New Project - Opinions/Advice Sought
12-20-2011, 09:50 AM
#1
Rennlist Member
Thread Starter
New Project - Opinions/Advice Sought
I have started the rebuilt of my old "sacrificial" GT engine, which misteriously destroyed cylinder 5 and 8 oil control rings.
So far the findings are good - no damage to any cylinder walls or bearing surfaces. I have also sourced new Goetze rings and some genuine VW lifters.
The engine is going in a 1984 S2 to complete the street sleeper look. This will be a car, that I would use on weekends and for roadtrips with my family. It would probably see one or two track days per year on road rubber, just for the hell of it. Nothing competitive at all.
The spec of the engine so far - 1989GT, tolerance 1, already balanced rotating assembly, VW lifters, 24lbs/hr injectors, 928 Intl headers and Sharktunable PEMs, Custom Y-pipe into 3.5" single pipe with two mufflers.
Would you:
1. Fit 968 intake valves. Cost in the region of $900 all in
2. Have the GT cams reground to S3 Elgin specs. Cost in the region of $800 all in
Do you think the 968 valves would make a difference on the GT motor? Do you think the valves and cams combo would really make a difference?
Intuitively you would think that some is good, and more is better, but things sometimes don't work out like that in real life...
What horsepower do you think the engine would make?
I could not help but grin when I think about it - a complete GT running gear under the beautiful body of a S2. Should fly with a good 100kg less to lug around than a standard S4...
So far the findings are good - no damage to any cylinder walls or bearing surfaces. I have also sourced new Goetze rings and some genuine VW lifters.
The engine is going in a 1984 S2 to complete the street sleeper look. This will be a car, that I would use on weekends and for roadtrips with my family. It would probably see one or two track days per year on road rubber, just for the hell of it. Nothing competitive at all.
The spec of the engine so far - 1989GT, tolerance 1, already balanced rotating assembly, VW lifters, 24lbs/hr injectors, 928 Intl headers and Sharktunable PEMs, Custom Y-pipe into 3.5" single pipe with two mufflers.
Would you:
1. Fit 968 intake valves. Cost in the region of $900 all in
2. Have the GT cams reground to S3 Elgin specs. Cost in the region of $800 all in
Do you think the 968 valves would make a difference on the GT motor? Do you think the valves and cams combo would really make a difference?
Intuitively you would think that some is good, and more is better, but things sometimes don't work out like that in real life...
What horsepower do you think the engine would make?
I could not help but grin when I think about it - a complete GT running gear under the beautiful body of a S2. Should fly with a good 100kg less to lug around than a standard S4...
12-21-2011, 12:59 AM
#3
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personally I would do the cams as well as the intake valves. these heads flow really well at the low lift scenario's and the 968 valves will help this greatly. not to mention it gets the intake and exhaust valves closer to the acceptable ratios.....
12-21-2011, 07:08 AM
#4
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Thread Starter
Problem is that both of you know your stuff and for the first time disagree? What to do? GregB - you around? Or Mike S?
12-21-2011, 08:40 AM
#5
Three Wheelin'
I'm following this post as I have an 89GT engine that also needs assembly. Don't hang me if I'm wrong but I think it was Greg Brown who said improperly installed 968 valves significantly hurt flow and that they weren't needed in "smaller" engines. I have a spare 85 - 86 shortblock and I"m thinking about using it instead. Cut the proper valve reliefs in the pistons, resulting in about 10.75 compression and running some healthy cams. The cams should reduce the engines dynamic compression. Then just squrrel away the stock shortblock so it doesn't get blown up.
12-21-2011, 09:20 AM
#6
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Thread Starter
I'm following this post as I have an 89GT engine that also needs assembly. Don't hang me if I'm wrong but I think it was Greg Brown who said improperly installed 968 valves significantly hurt flow and that they weren't needed in "smaller" engines. I have a spare 85 - 86 shortblock and I"m thinking about using it instead. Cut the proper valve reliefs in the pistons, resulting in about 10.75 compression and running some healthy cams. The cams should reduce the engines dynamic compression. Then just squrrel away the stock shortblock so it doesn't get blown up.
12-21-2011, 10:15 AM
#7
Rennlist Member
If you're using the car for ordinary road use, then you want to retain low end torque for easy driving ?
Resist the tempatation to go for "top end " cams, and retain the stock valve size. S3 cam should be fine.
