Rolling road dyno, worth doing?

Francis, are you sure about that figure? Given the standard 15% deduction for powertrain loss, that means your car was making c. 280hp at the flywheel.....seems like a lot for an engine that's had nothing more done to it than a compression bump. Was there maybe some head work, different cams, etc. involved as well?
- Dave

 

Could also just be Dyno differences. We would constantly get comments from customers saying something like, "your dyno shows 400 HP but the shop that built the engine showed 420HP!" The type of dyno, the settings for the dyno (which can be "adjusted" to produce the results you WANT to produce!), and the atmospheric conditions on any given day can change the engine's HP readings. Inertial dynos produce different results than "real" dynos.

A rant follows:
A chassis dyno can produce different figures depending on the gearing/gear selected for the run, the weather, and the settings on the dyno. YES, if a shop wanted to sell you something, they could do the dyno run/produce a chart, tell you that if you add their "whatever" upgrade you will get more power and, even if no additional power is produced, a change in the dyno settings could produce a chart that shows it is! Chassis dyno info is only "accurate" if viewed as a relative thing and only when the SAME dyno/same settings is used. IOW, if the same dyno (same settings) shows 300 HP before and 350HP after, it's reasonable to say there is around 50 more HP. But it is NOT ACCURATE to say that the engine is producing 350HP because chassis dynos base their output on a series of settings/assumptions, including things like drivetrain loss. That loss varies based on the drivetrain configuration and the losses also change in different gears. Engine dynos are the way to go but, of course, most people are not going to pull an engine to do a dyno run!! Engine dynos are usually found in dedicated engine-building shops.

IOW, the only way a chassis dyno is really useful in a one-time test is if several of the same car models are tested that day. If two 328's for example, are tested in succession on the same dyno and one shows 237HP and the other 225, I'd say that the first one IS producing about 12 more HP. If the same two cars had been tested in two different cities with the same HP results I wouldn't be comfortable using the figures to compare the cars.

 

This.

Since the OP is based in the UK, if you really want to understand what the thing is for then take it to the Alps.

Everything will make a lot more sense from the ride & suspension to the gear ratios - and indeed, there is enough power too.

 

I have two separate readouts over a couple of years on different rolling roads showing similar figures. Happy to send them to you privately. Head and cams are factory original. Just high compression pistons.

 

Great responses guy's. Yes, i forget my mini had about 100hp it would really shift but the thing that made it fun was sitting very close to the ground, manual steering, the car fit like glove and had essentially very little mass so could change direction as fast as i could think on a clear day. These are the basic characteristics of the 3x8 so i know i will be thrilled when i finally get to take it on some twisty back roads.

I have actually been on the phone with the guys servicing the car today and they are a day away from completing the reshimming of the valves, great guy called stewart owns the place who has a F355 Challenge he races, also it turns out they have a dyno right there. Trying to arrange a day this or next week to pick up the car and hopefully can schedule it to watch the car on the dyno, if it works out i will definitely get some footage and post some numbers here for anyone interested. He also mentioned some kind of part that can be fitted to give the ability to map the CIS system at least partially, this could be a way to make gains if inlet is changed such as throttle bodies or even just high flowing filters. Seems they really know their stuff which gives peace of mind when it comes to the work they are doing and if in the future i want to go down that road of tuning they have a history with the car.

 

There is a company.......here:

https://dkubus.com/?product=frankencis-dpr-controller-module

That has a setup that makes CIS programable through the WUR. This leaves the mechanical mass flow sensor in place (along with its flow restrictions) but in theory this would let you correct a buggered massflow signal caused by new cams to get the right mixture. I have never spoken to anyone who's used this setup so I don't know how well it works

If you change the intake to ITBs you would just remove the CIS and put it on a shelf. That will gain you about 20hp....and them you can add cams for another 20-30hp. This would be a $10k adventure and is reversible if that matters.

 

Amazing, is there anything you don't know? Just realized your the mad scientist reinventing the 308 into a v12 masterpiece, completely INSANE, i love it! I will let you know when i talk to stewart in person what advantages he thinks this could bring. I like the 10k figure and the ability to return to stock but realistically i think if going there it would be permenant as this car will never be sold. That settles it for me, i will enjoy the car for a year or so, learn her ways and find her limits.

