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Old 10-14-2021, 06:37 PM
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Since it's October I'd wait for a Black Friday deal on the Speedmaster heads and go with the appropriate piston dish. This assumes they discount them. You'll put that much $ in the 6X heads anyway

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Old 10-14-2021, 06:39 PM
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Ok. Which longer stroke?

4.00”

4.210”

4.250”

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Old 10-14-2021, 06:40 PM
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Quote:
Originally Posted by steve25 View Post
Ok. Which longer stroke?

4.00

4.210

4.250
Most likely the 4.250

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Old 10-14-2021, 06:59 PM
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Going through the iron heads you will spend close to new aluminum heads. I was planning on using the ported 6X heads on a 455 they came n but just tossing them on the flow bench and how heavy they were and the out of the box Edelbrock heads flowed more and weighed a lot less they are what went on that motor.

Even with the big chambers adding a stroker crank you can get either dish or mini domes for the CR you want.

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Old 10-14-2021, 07:16 PM
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So if you go .030” over to a bore of 4.150” and then to the 4.250” crank, when you use the -4 head at 91 CCs , then by my math using common numbers for deck height, head gasket volume and valve notch volume I come up with a compression of 9.39 to 1.

If you run the -8 head at 98 CCs then your at 8.88 to 1 in compression.

With that 4.250” stroke crank every 3 CC change will change the compression ratio by 1/4 point basically.

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Old 10-14-2021, 08:58 PM
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Quote:
Originally Posted by steve25 View Post
So if you go .030 over to a bore of 4.150 and then to the 4.250 crank, when you use the -4 head at 91 CCs , then by my math using common numbers for deck height, head gasket volume and valve notch volume I come up with a compression of 9.39 to 1.

If you run the -8 head at 98 CCs then your at 8.88 to 1 in compression.

With that 4.250 stroke crank every 3 CC change will change the compression ratio by 1/4 point basically.
Since the early 90's have always had 455 block surface squared & zero decked. That will add near an extra 1/2 pt of static CR.

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Old 10-14-2021, 09:20 PM
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All blocks that are to get over bored should first get squared and decked if you want your cylinders to be right, but thats not the way some folks go with there rebuild plans!

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  #28  
Old 10-15-2021, 01:52 PM
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THe -4's have been used by some folks. 10:1 seems to be a good limit on the top end of the compression ratio. But running 10:1 takes into a lot of factors that have to be spot on to make the deal work. Jim Hand and Cliff have successfully used these type of slightly higher compressed engines. But neither post here any more. Maybe others can elaborate more.
I DO know that a tight quench distance is needed, no sharp edges in the chamber or on the piston, getting the correct cam and degreeing it is important, and of course the carb has to be spot on. There are more details needed, I can't think of any more at the moment.
THese higher compression engine details also apply to lower compression egnines, also...

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Old 10-15-2021, 06:48 PM
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On the street, I would want a set of 670 heads. with a compression ratio of 9:1.. I would go for as many cubes as you can get. Big cubic inches with 9:1 low compression really works well.. I always had better luck with closed chambered heads. Use a cam like the 068 or even better the Crower solid made for Pontiacs.. Use a iron points distributor with a good set of Accel or Standard points set to 30 degrees dwell. Then pick up a Vertex Z-6 CD box and use the points to trigger it..

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Old 10-15-2021, 08:40 PM
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Well, for better or for worse, I picked up a set of 4's for 200 bucks. 4's seem to be harder to locate, so if I figure that 8's will work better before I start the build, I think I'll be able to find a pair.

Thanks everyone for participating in this thread. Feel free to keep it going and if anyone has a set of 4's that they used on a stroker, I would like to hear the results.

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Old 10-16-2021, 07:33 AM
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Many factors come into play in regards to making the most out of any combo, and some are listed in post 28.

Another factor to consider in regards to street performance is in the compression ratio used.

The smaller the chamber the more vacuum the motor will have and that goes a long way to helping out with idle and tuning for the Cam being run.

If you not looking to get passed the 415 hp level with stock heads then I would not choose to run more then a 9.5 to 1 compression with the amount of CID your looking into running .

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  #32  
Old 10-16-2021, 08:41 AM
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Quote:
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Well, for better or for worse, I picked up a set of 4's for 200 bucks. 4's seem to be harder to locate, so if I figure that 8's will work better before I start the build, I think I'll be able to find a pair.

Thanks everyone for participating in this thread. Feel free to keep it going and if anyone has a set of 4's that they used on a stroker, I would like to hear the results.
I have a 455 with #4s here. Is that considered a stroker? 4.21 vs 4.25 stroke?

It runs and has run well since 96 or so. 246/253 cam. Runs high 11s to low 12s with 3.55 gears. They are ported to mid 260s though.

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Old 10-16-2021, 08:55 AM
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Do we really need to define what a stroker is?

Even if during the crank grinding process for cleaning up journal’s if you had to go .010” just to clean things up, but yet you offset ground on the rods to .020”, then yes that small .010” gain can be called a stroker.

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  #34  
Old 10-16-2021, 01:19 PM
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Quote:
Originally Posted by steve25 View Post
Many factors come into play in regards to making the most out of any combo, and some are listed in post 28.

Another factor to consider in regards to street performance is in the compression ratio used.

The smaller the chamber the more vacuum the motor will have and that goes a long way to helping out with idle and tuning for the Cam being run.

