Edelbrock 75cc E-Street big block head

[heyoldguy]

So Edelbrock has produced a 75cc head designed for the STREET (notice the emphasis?).

The good news is, that if you are running a 8.7:1 compression 383 with 88cc heads, and you replace them with the 75cc E-Street head you go to 9.7:1 compression with the increased airflows of the aftermarket head.

More good news, the pair of heads is price at Summit racing for $979.95.

Why so inexpensive? It uses the same injection mold type casting as the RPM head BUT comes with heavier, less expensive valves, lighter valve springs and harder seat inserts in the heads than those used in the RPM heads. In addition they are not hand blended in the ports like the RPM heads and are not CNC'd in the intake and exhaust port openings like the RPM heads.

Edelbrock Tech couldn't tell me the shape of the 75cc combustion chamber. But they are supposed to be made from the same injection mold process  as the RPM head. Does that mean the same casting? Did they just mill the head differently to decrease the head cc's? If this is so, piston to valve clearance will be effected. It may not be a problem as low compression engines generally have the piston well below the deck.

Spark plug angle! Don't know for SURE, I forgot to ask, but the Summit Racing website SAYS they are straight.

Still, good news for those of us who are looking for a bump in compression, a replacement for old tired stock heads, and want a product cast and made in the USA.

[Challenger340]

" In addition they are not hand blended in the ports like the RPM heads and are not CNC'd in the intake and exhaust port openings like the RPM heads. "

Geez, I'd have PAID Edelbrock, NOT to do that stuff before...if I could have.

[Chryco Psycho]

also you lose approx 1 point of compression with the heat loss to alum so you are effectively back to square one

[XH29N0G]

I was just about to post a question related to these heads and Aluminum heads in general, which is below.  I do not know if it is all relevant.

Background:  I have a 1970 Charger with a 383 magnum that I bought from my father in 1983 (He was the original owner and it was our family car).  I have the original parts, but have been tinkering with it since the mid 1980's.  

It is stock except for:
   Headers (Hooker 1&7/8)
   Performer RPM manifold
   Holley 670 street avenger
   4.30:1 rear
   4 speed (OD)


I have seen a number of discussions on the various options for heads and the also recognize the fact that the headers I presently have may not fit aftermarket heads with angled plugs.  I understand the e-street are supposed to be straight plugs.

1)   My goal is not to build anything radical, and I would like to hear thoughts on the Edelbrock e-street heads (as opposed to the performer RPM heads).  Is there a reason to avoid the e-street heads for a mild combination like mine?  

2)   Are there considerations related to the valve springs that I should be aware of (I am most comfortable keeping the ending under 5000-5500 RPM and don't imagine exceeding 6000 RPM).  

3)   I assume the present heads are 906 (~84cc?) and the compression is supposed to be 9.5:1 (The dynamic test I did had about 135 psi on all cylinders which I gather is close to 9.5:1.  If the e-street heads seem like a viable option, would I see a difference (good or bad) if I went to the smaller 75cc (rather than 84cc) version?  I see comments already posted about this, but would like to hear more.

4)   Are there other things that I should take into account when considering aftermarket heads.


Ultimately, I think I will want to change the Cam as well, and will be looking for recommendations on something that will match.  I am not a mechanic and have not been trained, so if there are other comments or cautions, I would also appreciate hearing them.

Thank you

[heyoldguy]

also you lose approx 1 point of compression with the heat loss to alum so you are effectively back to square one

That is just not true.

[Rolling_Thunder]

also you lose approx 1 point of compression with the heat loss to alum so you are effectively back to square one

That is just not true.

It actually kind of is - ever wonder why you can run higher compression with aluminum heads without detonation?  Because Aluminum disperses heat differently - so for a more complete burn you need to raise the compression of an aluminum headed engine.

[bobs66440]

also you lose approx 1 point of compression with the heat loss to alum so you are effectively back to square one

That is just not true.

It actually kind of is - ever wonder why you can run higher compression with aluminum heads without detonation?  Because Aluminum disperses heat differently - so for a more complete burn you need to raise the compression of an aluminum headed engine.

You don't actually LOSE compression with aluminum heads, you gain the ability to run relatively higher compression without detonation because of the improved heat dissipation as mentioned above. Head material has no effect on CR.

[firefighter3931]

These look interesting but the powdered metal valve seats concern me. Definately not the same quality in terms of fit & finish as an RPM head which is reflected in the price. 




Ron

[heyoldguy]

also you lose approx 1 point of compression with the heat loss to alum so you are effectively back to square one

That is just not true.

It actually kind of is - ever wonder why you can run higher compression with aluminum heads without detonation?  Because Aluminum disperses heat differently - so for a more complete burn you need to raise the compression of an aluminum headed engine.

