craigw1

spent some time with my engine builder this morning

for some of you that have been following my previous posts, I have a series 5 tii motor (ex the turbo), street port, 48 IDA and RB street system. have done 1850 glorious miles since the rebuild. On the dyno she pushed 168rwhp (after some rejetting)

Well, my builder showed me some porting templates...a normal bridge (which leaves about 2mm before the water jacket), a j-bridge (goes thru the water jacket) and what he calls a monster port...basically a really big bridge.

he has some quiet time at the mo.....says we can tear it down, re-use everything (maybe replace the water seal), do the porting, upgrade to 9.7 s5 n/a rotors while we're in there, and slap it all back together.

then subject to rejetting, he reckons 240rwhp. Thats a massive 40% increase !

I'm def tempted.....but put so much effort in to get it to this stage that I want to enjoy it for a couple of months more.

what would you guys do in this position ?

MattG

iTrader: (2)

How long of down time are we talking?

clean85owner

I'd love to see what you would need for 240rwhp. I'm not doubting, I'm just curious as to just how big of a port is needed for those numbers. I say go for it. If the car is going to be used as a daily driver, I'd go with the first bridge port you mentioned. Longevity of the motor would probably be most rewarding with that port.

P.S. I'm pretty sure you'll need more carb. A 48 might get a little restrictive at those numbers.

P.P.S. I have a streetported S5 NA with a Mikuni 44. I wish I had a four port. Heh. I'm thinking that when it is time for me to rebuild, I'm going to use some of my old 4 port irons, touch up the ports (i.e. larger streetport), use my 9.7 rotors, and MegaSquirt it with the S5 EFI system. High compression, streetported, EFI 4 port = hawtness

Scott1982

Just drive it!
Scott

Rx Seven

iTrader: (12)

Depending on the bridge port you get besides upgrading your carb i think you might also need to improve your exaust system to get the most power out of the bridge port.

But it all depends on how big you go

Also I would do it if it could be done within a couple weeks so i would have to go through withdrawl from not driving my 7.

Naegleria_Fowleri

If you have another car as a daily driver then do it. Your gas mileage is going to go way down the drain with a bridge, and even though you are making a lot more power you'll have to rev higher to get it. Regardless, I say do it just because I love all motor rotaries. But like everyone else has said, there is a lot of other things you'll need to change to get enough fuel and unlock the power. Your carb is definitely not going to be flowing enough fuel.

Directfreak

iTrader: (2)

Don't do it. Tuuuuuuuuuuuurbocharge it.

Cowboyfun

^ditto

trochoid

iTrader: (6)

Bps are a pita to drive on traffic, fuel mileage will be way down, along with driveability. Drive it, gather up parts and turbo it.

craigw1

trochoid,

we spoke about turbo briefly....he mentioned something about

1) we have used carbon apex seals so these must be replaced with steel seals
2) something about the exhaust ports being ported so can't be turbo'd ??? (I guess he means the turbo manifold won't mate up properly...so maybe that can be slightly ported then so that it mates nicely to the housings ?)

anyways...once that is done you have to decide on blow thru or fuel injection. and either way, a surge tank needs to be installed along with a boost referenced fuel pressure regulator. and then the plumbing for the intercooler...and the intercooler itself...and the boost pressure gauge...and a show-off valve....etc etc

it just seems so much simpler/cheaper to remove the motor, stick in the n/a 9.7 rotors, port the bridge and put it all back together. then the only tuning is the jetting.

Rogue_Wulff

Like Trochoid says, BP engines are not traffic freindly. Even the smallest BP doesn't like to run under 3-4K, and they tend to eat the fuel at an alarming rate. These items added together, make for a car that is not as fun to drive anymore.
Many people have gone the way of a 1/2 BP, using SP primaries, and BP secondaries, but this style engine really should have a 2-stage type of carberation, such as a 4 BBL or twin staged 2 BBL. The Mikuni, Dellorto, and Weber (ect) 2BBL carbs run on both sets of ports full time, which negates the SP primaries allowing for better road manners.
You just need to decide whether you want a car that is fun to drive anytime, or one that is fun at times - a pain the rest of the time.

DwArF

I vote for turbo.

craigw1

u guys are raising EXTREMELY valid points here

This is exactly the reason why I did not go for the bridge in the first place. Sure I wanted power, but I wanted driveability too. Didn't want no 1500rpm idle with a power band that only kicks in from 6000-8000. So we went for the street port.

you know what ? The answer is clear. I will enjoy the car as is and slowly but surely save up and collect all the goodies.

My ideal setup would be a fuel injected turbo set up, not the std FI but throttle bodies.....hooked up to the microtech. SO there you have it guys...no more bridge port....fuel injected turbo as and when the budget allows. Did a quick back of the matchbox calc and I get to roughly $ 5,000. thats for the microtech, the fmc and piping, the boost referenced regulator, efi fuel pump, surge tank and throttle bodies (all new stuff). i still have the turbo and manifold, water and oil lines from the t2. Will recondition the turbo and then have to tap the front cover for oil return.

Rogue_Wulff

As for the builder mentioning the exhaust ports, on an N/A engine, the exhaust gets ported up towards the intake. This keeps the power cycle lasting a little longer, and gives better power. But, on a turbo application, the exhaust gets ported down, away from the intake. While this shortens the power cycle *slightly*, it also makes the turbo spool up faster, thereby adding more power back than is lost from the shorter power cycle.
Does that make sense?

clean85owner

My streetported NA S5 idles at 1200 rpm and doesn't make power until 5-5500 rpm... *shrug*