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Discussion Starter #1
I use stock type internals recently reconditioned and rebuilt with cast pistons. If I had the cam and springs to spin 6500 would the bottom end take it?

When is it important to switch to forged pistons or coated pistons? I don't want to risk making a mess of the bottom end for a little more power if it is not safe.

It is just tempting to try a xe274H and appropriate springs in the future for more performance when it would only cost $400 in parts. Maybe it's not even worth it.
 

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I think the bottom end being refreshed would handle it, did you replace the rods or at least put in ARP rod bolts? I've read that the stock bolts normally snap before the rod bend/cracks.
Do your heads have screw in studs? pressed in studs will pull out with the 274, I've read .050 lift is usually the line where you need screw in studs to go with any higher lift than that.
Forged pistons are normally needed for higher RPM >7K or forced induction/power adders/NO2.

Jon
 

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Discussion Starter #4
Ill check my build sheet on rod bolts.

I use GT40 heads that are pedestal mount. I am using them and 1.7 RR's now with .532 lift.

I think the bigger xe274H would bump up my rpm range to 6500 and be .560ish lift.
 

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I wouldn't think you'd have much to worry about with the bottom end; I'd be more careful about your valve springs and valvetrain setup. Make sure your valve springs are matched for your cam and the rpm you expect to see. I say this because I completely rebuilt a '68 302 for my '65, but ran original [but rebuilt] heads. I had an Edelbrock RPM intake and cam designed to spin to 6500, but ran the Edelbrock valve springs matched for the normal Performer cam. I ordered the correct valve springs, but decided to run the Performer valve springs for awhile, thinking it would do no harm. Well, I then broke a valve after less than 500 miles on the engine. This valvetrain failure cracked the block in two places and crushed a piston, among other things....basically destroyed the engine.
 

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amorrow02 said:
I wouldn't think you'd have much to worry about with the bottom end; I'd be more careful about your valve springs and valvetrain setup. Make sure your valve springs are matched for your cam and the rpm you expect to see. I say this because I completely rebuilt a '68 302 for my '65, but ran original [but rebuilt] heads. I had an Edelbrock RPM intake and cam designed to spin to 6500, but ran the Edelbrock valve springs matched for the normal Performer cam. I ordered the correct valve springs, but decided to run the Performer valve springs for awhile, thinking it would do no harm. Well, I then broke a valve after less than 500 miles on the engine. This valvetrain failure cracked the block in two places and crushed a piston, among other things....basically destroyed the engine.
A HUGE +1.

The bottom end of that motor, even in stock form...is fine for 6500rpm blasts (wouldn't hold it there continuously!). Your biggest problem will be in the valvetrain...between making sure you have the proper springs...and those bolt down rockers which play havoc on getting proper valvetrain geometry. Additionally, swapping flat tappet cams can be an issue all its own with todays oil...which is something to keep in mind.

All in all, for me...regardless of what cam is in a motor, it's never worth a cam swap until I'm prepared to go to a roller. The benefits are many, and the only drawback is cost...since you need the cam, lifters (have to use EXPENSIVE link bars if you go hydraulic roller), springs, and new pushrods.

Hope that helps!

Cris
 

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If its a street motor it will probably be okay; you are reaching the threshold for cast pistons at that point. What heads are you running?
 

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Why not put it on a dyno and see where your HP starts dropping off, you may not be gaining anything by revving it that high.
 

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fast68back said:
Why not put it on a dyno and see where your HP starts dropping off, you may not be gaining anything by revving it that high.
+1 , my 306 would easily rev to 6500 and above but why do it when max power is at 6000?
 

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In the old days, cast pistons and OEM bottom ends saw the better side of 6500 and 1.1 to 1.2 hp/ci. The key is how precisely the engine is built and for what time is it seeing WOT stress levels.

I built 289's for many years for drag racing that saw 500+ hp and 7500-8000 rpm with essentially OEM bottom ends (non-HP rods and crankshaft) with light forged pistons and dynamic balancing. The only 'modification' was installing Chevy rod bolts (those 11/32" ones) which was an easy way of mitigating bolt stretch.