You don't actually LOSE compression with aluminum heads, you gain the ability to run relatively higher compression without detonation because of the improved heat dissipation as mentioned above. Head material has no effect on CR.

I STILL SAY NONSENSE!

Where is the empirical evidence to support these statements? Where is your data? These same people often say iron produces more horsepower than aluminum at the same compression ratio, for the same reason, "aluminum conducts heat faster".

Who among you has tested aluminum and iron cylinder heads with the SAME combustion chamber shape, the SAME airflow and the SAME compression, on the SAME short block, to TEST the detonation resistance and horsepower differences?  Most, if not all of you, are repeating what you have heard from someone else and have never tested it. I have called cylinder head manufacturers that make similar heads from aluminum and iron and they haven't even tested the concept. They have pointed me to magazine articles on their heads testing the theory. So, some HAVE attempted this test, and their results do not support the theory, that because aluminum conducts heat faster, it has any measurable effect on the combustion chamber process.

Though the head manufacture said, that because their aluminum head was developed a few years after the iron, it has had the advantage of further development, and that it MAY have an airflow increase through the port, preliminary flow tests before the aluminum/iron test did not indicate any significant flow variances.

[bobs66440]

also you lose approx 1 point of compression with the heat loss to alum so you are effectively back to square one

That is just not true.

It actually kind of is - ever wonder why you can run higher compression with aluminum heads without detonation?  Because Aluminum disperses heat differently - so for a more complete burn you need to raise the compression of an aluminum headed engine.

You don't actually LOSE compression with aluminum heads, you gain the ability to run relatively higher compression without detonation because of the improved heat dissipation as mentioned above. Head material has no effect on CR.

I STILL SAY NONSENSE!

Where is the empirical evidence to support these statements? Where is your data? These same people often say iron produces more horsepower than aluminum at the same compression ratio, for the same reason, "aluminum conducts heat faster".

Who among you has tested aluminum and iron cylinder heads with the SAME combustion chamber shape, the SAME airflow and the SAME compression, on the SAME short block, to TEST the detonation resistance and horsepower differences?  Most, if not all of you, are repeating what you have heard from someone else and have never tested it. I have called cylinder head manufacturers that make similar heads from aluminum and iron and they haven't even tested the concept. They have pointed me to magazine articles on their heads testing the theory. So, some HAVE attempted this test, and their results do not support the theory, that because aluminum conducts heat faster, it has any measurable effect on the combustion chamber process.

Though the head manufacture said, that because their aluminum head was developed a few years after the iron, it has had the advantage of further development, and that it MAY have an airflow increase through the port, preliminary flow tests before the aluminum/iron test did not indicate any significant flow variances.

I agree regarding the detonation issue. I was repeating what I have read and I also read that it's not a proven fact (other than other's experience, but didn't want to incite a side debate) that aluminum definitely ALWAYS allows you to run higher relative compression. Much of that I imagine is based on deduction. It seems plausible and may be true, it just has not been scientifically proven.

My main point in the response was to illustrate that aluminum, as a material, does not cause lower compression than iron, all things being equal.

[heyoldguy]

 Well spoken. Your point is correct sir.

[Chryco Psycho]

You do not lose compression , you lose heat , so to get the heat back you need more compression weird how I have built engines with close to 11:1 compression for the street that run pump gas without pinging , try that with an Iron head !
We know it works wether you believe it or not .

[bobs66440]

You do not lose compression , you lose heat , so to get the heat back you need more compression weird how I have built engine with close to 11:1 compression for the street that run pump gas without pinging , try that with an Iron head !
We know it works wether you believe it or not .

Experience is the best teacher.   

[heyoldguy]

Again, you have to be smarter than your cylinder heads. I have a 11.9:1 compression IRON HEADED engine that makes 745 HP on 91 octane without any detonation. Weird huh?

[elacruze]

<sigh>

All else being equal, Aluminum dissipates heat faster than Iron. What that means in your combustion chamber is that cylinder pressure drops faster as the heat is absorbed by the Aluminum. *IF* your setup is wrong, the increased pressure of an Iron head will cause detonation 'sooner' than an aluminum head.

Capice?

This is well-documented in a jillion engineering papers, it's not really up for dispute.

[Chryco Psycho]

Again, you have to be smarter than your cylinder heads. I have a 11.9:1 compression IRON HEADED engine that makes 745 HP on 91 octane without any detonation. Weird huh?

ok so you are using quench heads with minimal clearance , loading the engine above 3000 rpm with a high stall or clutch
I did this as well in a race engine never loading the engine below 2800 rpm using 94 octane , no problem but try to get on the throttle at 1500 & the can of marbles instantly appears .
 

