308 Engine Rebuild & CIS to TWM Throttle Bodies Conversion Thread!

That look like a 2v set up...a 4v engine would need about a 30 degree bend at the end to match the port angle

 

I am waiting for an email from Frank to see just what is left available.......

 

11:1 is pretty much pushing the outside limit for good quality street gas in a street car I was told by the guys at Norwood's. That is why for safety/reliability/longevity I backed down to 10.5:1 to have a bit of a margin.

 

Yeah that's why I said with a stand alone ECU you can run the timing back down a little for street gas and then if you get the urge to unleash the beast you can dial it back up.

The new street Porsche's run from 11.3 to 11.7:1 depending on which model you reference and the ECU retards the timing automatically for street gas. I'm just suggesting to do the same thing "manually". Figured if you're in there you might as well get all you can.

So is there a drawback to running around town with 32 deg advance and on the weekend flipping a switch, adding some race gas and having an extra 20 or so horses to play with?

cheers

 

Ping ping ping ping ping ping BOOM....<silence>

 

Well must be a lot of ping ping ping before the BOOM ... like years???

425 very very hard hrs on my motor so far ... works for Porsche ... I know they're 4v engines but it's the principal of maximizing the engine internals which I think is a smart move ... you can be conservative with engine management.

Just sharing ... the Pizzaman can be conservative if he wants ... it's working for me but I also made sure to optimize anything I could to facilitate the higher compression ratio/minimize detonation.

Cheers

 

I agree with you for sure. Once you are up at 11 and over, I agree there are some other things in the motor that really have to be optimized. It all depends how badly you want those last few hp - in a racing car, yes every one is very important so you can go all the way. In a street car, I think some compromises made for reliability are not out of place, esp. with the variation in the quality of fuels in day-to-day driving. If the ECU has knock sensors like the modern cars, then it is a bit safer to run higher compression.

 

Chris,

I machined a set of 3/4" thick lexan spacers for Nick's 3.5 liter engine to go between the throttle bodies and intake manifold. The spacers helped get the linkage better in line with the throttle bodies and help to insulate the bodies from engine heat as well.

Dyno run is at Carobu's site: http://www.carobu.com/html/308_gtb_3_5l.html

The compression ratio listed at the site is incorrect. The compression ratio is 11:1 not 10.25 as listed. There is no problem running 11:1 on an all aluminum engine, especially with electronic engine controls. We made close to 340 hp with streetable cams and pretty lousy exhaust on the dyno. The fellow who assembled the heads screwed up with one of the shim unders. One was not on the valve stem but instead was sitting on the retainer. Lucky we didn't drop a valve during the run. I got the head back the way it should be. Nick has been too busy and the weather too cold in Wa. to get the engine back together. With better exhaust and running on a full seven cylinders, this engine will make a good 360 hp and be very streetable with the mild cams I specified and had ground up at Web.

Heads were ported, larger intake valve and trick valve job. I did quite a bit of flow testing to come up with a combination that obviously works.

Steve
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What a great engine! With the TWM EFI, a ported head, 11:1 CR pistons, cams and a street exhaust on a 2v head (!) on 3.5 liters yielding almost 97 hp/liter is terrific! If you get to 360hp that would be 102.8hp/liter ! Wow - on a 2-valve!

This was on 40mm itbs like Chris'? Any other modifications? Could you say what the head and induction bench flowed in CFM @10? I am trying compare the numbers on my ported head. I really learn a lot from engines like these and the Carobu dynos.

Many thanks!

 

Yes, I used the stock manifolds with 40 mm throttle bores. You would need a custom intake manifold to go any larger. Linkage is much straighter with the 3/4" spacers.

My flow data is at 28" off my SuperFlow 1020 bench. Multiply by .598 to convert to 10"

Intake

.050" 33.1 cfm
.100" 65.4
.150" 98
.200" 125
.250" 144
.300" 155.7
.350" 163
.400" 168
.450" 174
.500" 177

Very little was done to the exhaust

.050" 21.8cfm
.100" 41
.150" 68.5
.200" 92
.250" 115.6
.300 130.5
.350" 141
.400" 148.6
.450" 154
.500" 159

You can not get the intake to flow these numbers with the stock valve. The valve is not large enough nor is it the correct shape. It is impossible to correctly shape the port with the stock valve diameter.

The cams I used had an intake lift of .450" and exhaust lift of .400". A supercharged engine would probably benefit from higher exhaust lift. I would have used more intake lift if Web had a suitable grind. I will be working on getting some billet cams made this year with CNC ground profiles. That way I can get made what the engines actually need instead of using what is available from a list of masters.

This engine is very stout, especially the torque curve. Torque is what gets the car moving when you step on the gas.

I have not done any work on the 4V heads yet. Porting is not very good on those either but I think I can get them to work a lot better. The 4 liter will get a pair of reworked 4 valve heads when I get around to working on that project. Too many blocks to sleeve and not enough time!

Steve

 

If I am reading this correctly, you pulled 163 CFM with 28" WC @ .350" lift?

163 multiplied X .598 would convert to 97 CFM with 10" WC ??

 

That's correct. Note that the conversion factor will be close but not exact. The only way to get actual flow data at 10" would be to flow the head at 10".

Photo attached showing wooden radius plate glued on the intake face of the head for flow testing.

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Many thanks!!
I have posted my 4v flow numbers before, and although not with me now, I seem to remember the stock QV head reached max flow at around .350 in the low - mid 90s cfm at 10", or similar to your ported 2 valve flows - which makes them all the more remarkable to me. After porting and larger intake valves, with the manifolds and 44mm Webers in place, the whole kit n' kaboodle flowed about 107 - 108 CFM or so at 10" and 360 lift, approximating 180.6 at 28" at .360 lift. I could have gotton perhaps a little more with itb, but I think the head was again becoming the limiting factor and simple was a factor. These 4v stock numbers are also corroborated by similar numbers off of Kermits original flow bench studies on the QV head back in the archives.

Laurie at WEBCam had a test qv head, and determined as lifts exceeded about .360, the cam did not squarely engage the shim follower, which could lead to premature wear and shim flipping. I decided not to go with shim-under on mine, so was limited to the .360 lift for my requirement of a long term durable motor. I also kept near stock durations (although now I wish I had gone up to 235 or so) to maintain a good umph factor. Just a few numbers to compare

Many thanks to Steve and Carobu for setting the standard on these motors and giving us solid examples to compare to.

 

Steve, on that 3.5 motor, those little ports coming off the TB spacers - are they for the MAP sensor or IAC (idle air control)????

 

yes, the one steve posted on this thread. air tubes? for what - IAC?? or MAP...or...

 

Thanks as always for sharing Steve.

So is anyone in on a "group buy" on CNC porting?

Cheers

 

I have a pair of stock 2V carb manifolds here. These are off Mark Lewis 308 as I recall which is a US model, not Euro. I'm not sure of the year but I can find out. Same vacuum tubes on these as on Nick's 3.5. We ran a line to the map sensor off these tubes. The lexan spacers have no vacuum ports in them. The lexan spacers have 2 40 mm bores to match the throttle bores and I also machined a tapered slot for the fuel injector spray pattern.

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thanks Steve, I am rethinking on how i pulled MAP on my 308 twm conversion - currently i only am pulling MAP from 2 bores and not a clean signal, this gives me an idea on how to pull MAP from all 8 cylinders to get a cleaner signal....

 

How is the project going? Updates?