Pontiac.

My engine builder used KB ICON Forged pistons for my 400, the compression height is 1.72" so they did not zero deck my block. They had only 2 valve reliefs as well, which also helped with the total compression. I just measured my 6x-4 heads with a cc measuring kit and found they are at 93cc, so with my combination I'm at 8.7:1 compression. I will be running high octane even with forged pistons.

Also, you said you are getting a new rear seal, which is good, but I would just make sure it's either a Viton 2 piece or a BestGasket brand rope seal. If it's a factory replacement rope seal, just be aware you will most likely have to replace it.
81' ex-Turbo Trans Am - Resto-mod

Offline raypfaff

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Geno and Angelo thanks (again and again) for all your thoughts. I took the info you provided and called back and after a 15 minute conversation the person I was speaking with suggested the following. Knowing I want street ability with power output in the neighborhood of 350/450 he recommended a stroker 400. It would have forged crank, forged pistons and H-beam rods. They would still do the replacing of the harmonic balancer and flex blade. For the rear seal it would be a Viton. They are going to send me an email with a full break down of the other parts. The options they told me to think about in the meantime would be porting and polishing for the heads and consider the cam for the configuration. A 400 is what my car had originally so I am not worried about the trainee. Obviously a 455 and a stroker 400 are different animals and while I'm excited about the forged parts going in I'm going to wait to hear what you guys think about going with this stroker before pulling any triggers. AND if you have input of the cam I had chosen and if I should spring for the port/polishing I'd greatly appreciate it.

Offline Angelo

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A stroker is beyond my knowledge. I know they are awesome though!

The back of the Pontiac How to Rebuild V8 book by Rocky has about a dozen different engine combinations by various known engine builders. If you have that book, take a peak at the combinations, I think a 400 stroker may be in there.
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Offline raypfaff

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Actually I do have that book and didn't think of even checking in it for info on a stroker. Man do I feel silly. You guys have spoiled me with a wealth of info, I will check it out this evening. This is the info I have so far from my contact at the shop on the stroker setup.

Quote
The stroker kit will make the engine a 461 stroker and it is a scat 4340 forged steel crank. The rods are actually a big block chevy rod 6.800, H-beam. And pistons are a forged dish piston. Depending on the heads I am going to try to keep you at about 10.5 to 1 compression. Will have the heads info shortly. I still need to choose a camshaft to use in the engine also.
So cam specs arenít quite available yet as I am still waiting for a cost and I will go from there. We have lots of options cam wise but I need to know if you are going to run a stall converter or if youíre going to stick with stock converter. Also are you interested in going retro roller or stay flat tappet?  I think we should also run roller rockers too, which we would have to add studs and guide plates to the build, but I think doing this is definitely worth it.

All of a sudden my options seem to have exploded and I figured best to get input from you guys. Also 10.5:1??? That is quite the jump from what I was initially anticipating. My excitement for a stroker was initially for torque and power in the low rpms but would this set me back in street ability? Pump gas still good?

Offline 72blackbird

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The 400/461 stroker is a well known combo, but the original Pontiac stroker combination comes from the venerable 455. It's possible to use standard 455 pistons, stock length 6.625" rods, and a stroker crank with a 4.21" stroke and 3.00" main journals to create a 400/455 stroker- this combo can be less expensive than a 400/461 stroker kit if the parts are purchased separately. The main advantage of buying a 461 stroker kit is the convenience- as long as the kit is balanced it's basically a ready to install package, making it as simple to build as a regular rebuild. Pontiac 400's can also be stroked to up to 440 cid with a 4" stroke crank, and even a massive 495 cid with a 4.5" stroke crank. There is also a 4.375" stroke crank available, but I have yet to see any builds done with this crank.

As far as the 10.5:1 SCR goes, it all depends on what size chamber you use on the heads you plan to run. It's possible to run up to a 9.5:1 SCR with Pontiac cast iron heads and 91 octane, but any higher compression will require 92-93 or race gas. Aluminum heads have twice the heat dissipation rate as cast iron, so it's possible to run a 10-11:1 SCR on pump gas with them (SD Performance does recommend a 10.25:1 SCR limit with 91 octane however). Head choice will determine how much power you want to make- 500 hp is the usual limit with ported iron head/roller cam combos, stock aluminum heads will make around 525-560 hp, and ported aluminum head/roller cam combos can make around 600 hp.

The 400 block you have may or may not handle a stroker kit, since not all 400 blocks are created equal- the later 75-78 no.500557 400 block is too thin in the main saddle area to handle power adders like a stroker crank, nitrous oxide, or a blower. Earlier 67-75 no. 979xxxx and 481988 400 blocks are thicker in this critical area, and can handle power adders like a stroker crank. Look for the block ID number at the rear of the block on the passenger side, above the oil filter bracket.
« Last Edit: June 05, 2013, 11:53:57 AM by 72blackbird »

Offline raypfaff

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When I speak with the shop today I will ask about the casting number off the core. The 400 is not the motor in my car but rather a core they have at their shop. They have a 455 core and a 400 with a 461 stroker kit they recommended. My initial interest was in finding a '70-'71 455. Their output for those years were supposedly 350/450 out of the factory which was my power goal. I told the guys there I'm using the car for street only and wanted to keep the power output ideally 350/450 MAX 400/500. I'm more interested in torque and obviously being able to fed the car pump gas. He suggested going stroker for getting the higher grade of quality components and gaining additional power. I'll get the cast number to confirm the year and see what options they comeback with for the heads/chambers and report back. Knowing my goals at this point and the two options of the stroker 400/461 or a 455 is there any particular consensus or is the jury out depending on the rest of the stroker build?


