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RPM Increase Early Tonti Frame Big Block

Tonerjockey

Tonerjockey

High Miler
GT Contributor
Joined
Oct 28, 2008
Messages
788
Location
San Jose
This may have beed discussed earlier but Search Forum doesn't return any hits. If this is "Old News" please let me know.

Does anyone have sucess stories regarding increasing the max RPM on early Tonti frame big blocks (eg V7 Sport)? If so what helped... hindered... money/time wasted etc.

I am looking to rev to 8.5K or more. Current config peters out at about 7.5K.

Current config:
Stock Delortto VHB30
stock intake manifolds
Heads by Wyatt
Cyl by Millenium
J&P 12:1 pistons
stock cam
Carrillo rods
ehx headers and tailpipes tuned to max torque at 7.5K
multiple rear drive configurations available.
Metzeler Lasertech 4.00x18 rear tire

If I can get around 8.5K I can move to bigger cam and appropriate pistons.

I need to keep the bike looking stock...

Whatcha think?

Happy New Year!

Tonerjockey
 
If I remember correctly, the factory set a conservative red line of 7,800 RPM. I believe this was because of the valve spring technology. I did notice when I converted from timing chain to timing gears on my Mk V LeMans, it acted like it would never run out of steam. I looked down one day and noticed 9,000 rpm and still pulling strong. Next investment was a rev limiter.

There are many opinions about the timing gears available since wear of the aluminum gears can cause engine problems. I'm sure Pete and others will add their opinions.
 
This may fall under the category of "keeping the bike looking stock", but on my T3 the big limiting factor was really the 30VHB's. Mostly stock, the bike would wind to something resembling red line-but there was no point to it, because it would pick up revs too slowly, you had better acceleration by shifting earlier. Simply going to 32 PHFs (far more folk have had great results by going to 36's, but then you absolutely have to change carb manifolds, whereas it is just barely possible to use the stock metal manifolds on the T3-not sure what you are using- with the 32's by welding up manifolds then turning down to match) completely transformed the thing, it then became totally worth while to rev the thing much higher, though still within redline for me. So again, I didn't get a higher redline per se, but I sure did get a bike that reved up much, much quicker than with the stock 30VHB's which for all useful purposes were done by 5500.
 
Yeah I gotta stay with either the VHB30 or possibly get by with Amal 930 since they were used as substitutes at times by Guzzi.

Doesn't mean I can't bore them out though.

Tonerjockey
 
See corrections to earlier post-mainly, 30VHB's done by 5500 rpm, not 6500.

Also, I suppose boring out the VHB's would help, but I suspect much of the gain comes from the improved characteristics of the PHF design at higher rpms. But if you can't, then you can't. Too bad, the PHF's were certainly used on contemporary bikes (like the Duc mine came from), & many of them have found their way on to Guzzis of the time.
 
I'd suggest better ignition. When I replaced my old points, I instantly got another 1,000 RPM out of the motor, and believe me, it zinged; there was nothing subtle about how the bike got there.

Stock cam and 12:1 pistons? Seems like a wasted opportunity there.
 
Hye Shane,

I tried out a Megacycle X7 cam but couldn't rev high enough to get the benefit. I think I'll put the dynaIII back in and see how it responds. Good idea.

Tonerjockey
 
Next thing I'd suggest would be port-matching and flowing the intake manifolds. It seems like you may have inadequate air and gas.

Can you run alcohol?
 
Hey Shane,

The heads were done by a proven pro. His stuff holds several records. Big sunkin intakes... modified exh.

The volumetric efficiency is certainly suspect though. The exh system has been improved... and when I finish repairing the #$%^&* mill (which I broke @#$%^&) the intake manifolds will be opened so that the ID is constant from the valve to the bell (velocity stax).

re alchohol (nitro-methane-taco fat etc) that is fuel class. Once I can get "to speed" with gasoline I would like to try that... probably will need a new case when the heads blow off pulling the studs out by the roots.

I've heard stories of guys installing threaded rod "studs" that go all the way through the engine block/case... I wonder if the Guzzi crank would clear?

Thanks for the ideas. I certainly will post whatever works.


Tonerjockey
 
Tonerjockey wrote:
I've heard stories of guys installing threaded rod "studs" that go all the way through the engine block/case... I wonder if the Guzzi crank would clear?
Click to expand...

I don't know if they would clear the crank, but not sure why you would want to do that; 12:1 is not a super-high CR and there are plenty of Guzzis running that CR without the need to resort to extreme measures.

Have you had the bike on the dyno and looked at your air-fuel (AF) ratio above 7K rpm? If not, what color does a plug-cut show?
 
There are two issues here:

1. Making the engine survive at higher RPM

2. Making the engine actually spin to that higher RPM.

In the case of 1, the main limitation is valve bounce. The first move is to install stronger valve springs properly shimmed. The springs from the old Fiat 124 Twin Cam 1600 or 1800 are a perfect fit for most hot rods. Then it is a matter of weight reduction - fitting titanium valve retainers and stainless valves will provide some help.

Titanium valves help a lot but at a price as they have a limited lifespan and titanium galls on all other materials - contact Del West if you wish to pursue.

Fancy pushrods not so much - titanium is too springy a material and so offsets the extra lift of the cam and carbon fibre requires negative valve clearance when cold and may spontaneous explode.

The ultimate thing to do is install air valves as used in F1. It will be expensive and interesting and a first.

Other than that fit Carillos, forged pistons (Cosworth used to make excellent ones, don't know what is available now) and pray.

In the case of 2, your main problem is you are trying to make your engine breathe through a straw! 30mm is nothing - and I don't suspect there is a lot of meat there to bore. A cooking 950 should easily be able to handle 40's.

