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Old 06-23-2013, 01:34 PM
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SBC Not reaching potential

hi everyone I have a 76 vette and I recently finished my first engine build ever. It's a budget build that I was hoping to have push close to 500hp/ftlbs but I was on the road and got smoked by my friends bone stock '98 Mustang GT. I need help! Can you guys give me any pointers?

Here is what I have:

-Short Block
406 4 bolt block
Mahle flat top pistons
CAT H-Beam Rods
Cola American Forged Crank

-Heads
'67 "Double-Hump" from a 327 Corvette (65cc chamber), ported

-Valve Train
Comp Cams Mutha Thumpr (291* .520/.509 advertised)
*Slightly more lift due to 1.52:1 rockers
Lunati Hyd Roller Lifters
Lunati Voodoo Double Valve springs
Magnum Pushrods
Stock size 1.94/1.6" valves

-Intake/Fuel (91/93 Octane)
Single 750 Holley, single pump/dual feed
Edelbrock Dual Plane Intake
Mechanical Fuel Pump @ 7psi 80gph

-Ignition
Jack White Performance Distributor (40,000 volts) CHEAP-O
MSD StreetFire Wires
Copper-Tip Champion Plugs @ .030 gap


-Exhaust
Got a set of Shorty Headers in the mail
Side Pipe Exhaust with glasspacks only (No chambers)

-Tranny
Tremec 3550 with tko 500 internals (5 speed)


Hopefully someone can tell me where I'm at because I am STUMPED!!!
I'm only 21 and doing this on my own so I appreciate all your help.

FYI: I am looking to go electric fan and my diff gears are 3.36:!

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Old 06-23-2013, 01:51 PM
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Almost forgot, my Static Compression is 10.7:1 and my Dynamic is 8.3.
My Quench w/ gasket is .069"
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Old 06-23-2013, 02:17 PM
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hotrodders here do not condone street racing.
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Old 06-23-2013, 02:27 PM
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Those 165cc intake runner heads were designed to be used with a small displacement motor, not a 406. Throw those silly things over the fence and install a set of 200cc/210cc intake runner heads. 10.7:1 on pump gas needs aluminum heads. Swap intake manifold for a Edelbrock Performer RPM and mount your 750 on it. Use 14" x 4" air filter element. The motor has to breathe. Don't start bellyachin' about the whole mess not fitting under your Vette hood. I don't want to hear it. Cut the freakin' hood and make the good stuff fit. Bolt on a set of tuned, equal-length 1 3/4" primary tube size headers and an X or H pipe before the mufflers.
Use this tutorial to zero your damper so you will have a good starting point for timing the motor......
http://www.crankshaftcoalition.com/w...op_dead_center
Use minimum 20 degrees ignition timing at the crank, 14-16 in the weights, depending on chamber efficiency. Change out the rear gears for some 4-something pieces.

0.069" squish is leaving a lot on the table. Needs to be 0.035" to 0.045"

Moderate the fuel pressure to 5 psi at the carburetor bowl inlet. More pressure than that can overpower the needle and seat and allow the pump to blow raw fuel into the intake manifold, creating a tuning nightmare that you will not like.

I see you got snagged on those fosdick Comp 1.52 rocker arms. Holy crap, Batman, when is the word gonna get around on those steaming piles of poo? The tip does not need a roller, but the fulcrum does. Their engineers got it bass-ackwards.

Last edited by techinspector1; 06-23-2013 at 02:38 PM.
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Old 06-23-2013, 08:44 PM
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My question is why you connected the Mahle pistons to the Cola crank with a junk rod?
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Old 06-23-2013, 08:59 PM
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I reckon you know that thumpr cam is a poser cam, I've heard they're difficult to tune for any serious power...BTW, 500 hp from a SBC on a small budget?? There aren't many new to hotrodding people out there who have felt 300 real hp in the seat of their pants let alone a solid 500! How did you determine you were making that kind of power?
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Old 06-23-2013, 09:29 PM
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So, to sum it up
Wrong heads
Wrong intake
Wrong exhaust