Offline oldskoolubr

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Geno IS the MAN!   You can also get ahold of Rocky thru this site if you have any questions about the info in his book?!  He is a Hell Of a guy and very helpful and knowledgeable!  He is busy tho so be patient!  ;D

Offline 72blackbird

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Getting 400 hp/500+ ft-lbs. from a 455 or 461 stroker on pump gas is not hard at all for any Pontiac builder who knows what he is doing. Either combo is capable of producing monster torque with iron heads. The main advantage of the 461 stroker over the 455 is internal friction- the 400 has 3.00" mains vs. 3.25" mains for the 455, and has a slower bearing speed, which translates into less friction and heat generated. The 400/461 block also is a little stronger than a 455, since it has more metal in the main saddle area than the 455. So if the 461 is so much better than the 455, why is demand for the 455 greater than it has ever been in the last 30 years?

The 455 still remains a very popular choice because it's the original Pontiac stroker engine- it was making well over 450+ hp/500+ ft-lbs long before aluminum heads and stroker kits existed. Adding good forged pistons, rods, balancing the assembly, good heads, and required machine work for a performance build will yield the same results as a good 461, minus the cost of a stroker crank. The factory nodular iron crank is also good for 600 hp, despite what so-called Pontiac experts claim about newer cast 4.25" stroker cranks being stronger. You can use the factory 455 crank along with good quality forged pistons and rods, upgrade the 2-bolt mains to ARP studs, and it will handle 600 hp. I would only upgrade to a forged crank in the 455 if was using the engine in a road race or high rpm application.

There is also no definite proof the 461 makes more power or revs harder than a 455, although more 455's are getting rebuilt with 4.25" stroke cranks and 6.8" BBC rods (the main advantage being the larger bore of the 455 and a better rod-to-stroke ratio). So if given a choice between a 455 and 461 stroker, what is the best option? If you have a choice and both cores include the factory cranks, go with the 455- you'll save on the cost of a stroker crank and the 455 is already a proven performer.

Offline 72blackbird

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No, Randy- You da man! ;D

Offline Chuckles

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I have the later 400 casting. Mainly because at the time I didn't know of the weaker block and I already had money invested. But, I think my build will be more than ok with the addition of 4-bolt splayed billet steel main caps and ARP studs. And  other top notch forged rotating assembly. For info, I used the Ohio Crank 4.21" forged crank with 3" mains. Really nice piece.

Offline raypfaff

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Geno I think that was the exact bit of info I was waiting to hear about the 455. I'm going to see if they can give me options for it based on what you said here. In the meantime can I get everyone's take on what they have quoted for me in regards to the 461? In particular which of the items listed as extras would be needed and which I can do without?

Quote
PON-461SLB               
                    Item                                         Cost                                                       Notes         
Base price on 400/461 stroker engine    $3,445.00    L/B comes with Gaskts, oil pump, and break in oil. Price includes balance and parts         
                                                                              Stroker kit consists of forged pistons, H-beam rods and forged steel crankshaft, made by Scat.         
Core charge                                               $400.00    Refundable minus return freight            
shipping                                                        $195.00    Freight costs to a business in NY            
subtotal                                                    $4,040.00             
               
Extras                
Port and Polishing                                       $350.00             
balancing                                                       Included              
New SFI Balancer                                      Included              
New SFI Flexplate                                      Included             
Cam upgrade                                              $411.00    New comp cam kit, With springs, retainers valve locks. Specs avaible upon request         
Performance timing                                        $84.00    New double roller timing set          
Roller rockers                                              $215.00    Full aluminum bodied          
rocker studs and guide plates                      $110.00    Comp hardened studs and guide plates         
pushrods                                                        $75.00    comp hardened push rods.         


Offline 72blackbird

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$5285 for a 461 stroker with forged pistons, rods and crank seems reasonable, considering the rotating assembly often costs $1650-2100 balanced (depends on the brand of pistons and rods used too- be sure to ask what you are getting). $600 of that final cost is core charge and shipping,so $4500-4600 for a 461 long block is a typical price. I would also like to know what was exactly machined- a quality build should have been bored/honed with a torque plate, zero decked, main saddle align honed, stainless valves, heads serviced with a multi-angle valve job, hardened exhaust seats, bronze guides installed, guides machined for PC seals, intake surfaces milled to match the amount of material milled off of the block side of the heads.

I would also be concerned about what number iron heads were used- there are numerous Pontiac heads that have a 96-102cc combustion chamber. This size chamber will yield a 9-9.5:1 SCR on a 461, allowing use of 91-93 octane. The builder should also tell you what size pistons were used and how much the block was overbored- I don't think you'd want to buy a 400 block that was bored .060, which does yield 468 cid, but doesn't let you reuse or rehone the block should it need servicing. It's becoming harder and harder these days to find a standard bore 400 core, so I would be surprised if your builder started with a .030 over block- be sure to ask before putting the deposit on any build.

The "extras" listed are for the most part essential in a high performance build- you don't want a new cam installed with old valve springs, or stock used rocker arms. Full roller rockers aren't absolutely required, but do reduce heat and friction generated- at the very least you should run roller tip rocker arms (not as noisy as full roller rockers but better than stock rockers). The builder can also get a stroker kit with a cast 4.25" stroker crank that will save you around $300 as well- since you are shooting for 400-450 hp/ 500+ ft-lbs a forged crank is overkill and not required. No mention of 4-bolt main caps were made- not a must, since Pontiac 2-bolt main bolts can handle 500+ hp, but you should ask your builder about installing ARP main studs before machining the block.