Resist the tempatation to go for "top end " cams, and retain the stock valve size. S3 cam should be fine.
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12-21-2011, 10:43 AM
#8
Rennlist Member
Thread Starter
On the other hand I agree that it would be a pain if I get a 4000rpm to 6750rpm power band in a daily car...
But how do I get 350rwhp out of a 5ltr otherwise?
Oh, decisions... I just don't want to end like Dr Nick did, forever wishing he did the valves too...
12-21-2011, 12:04 PM
#9
Nordschleife Master
The 968 valves will net around 10bhp at the top end. It's a huge expense for little return.
The cams will net a much larger response than the camshafts.
The cams will net a much larger response than the camshafts.
12-21-2011, 02:59 PM
#13
Former Sponsor
My humble opinion...backed only by many of hours of flow bench work (on my own flow bench) and many, many engines.....built in my world. Different people will have different opinions and different results.
The stock valves will flow enough air to make well over 400 HP.
The installation of 968 valves has "hurt" airflow in almost every head that I've measured airflow on...that were not really well thought out and worked up on a flowbench....when "reasonable" suction numbers and velocity are used.. Like the problems with dyno results, flow bench data can "fool" the uninformed/naive. There can be flow increases seen when airflow is measured at 28" of vacuum....the rub is....how many engines can pull 28" of vacuum and what rpm do you have to be turning to be able to do this? I prefer to look at airflow numbers that are actually "seen", in these engines, instead of working in Never, Neverland.
To take advantage of the 968 intake valves, the ports need to get near the size of 968 ports. Ports that large are going to not be as good for velocity, hurting low end torque.
The "proper" camshaft will help. The trick is figuring out what is "proper".
Everyone that spends money on their 928 engine wants to have gotten the "proper" pieces...therefore everyone has great results...even when they are disappointing. "Human Nature" makes this not only possible, but almost an expected outcome.
The stock valves will flow enough air to make well over 400 HP.
The installation of 968 valves has "hurt" airflow in almost every head that I've measured airflow on...that were not really well thought out and worked up on a flowbench....when "reasonable" suction numbers and velocity are used.. Like the problems with dyno results, flow bench data can "fool" the uninformed/naive. There can be flow increases seen when airflow is measured at 28" of vacuum....the rub is....how many engines can pull 28" of vacuum and what rpm do you have to be turning to be able to do this? I prefer to look at airflow numbers that are actually "seen", in these engines, instead of working in Never, Neverland.
To take advantage of the 968 intake valves, the ports need to get near the size of 968 ports. Ports that large are going to not be as good for velocity, hurting low end torque.
The "proper" camshaft will help. The trick is figuring out what is "proper".
Everyone that spends money on their 928 engine wants to have gotten the "proper" pieces...therefore everyone has great results...even when they are disappointing. "Human Nature" makes this not only possible, but almost an expected outcome.
12-21-2011, 04:23 PM
#14
Rennlist Member
^^^^^yep!
just use your GT cams as they are. what do you mean, elgin specs. you mean, the 1mm more lift by taking some material off the base circle? if so, yes , do that. the lifters support it and that would give more gains than the port and valve work that would be much more expensive anyway.
just use your GT cams as they are. what do you mean, elgin specs. you mean, the 1mm more lift by taking some material off the base circle? if so, yes , do that. the lifters support it and that would give more gains than the port and valve work that would be much more expensive anyway.
12-21-2011, 05:16 PM
#15
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Would you:
1. Fit 968 intake valves. Cost in the region of $900 all in
2. Have the GT cams reground to S3 Elgin specs. Cost in the region of $800 all in
Do you think the 968 valves would make a difference on the GT motor? Do you think the valves and cams combo would really make a difference?
1. Fit 968 intake valves. Cost in the region of $900 all in
2. Have the GT cams reground to S3 Elgin specs. Cost in the region of $800 all in
Do you think the 968 valves would make a difference on the GT motor? Do you think the valves and cams combo would really make a difference?
One additional mod you didn't mention & might consider - porting the S4 intake manifold. We've tried to look at the whole engine as a system and tried to eliminate restrictions from any particular piece. Flow bench testing of the stock intake has shown that certain cylinders were being restricted below the potential of the stock heads.
IMO, the order of attack would be cams, then intake, then valves.
Last edited by Dennis K; 12-21-2011 at 05:51 PM.