Since all the chassis mods, suspension, wheels, tyres and brakes handled the only area i would like to bring upto date is the power but not by much, a 50hp gain would be perfect, ITB's and cams sound (literally) like the type of power increase i would like, more intake bark, faster throttle response and a vtec urge when it comes on cam. You see i'm a bit of a 2 stroke nut, had a '84 RZ350 YPVS Kenny Roberts Ed. producing about 45hp from factory, it was making 75hp when i finished it and made an already quick bike into a weapon, wheelies took nothing but hitting the powerband and up she goes, Toomey pipes made it sound like the proverbial Banshee people call that engine, and if i had not sold it i would not be writing this. So that's where i got my kicks but getting older now and value my life a little more.

 

A dyno is no harder on the car than driving on the road as long as you are not changing anything! Hell...every time I drive my 308 it hits the redline many times!

Now, if you are doing any crazy tuning on it...things can happen! I have spent hundreds of hours on a DynoJet 248 tuning my old diesel drag truck. It eventually made 1800 hp and was fairly reliable. But I blew up a couple of motors on the dyno and several on the track before I got there!

some videos of it doing 900-1000 hp on the dyno

https://www.facebook.com/video.php?v=207976632561806

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https://www.facebook.com/video.php?v=2542518892379

 

Hilarious, the Ferrari owner also tunes diesel trucks now i have seen it all! Yes it seems the guys doing the work are used to these cars so i put all responsibility on them lol Joking aside i think it will be safe to push her a bit and if she breaks it will be a good excuse to rebuild and improve as it sounds like you have done with your....Truck.

 

Absolutely not necessary…was just confirming the number wasn’t fat-fingered or an artifact of “The older I get, the better I was Syndrome”.
Congrats on getting a great outcome from your piston swap.
- Dave

 

There was a race kit that was hi-comp pistons, bigger cams (P6) and I'm not sure what else that would bump the stock 240crank to around 280-290 crank or 230-240 at the wheel. But if the cams in that thing are stock 237 is an amazing result.

 

*IF* you can find an inlet manifold!

(Not everyone can just reach for the TIG! )

 

Hm, Maybe not the best example butt, my son has a brand new e Audi GT over 500 horses, 0 to 100 in about 3 sec.......................he still prefers my ( standard) 328

 

I rode a RZ350 once. I guy I worked with had it, I milled the head for him then he had pipes (toomey rings a bell but ??) a d few other goodies. fun bike. With naturally aspirated 4 stroke that is built properly you should never get that "power band" feel....a sudden jump in the hp/tq means something is mismatched or out of tune. With carbs that was pretty common at cross-over points in the jetting, guys would spend days on the dyno sorting that out but EFI makes that a problem of the past. On my car the you feel the torque just build as the revs climb and then flatten around 7k but it doesn't drop a lot until aft 9k so 7k-9k is the "power band" but it happy everywhere, no bogging or hesitation and drives just fine at 1500.

IMO that is how a street car should be and you should have no problem getting a similar result...use a cam in the 240-250deg @ 0.05" lift range and you'll be fine (stock is 220 or 222?). ITB size - over size is better than under size generally....its not a think like carb size where bigger=more hp but less low end because EFI fixes all that. The stock 308 40mm carbs are a big flow restriction.....you want 45 or 48 TBs I think. Most of the internet info is BS so the easiest way to know what is right is look at motorcycles with similar hp/cylinder and do what they do. A GSXR-750 is about 150hp or 38/cyl and almost exactly where you should be...they use 46mm TBs google says and you know they tested everything so 46 is correct so 45-48 is what you want.

The challenge with BIG ITBs is coming off idle smoothly because a very small throttle movement means quite a large % change in air flow so getting the pedal to ITBs linkage ration right is pretty important, I use DBW so it simple to adjust in the ECu but mechanical linkage also works just fine once it setup right. The 2nd challenge is mixture control because most people with ITBs use alpha-n (TPS based) load sense and that struggles a big with very small changes in the TPS signal but most people make it it. I use speed-density (MAP based) load sense but with a special MAP sensor that reads all the cylinders separately which works very well.....and I through in a little spark timing retard to make idle more stable and then gently advance as the throttle is opened so huge 54mm TBs and it pulls away from a stop as smooth as my daily driver....as long as I don't try to actually open the throttle until the car is point straight, then it reminds you pretty quick that its 800 hp.