If you're running your engine continuously at 6500rpm, like in a road race or oval application, I'd build an appropriate engine. Nothing worse than an in-service failure giving you a bad day :)

Tip: better longevity and a better torque curve results from improving airflow in the heads rather than running a big camshaft. Do the heads right and a 'little' camshaft will really move things along. I tended to under-cam and over-gear with a loose converter to hit the suspension hard at the starting line and cook the 60 foot clocks. Then, just let 'er spin.

In any event, you should have fun. That's the important thing :)

Pat
 

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Discussion Starter #11
Thanks for all the responses. I made peak power about 5800-5900 rpms which is about right for my cam. I am using dual springs my builder set up for the cam.

I am using mildly ported GT40 irons.

I just figured at this point the best way to get a little more from this engine would be to change cam/springs etc... to spin it a little more.

I will probably hold off though as Cris stated. I might as well wait until I can convert to a roller cam set up and forget crossing my fingers to see if I can get through another flat tappet cam break in with todays oil. I can hardly even find 30w or 40w Rotella T anymore.

It's easy to daydream about the next build...

Ill stick with this one for another year or two and enjoy the new 4.11's. :)

Camachinist, what you are saying makes perfect sense. Big cams are NOT always the answer. It is all about the heads. I just don't see Fast as Cast Trick flows or Brodix Keith Craft heads in my near future.

Time to go buy a lotto ticket.
 

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camachinist said:
In the old days, cast pistons and OEM bottom ends saw the better side of 6500 and 1.1 to 1.2 hp/ci. The key is how precisely the engine is built and for what time is it seeing WOT stress levels.

I built 289's for many years for drag racing that saw 500+ hp and 7500-8000 rpm with essentially OEM bottom ends (non-HP rods and crankshaft) with light forged pistons and dynamic balancing. The only 'modification' was installing Chevy rod bolts (those 11/32" ones) which was an easy way of mitigating bolt stretch.

If you're running your engine continuously at 6500rpm, like in a road race or oval application, I'd build an appropriate engine. Nothing worse than an in-service failure giving you a bad day :)

Tip: better longevity and a better torque curve results from improving airflow in the heads rather than running a big camshaft. Do the heads right and a 'little' camshaft will really move things along. I tended to under-cam and over-gear with a loose converter to hit the suspension hard at the starting line and cook the 60 foot clocks. Then, just let 'er spin.

In any event, you should have fun. That's the important thing :)

Pat
I like this guy!! =D

More seriously though...everything above is right on.

hotrodder68 said:
Thanks for all the responses. I made peak power about 5800-5900 rpms which is about right for my cam. I am using dual springs my builder set up for the cam.

I am using mildly ported GT40 irons.

I just figured at this point the best way to get a little more from this engine would be to change cam/springs etc... to spin it a little more.

I will probably hold off though as Cris stated. I might as well wait until I can convert to a roller cam set up and forget crossing my fingers to see if I can get through another flat tappet cam break in with todays oil. I can hardly even find 30w or 40w Rotella T anymore.

It's easy to daydream about the next build...

Ill stick with this one for another year or two and enjoy the new 4.11's. :)
If your peak power is 5900, you should likely be shifting around 6200-6300 as it is. Possibly higher depending on the combination. If you aren't (meaning if you can't because the motor lays over), it could be that the springs aren't really right for the cam, and are effecting a rev limiter of sorts.

hotrodder68 said:
Camachinist, what you are saying makes perfect sense. Big cams are NOT always the answer. It is all about the heads. I just don't see Fast as Cast Trick flows or Brodix Keith Craft heads in my near future.

Time to go buy a lotto ticket.
Keep your eyes out for a good set of standard TFS Twisted Wedge heads. You can buy them often in used condition for under $1000 at www.corral.net (Do NOT FOR ANY REASON go to the tech sections over there lol...), along with decent rocker arms. You'll need new pushrods though. Anyhow, leave your current intake, carb, and cam on it to keep things in check rpm wise, and I bet you see 6500rpm and a substantial drop in your ET. I've a friend here that we set up with a pair of TFS TW 170 heads. The car's EFI, unknown mileage stock 302 bottom end, and he had a TFS 2 cam laying around, as well as the holley systemax he was using. 1 5/8" headers and 2 1/2" exhaust to dumps. On slicks, he went a 1.50 60', and [email protected] on his second pass. He blew a front tire on the big end somehow, and so didn't get to back it up. This is a full weight 86 Coupe, with a stock T5, King Cobra clutch, and 4.30 gears. Right about the same weight as our cars by the way. The beauty of it is those heads can be used to good effect on a 347 as well, and so aren't a big waste of money when it comes to an upgrade. Yes, the 190's are better...but are in the range of $1500-1700 right now when it's all said and done. The 170's would suit your build admirably, and can be had for good prices right now used.

