TB vs. rover Efi vs. carbs

minorv8 · Post by **minorv8** » Mon Oct 07, 2013 8:46 am

I am curious why there seems to be huge increase in hp figures when going to 4 x TB setup ?

Rover intake manifold should provide enough air as long as one gets rid of the restrictive AFM, ditto with big carb + single plane manifold. But Kokkolanpoika and mgbloke both have seen substantial gains with throttle bodies ?

If the engine gets all the air/fuel it needs to give top hp it should be irrelevant how it is fed. Part throttle and low revs is another issue.

kiwicar · Post by **kiwicar** » Mon Oct 07, 2013 8:57 am

Hi
there are many reasons for better results with individual throttle bodies over a plenum set up. First straighter shot at the valve from free air to the back of the valve leading to better flow across the whole port, this could also lead to more even fuel distribution within the body of the charge. Shorter induction length in itself helps flow, no plenum roof reflecting pulses back up and down the inlet tract. I would think 75% of any gain will be down to a better quality of mixture in the cylinder as opposed to better flow.
Best regards
Mike

DaveEFI · Post by **DaveEFI** » Mon Oct 07, 2013 12:26 pm

It's interesting that when Lotus re-engineered the Vitesse unit for racing they just went to twin throttle bodies on an otherwise standard plenum. Although cost might have been an issue.

The trouble with doing comparisons is how much else has been changed in the engine?

kiwicar · Post by **kiwicar** » Mon Oct 07, 2013 1:09 pm

Hi Dave
I don't think BL had R&D money for more than the vitesse badges, making new pattens for the plenum top required absolutly no R&D budget whatsoever I suspect all the money for the new moulds came from marketing!
You are absoultly correct about making comparisons, the only thing here is that I suspect these engines are maxed out along the whole inlet tract so anything helps.
Best regards
Mike

ChrisJC · Post by **ChrisJC** » Mon Oct 07, 2013 6:47 pm

So, on EFi, the inlet tract is effectively the distance between valve and top of trumpet. Throttle bodies with horns the same.

So I agree with the OP - I can't see why it would make any difference?!

Chris.

daxtojeiro · Post by **daxtojeiro** » Tue Oct 08, 2013 9:25 am

From what Ive seen on ITB setups the figures arent the whole picture.

You will lose some drivability using ITBs, as a plenum does make it easier to use in traffic and under most user's circumstances.

Ive also heard a lot of people say they lose some torque in the mid and high range, but again, it all depends on whats been done to the engine.

One thing is for sure, nothing looks better than ITBs

Phil

minorv8 · Post by **minorv8** » Tue Oct 08, 2013 9:25 am

I can understand if the gains are something like 10 hp but I believe in both cases in the original post the gains are much bigger. In Timo´s case 30-40 hp ?

Mgbloke has pretty much the same mods done to the Merlins as I have done. I did not see much of a gain but I had a rather mild cam compared to his cam. So, I would guess that in his case most of the increase comes from the induction, not the porting. Maybe it is time to fit that new cam that has been in the garage for 3 years ?

The Rover plenum is limited in volume and that is one thing. But US cars have something like 70 mm TB and also a plenum type intake and still produce substantial amount of power. In comparison, Rover stuff should not limit hp like it does.

It would be fun to see if someone experimented with a really big plenum. Of course fitting one under the bonnet is a chore

minorv8 · Post by **minorv8** » Tue Oct 08, 2013 9:28 am

Ive also heard a lot of people say they lose some torque in the mid and high range, but again, it all depends on whats been done to the engine.

Interesting, if you lose torque in the high (any) range you also lose hp.

SuperV8 · Post by **SuperV8** » Tue Oct 08, 2013 12:20 pm

I'm sure I read somewhere the reason for ITBs was because the tame wild cams? If you use wild cams with a plenum it will have lousy idle/drivability. so you would need to look at both inlet and cam when comparing pros+cons. If you use wild cams with a plenum it will have lousy idle.

It's not just with V8's. It seems the default upgrade with any 4 banger is to fit ITB's at huge expense!

Tom.

SimpleSimon · Post by **SimpleSimon** » Tue Oct 08, 2013 12:49 pm

The Rover plenum suffers with big time cross contamination between cylinders with big cams & the intake runners are not equal in size and shape

IMO done correctly you cant beat a carb choke/TB per cylinder, on screaming Ford 4 cyl's from my youth you get a massive hike in drive-ablity & torque and top end gains also this is why the like of BMW M3's use TB's because you can tame those nasty cams a plenum would be awful on the same motor

and what Phil/Dax says that sound

r2d2hp · Post by **r2d2hp** » Tue Oct 08, 2013 2:09 pm

If I recall correctly Mark Adams once removed the plenum when on the Dyno and the power decreased, so tend to think there is more to the plenum that people think.

Cobratone · Post by **Cobratone** » Tue Oct 08, 2013 6:28 pm

I gaineed approx 10% when I went from Rover 70mm plenum to Jenvey throttle bodies! They're now on my 383 Chevy engine

DaviesDJ · Post by **DaviesDJ** » Fri Oct 11, 2013 8:02 pm

Been thinking about this one, induction charge temperature may also be a factor, ony one small surface in contact with the engine- large amount of surface area cooling for the runner and no coolant reservoirs around the runners- cooler charge and more power- Dave vizzard frequently coated and foam filled his manifolds and drilled out parts of the castings to desperate the water ways. I put foam over my Eddie performer and all I did is make a mess I think;-)