Modified Degoverned Big Block Redlining?

Hollywood1

I know a lot of you guys are hitting the 40's MPH with your Big Blocks. My question is, are your engines redlining while at max speed or is your engine hitting a max RPM that it won't go past?

For instance, on my 35hp buggy project, in neutral I can rev it up to 6000 to where I feel like that's pretty much limit, so I'd say putting redline beginning at about 5-5200rpm's would be suffice.
But when I'm running it in the buggy, I'm topping out at 4600 and it won't go past that point.

The mods I have on the engine should be listed below. If not I'll list it ASAP.

So my concern is if I should be looking more into the Carb, Intake, or clutch tuning. Or should I just settle with how it is.
I have tried pretty much every jet size in the Mikuni but I'm wondering if the carb is just too big. 40mm mikuni Roundslide bored out to a 42mm.

Maybe my intake is too long and should be shortened, I'm sure shortening couldn't hurt regardless.

Primary and secondary were fully engaging at 3500 RPM's.
So on the 1190 Primary Drive Clutch, I went from 1800 springs to 2300. Made a nice difference in pull but didn't change max RPM's being reached.

Secondary spring was reading 80/120, so I ordered an EPI 120/225 spring to give it a try.

It's currently topping out at 50MPH but not quit sure if these big blocks just lose all torque after 4600 RPM's or if there is something else I should be looking into aside from forking over $350 for a Billet Flywheel!!

BGW

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1989Marathon

Is the cam stock?

Hollywood1

I tried adding specs on my signature but it didn't work.

Here's what I have.

LT Minibuggy
35HP Vanguard
Billet Push Rods
1 piece Exhaust Valves
Hi-Rev Shims
Advance Timing
Performance V-Twin Cam
Mikuni Roundslide 40mm bored to 42mm
Custom intake with Uni and Pre-filter
Custom Exhaust W/Akrapovic can

Attached Images

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sho305

Mostly a function of the cam, while other mods help such as ported heads and free flow airbox/carb/intake and exhaust....just like most engines. Stock engines will valve float usually and you need a rev kit, but the cam is pretty weak above 4500 in most lawn engines as they were never designed to run above 3600 anyway. What it will rev free and what it will pull are two different things, free rev means little other than your engine didn't blow up doing that. The right timing advance can also help them rev out better. If you only pull 4600 its likely your max power is under that.

My clone has a lot of mods other than the stock carb and cam, it pulls to over 5K no problem but that is only 38mph gps in my golf cart. But I can tell it pulls the hardest at about 4-4400 rpm, higher is just runout. It would not go over 4300 with the stock valve springs. I took the governor out before I installed it. But with a clone you have to put a better rod in to use a cam, the stock one will not oil at higher rpm.

1989Marathon

sho's got it from here. Good luck in your pursuit of rpms.

sho305

I'm just the little clone boy lol, no supercharger on my little one cylinder....

I'd find out what 'performance cam' you have and what rpm its supposed to run at. If your not seeing it then you may have some other problem unless it is geared really high and shifts at too low of rpm. It sure looks nice but I'm not that familiar with mods on the large vanguard twins (30hp+).

Hollywood1

Ok thanks guys.
The new Secondary spring should be in by next week. I'll post results of how it feels with the stiffer Secondary.

bokeasmowl

I've been told I can run my motor all day at 5000 rpm with bursts up to 7000. Now that's getting with it. This motor started its life as a 18 hp.

beater cart

Have you looked at any of these guys set ups?
http://www.backwaterperformancesyste...lackDeath.html

I think it could use a little more carb. Also pull the heads clean them up a little and mill them take around .030-.040 off of them and see where that gets you.

Hollywood1

I've heard of milling the heads, but haven't read about it on the 35HP's.

I don't quite understand using an upgraded super thin Gasket to lower the cylinder, and then milling the heads. Don't those mods contradict themselves?

New Driven spring came in today so I'll give it a shot tonight.