308 carb airbox restriction discovered

What I was trying to express was that the engine "falls off" at 7,000 RPM with the airbox mods due to lack of fuel more than lack of cam, highlighting the difference in A/F ratios between the two set ups.

Before the mods it would rev past 7k more readily than it does now.

 

I am guessing your power band will start at 6,000 RPM. Your redline will probably limited by your fuel delivery system and the amount of courage you have to keep your foot planted firmly on the floor.

 

Russ,

I PM'd you regarding the filters. Did you get it?

Thanks

Henry

 

Any one have a stock air box. I gutted mine and don't like the intake noise and want to go back to stock. Thanks

 

Is yours in good shape? I was planning on performing the 'procedure' on mine soon, but perhaps I could try yours, and assuming I like the sound I can just send you mine for a swap.

 

I think that removing the "insulation" would help with the flow, but what about the oval inlet? DJ did his modifications on a '76 airbox and opened up the "snorkel". This would be the way to go. Do you guys think that the insulation portion is still the most restrictive part of the airbox? I was just thinking that the "necking down" of the snorkel (along with the flap) could also be kind of restrictive. Would removing the insulation be worth it if the snorkel wasn't modified?

Henry

 

Henry,
Take another look at the first couple of pictures I posted of my stock airbox. There is an external shot of the very end of the snorkle and a subsequent shot looking into the end of the snorkle inlet. In that shot you can see an even smaller oval inlet inside that is comprised of the perforated metal and fiberglass.

In my opinion removing the perf metal and insulation will make a huge improvement. The only reason I customized the other box was to save my stock box. The mods were basically to extend the short 1976 snorkle out to the same dimensions as my original box. I smoothed things inside and out for flow and looks. I did open up the diameter of the inlet somewhat but I still use the stock bellows.

You should net nearly the same performance gains.

 

Well, I pulled my airbox off yesterday to get to the water pump and I can say that #24155 did not have the obstruction that is the topic of this thread. Dang, I was a bit disappointed as y'all had me looking forward to a cheap & easy 5% increase in horses.

Those short stacks still look intriguing though.

 

my euro spec 308, #24081, does not have any insulation material in the airbox either, so much for keeping things quiet in switzerland

 

Paul
Look at the Carobu site or talk with Tate. THey've posted dyno runs with a variety of different configurations, including something I believe is close(-ish) to your set up.
Philip

 

Russ
Stop messing around. Here's what you need. Steve tells me the sound is extraordinary.

Steve, hope you don't mind me posting the pic.
Philip
Image Unavailable, Please Login

 

So if we go under the consensus that the early U.S. 308's ('75-'77) were supposed to have 240 HP and the Euros for those years were supposed to have 255, and the difference is 15 HP, then...

we can conclude that at least 5-10 HP of that was as a result of the intake on the U.S. airbox designed to reduce noise. Add the U.S. emissions stuff (thermoreactor muffler, air pump, leaner jetting etc.) and that makes the rest?

What I'm asking is...can we make the U.S. versions as powerful as their Euro counterparts with the right mods, or are the cams or something different too? (I know they are on the later carbed models, I'm talking early ones).

Birdman

 

5 bhp for the header - port alignment.
Maybe more if they have a 4:1 rather than triple Y.
DS worth 5?

 

Birdman,

I think you have most of it:
Airbox
Carb Jetting
No air pumps or thermal reactors/cats

To this i am guessing that we could add ignition timing, (I am guessing that the advance curve and initial timing are different).

I believe the intake cam might be retarded a bit relative to the usa cam timing, moving the power band up in both senses.

With the additional hp needed to do the oil scavenging, i don't see how a drysump could yield more power. For sure it is a better idea, but if the crank is not dragging through an oil bath, i don't see how more hp could be made with a ds.

couple of beers and i get a bit speculative - not necessarily smarter.

my .02
chris

p.s.
If we are able to optimize jetting with an air fuel meter, go with a less restrictive, (than euro) exhaust and perhaps be a bit more aggressive with the advance curve, add better igiition, (msd, ect). I don't see why we couldn't exceed euro hp numbers, particularly if we did a bit of port matching on the exhaust and intake.

Mas Tequila

chris

 

One thought on the HP speculating. On my engine, I found that my pistons stopped short at .055" inch below the top of the bore. When I spoke to Brian Nutter at Wiseco, he confirmed that that has been his experience in working with all 308 engines, including the QV. Using a stock piston and calcualting compression ratio with that piston at the top of its bore does yeild a ratio of 8.8:1, but with it down .055", the "actual" is far below that, more like 7.5:1. For example, my engine had the Borgo 7709 LM pistons for 9.7:1, yet in reality only came out to about 8.4:1. Only after removing the .055" did I yield 9.7.

I am of the opinion, for now at least, that the 255 HP quoted by Ferrari is for a spec blueprinted engine, and that unless you bring your "stock" motor up to spec you will never achieve that range of HP. In a conversation some years ago with someone at Norwood, but not James, they stated the DS being worth 15 - 20 HP, but as stated elsewhere I dont see how that is possible unless the crank is smacking oil in the WS motors. I do notice however, in looking through parts on the F of UK site, that the euro DS motor shows no windage tray. So perhaps with the high amount of oil flow, and the large amount available in the sump, the crank "can" draw oil up into itself due to high airflow turbulence? And its then possible that the windage tray is trying to prevent this? And that it is then possible that the DS totally allieviates that potential?