Hope that helps!

Cris
 

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Discussion Starter #13
Yea that is a good help. I could also fetch a few dollars for my my GT40's considering they have all new hardware and almost new aluminum roller rockers and mild port work.

Can the TFS TW 170 heads be used with my pistons and headers without modification?

The only problem I see is that with my flat tops and 53cc (measured) chamber heads I still only make 9:7:3 compression. Would't I go way down with their 61cc chamber? I guess I could have them milled.

...and you are saying the 170 can be used on a 347 in the future? Maybe with some porting if I ever build a 347 they would be even better.
 

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hotrodder68 said:
Can the TFS TW 170 heads be used with my pistons and headers without modification?
That would be difficult to say...it depends entirely on your cam, which I've never used. I do think it likely they'd fit though...as with the TFS 2 cam, Keith's heads fit without modification. If they did in fact require cutting (we've since changed cams in Keith's motor, and had to flycut it in the block), there's a simple procedure I can talk you through which will allow you to cut the piston in the car...100% accurately and without issue. Costs about $25 total.


hotrodder68 said:
The only problem I see is that with my flat tops and 53cc (measured) chamber heads I still only make 9:7:3 compression. Would't I go way down with their 61cc chamber? I guess I could have them milled.
That's an amazingly tight chamber for a GT40 head!! By my calculations, with a 4" bore, 3" stroke, 4.100"x.042" gasket, 5cc in valve relief, and 2cc in ring lands...you're at 9.84:1 compression. This also assumes zero deck. That's pretty respectable. With a 61cc chamber that drops to 8.92:1 (which would work, but certainly isn't optimum). A mill to a 56cc chamber nets you 9.47:1, which is more than enough.

Realize...Keith's 11.50 pass was made with out of the box TW 170's, on a BONE stock, 100k mile plus shortblock that was over .010" in the hole on one side, and .006" in the hole on the other. His compression was measurably less than yours will be (although to be fair, he had a much better cam).


hotrodder68 said:
...and you are saying the 170 can be used on a 347 in the future? Maybe with some porting if I ever build a 347 they would be even better.
Most definitely. If you take the average cross section, a TW 170 is roughly equivelant to a Canfield 195/AFR 185. The truth is that the minimum cross section (far more important), is LARGER than either of those heads. That gives you some idea as to their suitability for a 347 in as cast form. If you had them ported professionally by a reliable porter...those heads on a 347 would be very, VERY respectable pieces. If you sent them to TEA for a serious CnC job (their Renegade porting is an awesome thing)...9 second power is available.

Here's a link:
http://www.totalengineairflow.com/products/fordhead/tfstw/

Anyhow...just some information for you to digest. As I said, the TW 190's are a serious piece out of the box...but if budget is in your build sheet, a set of quality used 170's will more than do the trick.

Cris
 

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Discussion Starter #15
Wow this is really great information. I could probably talk about this topic all day.

My GT40's are indeed a very tight chamber. Wayne Calvert Engines measured my block and CC the chambers on my heads and they said the heads were 53 CC which I don't doubt one bit. The chambers were so tight the valves were almost to the edge of the chambers.

The block is not zero deck from what I remember but maybe it was close to yield the 9:7:3 ratio that he came up with. They have been doing machine work and assembly on serious engines since the 50's when NHRA drag racing came alive. Very cool little shop here in North Texas.

Anyways, I will keep my eye out for some Trick flow heads in the future. If I end up with this combo for the next year or even two it wouldn't be bad to concentrate on tuning the carb (currently jets are box stock) and having fun with it.

When it is time even if I have some TFS TW heads on this engine I can start building a nice 347. I am not sure I want the headache of a 393 or 408 and having to upgrade breaks, transmission, etc...

Anyhow a bottom up build is a few years off right now...

Thanks again.
 
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