HP TUNING: where to start?

[maytag]

Okay... now that I'm about to pass my smog test (cross yer fingers, but I ain't worried) next thing is to go looking for some more zoot.

I'll look to the easy stuff (for me) first.
My car is a '76, with the 1800. largely stock, as far as I know.

What do y'all recommend? What do these motors respond well to? I've been building my own exhausts on motorcycles for years, so I ain't askeered to do this one. But how does this motor respond to freeing that up?

I know there are others on here who've done the bench testing, and can save me some learning curve. I'll be happy to share what I learn as well, as I go.

Do I want to do some port work on the head? maybe just unshrouding valves, matching the ports, etc etc? Polished runners?

Is there a head-swap that is the real ticket? I've seen some cams on IAP's site. What are they REALLY worth?

What kind of radical stuff have y'all done?

[So Cal Mark]

all of the hp in a twin cam is in increased breathing.

[narfire]

How much loot do you want to lighten the wallet by?
You'll notice a difference with headers and a bit bigger carb/single plane manifold. Bolt on improvements.
Do you have emission testing there?
If your gonna yank the engine... well were do you start more important where do you stop
Take a look at Halg's thred.. he put a supercharger on his,some kick-ass engine there.

[maytag]

all of the hp in a twin cam is in increased breathing.

on the front end first? Or letting it breathe with exhaust improv first?

I'm good at the fabrication end... less good on the tuning / sizing end. Yes, we do emissions testing here.... but I'm confident I can "squeak" by with the folks I know, more than with the specific compliances.

I'm good at building headers; any suggestion on a primary tube diameter / length? 4-2-2 w/ a crossover? or is a 4-2-1 better for scavenging with the Fiat firing pattern?

Intakes: I've been toying with some individual FCR's (flat-slides) or something like that. How many CFM does this motor like to see, total? And what is the realistic rev-range on the bottom end? With cams? Balanced?

I'd kinda like to stay normally aspirated, 'cuz it feels more "authentic" to me.... even if that makes no sense, it's a visceral thing for me. So turbos and superchargers are not on my list right now. But I'm definitely up for some head-work, as well as some exhaust & intake work. "Looks / sounds cool" is just as important to me as "works-well".

[manoa matt]

The 76 is a good starting platform, a 2L would be better.

The 76 already has the single plane intake manifold, the stock 32 ADFA is a pretty good carb, but you might want to upgrade to a 34ADF or a 32/36 DFEV for a boost. The 32/36DFEV will require a spacer between the carb and manifold, IAP has them. A free flow air cleaner will help it breathe and will make it sound great.

The 76 has a 4-1 exhaust manifold that is a bit restrictive. Idealy you will want to switch to a 4-2-1 exhaust. With cylinders 1 and 4 joining, and cylinders 2 and 3 joining. Keep your primary pipes aroun 24" and the secondary pipes around 10" A 1 5/8" or 1 3/4" primary pipe diameter will work for the headres, when the secondarys join try to get a 2.25" or 2.5" pipe all the way back to a free flowing muffler. You may have to temporarly plumb a catylitic converter into the system to pass emissions testing.

Removing the emissions air pump, injection rail, EGR system, and block off some carb emissions ports will give you a few extra HP. It wouldn't be too hard to remove and reinstall all the emissions stuff when you go to take the test.

Porting and polishing will help some, Don't go any smoother than 80 grit on the intake runners. Polising to a mirror finish can actually hurt flow.

The stock compression is around 8.1:1, if you had a 2L block and a 1.8L head you could bump the compression up to 8.6:1. With a stock 1.8L block and head, the only way to increse compression is to add high compression pistons. Some longer durration cams will also help increase compression, but not much.

You have to watch it with performance cams. Some manufacturers use stock cast iron cams and re-grind them. Usually the base circle is smaller which means you need thicker valve adjusting shims, valve lash caps, or cut the valve seat so the valve sits deeper in the head. The best cams will be machined from billet steel.