Sorry if I highjacked the thread in anyway from the aircleaner mod.

 

Paul, just about every manufacturer uses a hand built, carefully blueprinted and assembled motor for the testing. Most of the are Stats gained from an engine dyno, whjich does not use any motor driven accesories such as Alternator, water pump etc. This giives them great advert numbers, but that its the extent of the numerical comparison, as we use the accessory stuff on the cars in daily use. All part of sales slant ya know. when everyone else post figures based this way, it forces a manufacturere to follow suit.
Sales disclaimer: This post is based on prior knowledge, and experience on engine dyno's and does not in any way promote for sales any products, in any way shape or form.
Kermit

 

I cannot imagine that the cars destined for Europe were built with different pistons, compression ratio or better header/port alignment than the ones coming to the U.S.

Of course the engine can be fine-tuned to deliver more HP. I'm also quite sure that the HP figures, both Euro and U.S. were exaggerated and you probably wouldn't be able to measure those numbers on a dyno, especially with a 25 year old engine. But my question revolves around the actual differences between the Euro and U.S. engines.

For the early 308's ('75-'77) what were the differences? It seems that this airbox restriction is a "new" difference that nobody noticed (or said anything about) before--and makes a fairly substantial difference in HP. Assuming that the other known differences are related to emissions (thermoreactor/air pumps/jetting), is this it?

At this point, few cars still have a thermoreactor on them, which means they have something aftermarket that flows better and have been (hopefully) jetted properly for that exhaust. If you are not driving an air pump off a camshaft, and the restriction in the intake is removed...are you now effectively driving a Euro HP 308, (with wet sump) or am I missing something? Did the early 308s have different cams for Euro vs. U.S. spec like the later ones? Were there actual timing/advance curve differences that made a difference in HP?

My point is that the emissions stuff alone never seemed to be enough to make up the difference in HP between the U.S. and Euro specs, and this airbox restriction seems to be able to make up the difference. When Cavellino_Nero mentioned that his Euro 308 hasn't got the restriction, it got me thinking.

Birdman

 

Jonathan
The measured/dyno experience of a leading tuner (Casey) and several of us have observed the differences between US and Euro headers and the (awful) port matching on the US headers. Tate measured 5 BHP. This is pointed out earlier in this thread.

Second, the (intake) cam timing differences between Euro and US cars have been noted by several august sources, including Allen Bishop. This will help torque and top end.

Third, many Euros were dry sumped. I can't demonstrate the difference. However a race tech with 20+ years experience tell me this has some part to play. A DS motor will make more power than a WS on the road when the oil bath is not being shot around all over the place.

Fourth cam profiles. I have somewhere the specs for my 252 degree duration (IIRC) 1977 US spec 308 B cams (which are oiled and sitting in boxes in my basement). The chief tech at the F dealership measured them and I can dig the data out. I believe (but do not know for sure) they are the same as Euro cams. Anyone measured the euros?

Finally, I do believe (but do not have data to show that) the exhaust systems in the US are (or were) more restrictive than the euro counterparts.

Were the Euros head skimmed versus the US? Who knows. CR was slightly different on the euro/US QVs.
Philip

 

My 308gt4 UK model had the restriction in the airbox, also I think that engines were different to American ones. I know that my heads(porting) have been finished by hand possibly from the factory as I don't think it had been apart until I did it, we still used leaded petrol until mid 80's and had a higher octane rating. I took mine out about 9yrs ago after talking to a Race mechanic here in the UK. They used to remove it for their race cars. Does help to increase flow to carbs and a nice sound. Looking forward to Spasso dyno run with the shorter stacks on, will poss buy after results but need to see if low down torque will suffer much. Hopefully some one with more knowledge of engine differences will be along shortly.

 

Welcome to the 70's, SAE net HP doesn't use externally driven accessories.

Ringer motors aren't any more important than marketing. I've participated in a meeting at a former employer to decide what the different flavors of a particular 4 cylinder engine would be rated at, with discussion about "how far can we stretch it" for each one.
Note that my current employer uses the average of 3 production-line built engines' output, hence our long lead press articles are always "estimated" horsepower.

 

Well, seeing some of the lengths Ferrari obviously went to to wreck the horsepower that the US engines could make, just adds sauce to the goose. I think I am having more fun learning all these tricks they used to stump us than I have ever had yet to date. Restricted aircleaners, raised blocks to shorten the compression, mismatched intake and exhaust ports, screwy cams with screwy timing, I find it all absolutely facinating. I am just glad I am in the process of rebuilding my engine today, that at any time in the past where something like these web forums didnt exist, where we enthusiasts couldnt question each other. You ever stop and think that maybe Enzo screwed all of these engines up, to force us to get our hands dirty and learn how to make it run right? I hope he smiles down as we find his secrets.

 

Agreed! Enzo was just messing with us Americans!

Birdman