If you not looking to get passed the 415 hp level with stock heads then I would not choose to run more then a 9.5 to 1 compression with the amount of CID your looking into running .
Steve mentioned the threshold of 415 HP. HP numbers are tossed around here, all the time. Many folks have achieved high HP numbers in their engines, many are wanting same numbers.

My point: the 400 HP level is a pretty stout running engine, nothing to sneeze at, a VERY good running engine. On paper it sound like an engine that is giving up some power in a compromise type of build, NOT really!!! 455's can easily make 500 HP, but nothing wrong with one that makes 400!!!

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Old 10-16-2021, 01:39 PM
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used these type of slightly higher compressed engines..
I'm sure hundreds of people have.

We built a 455 - 25 years ago. ported 670 heads. 20 cc dish piston. zero decked.
235 / 245 @ .050 - 110 LSA cam. Ran pump gas for many years until upgrading the shortblock to E-heads.
We didn't think it was any big deal, not sure why some do?

Jim Hand ran 11.4 in a more than 4000 lbs car with iron d-ports and flat tappet. A class by himself. Going 11.7 at 3700 lbs is not the same, hundreds if not thousands have done this. 99% don't post here.

I'm impressed with a person running 11 to 1 compression with cast iron heads on pump gas with a mild cam. I've seen it claimed but how legit?


Last edited by pastry_chef; 10-16-2021 at 01:49 PM.
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Old 10-16-2021, 05:20 PM
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I have done both 6x-4 and 6x-8. I can’t think of any reason that you would want -8 heads starting with a clean slate and can pick pistons out to put the compression where you want it. I think Skip alluded to that.

There really isn’t a close to enough info on the plans of this “4.25 6x street engine” to nail down where the compression should be. It is a bit like asking a tailor to make you a 3 piece suite and only telling them what size sweat pants you wear.

Most people with 450-470 Cid combos using stock cast iron heads for pump gas have the best results 9-9.5 scr, and the cam will be either size of 230*@.050”. If you want a very mild cam with less than 220*@.050” I suggest staying down close to 9:0.

I currently do not have a cast iron headed Pontiac pump gas combo with less than 10:0 compression. One is up at 11.0:1, and it is a 4.25” 6x-4 combo . Higher compressions can be done, but most street builds are better served by lower compression than we run, especially when the heads are stock with no porting.


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Old 10-16-2021, 06:24 PM
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I was really glad when Jim Hand changed to 6X heads on his wagon engine, although he was wanting to keep using his 64's, but ran into a problem with them (I think... Jim?).
His heads are/were 6X-4's with modifications detailed in his book. I am sure he performed all the modifications he wanted, then had them milled to the chamber size he desired for his specific chamber size/compression ratio, I believe was 10:1. I truly like his way of doing things. Most of his parts were salvage yard available, and spending money where it was needed the most, valve train and other essentials...

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Old 10-16-2021, 07:10 PM
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One of the 64 heads started leaking coolant, that is when Hand made the switch to the 6x-4s. Rocky Rotella showed me that particular heads and let me look it over. Very nice looking port work, shouldn’t have been close to hitting a coolant passage. IRC it flowed just over 250 cfm @28” on the intake and slightly over 200 on the exh. The 64s are fairly well known to have smaller port volumes against other d ports, might explain why he had trouble.

I think Hand gained a fair amount of performance with the 6x-4 combo, almost 20 cfm on both the intake and the exhaust. 260 something on the intake and 220s over on the exhaust. There is a lot of flow potential on a 6x if you put in the work. IMHO they are a great head as cast though too, not unusual to see them out flow some of the older heads as cast. I tested one very early 6x-4 from a 76’ 350 that nearly made it to 220 cfm. Upper teens anyway, most of the older d ports I have tested barely made 200-210.


Last edited by Jay S; 10-16-2021 at 07:24 PM.
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Old 10-16-2021, 08:29 PM
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I'm impressed with a person running 11 to 1 compression with cast iron heads on pump gas with a mild cam. I've seen it claimed but how legit?
LOl, I am on a 8 + hr work road trip from the WI/IL border to AL, so being a bored pickup passenger, I will take a swing at that…..

Some could be legit, it is easy to miss estimate the compression though when the engine is near to slightly over 11:1. A few cc’s swings the compression quite a bit, if they didn’t check all the volumes it is a good bet the SCR was over estimated.

We have build some dual fuel propane/pump gas engines with high compression up around 11:1. Octane for propane is well over 100, so we raised the compression to utilize the octane more. They were a little picky on pump gas but not as much as we expected. Never did it with a Pontiac, but I think the size of the cam matters a ton. In the 11:1 small cam scenario I think it is opposite of what people talk about with “bleeding compression”. A very very small cam the engine can’t breath well enough to pump as much compression as one might expect. It may pump a bunch of compression on a compression check but doesn’t use it efficiently at all. If you put really big flowing heads for the cid, with a big CSA and combined it with a small cam I think the same thing would start to show. The octane requirement would raise, but not as much as one would expect.

I have seen that same thing play out on some of the old 60s era high compression 2 bbl engines,. An Pontiac example would a factory 389 2bbl 290 HP. The one we had would run better on less octane than it’s higher HP version but had the same compression.. More cam (still mild) and it made it worse. What you don’t want in a streetcar is so much compression that you run out of head flow for the cams power band trying to get the compression under control.

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Old 10-16-2021, 08:30 PM
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No wonder those 76-79 T/A's (400's) ran so well, stock, even the lowest HP engines like mine were peppy and fun to drive. That teenie weenie cam and 16-18 degrees initia,l some how worked!!!

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