Port Polish HP Loss

[Dominic]

Does anyone else besides me feel that porting and polishing the intake and heads is actually going to cause a powerloss?

With only 350cfm of air flowing through the stock heads, (not much), I feel the porting and polishing dimenishes the returns from a cam on our cars. SB Chevy's have this issue, and I think ours do to.

I am going to try a cam in mine with new rockers and springs/retainers; I'm leaving my heads alone, and I'll let everyone know what kind of power increases I get on the dyno.

Increase the ports and you lose velocity for the same amount of flow, and I think with such little flow we don't need porting and polishing.

[Silver3800V6FBodyKY]

Dominic, I don't think we loose power, but I don't think we gain a tremendous amount. I think we gain a lot more from the cam than from the Porting and Polishing of the heads. I'm doing the same thing you are though, I'm getting a 220/228 with .520 lift along with stiffer valve springs, retainers, locks, and chromoly pushrods. I expect at least a 10% power gain from this.

[Tiago]

if you aren't flowing enough air, get a bigger cam, that will take care of that ;)

[Arctc Wolf]

A cam can only do so much. eventually, you'll have to open up the heads to get more air in. the idea behind porting is to make the air flow more smoothly, not so much increase the volume of the intake & exhaust paths. Eventually, you'll have to get bigger valves put in to flow the highest amount of air into the cylinders. I can see how excessive polishing will reduce power because you want some turbulence to help mix the air/fuel mixture. Having a totally smooth surface doesn't help mix everything up.

[Silver3800V6FBodyKY]

I'll probably have my heads ported when I have a forced induction system. Then the CFM will increase greatly, and the displacement of the heads will be benificial. But until then I'm just going to run a cam.

[Dominic]

<blockquote>quote:</font><hr>Originally posted by Silver3800V6FBodyKY:
I'll probably have my heads ported when I have a forced induction system. Then the CFM will increase greatly, and the displacement of the heads will be benificial. But until then I'm just going to run a cam.<hr></blockquote>

I agree wholeheartedly!

However isn't your cam spec a little large for n/a? 220/228 is HUGE if you also go with 0.520 lift... Why did you pick that over say the compcams cam?

Also you should gain approx 12.5-15% more power with just a cam... around +25rwhp.

[ July 15, 2002: Message edited by: Dominic ]</p>

[Silver3800V6FBodyKY]

I've told Tom my situation and he suggests that cam. I've thought long and hard about it though, and it the lift does scare me. I like the duration, but I'm wanting something with around .450 - .475 lift. We'll see though, I haven't commited on buying from Tom yet, I'm looking at the Grand Prix Store setup. They're a lot cheaper, and I already know the power gains. It's pretty attractive.

[Dominic]

<blockquote>quote:</font><hr>Originally posted by Silver3800V6FBodyKY:
I've told Tom my situation and he suggests that cam. I've thought long and hard about it though, and it the lift does scare me. I like the duration, but I'm wanting something with around .450 - .475 lift. We'll see though, I haven't commited on buying from Tom yet, I'm looking at the Grand Prix Store setup. They're a lot cheaper, and I already know the power gains. It's pretty attractive.<hr></blockquote>

Has he tested this cam? Have you asked him how he is deriving these values? At one time he said 210/214 was the most he thought we needed, did he somehow change his mind? I'm very interested in this - Even desktop dyno 2000 (which Magnus thinks is junk :D ) doesn't think this is a very appropriate cam.

I'm not sure if you'll gain anything from more duration, all it will do is make it a very high rpm cam. The compcams design will idle smoother and have more 3500-5000 pulling power, probably maxing around 5800, whereas this thing sounds like a 6500-7000rpm powerband cam to me!

[ July 15, 2002: Message edited by: Dominic ]</p>

[Silver3800V6FBodyKY]

Not sure how he came up with the numbers but that's what he told me. I'd say there is a 90% chance that I'll stay safe and go with the Grand Prix Store cam. It's proven, and it's cheaper. Plus I don't have to calculate Pushrod length like Tom say's I'll have to. So I'll probably get the Safer 206/212 cam.

[Magnus]

Just an FYI.. The grandprix store is a store.. not a cam. They sell a few COMP Cams for us however. ;) You can buy a cam that they see, 206/212 directly through COMP for $299 or $305 I believe.

Also, my COMP base circle was different than my stock one. Had I not had the heads milled .020" I would need .020" longer pushrods than stock (to maintain stock geometry).

- Keith

[Silver3800V6FBodyKY]

I know that Magnus. But the Grand Prix Store only sales that one cam, and I'm sure Comp. Cams sales any lobe you want, so it's just a way to know which cam I'm talking about.

Anyway, what would happen if we put the L67 Cam into our engine? Just a thought?

[Magnus]

Grandprix store sells 3 cams.. all COMP cams.

200/212 115LS
206/218 115LS
206/212 113LS

All will work in our cars. The 206/212 113LS would probably be the best on an NA application.

I don't like when people refer to their cam as "Grandprixstore" cam or whatever,.. its not very specific at all. I prefer COMP 206/212 or COMP 212/212 or COMP 218/224 etc. etc.

COMP offers many lobes to choose from. Call up the cam help line and they will definately help you pick a cam. They know what works, they have the above info.

Another thing that bothers me is when people say they are going with a big cam, say 220/228 but don't say which cam.. a Crower regrind or a COMP XE grind.

A COMP XE 212/212 would probably make more power than a crower 218/218 regrind and probably the same amount of power as a 224/224 regrind.. the XE lobes are just so much faster.

However a crower 206/206 would probably idle like a COMP 218/218 as on the regrinds, the .005 duration is MUCH larger where as on the fast XE ramps, the .005 is very small.

Lets look at an exampe..
212/212 duration @ .050
Duration @ .005 w/Reground Crower 280
Duration @ .005 w/True COMP 260
Duration @ .1 w/Reground Crower 170
Duration @ .1 w/True COMP 200

All those #'s are just guestimates to give you the idea.

With a reground cam you will have more overlap because of the slower ramp rates. But with a reground there will be a lot less stress on pushrods and valve springs.

[Silver3800V6FBodyKY]

I see what you're saying now. I'm going with the COMP 206/212 cam because the LS is 113 as the COMP 206/218 has a LS of 115. Although if I decide to keep my Nitrous I'll go ahead and buy the 115 LS, but I'm pretty set on selling it.

[Ironman24]

I'd highly suggest getting the 113 LS cam for nitrous use or for NA use. The exhaust duration is bigger than the intake which is great for nitrous. I've had great results running a Crower regrind with 113 LS on a 100 shot and also with the blower.

[Dominic]

So does the COMP 206/212 require the longer pushrods or is it okay with stockers?