Engine wizards please chime in
11-08-2008 | 12:46 PM
#16
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From: saratoga, ca
ditto what was said.
however, I would leave the heads alone and just do the cams or probably have the cams increased for lift by 1mm as it can work with no lash caps for the hydrolic lifters. that 1mm more lift would give more hp than the increased valve diameter i would imagine.
mk
however, I would leave the heads alone and just do the cams or probably have the cams increased for lift by 1mm as it can work with no lash caps for the hydrolic lifters. that 1mm more lift would give more hp than the increased valve diameter i would imagine.
mk
11-08-2008 | 03:30 PM
#17
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Cause i make these posts all the time
but i dont start it off with "im not trying to be rude" So lets call it what it is, i can respect that 
Your right i haven't put together a stock block with 39mm intake valves. I do believe my original post did mention that "i dont think" but let me go back and check it out and i will adjust it if necessary...... or do we think the point has already been made?
11-08-2008 | 03:35 PM
#18
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Sterling,
This is my original unedited post, you can see whats CLEARLY said in the beginning.
I also believe you said that everything does fit, but just barely. And as you mentioned when you take into account an engine expanding when its warm then you may have contact. Agreed
I dont know what your talking about when you mention 968 pistons. That was never discussed in this thread......... or i really missed that one. This would be a stock bottom end (new rods) and heads modified to fit the 39mm 968 intake valves (WHICH ROGER IS PRATICALLY GIVING AWAY!
)
I think its safe to say that my post was stated simply as opinion, I do see "I think" in there.
This is my original unedited post, you can see whats CLEARLY said in the beginning.
I also believe you said that everything does fit, but just barely. And as you mentioned when you take into account an engine expanding when its warm then you may have contact. Agreed
I dont know what your talking about when you mention 968 pistons. That was never discussed in this thread......... or i really missed that one. This would be a stock bottom end (new rods) and heads modified to fit the 39mm 968 intake valves (WHICH ROGER IS PRATICALLY GIVING AWAY!
)Jim,
I am no expert here but think i can handle this one
No the pistons dont need any modifications, only the heads and their seats.
The S3 cams do need to be modified but i dont know specifically how, I do know they are apparently the same as GT cams but they are longer physically so must be cut down or something like that.
I know Roger was talking about replacing rods in his car which he will keep at 5.4L. I would replace those i guess. Please do tell, what rod manufacturer your using and what those were going to run.
And it was a pleasure to meet you at Sharktoberfest last month
Cheers
I am no expert here but think i can handle this one
No the pistons dont need any modifications, only the heads and their seats.
The S3 cams do need to be modified but i dont know specifically how, I do know they are apparently the same as GT cams but they are longer physically so must be cut down or something like that.
I know Roger was talking about replacing rods in his car which he will keep at 5.4L. I would replace those i guess. Please do tell, what rod manufacturer your using and what those were going to run.
And it was a pleasure to meet you at Sharktoberfest last month
Cheers
11-08-2008 | 04:34 PM
#19
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From: Beverly Hills, CA
968 engines use 968 intake valves... measure the intake valve pockets on the 968 pistons to see the clearance needed for the larger valves. 968's have larger valve pockets than S4...
I really didn't mean to be rude... but even saying that you think you can handle that is an opinion.... and you need to clearly state that you have done no comparisons..... or measurements....
I've had them side by side the pistons as well as the valves, done the measurements with calipers and done contact tests with clay. If you don't notch the pistion, don't even bother having the work done for the intake valves as you will have issues. Porsche saw fit to have larger pockets for larger valves... so that is one thing I'm not going to try to re engineer how much tolerance is needed.
I really didn't mean to be rude... but even saying that you think you can handle that is an opinion.... and you need to clearly state that you have done no comparisons..... or measurements....
I've had them side by side the pistons as well as the valves, done the measurements with calipers and done contact tests with clay. If you don't notch the pistion, don't even bother having the work done for the intake valves as you will have issues. Porsche saw fit to have larger pockets for larger valves... so that is one thing I'm not going to try to re engineer how much tolerance is needed.
I don't doubt you've done this work. Youve done a hell of allot for engine development and i love reading your posts.