[firefighter3931]

Again, you have to be smarter than your cylinder heads. I have a 11.9:1 compression IRON HEADED engine that makes 745 HP on 91 octane without any detonation. Weird huh?

I can see that being possible with a large cam with lots of overlap in a controlled environment (dyno cell) but in the real world with 190* engine temps and a smaller/streetable cam it would be impossible.

I'd imagine that the cylinder pressure at low engine speed (load condition) is very low to keep a combo like that out of detonation.



Ron

[heyoldguy]

<sigh>

All else being equal, Aluminum dissipates heat faster than Iron. What that means in your combustion chamber is that cylinder pressure drops faster as the heat is absorbed by the Aluminum. *IF* your setup is wrong, the increased pressure of an Iron head will cause detonation 'sooner' than an aluminum head.

Capice?

This is well-documented in a jillion engineering papers, it's not really up for dispute.

<sigh>

Oh I capice!

A jillion engineering papers! How foolish of me.

You've measured this sooner detonation or can point me to one of the jillion papers where it has been measured in an internal combustion V8 engine? The quantity of the effect is up for dispute.

Don't worry, I'm done.

[Chryco Psycho]

Apparently we are uneducated fools I must have missed how many millions of engineering papers
Care to share just one ?

[redmist]

I  think you guys are going about this wrong. It's not that you CAN run a point or a half a point higher compression with aluminum heads, it's that you have to in order to regain the heat loss associated with the aluminum.

So an Iron head would make more power if all the specs were exactly the same between Iron and Aluminum. Assuming that the heat retention in the combustion chamber was larger on the iron head because of it's lesser heat dissipation properties. That is why almost all modern cars are 10:1 compression. Because they use Aluminum heads. Why do they use Aluminum heads? My guess is to save weight, and also prolong tool life during the machining processes involved with manufacturing.

The problem with this is all the "car Guys" think that because you are 1 point of compression higher then the other guy with your aluminum heads, you will make more power. This is not always true as the guy with the Iron head may retain heat better and get better combustion to go with that.

I could be way off, but that's the way I have always looked at it.

[heyoldguy]

www.chevyhiperformance.com/techarticles/83858_iron_vs_alloy_engine_heads/index.html

www.carcraft.com/techarticles/ccrp_0602_iron_versus_aluminum_cylinder_heads_test/index.html

If these won't come up, just go the their websites and search......iron. On carcraft it's page 17 article 170, on chevyhiperformance it is page 3 article 24.

I'm willing to read other articles if you have them for me.

[Challenger340]

As always...I believe just DO....whatever works for YOU....no point arguing fella's.

[mhinders]

Don't stop this interesting discussion! I'd like to hear more from you experienced guys.
Personally I'm just a beginner but I've been struggling with the heat transfer explanation, and it's good to hear that this is maybe just one of the many "foggy facts" circulating!

[elacruze]

Apparently we are uneducated fools I must have missed how many millions of engineering papers
Care to share just one ?

Did I insult you? That wasn't my intention.

If you're an engineer, you already know this or can use society resources to find one.
If you're not an engineer, you may not know this and you haven't been able to find any free ones online and you're bluffing.

I'll work on providing one, at least posting a scan of a paper provided to me.

[Budnicks]

I'm with HeyOldGuy on this one, it's a replacement aluminum head, with smaller combustion chambers.. If all things were equal, with flow, valves, combustion chamber etc., The weight saving alone will offset almost any negative effects of the maybe a couple of HP/TQ lost buy heat exchange difference's...  I did read both of the article HeyOldGuy listed, the people doing the test even could believe the outcome & were dumbfounded & were trying to disprove their own findings... Think of it like this the 50-70+lbs. of weight savings with the aluminum heads, it takes weight off the front of the car, better weight balance/distribution, better weight transfer, less tire performance/wear, better shock performance/wear, better brake performance /wear, better handling, better looking engine bay, cooler intake air/fuel charge & cooler carb/EFI fuel temps, blind helicoiled exhaust flange bolt holes {"not going into the water jackets", rusting & breaking when trying to remove them}, 5/8" thick decks, modern more efficient combustion, better than stock flow rate 291cfm int./217cfm exh., larger intake/exhaust 2.14"/1.81" valve, better than stock valve springs etc., 0.600" gross valve lift capabilities & lastly smaller combustion chambers in the heads too boot... I'm sure I forgot something, but there is a few things listed that help the overall performance & use with aluminum cylinder heads on these heavy old front heavy cast iron engine V-8 muscle-cars, it's not just what it does in a dyno cell, it's other advantages that add to the overall experience & improvements of the whole cars performance package...   That's My 2 cents... Thanks HeyOldGuy for bringing this to our attention