JakeRobb

I have a bunch of questions (pretty standard for me).

First, my situation:
- My car is a daily driver ('02 Z28).
- It sees occasional recreational strip and autox use. Strictly for fun.
- Street manners and drivability are my #1 priority.
- I'd like to do a moderate heads/cam upgrade
- I'm planning on a turbo setup (a few years off at this point)

Right now, I'm considering AFR's Mongoose 205 and 225cc heads. AFR seems to have a good reputation, and I read in Hot Rod that they yield performance very close to that of a set of ported LS6 heads, and at about half the cost.

I know very little about cam select, and so I haven't even begun to narrow down the options. I'll be reading the cam threads on ls1tech soon.

On to the questions:

1. Which technique is preferred?
A. Choose cam first, then choose heads
B. Choose heads first, then choose cam

2. Should I be considering other heads?

3. How much more power can be had from the 225 vs the 205cc heads? Assume I get a well-matched but not-too-agressive cam in each case.

4. I have read that a loss in low-end torque should be expected with the 225cc heads -- are there other compromises I would be making (for instance, in the drivability and/or sound)?

5. What is the 205/225cc measurement actually measuring?

6. There is another cc measurement (typically in the 65-75 range) associated with heads. What does that measure?

What else should I be asking?

Thanks!

teke184

wow...lots of questions

i think it's better to pick the cam THEN pick the heads. since you need to know the powerband that the cam will operate in, as well as the cams lift to pick the ideal heads. there is no sense getting heads that flow 320cfm at .650" lift when your cam only has .550" lift.

the 205/225 is a measurment of the intake runner volumn. in general, the bigger the volumn the more power you will generate in the top end, while your low end gains are less. a smaller intake volume will give better gains in the low and mid range, but will not yield as much at the top end. now i'm not saying you'll LOSE low end power....you just won't gains AS MUCH.

that being said, since you want a DD and something for AutoX...low and mid range is important. so the 205s would be your best bet. they will help generate great torque at lower rpms, at a more useable level.

it's hard to say how much you'll be "losing" by going with the 205s. but since i think your goals are for low and mid range power, the lose wouldn't be a concern.

consider other heads if your budget doesn't allow for AFRs...since they are generally considered the best aftermarket heads. other options would be the new Dart 205 heads. they cost around $1500 and flow similar to the AFRs and have a smaller combustion chamber (more compression...little more power). they are pretty new so not many people seem to be runing them. they are the ones i'm looking at. partially due to cost...partially just to test them out.

the 62cc, 66cc, 72cc...those are measurements of the combustion chamber...basically determining what the final compression will be. i think stock is around 66cc. and i was told that the 62cc of the Darts would bring my compression up by about 0.5, which is a ratio. so if stock is 10.0:1...the heads will raise it to 10.5:1.

NOW...
when you run boost you want a LOWER compression in order to prevent detonation on pump gas. most engines that are built for boost run between 8.0:1 and 9.0:1 give or take. although doing this without putting boost on the car will actually drop the hp.

so if you plan to putting the turbo on later, you may want to wait on the heads untill you can do the heads and turbo at the same time. otherwise lowering the compression now (with bigger cc heads) will probably negate alot of the power picked up from better flowing heads. and you'll be stuck with that for a few years till you get the turbo. and who wants to buy one type of heads now...and different ones later?

if you really plan to boost the car...it's gonna take alot more thought.

how was that...did it answer some questions?

teke184

just for some specific information...

when i had my cam installed and dyno tuned it made 382hp at right around 6400rpm

peak torque was about 370lbft at 4900 or so.

and what was more noticable was how flat the torque curve was from 3000rpm up to it's peak just below 5000rpm.

3000 - 330#
3500 - 342#
4000 - 360#
4500 - 362#
5000 - 370#
5500 - 350#

here is the graph, ignore the torque reading on the second run, the clutch slipped and it spiked. you can see where it slipped on both runs.

JakeRobb

Yeah, that answers a lot of questions. I also found some good info on LS1Tech.com. I'll post some links in here later.

Livernois Motorsports apparently has Stage 1 ported LS6 heads for under a grand now. That sounds hard to pass up.

Given that it will be at least a couple years before I get the turbo setup, yes, I think I might get heads now, and then new ones again when I get the turbo. I'm sure that, in a couple years, there will be someone with stock heads that's interested in buying my used ones.

I know you can play with the compression ratio by getting different head gaskets, but I'm also considering switching to a low-compression crank when it comes time to do the turbo.

I might not do the turbo at all... it really depends on how happy I am with it once I've done all of the other bolt-ons. Plus, I'm kinda counting on about ten grand falling from the sky in order to do the turbo setup the right way.

teke184

what exactly is a "low-compression crank"??

to change compression you have change what is actually forming the shape of the combustion chamber...the heads and the pistons.

i've already covered how the heads can increase/decrease the size.

pistons are similar, domed pistons have a hump in the top of them (stock is flat) which reduces the "space" in the combustion chamber...increasing compression.

dished pistons have concave area "cut out" to add space to the chamber....lowering compression.

the crank only controlls how far up and down the piston travels in the cylinder. as far as i know you don't change that to accomodate changing the compression.

as for the LS6 heads you are talking about...get the specifics of what the runner size is. i looked up the ported LS6 heads at VRE and they show them having an intake runner size ranging from 225 to 237cc. this will depend on the porter as to what the final size is.

i think you'll be better with the 205s!!

besides...the price you mentioned for the LS6 heads...does that include any core charge?? since you don't have ls6 heads to trade you may have to pay for the heads AND then the ~$1000 for the porting.

JakeRobb

No core charge. See for yourself. The guys on LS1Tech couldn't believe it either!

JakeRobb

Intake runners are 215, chamber is 64.

Kraest

What you read in Hot Rod is extremely incorrect. In fact a set of ported LS6 heads cost nearly half the price of a set of AFR 205 Mongoose heads and perform better, not the other way around.

Mike

teke184

yeah...AFRs are pricey...

not totally convinced it's worth it.

like i said, i like the price and advertised performance of the Dart 205s. that is why i'm really looking at them when i get the $$ for heads.

JakeRobb

I'll pull out the issue tonight, but I'm pretty sure that's what I read. If I read it correctly, I'll have to remember to take their articles with a bigger grain of salt.

teke184

AFR heads are usually around $2200

i can't imagine that the LS6 heads are more than that.

Kraest

You can pick up a used set for $400.

Mike

JakeRobb

I checked -- the heads I had read about were $4500 TPI Specialties hand-ported LS6 heads with titanium valves and lots of other goodies.

teke184

GOOD GOD!!!

did they dip them in 24kt gold and pack them in diamonds??

thats just plan insane.....i've seen them from $1400 up to around $2200