Charley B

In being able to afford the kind of engine build I would love to do; you have already offended me.

ShawnSmith

I'll do my best to share - both in dyno charts, stories, and perhaps in free rides at gatherings...

Louie928

Shawn,
The increased displacement from 5L to 6.5L will give you all the torque you can handle without doing much else. Roughly speaking, displacement will pretty much determine peak torque, and breathing ability of the heads, valves, and cams will determine at what RPM the peak torque happens and how far it extends upward in the RPM band. The further up in RPM the torque extends determines the peak hp and area under the torque curve. General engine design is that for industrial type use, large displacement but poor breathing, is used. That is lower compression, small valves, and mild cams. This will give a lot of low end grunt which is great for pulling heavy stuff, climbing hills, etc. The engine may be under heavy load for extended time so the lower overall (limited) performance will help ensure longer life of heat sensitive components. Overall, the area under the torque curve isn't a lot (compared to what it could be) because the torque runs out quickly after the peak torque RPM. Sporty type cars will have engines with a different design goal. Since traction is often limited, as well as strength of the driveline, excess torque at the low end of the RPM range isn't required and may well be a detriment. A steep rise of torque as RPMs rise can cause problems when exiting corners. A broad power (torque) band is desired. Especially torque at higher RPMs. For these engines, more effort will be put into allowing better breathing at higher RPMs. Peak power demands are relatively short so more peak heat (fuel burn) can be tolerated. This design may slightly decrease low end torque, but with enough displacement, there is plenty of torque anyway. Having the torque extend further up into the RPM range increases overall area under the torque curve and gives the car some life when driving.

A couple suggestions. Do have 968 intake valves installed. Do use better cams such as GT or modified '85/'86 cams. Don't intentionally squeeze down the exhaust (by using the stock system) and choke off what could otherwise be a great motor. Use high flow cats. Dave Lomas sells great high flow cats. Use at least 2.5" dual exhaust, or a 3.5" single. Keep the stock manifolds if you don't want headers, They won't hurt much at your expected power level.

Louie

ShawnSmith

Louie,

Yes, the project will include larger 968 size valves, along with appropriate porting of the head. Exhaust plan is for a 2.5 inch system, x-pipe, high flow cats, mids, and then I may have GB experiment with both the stock end muffler and an RMB to see which one gives the best sound/power tradeoff. I honestly don't think the stock final muffler is a serious restriction - it's just heavy and it makes the car quieter...

3 inch exhaust is gonna be too darn loud for my goals.

Greg has built many of these motors, and he has his preferred package of goods which he knows work best together for a street setup. I'm going to mostly defer to his defaults, with maybe one or two tweaks in the interest of "trying something slightly different".

ShawnSmith

> are you going to dismantle your 28k mile engine to build a stroker?

Yes. More specifically Greg is gonna do it.

I understand this is not an entirely rational move.

Louie928

Good, that should give you about 410-430 rwhp and decent torque above 4500.
Louie

ShawnSmith

> Personally I would buy a seperate block for GB to work with, and then you have a low mileage S4 engine to sell.....

That makes good sense, but I kinda like sticking with this original motor (even if I wind up replacing most of its parts)

mark kibort

This may have been answered, but just a 6.5 on a stock S4 is limited by cams and intake (including heads) with GT cams, i imagine that guess of 350rwhp goes to near 375rwhp. pull off all the smog an put on equal length headers and you are near 400 (stilll a guess, a hopefull one)

I still think an easy way to do this is to just do the stroker crank, find pistons and 968 pistons and put it together like you a stock engine. Ive done this a few times and its a pretty easy and cheap assembly process. (relatively speaking)

joe and Mark A.'s strokers have bigger valves, higher lift cams, and that 75hp CF intake. after the intake and MAF mods ,they went to 500rwhp (from near 420rwhp with not to many other changes)

mk

Red UFO

I don't understand why all that money to get 330-350 hp when you can just buy a Euro and get close to that.

IcemanG17

When they say 330-350hp they mean wheel HP....I haven't seen a 16V dyno higher than about 290whp and that was a 5.0L euro in scotts race car.... Most 4.7 Euros tend to dyno around 260whp or so...

ShawnSmith

> When they say 330-350hp they mean wheel HP

Exactly. 350 rwhp is an easy 80 hp above stock (euro or otherwise)

If I can get my motor to 400 rwhp that'll be basically 150% of the original output.

GregBBRD

Shawn:

Good news. Your block is rumored to be about ready to ship back to us. Mary called and they claimed that it should be done in the next couple of days....don't hold your breath, yet.

Your heads are back from the machine shop and have the bigger 968 seats installed.

Chips from your heads fly, this coming Monday. Yeah, I know it's a holiday, but the porting thing takes a whole bunch of concentration and non-interruped time. (Tough to get during the week.)

I've got some new things done and have a couple of new ideas.....

Stan.Shaw@Excell.Net

I guess I over looked this thread when it started. I am not an expert, but can provide some answers to some questions
I don't know about the strokers only producing 330-350 rwhp, but would suspect as speculated they are just stroker short blocks without the cams and head work to get the extra hp. Based on what has been done before, getting to @400rwhp should be straight forward, but includes 968 valved heads and at least GT cams. Based on my build in progress experience, you can add $5k to the cost with just those items.


The 500+rwhp stroker motors do not have forced induction.

Off the top of my head, all of the following are stroked and bored @6.5L, none are forced induction, all are @500rwhp (possibly even in the order of their appearance):
Joe Fan
Mark Anderson
Tom Falkenbeg (Don Hanson's old race car)
Louie Ott
John Veninger

All of the above

Stan.Shaw@Excell.Net

Based on my research the key point here is that @400-420rwhp is often achieved with a stroked/bored motor, including head/cam work.

The jump to 500rwhp is the result of intake work. Mark & Joe have effectively one-off carbon fiber intakes with throttle bodies. Tom F., Louie O. and John V. all use throttle body intakes with adapter plates. Engine management varies from stock (possibly with Sharktuner) to DTA to Motec.

Devek did claim to produce a 500rwhp motor by modifying the stock intake, as I recall. I don't know where that motor is or if the result ever made it to be a product that could be sold.

pcar928fan

Stan,

I know they are not forced. I have seen (with my own eyes on a dyno) a 6.5L motor pull 380rwhp (or maybe it was closer to the 350 I mentioned) in the above post...

Just seemed amazingly low from my perspective and if I had spent that much money already I would be PISSED if my car was not pulling at least 400 after the time, money, and effort these engines take.

You may well be correct though and it may not have had all the important head work done to it... That may be the big difference. Not to mention it may not have been well tuned before that dyno run, thus maybe it was running to rich or something, certainly not optimal anyway.

Thanks for the reminders that it takes more than just 6.5L to make big power, but THAT is a good place to start FOR SURE! Was thinking last night how if the 928 had been released originally w/ the 5.0 300HP+ motor that was planned the GTS's would have ended up at 6.5L and been making 450HP+ and we would probably still be able to go down to the dealer and look at new ones for sale today!