All you can really to do is increase the CR to something really impressive because your Volumetric Efficiency at Wide Open Throttle aint going to be much. The problem is it will detonate like mad at lower RPM. The other route is to run fuel that burns quickly - like toluene and adapt the engine to run on that.

I'd find a class that wasn't so restrictive.

ChrisR
 
Is the engine limited in every gear or just in 4th/5ht gear? If in the lower gears too, the reason for this must be found. Can be ignition, valve springs, cam wear, high speed knock p.ex.(points bounce?)
What stock camshaft is in the engine? V7Sports B10 or standard LM123T345C23 cam?
Valve diameter installed in your flowed heads?

If the engine runs still on 750 cc and the ports flow very well, the rpm where max power occurs might be higher than the desired 8500. Megacycle X7 was over the top - mid range and top end cam according their data sheet. B10 might be also over the top. A cam with less duration and slightly more lift than stock would do the trick better.

The power of an engine depends on the flow capability of the head - a 750 with heads that flow the same like on an 1100 can both have the same power of 100 HP - the 1100 at 7500 rpm and the 750 at 11000 rpm. The 750 has to rev much higher until the speed of the incoming gasses reach the same limit in the port.

This example shows how a pushrod engine comes over the limit of the valve train when port flow and cam are exagerated. Cams with less duration and strong acceleration off the seat make a better VE and should allow the desired rpm too in such a small engine. Important ist the correct valve spring to get the 8500 troublefree with the cam installed.

Going to ultra light and expansive valve train components makes no sense if there is everything under control for the used rpm limit. Cost is high for maybe no benefit.

Ignition advance can be between 30 and 45 ° for best power - this is what you have to try out on the dyno - there is a combination of uncalculable parts in your engine.
 
Two further observations:

There are different pistons and different rods in the engine - both requiere a new balancing of the crankshaft. Otherwise bearing forces in the crank can get very high - not desireable in an engine that shall rev that high.

If you can't overcome the 30 VHBs, try to streamline the bore for the internal passage af the gas - there may be something to gain.

And: Try to develop your engine around a torquey camshaft because a 750 engine is not that tolerant to cam duration than an 1100. A good drivable cam in an 1100 is a screamer in a 750. Making a pushrod engine into a screamer is not the way to go. If you have a cam that works well up to the desired limit, do not change it any more. This will upset all your previouus work, you start almost at the base line. Make some trys with different timing on the dyno and if the best tuning is foud, leave it alone.
 
Good food for thought there motoguzznix.

Engine balanced for current configuration. 60%

Will pull past 8K in lower gears.

Stock orig V7 Sport cam currently installed.

I will get it on dyno hopefully this week and work on the timing.

Spare set of intake manifolds and carbs... intake smoothed to 33mm all the way from valve to end of vel stack.

After this next dyno run I'll install the smoothed intake manifolds and carbs and see what happens.

Right now I dunno the valve diameters and spring stregnth.

Thanx,

Tonerjockey
 
Following up on motoguzznix's thoughts, lets remember that at least on the 2-valve motors, irrespective of peak HP numbers, Dr John in his race bikes got the best lap times with the small valve heads, going for mid range HP over peak HP. That was the path to winning for him.
 
But in my case I only want/need top MPH through the traps.
My shot at Land Speed Racing is all about highest speed through the traps at 1.3 miles at El Mirage or 5 miles at Bonneville.
I need top HP at the speed just breaking the current record for my class. 127 MPH in El Mirage and 120 Bonneville.

Thanks for all the ideas and keep em coming pls.

Tonerjockey
 
The main problem with the valve train is that the hemi geometry limits the amount of lift and overlap and compression you can have.

You can recess valves and put cutouts into the piston but Valve to valve clearance is the limitation. All you can do is whack the valve open and closed as quickly as possible which suggests going to a roller lifter. I would be talking to the cam gurus at Crane etc and see what they suggest.

If you are going to do this seriously then you should buy an engine dyno and fit appropriately large cooling blowers.

The good thing is that tuning for WOT is fairly simple. At 130mph ram tuning starts to become effective. Also a crankcase vacuum scheme might help (See Jegs - they have kits). It is cheap to do and you can validate it fairly easily on the dyno.

The other thing is to find a real porting expert - Like Mike Rich or my favorite Steve Boszo. it will be expensive. In fact it is the most expensive thing. If they don't have a flow bench and/or brag about the polish of their work they are charlatans.

The problem is that there is only so much you can do with a 30mm carb.

As Smokey Yunick used to say, the road to speed is paved with broken parts....
 
Hello Toner

The B10 cam is one of my least favorites for any Guzzi engine.
The intake lobe is a lot higher than the exhaust - not good for a free breathing engine.
Acceleration off the seat is very slow which results in a duration of 350 - 360 ° at 0,22 mm valve gap. This puts VE down.

I would stick to a cam with a smaller lobe (=less duration) and approx. the same lift. In the Megadyne range I would give a try to the X3 or the X10 profile, X10 the absolute maximum a 750 engine might tolerate.

When varying the timing of the cam on the dyno, pay attention for valve to piston clearence - this changes when doing so.

The only thing you need for max speed is HP - the dyno will show, where max power ist archieved. The final drive has to be matched.

If your pistons have a big dome, twin spark is an asset.

Keep us posted with the dyno results - maybe you can post some graphs?

P.S.: A roller tappet requieres a completely different cam lobe design and limits valve acceleration more than a flat tappet. But for very high reving pushrod engines it is a good thing. Strong valve springs can not ruin the cam quickly.
 
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