I had a little bit of Tuesday madness today so I decided to get the car on the dyno. I did not do any tuning on the dyno and I am very pleased with the preliminary results. 253bhp with 216lbs torque, and it's a wonderful flat torque curve. Some yahoos said I could not get a perfectly flat torque curve with these wild cams This is somewhere north of 300bhp at the flywheel. Anyway, the engine runs too lean above 5k rpm running between 14.1:1 and 14:1 which is where peak power is starting to come in so I'm definitely missing a solid 10bhp+ from that alone. These dyno runs were also done with a conservative amount of ignition timing. I did not want to push the timing too much with it running lean like this. I'll dial back the air corrector jets to richen things up a bit up north, dial in some more timing, and then really make some power. I know it's on the table which is all that matters now. The dyno a/f ratio meter could not read off my exhaust correctly for some reason so I just datalogged the results on my meter. I have no doubt once I iron out the a/f ratio and dial in a bit more timing I will see something north of 270bhp at the wheels. Regardless, I am very pleased with the results as even in its current tune this is better power than a stock 348, 3.2L Acura NSX, and a stock Porsche 930 turbo. Well worth the build. Oh and I had the thing weighed on corner scales while I was there. Had about a third tank and it weighed just under 2800lbs. Light and fast. As a side note, the 3.4L NSX there was in for a destroyed gearbox. It makes 247bhp at the wheels. Not nearly as pretty as the Pininfarina lines Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
You can see on the graph where it gets lean. The line gets a bit nervous especially over 6k. There's good power to be had I'm just excited that I get to tell the Porsche 911 guys who build 3.4 and 3.5L engines what she did They always make awesome power.
If I recall you're running carbs still right? you're scary lean at 5k and up, do you happen to have a knock sensor in place just in case? there is lots more power to be had here, the problem is the throttle blade dia on the stock webers, and the lack of fuel. I'd suggest an O2 sensor and display, I like innovatives stuff http://www.innovatemotorsports.com/products.php that way you'll be able to log and record runs as you tune the carbs. from memory the best AFR to Tq on the dyno was around 11.8~12.2 from 4k to redline. with 14:1 it's got to feel like a slug compared to where it should be.
Oh yeah, it's lean but it's not 'scary' lean IMO, then again perhaps my definition is way different. Yes, it needs to be much richer north of 5k though, lots of power there. I have an innovate LM1, but I rarely have the opportunity to wring it out in 4th gear simulating a dyno run, obviously for legality reasons lol. Yes, still on 40dcnf carbs but with 34mm chokes. Lots of jet changes to far :/
Are you still running a stock flywheel or did you go with a lighter aluminum one? If lighter, how noticable is the difference?
Hi Mark, It sounds like John's engine is up on torque and very flat at that, so he shouldn't have any worries about ging lighter. I have taken the stock 308 wheel from roughly 16 pounds to about 8, but still retain the stock, (heavy) pressure plate. There is a noticeable improvement in engine liveliness and i have no worries about going this far. For perspective, i have lightened the wheel and gone to an aluminum pressure plate on a 4 cyl 914 hotrod/autoxer and been ok with street use. Lightened the wheel on my work truck, 95 2.4 4 cyl, (pumped) and stalled it almost daily, but the massive improvement in engie responsiveness is again very worth it. If you are not into driving, responsiveness or aceleration, then lightening the wheel is only going to be an agrivation - otherwise, go for it. I had a local motorcycly machinist, rejoicing in the name, "Storym Winter" do my wheel for about $400 and no balancing work was required subsequent to lightening, ( he had a very nice computer controlled mill). Happy to chat about it, chris Image Unavailable, Please Login
That's a good chunk of weight there. Once I have this apart again for a clutch or something I'll look into it. As for now, I'm going to drive. I've wasted enough time 'under' this thing haha
Hey Chris! Thanks for the input. I just ordered a light weight flywheel from Carobu. They claim that it is 10 - 12 pounds lighter than the original. With the 3.5 liter conversion that they are doing, I think the engine will rev pretty quick. Bert has a great dyno that he uses to break in the engine. I may ask him to do a run with the stock flywheel and then one with the light weight wheel to compare the difference. I'm curious to see if there is much more torque/hp. I'm hoping to have the car back in early sept. It is hard to think of anything else these days.
Hi Mark, I wouldn't expect any increase in torque or hp with a lighter wheel, BUT what you will notice immediately,is that the engine spoolls up more quickly because it isn't having to expend effort accelerating the mass of the wheel. This is immediately felt as a more lively engine, one more eager to rev and quicker to decelerate when you take your foot off of it. What you will get is a more responsive engine, not one with bigger numbers. You will however be the first one to end of the straight, (all else the same escept for the mass of the wheel). I am envious of your getting a 3.5, sounds like a very very nice upgrade. Shiny side up, chris
Thanks Chris. I already got a couple of local F-chatters lined up to take it for a spin. They may follow suit if they like the results. Come out to CO for a ski trip or something and I'll let you check it out (weather permitting).
Great news John, Paul messaged me right away about it. How many miles before you decided to dyno? I have just passed 1450 miles since the 3.4L rebuild and the engine seems to be really tightening up in a good way. I am still interested in seeing if the titanium crank+rods makes much of a difference once we are both dialed in. Keep us in the loop as you tune up, sounds like you still have a modest amount of upside left. With that in mind, how much do you think you can squeeze out still? Brett
I'm at a bit over 1000 miles on this engine now. I'll get 270bhp at the wheels, easy. Maybe more. For example: when I first obtained my 308, I immediately wanted to dial it in because I knew it had never been done before. The very first dyno run I did was 180bhp at the wheels, not bad, that's a healthy 308 figure. The engine was running right around the 14:1 a/f mark where peak power was made, and that's just not acceptable, not at all. However, I did have the ignition and timing sorted well. So, I spent some time rejetting and came up with 199.7bhp at the wheels, and that was with a 12.8:1 a/f ratio if I remember right. So, all I did was richen it up a bit an I made 20bhp at the wheels. By richening the mix, I could also add a degree or two of timing. I suspect I have at least the same amount hiding in this 3.4L engine. Remember, all the data flow data and engine data that was charted for this engine said it would be good for right around 330bhp. I'd say we are about 20bhp off that mark, but it's not at all unreasonable to get there.
Has the torque gone up proportionally with the hp? What do you think the final torque values will be?
Torque will probably not increase as much as bhp as I'm seeing the a/f mix at peak torque figure is just about right. I'll get it over 220lbs, definitely. What's interesting to note is that my Lemans spec engine with P6 cams petered out at right around 6850rpm. I believe this is a testament to all the head work I did as the power clearly wants to continue beyond 7k, but the mix is not allowing it at the moment. We'll get there
It's not stupid fast, but it's without a doubt quick and the smile on my face is directly proportionate to how buried my right foot is on the throttle. Every bit as quick as a 996 or NSX or the like.