"Intakes: I've been toying with some individual FCR's (flat-slides)" Are you talking about motorcycle carbs? Something like 4 Mikuni's side by side? I saw a manifold and carb setup like that about two years ago on ebay, so I know its been done before. I don't think it would be worth it. Jetting and tuning would be a nightmare. If you want individual throttle bodies, the standard setup for Fiats is dual 40mm IDF's

[maytag]

The 76 has a 4-1 exhaust manifold that is a bit restrictive. Idealy you will want to switch to a 4-2-1 exhaust. With cylinders 1 and 4 joining, and cylinders 2 and 3 joining. Keep your primary pipes aroun 24" and the secondary pipes around 10" A 1 5/8" or 1 3/4" primary pipe diameter will work for the headres, when the secondarys join try to get a 2.25" or 2.5" pipe all the way back to a free flowing muffler. You may have to temporarly plumb a catylitic converter into the system to pass emissions testing.

Exactly the sort of info I was looking for!! Thanks!

Porting and polishing will help some, Don't go any smoother than 80 grit on the intake runners. Polising to a mirror finish can actually hurt flow.

Agreed. On long runners, we used to mirror-polish 'em, and then drill little 'divots' in the end, to create enough turbulence to re-atomize properly, but these are clearly not long enough for that.

You have to watch it with performance cams.... The best cams will be machined from billet steel.

Do you have any first-hand experience on specific grinds? Or even various manufacturers?

Are you talking about motorcycle carbs? Something like 4 Mikuni's side by side? I saw a manifold and carb setup like that about two years ago on ebay, so I know its been done before. I don't think it would be worth it. Jetting and tuning would be a nightmare. If you want individual throttle bodies, the standard setup for Fiats is dual 40mm IDF's

Yes, I was actually thinking about some FCR's sitting on my shelf. I can't see any reason it'd be harder to tune / jet than a motorcycle motor, can you? I mean, the operating RPM range is significantly smaller (effectively HALF) what a 4-cyl motorcycle is.... and I never had a problem getting those right. ?!?!? But I'm still new on this side.
I've SEEN the dual IDF setup. Looks nice. Very expensive. Not terribly "unique"... as it gives me that feeling of "Hey! Look what I just spent $2000 on!" instead of "check-out how cool this is!"

I dunno.

But this is ALL excatly the sort of info I was looking for.
Have you messed with lightened flywheels? What's your take?

[Kevin1]

The idea of adapting 4 individual Mikuni CV carbs has always been a temptation, these carbs have alway been pretty easy to tune on bikes I've had, and they perform extremely well. Another idea is going with fuel injection and four individual throttle bodies if you are looking for something different. I haven't tackled either of these personally, though it seems like both are workable upgrades that are a little more "individual" than going with twin Webers. Then again, the twin Webers have a long history of success!
Regardless of carb or FI, I would start with porting and polishing the head, doing a good 3 angle grind on the seats, and match the manifold to the ported head. Jon Logan carries a great dvd from Guy Croft on Head prep for our cars. Beyond that, you can look into cams, headers, and exhausts that will allow better flow in and out. There are some stock options for the exhaust manifold/headers that flow better than what's on there, or go whole hog and contact SoCal Mark about his manifold. Whatever you do, it has to be all done together to achieve the greatest benefit. An while you are at it, I would add adjustable cam pulleys so the cams can be degreed accurately.


I think I just talked myself into the beginning of my next winter project - anyone have a spare 1800 head?

[manoa matt]

"Do you have any first-hand experience on specific grinds? Or even various manufacturers?"

The only first hand experience I have, is with the cams I have (Alquati billet steel cams, they are NLA new) As far as re-ground cast iron cams, the jury is still out. Some people swear by them, while others swear against them. You be the judge

If you want something unique like motorcycle carbs then it will be just that "Unique" Don't expect anyone to know what a ball park jetting will be or how to tune them, You'll have to figure that out for yourself. The main problem I forsee with those carbs is the manifold. You need intake runners of a tuned length to take full advantage of the carbs. Mounting them too close to the head will result in poor atomization and overall poor performance. A second possible problem is the range of jets available for those carbs.

The advantage of Weber IDF's is that many guys and gals have been down that road before and if you post a symptom or problem, chances are someone will know exactly what is wrong and how to fix it.

If you search in the "custom" section you will find a post on individual throttle bodies, very interesting, but also a lot of work was put into that. The maker had to figure some things out on his own, which took a while.

Kevin, I have a spare 1800 head. I need to bead blast it and crack test it first before offering it up, but let me know if you are interested. matt.scarton@gmail.com