Epyon127

I know this topic has been beaten to death but I have to ask:
If Street Ported AFR 195cc LT4 heads are $1720
and Stock LT4 heads are about $687 each ($1347 for 2)
Why would I not spend the extra couple hundred for the ported AFRs?

I am considering these for a LT1 to LT4 top end conversion.

tjwong

The AFRs will blow away a set of stock LT4 heads. If you are using them on a stock motor then you should order them with stock chamber volumes. That is the nice thing about AFRs, you can order them custom for your application.

Plus you can be assured that there will be no chamber variation between any chambers. Where a stock casting can have up to 4cc chamber volume variances. Plus the AFR heads come complete with springs suited to your camshaft, they are made with a thicker deck if you ever plan to upgrade your engine to say a blower or add some spray they will take it fine.

For less than $400 difference I would take the AFRs any day over stock GM castings. For a bit more you can get the 100% CNC heads! The GM castings are nice heads, AFR just improved them.

tpi 421 vette

:iagree: Some guys think ported LT4 heads are the way to go, but personally for a maximum effort engine, the AFR heads rule. Plus you have alot of port volumes to choose from.

tjwong

Thats right if you want a killer normally aspriated LT4 you can go with the exotic 215cc raised runner heads. There isn't a ported stock casting that would or could come close to the 215's. One BIG drawback is that those heads will require a sheetmetal manifold which is BIG BUCKS. Some will say that they can port ahead to match these heads, but its just not flow numbers that make these heads rule. The other factors are port velocity, swirl and chamber configuration to name a few.

It is also that the runners are totally different which makes them flow more and at a higher efficiency level than a standard port of larger demensions.

Darkness

I totally have to agree with you, even though some reputable shops like more, cnc, AI or GTP claim to port LT4's to flow ~300cfm, the AFR's are better designed period and can still be ported.

:cheers:

Jim85IROC

215s are huge. If you're running big cubic inches, or plan on having a car that is worthless below 4,000 rpms then great, but if this is a 350 and it's a driver, I think the 195s would be plenty.

1996man

what kind of cfms are the AFR 195s and the 215s running out of the box? before you have them ported?i have seen flowbench charts of lt4 heads done by CNC and they were reading somewhere between 305-310. which is quite a lot.... especially since you dont have to buy new heads. although i dont know how much AFR heads cost or how much it costs to have CNC do a stage 3 on your LT4 heads though. it would just make things a lot less confusing if when we reffered to ehads we mentioned the flow of them in CFM instead of just saying this one is better than that one ect

LT4POWR

Ported AFRs are better than stock LT4s, no question.

1996man

yes i understand this but i am curious how they compare against ported and polished LT4 heads

STL94LT1

Here is a head flow comparison of different LT1/4 heads.

www.fierolt1.com/lt1_lt4_headflow.htm


[Modified by STL94LT1, 10:12 AM 10/10/2003]

96GS#007

:iagree: You need to match the heads to your engine. If the intent is to run a 350 with something like the HOT Cam, big flow numbers at .600 lift are pointless and a waste of money since the cam is .525. The bigger the ports, the lower the velocity, the more you lose low end. Determine the desired "end state" for your motor (i.e. when will you decide to put down the tools down regarding mods) and then match to that. It's easy to make things bigger in the future if needed :)

tjwong

:iagree: In the end you have to remember to make sure that all your hard earned dollars that you spend on parts to give your engine more power and to make your Vette faster. That all the parts you buy works together in harmony. Just buying the biggest and baddest may not necessarily work out the way you want.

Case in point, teenager named Harry buys a Comp 306 cam for his bone stock LT1 and wonders why it runs like crap :confused: Just because it works great in some other guys car with heavy mods don't mean its going to work in Harry's stocker.

Or the truck user that tows, wants more power and buys a big cam and a big carburetor for his tow rig. Then wonders why he lost all of his bottom end.


[Modified by tjwong, 9:29 AM 10/10/2003]

No Go

Cylinder heads are full of black magic. :)

When comparing head sizes, flow benches, etc...one definitely needs to take it with a grain of salt...

Case in point, I had my OEM LT4 heads CNCed by CNC Cylinder Heads in Florida...Stage III. Stock LT4 castings are ~195 intake port volumes...my finished volumes are 219 cc intake and 76 cc exhaust.