I thought it was clear that I thought i could handle the post, CLEARLY you think i was wrong, so thats cool, i stand corrected. So to my original post saying no you dont need to cut the pistons, I am wrong, i dont know what the hell im talking about when it comes to 968 valves and otherwise stock 928 pistons.
lets not make this some war or words, your right im wrong
11-08-2008 | 06:22 PM
#20
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From: Conshohocken,Pa.
Sterling is correct. When I built my motor I flycut my own pistons myself in a Bridgeport to accept the larger valves, not only for the valve head diameter but also deeper for several reasons. Although I did install heavier valve springs, valve float is always a possibility. Also I wanted extra room for higher lift cams in the future. With all the effort & money I put into my engine, mods were made with reliability insurance in mind. Can't afford to do it twice. And if I decide to do more radical mods later the shortblock was done so it could handle the additional power. So the pistons were flycut to handle any future mods as well as engine tolerance 'malfunctions'.
Hammer
Hammer
11-08-2008 | 07:12 PM
#21
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From: Mount Mort, Ipswich , Australia
The piston cutouts are deep enough but not wide enough , you will need to widen the intake cutouts to allow for the wider 968(928 part no.) valves , yes I would rebalance the assembly just to be sure , the newer rods should be same as the the older ones given newer construction,
PS the cutouts are deep enough to take larger lift cams than the modified s3 cams.
PS the cutouts are deep enough to take larger lift cams than the modified s3 cams.
11-08-2008 | 08:54 PM
#22
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From: Rep of Texas, N NM, Rockies, SoCal
I spoke with Elgin a few days ago. He is no longer modifying the S3 cams for S4 heads. I'm looking into a new source for the cam changes. Should have some info late next week.
11-08-2008 | 09:09 PM
#23
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From: Beverly Hills, CA
11-08-2008 | 09:35 PM
#24
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Jim, i'd put about 5-7psi though that engine and a good crank case vent system to wake it up long before i'd start messing with heads and valves. Heck even 3-5psi makes a huge difference. Each his own
11-08-2008 | 09:47 PM
#25
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From: Rep of Texas, N NM, Rockies, SoCal
He's semi-retired. doesn't want to fool with it anymore. Let most of his employees go, and now just futzing around in his shop. He didn't sound very interested in doing any more Porsche work at all.
11-08-2008 | 10:10 PM
#26
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11-09-2008 | 10:17 PM
#27
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From: DFW Texas
In general GTS motors have incredibly mild cams.....and respond VERY well to GT cams..... Around 330+ whp with just the cams.....
With 85-86 cams modified to fit would be similar....of course having those reground by elgin would be a monster....maybe 400whp?
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With 85-86 cams modified to fit would be similar....of course having those reground by elgin would be a monster....maybe 400whp?
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11-10-2008 | 02:54 PM
#28
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From: Stockton, CA
11-10-2008 | 10:28 PM
#29
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From: lawrence,kansas
Hi Jim,
I am putting in gt like cams from drnick right now and hope to have more hp ...but the sc is already installed and I have the sharktuner and programmable chips in it now also...I can un hook the sc and blow some chips with the cams installed and give you an Idea of the hp gain just from the cams if you like.
andy
I am putting in gt like cams from drnick right now and hope to have more hp ...but the sc is already installed and I have the sharktuner and programmable chips in it now also...I can un hook the sc and blow some chips with the cams installed and give you an Idea of the hp gain just from the cams if you like.
andy
11-10-2008 | 10:50 PM
#30
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From: saratoga, ca
now that elgin is out of the 928 cam business, i guess ill have to figure out a way to fix the broken sprocket Holbert cams. I heard there was a guy in Canada that could fix and replace the sprockets on solid sprocket cams. I did get a quote for about $1000 to fix them. However, with a little base circle grind, that could be a hot cam for about $1500.
I would like to eventually get a set of stock S4 heads and put 968 valves in them, with the modified cam, bolt it all up to the new stroker motor. that way, i could replace all the stock stuff on the original Holbert engine.
mk
I would like to eventually get a set of stock S4 heads and put 968 valves in them, with the modified cam, bolt it all up to the new stroker motor. that way, i could replace all the stock stuff on the original Holbert engine.
mk