I've done an exhaustive search and couldn't find the answer to my question.

I have been considering a heads and cam upgrade. I am in California so smog certification must be taken into consideration. A 220/220 .58x/.58x 114 LSA range cam is about as radical as I can go for smog. A ported and polished set LS6 heads seem like a cost effective choice, but I have some reservations.

My question is, with this combination would I loose low to midrange torque?

Porting and polishing will increased the volume of the runners which will affect the flow rate and low to midrange torque. While every thread I hae looked at confirms that there will be notable power gains, I can' find any dyno graphs or comments on the affect on lower rpm power? If I go to the time and considerable expense to do this, I want to see a gain throughout the entire HP/TQ curve. Last thing I want is to loose something in around town drivability.

Thanks in advance.

 

that is not a real popular cam may be why you dont find any charts.

Bigger ports HURT low end torque quite a bit. You could just polish the runners and not make them bigger. Polish I mean look for ruff edges and smooth those out.

 

True.

Most cams on this board start at 224 duration. I would just like to know if in general people see a drop in power through the low to mid rpm range with reworked LS6 heads. Of course a bigger cam will affect the power output. But in general what would the affect be on the lower end?

 

You may be able to find some before and after charts in the Z06 section to see how the low end power responds to porting. You may not find the cam but since they start with regular 243s it should give you an idea.

 

Not sure if alot of guys are porting the LS6 heads versus going with an aftermarket head ie. Trickflow, AFR

 

If cost is an issue, I would just look at port/polish the stock LS1 heads. If you are having to buy a set of LS6 heads to port and polish, I would look at the aftermarket heads (IMHO)

 

That was my first cam. It will definitely satisfy smog requirements provided you have a proper tune. Yes you will lose slight low end grunt as power is moved up in the RPM band. That is why 4.10 gears are the next mod to do to after any H/C setup.

You will still retain "daily driver driveability".

 

Perhaps I should have a little more detailed. But I am talking about LS6 factory heads with CNC porting stage 2 (whatever that means) from a reputable company. I want to stay with something factory or CARB certified. I don't want to get caught by a knowlegdible inpector (smog tech or LEO) and be forced to swap the heads out immediately.

My searches have revealed, by concensis from this board, that a ported set of 243 heads beats a ported set of 241 heads.

BTW, I am aware that AFR's have a CARB #. But that is not the topic of this thread.

Thanks for the replies.

 

that's exactly why I went w/ texas speed's ported 5.3l heads(220cc intake runner) instead of their ported 243 heads. I might have given up 5hp top end, but felt like it'd have better torque. I didn't loose any lowend switching to them w/ my 224/220 116 XER and when I switched to a custom 218/230 116 XFI I actually gained 20ft/lb and 10hp(both idle like stock at 725rpm and would pass emissions)...a smaller intake duration will help crutch velocity and make more power on a too large intake port...afr's would be ideal for you

 

IIRC small port runners and smaller duration cams, Increase piston vacuum which INCREASE air velocity to fill the cylinder and combustion chamber This means MORE low to mid range torque.

Large port runner heads and long duration cams, may not have as much vacuum to fill the cylinder and combustion chamber as quickly and kill low end torque, but provided high end HP.

Big numbers are sexy as hell, but do they provided what you want your car to do?


on a 346 or even up to a 402 I would not put any larger runner then a 215 head. but that is just me, I want HUGE SOTP torque acceleration out of corners.

 

(just an aside) i just bought a pair of ls6 heads and dont plan on having them ported for this reason (and money). you also have to remember that the stock ls6 heads without milling will raise your compression ratio from 10.1 to 10.5. This could also affect low end torque probably in a positive way and possibly making up for the cam loss of low/mid torque. just a thought

 

dont port them. But before you put them on if you see any ruff edges inside the runners, you can take a small dremmil sand wheel and smooth those ruff edges out a bit. That is what I did on my 243 heads I bought.

 

Links to some graphs of 220 & 224 cams:

http://www.ls1tech.com/forums/genera...dyno-data.html

http://www.ls1tech.com/forums/genera...ta-inside.html

http://www.ls1tech.com/forums/dynamo...ta-inside.html

Looks like the 220 gains 10ft/lbs@3k but gives up 9hp on top.

The LS6 heads also gain .5 in compression ratio over the LS1 heads.

 

i agree. i just smoothed out the runners on my 243's and they are great still. i have a 228R texasspeed cam with their LT's and made 409rwhp the 243's are a good head if you want better flow then stocker LS1 heads and are cheap enough.~Cole~

 

I have more torque and low end power with my 224 / 224 581/581 112 then most big cam cars. 243 heads that have been polished a bit. and I use 918 springs

Out of a corner I can pull most LS7s and almost all ls6 mid to large cam cars up to about 125 mph, then I am toasted.

 

You might consider forced induction. By the time you do cam,heads,headers, gears you wil be close to the same $ amount anyway. Plus it will still drive like stock. Until you floor it that is.

 

That's usually about the point I start letting up. You see, I don't track my car. So this is good info. Looks like I have no worries about a ported or CNC LS6 heads. I saw a graph in the Z06 section. It showed no loss of HP/TQ at any rpm.

 

This is a consideration. But I have quite a few friends who are using FI. While streetable and providing ultimate power, FI does have it's problems. I will probably get a chance to ride in both a H/C and a S/C car before I decide.

 

Many times when you see a dip in a hp or torque curve, that MAY mean the car is OVER cammed for the intake.

The cam and valve events are attempting to suck more air then is available ( not quite but that is as close of an explanation that I can think of ) then the dip in the curve

the valve events at that dip in the rpm curve are not performance at optimal level. The cam may be TOO big, lift or duration.

I have driven too many vettes with cams that i cant remember. But those larger cams, high lift or worse high lift and long duration, have OK acceleration between 2500 and 5000 rpms, but a fricken rocket ships above 5000 rpms. and are dyno MONSTERS.

were smaller cams have great acceleration off the line or from a roll race or out of a corner up to 5252 rpms. Between 5252 and red line they are just OK. The dyno number are just so so. but low to mid range torque is fantastic.

That is why we ask, What do you want your car to do?

Personllly I would really love to do a forged dry sump 402 but that just may not be in the budget.

So most likely will will pull the 243s off my engine, take out the 224/224 cam, put on AFR 205 heads and a 224/228 581/588 112+4 cam, plus a dry sump system which I already have.

Prices on Fast92 intake is great. Not sure if I will do a Fast 92 tb or a tpis oval tb. or stick with my LS6 intake and tpis 78mm tb. Which ever combo will provide the most low to mid range torque That SOTP out of the fricken corner and UP to 150 mph ASAP ( red line 4th gear)

 

Bang for your buck just have your stockers ported. Instead of having them totally reworked focus on the bowl, chamber and a good valve job. Leave the runner alone for better flow acceleration which will help with tq.