[i82much]

Originally Posted by i82much

I mean hey, if I had some really nice headers and was upgrading from iron d-ports to aluminum heads, I don't see spending the extra cost for new headers if you are talking about a 550 hp build, something you can drink and drive daily.

But if you don't have headers already and new round port heads cost about the same as new d port heads ....

Sometimes I say things and just wish you guys would give me the reaction I am looking for ...

[Gach]

I would always go with round ports, and buy headers. D-ports and manifolds are going to be limited. A set of round port heads and a nice Hydraulic cam will make 500 hp, like falling out of a tree. 500 hp in street car is killer. And crazy street able. Thats just me. Are there good D-port combo out there sure, but you can bet they’ve ported. But E-head out of the box will make 500 hp and you don’t need a hydraulic roller cam.

[JLMounce]

From my personal experience, cost was the number one factor for going KRE D-port. Assembled Performer RPM's as cast were about 400-500 more than assembled as cast KRE D-ports when I purchased. I also trusted the products going into the KRE heads over the Edelbrock offerings.

I also already had a set of D-port headers. That would have added another 500-700 for headers and whatever exhaust work would have been necessary to get those set up with my existing exhaust at the time.

In 2015 when I was doing the top-end on my engine, HFT failure reports were rampant and almost nobody knew anything about why. I opted for a roller as a result which upped the cost. I didn't have faith I wouldn't lose a cam/lifter so I spent that extra I didn't spend for the round ports on the roller cam.

[Gach]

Originally Posted by JLMounce

From my personal experience, cost was the number one factor for going KRE D-port. Assembled Performer RPM's as cast were about 400-500 more than assembled as cast KRE D-ports when I purchased. I also trusted the products going into the KRE heads over the Edelbrock offerings.

I also already had a set of D-port headers. That would have added another 500-700 for headers and whatever exhaust work would have been necessary to get those set up with my existing exhaust at the time.

In 2015 when I was doing the top-end on my engine, HFT failure reports were rampant and almost nobody knew anything about why. I opted for a roller as a result which upped the cost. I didn't have faith I wouldn't lose a cam/lifter so I spent that extra I didn't spend for the round ports on the roller cam.

Very understandable. Sure you weren’t disappointed

[Stan Weiss]

I am not sure where the idea that you need 80 exhaust to intake comes from. I would guess the BES Pro Ports are about the top for an "E" head and they are no where close to 80%.

Stan

[jhein]

I think it may come down to the fact there are probably more street guys then race guys. Street guys can get the power they want from the D ports easy. Then you don't have to change your exhaust or choke. Those were my reasons.

[Gach]

There’s definitely more street guys then race guys. There’s a lot to take into account when you’re making that choice. None of it is cheap anymore either. I can understand if you have a car with no headers now, then having to do the modifications.

[chiphead]

Originally Posted by Stan Weiss

I am not sure where the idea that you need 80 exhaust to intake comes from. I would guess the BES Pro Ports are about the top for an "E" head and they are no where close to 80%.

Stan

I know I've seen that ratio parroted here. The reasoning given is that as exhaust flow approaches 75% of intake flow, you can reduce the exhaust valve duration. A single pattern cam becomes an option at that point.

From what you posted, looks like 65% is the bogey for a max effort engine. So a 330CFM intake port only needs 215-220CFM from the exhaust at max lift. The edelbrock head posted earlier has about 65-70% I/E ratio at 550 lift I compared.

That tells me that a ported D-port exhaust isn't a major restriction on a N/A street motor. How many Pontiac street motors have over a 330CFM intake port?

[steve25]

The ratio of Exh to Intake flow a given combo needs is also very dependent on the motors compression ratio and the stoke employed .
It also seems that no one is factoring in the 3 to 5 extra % you can pick up in Exh flow by just bolting on the right size header tube.

A 68% Exh to Intake ratio that's right on edge of that so called 75% magic numbers then climbs to 73%.

[Stan Weiss]

Originally Posted by chiphead

I know I've seen that ratio parroted here. The reasoning given is that as exhaust flow approaches 75% of intake flow, you can reduce the exhaust valve duration. A single pattern cam becomes an option at that point.

