My heads ported for my 385 ci motor are 236cc intake

 

My question is this, how in the hell can more air flow through a smaller hole? If you have a small runner size how well can the head really be ported ? I'd be happy with a bigger runner size myself at least you know it was ported and some actual work was being done. What we need around these boards is some damn honesty.

 

Best analogy is this.....

Which is better in terms of traffic?
1) 5 lanes of cars going at 20mph, or,
2) 2 lanes going at 80 mph?

Same goes for intake runner volume and port velocity. At the end of the day, both cases may let the same # of cars go by. But in terms of engines, we know the faster moving air burns more efficiently. So I'd say there is definitely a delicate balance between sheer volume and air velocity.

My heads are said to have a 226 cc intake port but I've read where they actually check at closer to 230 cc's. I was going to check mine, but just ran out of time. However, I think they made good power with the TR224 cam (415 / 404) and are also doing well with the F13 cam too. So I'd say don't worry about it.

 

In terms of conventional thinking, the larger runner will support larger cubic inches, especially at higher rpm's. Hopefully Jay knows something we don't.

 

On a 346 you would have to rev the **** outta that motor for it to make power. the smaller runner keeps the air speed up and producing good torque down low. the larger runner volumes are for strokers and engines that live at high rpms. This is why the AFR heads should make power small runner=greater port velocity= more torque down low. And they flow just as well as a ported set of casting at 236cc

 

Were these the hand ported Ab Speed heads or cnc ported? Does anyone have some hard numbers here, track times, dyno figures, even driving impressions? For that matter, for anyone who knows there runner volumes (cc's) on anybody's heads, (TEA, MTI, etc...), let us know.

 

MTI 5.3 2E are 215 int/78 exh

 

Jay explained to me that with a 2.02 valve the runner volume is 225 and with the bigger 2.055 valve its closer to 230 becuase the shape of the valve and it sits higher on the seat.

 

Air speed/velocity as well as airflow numbers do not have a direct correlation to hp or rpm it will opperate the best. I can take a 230 cc head, mill .080 off the intake flange and now I have a 215 cc head. The average cross sectional area did not change, nor will it perform any differently, a smaller port will usually perform better at 2-3000 rpm. I'm just trying to say, A 230 cc head is not inpractical for a LS1, We do them all the time. My point. there are a lot more important factors in the LS style heads than airflow and volume. It is too bad the is the most effective marketing tool though. (other than cost). I really like the new AFR castings, for this reason. they filled all the dead areas, gave us material to work with, and makes it very possible to have the small runners. we'll see a whole lotta data in the months to come, the days of only having OE heads to work with is over.

 

So are you guys saying since I've got a 346 with intake runner volume of ~240 and exhaust runner volume of ~90 that my bottom end is going to suck?On the other hand are you saying that these 5.3's will be good for a 382 or 408 since the runners are so large? I've never heard of 5.3's being used on big cube engines.

It sure would be nice if others would jump in withinput on runner volume vs. hp regardless of head brand.

 

You don't ever hear of 5.3 heads on big cube motors because of the combustion chambers. Compression would be too high for a street motor and it would be too much additional work to open the chambers up versus starting with a head that already has a larger chamber.

 

If that being the case, why did I find as little as 1 cc difference when I replaced my 2.055 valve on this head with the original 2.00 valve which makes it now 231 cc's? I checked it twice.

 

I was confused when I read that as well. Maybe Jay can shed some light on this?

 

Thought Jay used the CNC process to get the head roughed out about 9/10th's then did the fine porting by hand?

Jay may hand tweak the runner a little differently to match 2.055 valve for best flow than he does with the 2.02 valve.

BTW aren't the GMPP LS6 heads offered thru GM that LPE CNC's ~250 cc runner volume? That seems toward the big side IMO.

 

no that was me .... My flow numbers were different then posted above .... still no power though ... redynoing with the 7.4s in there ....

 

If I could add my .02c's worth.

Compression Ratios, both Dynamic CR and Static CR are the foundation for which any engine is built. The Intake, Cam Profile, Cylinder Head and Exhaust determine what Peak HP Rpms your engine will reach. This also sets the stage for the rpm range wherein the earlier rpm's Peak Tq is reached.

So, by setting this Peak HP range you also have set the earlier Peak Tq rpms - there is definately a correlation between component selection. If you mismatch this relationship to the cam, cylinder head, and intake runner based on desired peak Tq/HP rpms, then you have an engine that is not as efficient as it could be for all rpms upto peak Tq/Hp rpms.

Just because you can run a larger cylinder head, bigger cam profile, higher compression doesnt necessarily mean you should.

The Dynamic CR (Cam Duration to Total Chamber Volume relationship) determines the optimum Static CR required-based on the peak rpms the engine is expected to run. The Cylinder Head Port Volume allows the engine builder to fine tune this desired RPM Range where the engine is expected to run. Both the Cross Sectional Area of the port and the Length of the Port (This inculdes the length of the Intake Manifold's Port) will determine this peak rpm range.

In any engine, but especially on a performance engine where wide open throttle is expected, there will be a very real and delicate balance between Compression Ratios, Port Pressure and Cylinder Pressure within the confines of the Cylinder Displacement based on an expected peak engine rpm.

Port Volume is relative to Cylinder Displacement while the Valve Diameter is relative to the Diameter of the Cylinder Bore itself.

As far as larger port volumes being better suited for strokers: all the term stroker means is that a stock engine's displacement was altered with a different crank stroke. So we should not be arguing which head is better for a stroker or non-stroker as that is a very relative term. Relative as in how large is the stroker or how small is the stroker.

Therefor, we shouldn't be arguing which head is best for a stroker, rather we should be arguing which components are best suited for a specific displacment based on the intent of that engine at a specific rpm. This would require us to categorize the different distinctions of performance and then apply the basics of airflow velocity to each category.

A basically stock (including all modifications that still allow the enigne to be ran on the street with pump gas) with a displacement of 346 and a Static CR at 11.0:1 or lower will be more efficient with a Cylinder Head Port Volume in the range of 190 - 205cc. Hmmm, 205cc (?), huh; maybe AFR knows exactly what they are doing by coming out with their Mongoose LS1 Cylinder Head with the 205cc volume.

Remember, if you mismatch the components based on the peak rpm range where that engine is expected to be ran-simply because you adopted the "More is Better" theology, then you have an inefficient engine at all rpms.

I guess the only way any of us will really know how much the larger ports hurt engine performance is to Dyno test two LS1's of identical components with the Cylinder Heads being the only difference.

With what we know at this point IMHO I would say 236cc is way too large for a stock displacement of 346 with 11.0:1 Static CR or less.

I would further be interested in knowing if anyone has purchased and cc'd the AFR 205 Mongoose Heads.

Kevin,

 

To answer your first statement, these heads are not finished by hand, they are as cut by the cnc. And yes the GMPP LS6 cnc heads are the Lingenfelter LS6 cnc heads. They just cost less through GM.

 

Has anyone that's bought the cnc'd version of the head made good power yet? These heads look good for the money but I can't find anyone who's had much luck with them since the company has went to cnc. Maybe it is due to the runner volume?

 

Jay's "hand touch up" includes partially unshrouding the valve stems from what I can tell.

Going back to runner volume, it is my opinion that port cross section is very important to velocity. Even if total runner volume is large due to say very large bowls port cross sectional area may still be reasonable to keep up velocity.

Also think about the ever increasing size of the runners of recent after market intaket manifolds. At some point won't velocity be degraded. Same applies to the ever larger and larger TB's.

 

Yikes, this is a scary thought. I'm about to pull the trigger on a purchase of his heads.... Is the info above "true"?