What should I do with my diff?

[hybrid]

I guess Woody knows what he's doing, but 180cc heads seem pretty small for a 363. Will definitely be streetable though.

[Shaunp]

Hybrid the Trans-am engines run well over 500 hp with max inlet port of 200cc. The rules say 190cc and allow an increase to 200cc as a result of port matching and bowl blending. The scrutineer measures it as well before they seal the engines. He will be building it for torque not HP.

[xpconnor]

Hybrid the Trans-am engines run well over 500 hp with max inlet port of 200cc. The rules say 190cc and allow an increase to 200cc as a result of port matching and bowl blending. The scrutineer measures it as well before they seal the engines. He will be building it for torque not HP.

Thanks for the replies guys. Shaun you are right I said to him I want heaps of torque and if it's all over by 5000rpm I am not worried. How often do you rev street engines past that point anyway and even if I do it will still hall arse.
From your explanation if they do a bit of work on the head would it flow more like a 190 then a 180 anyway?

[Shaunp]

I suspect they will just match the manifold to the heads wouldn't increase it too much.
Tim everyone gets carried away with cams, carbs and heads, most blokes have way more then they need. You told him 5k rpm is what you want, so there is no point lifting the power band much past that with bigger cams heads and carbs, they pull the 351 T/As up around 7k with 200cc heads, 2k more then you will. Port size is a big factor in fuel usage as well, due to gas velocity, smaller the port the faster the gas flow is down low which will give the throttle response. He won't over build it to something you don't want, hence why he is putting a 650 DP not a 750, he is trying to give you max torque and throttle response when you jump on it around town and cruising even at speed. 363 is a pretty big engine with a large 4-1/8" bore, 65's are a light car it will come off the line pretty quick. By the time it's doing 5k in second everyone will be way behind you. The larger 205 and bigger heads are really most suited to 393/408 engines in my opinion.

I could have put 185 heads, as many do on my little stock stroke engine, but I put 165cc on it, same as the cam, I put a cam in that is all over by 5800, that's plenty. I had wild over cammed engines when I was younger and sillier, now I want a good enough idle so it won't stall when the AC cuts in, if I want it faster I'll build a bigger cube engine, Hmm like a 363.

The interweb tells you need the biggest of everything, it's not true.

[boofhead]

The key is matching up the Cam, Heads, Gear and (if using one the) stall converter into a package that matches your intended usage pattern.

From the details of your plan then it all matches as far as I can see - well done. It will be a nice set up which you will enjoy for many years.

[boofhead]

BTW: Just because you are limiting the rev range (in this case through limited head flow) does not mean it will have more torque than an engine like the Trans Am engines. They are the same capacity so it will have less - mathematically it must have lower peek torque - all though peek torque will be less it will be lower in the rev range. So secondly you may have more torque at your peek than the Trans Am engine at the same rev point but not overall more torque when comparing peek values. Every single engine has a mathematical relationship between HP and Torque where HP and Torque must be the same at 5200 RPM - no getting around it. Look at any dyno graph and this must hold otherwise it is BS. Also, HP is related to RPM so simply more RPM equals more HP for the same capacity engine (assuming equal tune etc). We obviously compensate by adding capacity hence the larger engine is a way to get more HP though RPM limit sets it ability to produce HP/Torque. So you can get lots of power from a 302 no problem just need to rev it (so you need to build it [engine and running gear] for the intended high RPM).

[Shaunp]

Yes a "correctly" put together engine package is built to do it's best work in the rev range it will spend most of it's time in, in this case off idle to 5k not 3k-7k. There is no point building a Trans-am engine for a cruiser although a lot try to do that, sounds great, is a good talking point but not nice to use.

In this case the rev range is limited probably by the cam & carb in the first instance, the heads won't stop it from revving to 6 or a bit more, a 351 will do that with stock heads with the right cam, but they will building torque low in this engine, I suspect the cam will play a big role in this.

Ultimately it would make more power and torque with bigger heads cam and carb but higher up in the revs, then requiring a lower diff and bigger stall, its a trade off on driveability and fuel usage.

Engines are bit of a pissing competition if we get caught up in big numbers on the dyno particularly a big HP numbers the car becomes worse to drive.
This car will drive like pussy cat, but is large enough to jump out of a hole when asked, you'll have no issue dusting new V8 Holden's off the lights if you get traction.

[hybrid]

Yeah if he's been told that 5k is all it needs, the 180s will do the job fine.
My cam is my limiting factor right now, but it sounds OK and drives nice, so it can stay as it is.

[xpconnor]

Good to read that you guys all agree with the plan.

Like most car guys of course I would love to be able to tell the bloke next to me that my car is running over 500hp and bla bla bla but then i get in it and it drives like a pig around the street..... not much point in that. I currently have an R33 and they have a brilliant engine but in reality the fun only starts above 3000rpm. From driving that around for a few years now I know that for a cruiser I definitely want more bottom end power.

Most importantly the boss wants to be able to drive this car as well so it needs to be something she can get in and feel comfortable with.

[hybrid]

Just tell them you have 500HP anyway if you want, who cares

Mine has 289 badges on it... nobody knows any different.

[xpconnor]

Just tell them you have 500HP anyway if you want, who cares

Mine has 289 badges on it... nobody knows any different.

Mine will have 289 badges also and hopefully other then some alloy heads and a different manifold most of the population will just look under the bonnet and think it is fairly standard.

[Shaunp]

No reason you couldn't paint the heads black as well if you wanted to.

[xpconnor]

No reason you couldn't paint the heads black as well if you wanted to.

I think I will leave them bare to start with, as it is a bit of a shame to paint the nice alloy look, but if I decide I don't like it I will just paint them myself before the engine goes in the car.

[boofhead]

I am with Hybrid - tell them its 500 HP if you want to - they are mostly spewing BS as well.

I had a R33 many years ago - did the engine up and had lots of grunt - nice car good memories.

Most people will have no idea what they are looking at. A bit of bling looks nice in the engine bay - it will cost you so I agree let it shine a little.

At the end of the day, you will have a big engine in a light car - it will go very well and cruise around like a pussy cat. Purrrrfectttt..

[Stallion67]

Sounds like the old argument between power and "useful" power