219 cc should mean my car won't run below 5000 rpm to many in a 350 cu in, but it seems to work fine. I pull 53 mph at 1200 rpm (6 th gear) on the way to work day and day out and it doesn't feel any different in the backside compared to pre-CNC ported heads-all else the same. And the chassis dyno proves this out...I lost nothing at lowend (started testing at 1500 rpm) and gained some 33 RWHP. I was (optimistically?) hoping for more, but heh.

Other benefits of stock OEM castings is everything fits-valve cover has the same retention setup, nice oil leak resistant raised rails, light weight (25 pounds complete compared to my recent 210 AFR purchase of nearly 40 pounds), etc and they look stock. I run stock exhaust manifolds and the car appears comletely stock-until I pass the Z06 on the back straight. :D

Also with aftermarket heads, they may not be ready out of the box. They may say they are, but looking at my complete AFR210's-they needed a good cleaning at the very least. I pick them up from the machine shop tomorrow with flow numbers, cc's, etc. By the way, these aren't for an LT1/4 engine.

So if you don't have an LT4 already, I would choose AFR's, but if you have LT4 heads...then maybe not. :)

Darkness

Thats weird that you only gained 33rwhp from the stgIII heads!!! But then again your stock #'s were 260rwhp, and normally LT4's dyno ~300 at the wheels.

No Go

Little update...returned from the machine shop and the AFR's turned out to be a quality product! :)

Flow numbers were as advertised, valve seat sealing was right on, and volumes were within a couple of cc's. I'm happy. :)

Weighed in at 31 pounds actually... :bb

As far as the low increase...33 RWHP equals ~40 flywheel horsepower, so could be expected...stock LT4's are pretty good and HOT cam may not be utilizing the heads .600 lift to its full potential. I do have plans for that type of camshaft in future so...we will see.:)

tjwong

Ahh 31 pounds.....but there is a reason that they weigh more. And its because they have a much thicker deck than a GM LT1/4 casting. Making it stronger often sacrifices weight savings. Is it necessary, well that depends on your application. In mine, I feel more comfortable knowing its stronger with a blown application. Was it needed? Hmm maybe and then maybe not. Weight savings wasn't in my plans so for me it didn't matter to much, I was after strength and quality.

One thing that I have found with AFR is that there is a skight difference between their off the shelf units and a set of custom heads built for you to your specs. I have ordered 4 sets of custom heads and one set of off the shelf LT4 replacements for a stock engine.

Their built to spec heads are bar none the best in the industy (my own opinion) I can count on them to be right on and never had a need to have them checked by a third party. A set of off the shelf units are also very well made and will flow as advertised. They also are of equal or better quality than most other manufacturers such as Edelbrock, and Dart. But bar none their special order or built to spec units are the one of the best in the industry. The other is Dart Machinery built to spec heads. I don't have any experience with Brodix so I can't say but from the ones I have seen they too offer an excellent product.

Another point is, AFR also sells bare heads to a lot of performance shops that build from the AFR Platforms. Depending on what machinery they have and who they are, those are the ones I would be watching out for. Once the bare heads are out of AFRs sight their QC don't apply any more. So if one of you may have purchased a set of AFR heads from Joe Blows Speed shop, they maybe AFR castings but that is where the similarity ends. All parts and machining are by "others"......

But unfortunatley manufacturing mistakes occurs everywhere and to everyone sooner or later. A friend ordered a set of LT1 heads from AFR and they won't "drop" over the dowel pins on the block. We haven't got to the bottom of it yet as he is in the mid-west and I am on the west coast. But its something I have never run into with any manufacturer so I can't say what exactly went wrong yet. The old saying "S**T happens" and it just did to a friend....:confused:

And the comment of a stock head having the best fitment. Well I would most certainly agree with that statement. Nothing fits better than what the General gave us.


[Modified by tjwong, 12:38 PM 10/11/2003]

96GS#007

The shop that No Go uses for testing has a Mustang Dyno. On a Dynojet, his car would be putting down 360 - 370 at the rear wheels right now. Stock would have been in the 290 - 300 range vs the 260 on the Mustang Dyno. 70+hp from the HOT Cam, head work, and catback exhaust is pretty darn good :)