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Discussion Starter · #1 ·
Just finished the short block (454, 60 over) to discover the 28cc dome pistons (Mahle 92891411) hit the semi-open Edelbrock head (60455) raising it 1/4" above the deck.
I used some ink on the pistons to see where in the heads they make contact and have also made clay molds to create replicas so as to see how much to take off the head for clearance. Looks like I'd be better off with an open chambered head, but really don't want to have to sell what I've got and buy more.
My preference is to grind and open the chamber up, rather than have to get the pistons machined.
After having seen the difference in open chambered heads (to get an idea of what I might have to grind/dremel off) I noticed that most open chambered heads come with far more intake runner volume than what I would be working with: around 300-320cc compared to the 290cc I have in my Edelbrock perf RPM (60455).
So then I considered what my cam would actually like/need and it turns out, being a lumpy solid roller cam (COMP 11-773-8) XR292R, these Ed heads might actually choke and starve the cam of much needed intake.
So I'm at a bit of a loss and my machinist, who chose the pistons, suggested I stay away from open chambers as they will kill my compression which is also much needed for this cam.
My inclination is to do some chamber work and see how it all goes, but being that the heads are brand new, I'm a little nervous and would hate to run into a water jacket :oops:
Has anyone been in this predicament? What do you think is the best course of action?
Many thanks in advance : )
 

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Discussion Starter · #3 ·
Nice cam.

Why oval port heads ?
Well the intention was to simply deck the block, keep the bottom end more-or-less stock and bolt on an Edelbrock top end kit, which inc the heads, a hydraulic roller and air-gap intake..... one thing led to another and now the project has taken a big turn. I guess I want to see if the heads, from the top end kit, can be used, otherwise there won't be anything (except maybe for the air gap intake) that I'll be using from the top end kit.🥴
 

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290 cc runners are plenty big for a street driven 454 and will not choke the engine.

My 2 cents - modify or replace the pistons. Less $$ than new heads and zero risk. If you try and fail modifying the heads you are screwed.

Ask Eddy their recommendations on pistons. They should know what works best with their kit.
 

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Discussion Starter · #5 ·
290 cc runners are plenty big for a street driven 454 and will not choke the engine.

My 2 cents - modify or replace the pistons. Less $$ than new heads and zero risk. If you try and fail modifying the heads you are screwed.

Ask Eddy their recommendations on pistons. They should know what works best with their kit.
Yeah I think you might be right. I've found someone who can machine part of the dome off for a few bucks a piston. Might be the way to go. I was originally worried about it affecting the balance of rotating assembly though.
 

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Yeah I think you might be right. I've found someone who can machine part of the dome off for a few bucks a piston. Might be the way to go. I was originally worried about it affecting the balance of rotating assembly though.
I would call Mahle before touching the pistons. Most modern pistons are hollow dome and there is not much room for removing any of the dome.

I would not be too concerned with the balancing. I doubt that you would take more than a couple of grams off the pistons.
 

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“So then I considered what my cam would actually like/need and it turns out, being a lumpy solid roller cam (COMP 11-773-8) XR292R, these Ed heads might actually choke and starve the cam of much needed intake.”

Get rid of those truck/motor home heads. Every performance BBC made had open chamber, RECTANGULAR Port heads.

Your car will run w/truck heads, just not up to full potential.

Gonna have to change oval port intake to HiPerf rectangular port style.
 

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That is a rather serious cam for a street car, It will likely not be very happy under 2000rpm

Did Mahle confirm the valve to piston clearance? I could not find any good info on these pistons.
If they are an OE replacement TRW style, they will probably not clear the valves with that lift.
I had clearance issues on both the intake & exhaust with that cam. Had to take about .100 off the piston to get minimum clearance.

I would lean towards a better piston that is designed around your heads & cam.

As stated above, the heads may be small for that cam also.
 

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“So then I considered what my cam would actually like/need and it turns out, being a lumpy solid roller cam (COMP 11-773-8) XR292R, these Ed heads might actually choke and starve the cam of much needed intake.”

Get rid of those truck/motor home heads. Every performance BBC made had open chamber, RECTANGULAR Port heads.

Your car will run w/truck heads, just not up to full potential.

Gonna have to change oval port intake to HiPerf rectangular port style.
Why would he change to a rectangular port head for the street? In fact the Edelbrock heads outflow a stock hi perf rectangular port head without the sacrifice of torque down low.
 

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Why would he change to a rectangular port head for the street? In fact the Edelbrock heads outflow a stock hi perf rectangular port head without the sacrifice of torque down low.
Because most every performance BBC engine builder uses rectangular heads.

We can crunch #’s and justify purchases at will, I am not an innovator.
Just copying what the big boys do !

I have never heard a complaint from the owner of a rectangular port 396/427 about torque.
 

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Rectangular Ports aren’t what is hot on the streets anymore. A guy with a 10.5 to 1 496, AFR 265 cc Oval Port heads, out of the box, not ported one bit, and a special designed Chris Straub hydraulic roller cam made 650 hp in a Chevelle. On Team Chevelles site. Peanut Port heads are definitely not a great decision but aftermarket or large port 781 or 049 heads work really well. Had a set of 781s with one sized larger valves on top of a 468 with solid roller cam and a Victor Jr intake. It would rev past 7000 rpm no problem. I generally shifted at around 6400. Revved so fast!
 

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Discussion Starter · #13 ·
After measuring the thickness of the piston crown, I found that I have .247" of meat to play with. So if I simply keep the heads and pistons, I might have to grind both to make them fit.
Has anyone had to grind heads and/or pistons to make them all fit together?
 

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Even Edelbroke (which I don’t consider a hi-performance shop) offers only one
oval port vs 19 rectangular ports in their “performance” line.

I have a oval port 396. Fun car, IMO
not a performance car.

Font Material property Gas Advertising Publication
 

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I'm sure you can probably grind to fit.

A lot of you guys are way more savvy than I will ever be.
To me there are 2 concerns with grinding:
1) I would worry that the pistons would not balanced after grinding.
2) I'd would worry about grinding too much off of heads. Integrity issues?

It seems the safest thing would be to get a set of pistons that fit correctly and don't grind anything.

Or is grinding a safe option for correcting clearance problems?

By the time you pay a machinist to grind, wouldn't new pistons be a better idea?
 

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You can mill the heads and you can cut the domes on forged pistons.
 

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Discussion Starter · #17 ·
I couldn’t bring myself to grind the pistons. I’m worried about both balancing and weakening the material. I also don’t want to risk creating inconsistencies in the combustion chambers by grinding out the semi-open chambers of the head. All points that you guys have mentioned.

So I’ve got my eye on a new set of heads: AFR 3650 which still has 300cc oval ports and an open 112cc chamber. The chamber looks like it will accomodate for the domes. I spoke to Mahle and they said those heads should be fine. It’ll be a big purchase, but I figure I’ll get some cash if I sell the Edelbrock heads
 

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Discussion Starter · #19 ·
Are rectangular heads so much more $ ? I know a new intake would be required.
I'm just not sure I'd be utilising the potential of rectangles as I won't be doing much strip time. It will mainly just be strong street motor. Besides, many modern oval ports can outflow rectangles below 5000 rpm
 

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Hear this a lot, would like to
see unbiased dyno reports on
same motor, one with truck heads,
one w/rectangular heads, 3000 RPM up.
 
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