928ntslow

Nick, how did they arrive at those numbers? Did they work off of a dyno sheet and engine specs? Where did they say the power band would change? What increases would you expect? Is this based on a stock GTS engine, no mods?

drnick

brendan, id been looking at the 928 developments website and the specs phil t. offers for the 32v as a comparison point and these seem in keeping with the trends.

my only concern now is whether i need to uprate the valve springs, any opinions?

BC

IMHO (and with many conversations with people of knowledge), when you increase the upper rev range of where the cams will work, you will be shifting up there more, and therefore you will want springs to be working well as that higher limit - so yes, stiffer springs is definatley something you (I would) be looking at as a "safety net".

I am personally going thorugh the process to add stiffer springs to my 78/EFI motor. Crower makes a very nice set for 80 dollars that requires some customization in the spring seat and valve height area. The current OEM springs are 60 dollars EACH SET. 60x16 is not what I wish to pay. Some R/D has been spent on seeing if this will work, but hopefully the benefit will come later. Crower as well as Crane should have some nice springs right around the size of the 32V cars, though you will want to pay close attention to spring tension and heights of the originals - as we all know, too much=more valve seat wear. Chevy retainers and springs are sloppy together I have noticed, and in stark relation to Porsche's tight tolerances, it almost seems like a step back in that department, but I just can't afford spending big money in the wrong places - i.e, up to 1000 dollars for springs! Well see how much money is spent down the line on the change and if it was a good idea.

drnick

keith, i sent them some basic info regarding the stock GTS engine including displacement, redline and peak HP/torque with rpm figures. the only other requirement was that the car would be street driven and the cams could be used with the stock lifters. they said i could expect both peak HP and torque to be higher in the rev range - i will dyno and see! the figures theyve suggested use more lift than the GT grind and slightley less duration.

brendan, looks like i should take some advice on this one and speak to my mechanic whether new springs are absolutely necessary. id like to retain the stock items if possible to limit costs but not if this is a severe compromise.

as far as i know this is the 1st time GTS cam specs have been made known widely - is this so?

rob rossitto

FWIW, those specs have a tad less lift (.404/.374) than my modified GT cams, that can run stock springs and lifters... for my stroker, the powerband for my grind is supposed to be from 3k-6krpms... don't know how much the extra stroker displacemnt plays a role in cam curves, but I suspect you'd be ok w/stock hw at those lift numbers... ie no coil bind, floating as long as you keep it to stock rev's .... hope this helps...

drnick

yes rob, that helps a lot both for my peace of mind and even more with domestic harmony - now i will be able to buy my girlfriend a christmas present!

rob rossitto

best to verify w/a real engine builder, as I'm just an armchair hack... it will also depend on the profile as well... lots of stuff to consider, but if your proposed profile isn't more aggressive than the modified GT I have, I suspect you'd be fine... I've found it's best to cross ck w/a few pros and if they all come up w/the same answer independently, you're probably on the right track... regards!

BC

Absolutley. If those grinds will not net more power to get you to 7000 or above, then no reason for new springs unless the current ones are worn. My point was that over that, you will need more pressure, and maybe even lighter pieces.

drnick

i might have a raised rev limit as im installing the GT EZK controller but thats still under 7K. hopefully it will have 'big gobs' of torque down low as well as 'insane' top end - as compares to my S2 currently, i think 400 HP at the crank will keep me pleased for a while.

i may need to have it tuned after its installed and running, whats the difference between simply tweaking a RRFPR or having custom chips burned, do i need both?

Lagavulin

I would be leery of anything from 928 Developments, period, especially the camshafts and specs (..firstly, where are the dyno-sheets for each grind???). Back at the ranch, the 928 grapevine has it that some people running those cams of his have been breaking timing belts, and we all know what that means repair-wise. How could that have possibly happened?

Let's suppose Phil 'borrowed' those cam specs from another 32v engine like the Ford 4.6L which runs a timing CHAIN. Using that same cam profile on another 32v engine which instead uses a timing BELT, it would seem that the loads generated by the more aggressive profile are apparently too much for the belt to handle.

So learning from other's expensive mistakes (..the 'best' way to learn), I would be be careful regarding any spec which is more aggressive than the factory GT grind, and would make sure the grinder knows that the cams are powered by a belt versus a chain.


Now for the discussion on the GTS to GT cam swap and the resulting dyno sheet on Louie's website.

It is important to note that when the GTS was dyno'd with it's stock cam, it also had the stock exhaust. However, when the GTS was dyno'd with the GT cam installed, Louis'e fabulous x-pipe was installed too which makes any comparisons between the cams all but impossible to do. That x-pipe is worth 15-20rwhp all by itself, and is a great piece of hardware.

A much better test for us gearheads would have been to dyno the stock GTS, and then dyno it again with Louie's x-pipe installed. Next, install the GT cams with the x-pipe already installed and dyno it one last time. Only then would we have a clearer picture as to how much the cam-swap alone was worth.

No matter what though, the resulting horsepower gain is impressive!

heinrich

What Lagavullin said (did I just say that?? )

Before buying from any vendor, please please first talk with their customers. Locally we have a number of 928's that have had enhancements and developments installed..... a TALK TO THEM FIRST.

shaaark89

lag,
i'd be curious to know who's broken timing belts with those cams. pm or email me if you'd like.
heinrich,
i'd appreciate any info you may have as well. i saw the recent dyno posts on the pacnw site.
reason is that i have a set sitting on my bench which were destined for the racecar, but it's on hold pending further investigation.

BC

Breaking timing belts can *I think* be related to higher spring pressures, no? This is a concern of mine as my 2V will have some higher spring pressures when its together.

928ntslow

I think I will be able to supply those dyno numbers in time. My GTS is stock except for the recent RMB, but it is easy to put the rear muffler back on again...RMB is not going to account for much anyway. The exhaust system will be modified to accept the X and Hi flow cats with Borla mufflers. At a later time, I will do the cam swap.

I would like to see what the outcome is of some of the other GTS cam swaps before I do mine. I only want to get in there once. So I will be putting a list together of "necessary" components.

Fastest928

I have done at least 4 GTS to GT, and as many S4 to GT cam swaps and have swapped cams in all engine configs 5.0, 5.33, 5.4, 6.0 and 6.5.....

The difference between all 4V 928 cams is minute...in camspeak. Even the DEVEK B1 grind, used by many, including us in our 450-550 (and 600 ) rwhp engines and Kelly Moss for their monster engine is still my "concept" of a slightly modified street cam. Although hard to tune for perfect idle....and it is just a tick more duration and lift than the stock GT cams.

The B2 cam, which after years of research and should be capable of reaching 650-750 rwhp at less than 7000 rpm....will not be that radical.

Anyway, I will check with a few cusotmer and see if they will let me post their dynos...I have three with apples to apples dyno sheets.

Marc
DEVEK