From what you posted, looks like 65% is the bogey for a max effort engine. So a 330CFM intake port only needs 215-220CFM from the exhaust at max lift. The edelbrock head posted earlier has about 65-70% I/E ratio at 550 lift I compared.

That tells me that a ported D-port exhaust isn't a major restriction on a N/A street motor. How many Pontiac street motors have over a 330CFM intake port?

If one wants to look at exhaust intake ratio to figure needed cam split they also need to know CR.

Stan

[grivera]

In my case I wanted LBMs on my Firebird so the dport E heads were an easy choice. The car previously had Hooker SCs and they hung lower than I liked.

[Stan Weiss]

Originally Posted by steve25

The ratio of Exh to Intake flow a given combo needs is also very dependent on the motors compression ratio and the stoke employed .
It also seems that no one is factoring in the 3 to 5 extra % you can pick up in Exh flow by just bolting on the right size header tube.

A 68% Exh to Intake ratio that's right on edge of that so called 75% magic numbers then climbs to 73%.

Steve,
Wouldn't it depend on how (with or without pipe) the so called magic 75% was originally figured?

Stan

[i82much]

Originally Posted by jhein

I think it may come down to the fact there are probably more street guys then race guys. Street guys can get the power they want from the D ports easy. Then you don't have to change your exhaust or choke. Those were my reasons.

I didn't know about the choke issue, that makes sense! And it sounds like the exhaust issue doesn't mean much at the power levels of most street cars.

[Jay S]

As long as I can get my snow tires to hook up. I think am good, no need switch too round ports yet.

One of the guys on here…790HP@6700, 689TQ@4900…that was just NA, but that wasn’t enough so he sprayed it with IRC.. a 400 shot of NOS, 461 with 325CFM KRE D ports…Jut saying, that is a pretty darn efficient port for that much HP and only 325CFM.….not mine, but I have a some of his parts on my engine. He has since switch to 528 cid high ports and is knocking on 1000HP, on top of that he has that NOS system. Yikes!

Can’t argue with the round port headers are better and much easier to work on. If us D port guys only knew better…

[Formulas]

Speaking 2nd gen Fbody, When it comes to headers it just sux to have alot of under the hood round port awesomeness and look under it and see crushed expensive headers.

Dport headers tuck a bit better.

Be nice if say Hooker made large tube race headers ( which they do) for track use and med tube dia in TriY config for HP. street use in stainless for both ports

[77 TRASHCAN]

Originally Posted by Jay S

As long as I can get my snow tires to hook up. I think am good, no need switch too round ports yet.

One of the guys on here…790HP@6700, 689TQ@4900…that was just NA, but that wasn’t enough so he sprayed it with IRC.. a 400 shot of NOS, 461 with 325CFM KRE D ports…Jut saying, that is a pretty darn efficient port for that much HP and only 325CFM.….not mine, but I have a some of his parts on my engine. He has since switch to 528 cid high ports and is knocking on 1000HP, on top of that he has that NOS system. Yikes!

Can’t argue with the round port headers are better and much easier to work on. If us D port guys only knew better…

Do you run studs in your snow tires???

[Steve C.]

On the subject of the intake/exhaust flow ratio. Here is what Harold Brookshire from UltraDyne said on the subject within a post here on PY:

"On most cylinder heads, whenever I have around a 75 percent exhaust-to-intake ratio, I use an 8 degree bigger exhaust cam.
If the ratios under 70 percent, I use 12 degrees, and around 80 percent, only 4 degrees.
Whenever the ratio gets around 85 percent, single pattern cams seem to work as good as anything."

BUT this was not specific to Edelbrock heads at the time. That could be a general statement from him with factory heads in mind.

.

[Formulas]

Originally Posted by 77 TRASHCAN

Do you run studs in your snow tires???

Nice sparks on burnouts

[Steve C.]

And another subject that relates to the type of Edelbrock cylinder head. The older style combustion chambers or the heart shape.

How combustion chamber design relates to engine performance

https://www.motortrend.com/how-to/02...stion-chamber/


.

[Jay S]

Originally Posted by 77 TRASHCAN

Do you run studs in your snow tires???

Sure, it was -17 here last week, so the studs work good for the lake ice drags. Plus the cold lake bed is where the drink and drive daily thing works good together too, keeps your senses dulled some so you don’t notice the cold. Just got to remember to steer clear of those ice fishing huts.