When the cams are out so all the intake valves closed the shop might be able to stuff the ports with paper towel and open up the flange to use a 348 intake gasket then match the new ITB manifold to that. All the older ferrari ports had an hourglass shape that is smallest at the flange and opening that up adds 2-5% more flow...not a lot but not nothing either.

 

that is an issue but I know a guy if he needs help

I guess today most places will 3D print a mold and have it cast. I work pretty quick with the TIG so about $2k is where I'd be to knock something out but print and cast might be cheaper...I've not ever tried that path but I probably should.

 

@mk e Just great info, i know its not to everyones taste to modify classics particularly Ferrari's but for those that are curious these forum posts are pure gold. Talk is cheap but real world experience...Priceless.

 

"i know its not to everyones taste to modify classics"

It's funny how, back in the day, most guys who bought Ford/Chevy/Mopar muscle cars modified them almost immediately. Most commonly carbs/intake manifolds/headers. In 2025 people want their old muscle car to be original; back in the day nobody did!

People are strange...

 

The thing with muscle cars is the nostalgia never lives up to the experience, after modern cars they are shockingly vague to drive, huge barges that go faster than they can turn or stop, a few tasteful mods to brakes, suspension help but even then they are better to look at in general.

I drove a 70's ford pinto once when i was in the states, i had driven capri's, cortina's, escorts, marina's, mini's, even ford anglia's in the UK priorly and i can tell you that pinto was the worst POS i ever got behind the wheel of. I also drove a 70's CJ jeep for 5 mins and was very glad to hand the keys back. Addmitedly these are not muscle cars but the same sloppiness applies just with more power, so different to the europeans, Citroen excluded for reasons.

 

I read 45-65 year old men buy what they couldn't afford in High School so 20-40 year after a car was made is kind of the sweet spot for value but also its a completely different set of buys than the ones buying the cars new. That probably has a lot to do with stock vs modified over the years.

This is likely blasphemous but when I got my QV I loved the noises and vibrations it make but it handled like pig. There, I said it. It just plowed into the turns....not muscled car bad by any stretch but my 1st trip to the autocross was embarrassing and the car was only16 years old at that point. The suspension is tuned to feel sportier than the average sedan but comfortable on the highway....its a GT car for older men which are exactly the people who bought them new so ferrari knew what they were doing as did Detroit. Muscle cars are mostly a car you could justify as a family car but still go light to light if you please or the strip on the weekend. And that's all fine......but there is no such thing as a production car that drives like a racecar so some of us just can't help but "fix" them so they do. 308s are too expensive now though...shopping today I'd probably grab a 360...and stuff in a modified 456/550 engine

 

Exactly, i knew when i bought this car from watching a few autocross videos on youtube that the handling was of the GT compromise, Not something that when pushed excels at anything in particular, but at 7 tenths a perfect little sports car for the masses or at least the privilaged few. This is why i updated the suspension first, it is the obvious week spot only because tech has really moved on with the invention of electronically controlled dampers, the fact you can fit these systems to a 1986 car is a game changer. The "having your cake and eating to" scenario, combine this with modern tyre tech and better brake fluids and pads and you have a recipie for what gear heads are longing for, light weight, analog controls and customizable handling to suit the occassion. I'm so excited to taste this cake when it's done!

 

The 308 (and I assume the 328) responds very well to changes you mansion. This video is nearly 20 years old so supercharged V8 not V12 and what i would call fast street suspension tuning but I did win my class that day and the fact that wathcing it it looks slow is a testament to how well it changes direction, completely drama free, all the front end plowing gone.


I was hoping to get back out this year to really test what i would call autoX/mild track tuned suspension but it was not to be...next year. On the street though it was noticeably improved as far as responsiveness and stability so I have hopes for it out on the autox course.

@FastandSlow - Where did you end up spring rate wise?