AintQuick made a post on Spins latest thread that got me thinking about my mod goals. Has anyone out there just done a heads only mod and kept the stock cam? Thoughts?

 

 

found this:
http://www.vincihighperformance.com/...graph%201.html

 

That's what I am leaning towards right now... I discussed this a little bit with my tuner and he reflected my thouhts on the subject:

- You will gain gas mileage (AFR claims that their 205 heads net 3-4mpg better than stock heads. I think this is overly optimistic but I can believe 1-2).
- You will gain power. I've heard as much as 30WHP.
- It will not make as much power as it otherwise would if you had a cam.

I wonder if there is a small loss of low end torque associated with this?

 

here is another find. Sorry it is also AFR though. It seems both articles are on LS1s. Not sure if LS2 would benefit as much?

http://www.gmhightechperformance.com...all/index.html

Lets say you save 1 gal of gas per tank and use 1 tank a week. Thats about $4.20 a week savings and it would take approx 2 years to pay for the AFR heads plus install $.

 

why a loss down low? If the heads are milled to the stock 64cc chamber size the compression would be equal and low end equal-right? Or take the AFR that has a from the factory 66cc and use a .040 gasket to get the OEM compression back?

I think Spin once told me using a thinner gasket is better than milling since milling effects flow.

Nice if Tony Mamo jumps in this thread.

 

A member alerted me to this thread....

The bottom line is switching from stock heads to AFR 205's will pick you up everywhere....even with a stock cam. Doing the same and increasing compression at the same time by milling them and/or running a .040 gasket is even a better move and will net you even more gains.

Better throttle response
Better fuel economy
More torque and horsepower from the crack of the throttle till redline
Better part thottle response and improved SOTP feel.
1-2 MPG without a compression increase....2-3 MPG with the compression increase (maybe even 4 MPG on a straight freeway run for a few hours like a long roadtrip etc.).

Addind a SMALL performance cam takes everything up another notch as well with ZERO downside in drivabilty or idle quality. A 220/224 comes to mind if your very conservative or a 224/228 if you dont mind a slight performance "lope" at an idle but still retain perfect stock like driving manners.

IMO, do the heads in conjuntion with the cam....its not that much more trouble (or that much more costly) and it adds nicely to the performance gains with zero compromise in drivability....still passes the sniffer to those that are curious as well.

Hope this info helps....

Tony

 

Thanks, Tony. I enjoyed our talk at SEMA, we'll be back this year, and lunch is on me and Spin.

 

My reasoning was that with larger port sizes the airflow velocity will be lower leading to poor cylinder filling at low RPMs. You see this on the LS3 motors which make more top end than the LS2 but at the cost of reduced torque and hp below 3000RPM. This is speculative though; I have no real world data to back it up.
Re: Compression ratio: You have to be careful about altering the compression ratio; if you drive somewhere where 91 octane is the only fuel available the high comp may lead to some knocking... Also there are risks associated with altering the "squish area" between the piston and the combustion chamber, particularly by using thinner head gaskets. I know several people (Spinmonster comes to mind) have had good success with that, but it is something to keep in mind. Some times if you make that area too thin you can make the combustion characteristics of the chamber poor allowing very little timing.

Still, I'd go with what works... I think there is plenty of data out there that shows AFR heads are a winning combo... Does anyone know where I can buy a set?

 

I think the 205 runner is close to OEM size and the velocity IS greater than OEM so no worries there.

Power,
if you went AFR 205's only what would you do? Mill them to 64cc or use a .040 gasket?

 

I would prefer milling, with the reasoning that that will affect squish area the least. I would like to know what the guys at AFR think first though.

 

please keep us informed if Tony does not get back on this

 

Interesting thread

 

more info:
http://www.gmhightechperformance.com...ads/index.html

 

 

And another interesting option:

http://www.gmhightechperformance.com...ads/index.html

 

Thanks for the info. If my memory is correct on this forum, a cam change is manditory with special attention to compression ratios for that set up otherwise the bottom end is very soft. IOWs one cannot just bolt up the intake/head combo and go--right?

 

Its not that cut and dry... The general rules of thumb are:
You can do heads/intake manifold and not retune; it will run fine even if the AFR gets thrown a bit off by the airflow changes. It won't make anywhere near its power potential though; much like headers, most of the gains come from the ability to tune the setup for more ignition timing/leaner AFR afterwards.
You don't have to change the compression ratio when you swap the cam. In fact most people doing cam swaps don't touch anything else on the car. The cam will move the entire powerband up higher so there will be loss of low end. Some times to compensate for very large low end losses associated with big cams the compression ratio is raised but this is a large expense and is not mandatory if you can live with less low end. Also, very mild cams can run untuned. Again though, most gains will come from tuning the setup.

 

This is my next mod! Great information.