If money is the biggest issue, and you need to minimize spending. Pull the heads, sell them, someone WILL still pay decent money for them. I will get bashed, but pick up some Pro-Comp's through Skip White, 200cc
If its just a performer intake, sell it, buy a performer rpm, it will fit with the right air cleaner.
Then set your dist up with 24* initial, 12* curve for 36* total,
Buy some 411's and let it eat. It won't be 500hp, but it will shock you compared to what you have now
**-edit**** with the mutha thumpr, or worse the big mutha thumpr, a stick and 411's you will likely be best to just lock the timing out at 36*, add an ignition interrupt to the HEI power wire and call it good.
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Old 06-24-2013, 03:37 AM
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No idea why its a slug with a roller cam. first thing to check is that you get full throttle with the gas pedal...

My street Camaro ran mid 12s back when I had that with camel bump heads.They are not the best head or even close to good.What tech said is a good start.You can leave the side pipes on though,,,,
I didnt cut a hole in my hood,I bought a complete hood with a scoop,,,not that expensive,,,
You did not state what RPM range your engine is happy working?
I run a 3.50 gear in my Vette and it is good for my engine.your TKO 500 gear set should have a 3.27 first gear.With 11:1 first gear your car should destroy the Mustang???(on the track)
your Vette should hook well even with street tires.If your engine does not rev fast and clean to 6200 RPM we need to work backwards from there
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Old 06-24-2013, 05:12 AM
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Definitely the cam,heads,& .069 squish are holding it back.Keep in mind tho,you will need to take a minimum of .025 outta the squish which is gonna raise compression even more.If you change heads,you will likely need to increase chamber volume if you wanna run pump gas.Probably @ least 68cc minimim.Do the calculations before buying heads. Try cams with different IVC points.

Last edited by jokerZ71; 06-24-2013 at 05:26 AM. Reason: misprint
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Old 06-24-2013, 05:20 AM
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Vinnie,good call on the throttle linkage.Often overlooked.I had a 65 Comet Cyclone that I built my 1st motor in @ 17.It just wuzn't doin what I thought it should.Finally found out the firewall had a crack where the linkage brackket wuz attatched.When throttle reached a certain point,the crack wuz flexing.I wuz @ least 1/4" or more from gettin full throttle.
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Old 06-24-2013, 05:45 AM
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Quote:
Originally Posted by MrDedham View Post
hi everyone I have a 76 vette and I recently finished my first engine build ever. It's a budget build that I was hoping to have push close to 500hp/ftlbs but I was on the road and got smoked by my friends bone stock '98 Mustang GT. I need help! Can you guys give me any pointers?

Here is what I have:

-Short Block
406 4 bolt block
Mahle flat top pistons
CAT H-Beam Rods
Cola American Forged Crank

-Heads
'67 "Double-Hump" from a 327 Corvette (65cc chamber), portedsell these to a corvette/camaro guy that has to have dated and coded parts,you know the chauk mark type and get a set of alum heads with 64cc chambers 200-210cc intake ports

-Valve Train
Comp Cams Mutha Thumpr (291* .520/.509 advertised)
*Slightly more lift due to 1.52:1 rockers
Lunati Hyd Roller Lifters
Lunati Voodoo Double Valve springs
Magnum Pushrods
Stock size 1.94/1.6" valves without knowing the rest of the car(trans ,rear gears,tire dia) can't say much here only that the valves are small, the cam is for the profairground guys and the rockers need to be full rollers

-Intake/Fuel (91/93 Octane)
Single 750 Holley, single pump/dual feed
Edelbrock Dual Plane Intake
Mechanical Fuel Pump @ 7psi 80gph so it's a 750 vac sen holley is it tuned or just bolted on, are the 2nd opening fully

-Ignition
Jack White Performance Distributor (40,000 volts) CHEAP-O
MSD StreetFire Wires
Copper-Tip Champion Plugs @ .030 gap
timing is ??



-Exhaust
Got a set of Shorty Headers in the mail
Side Pipe Exhaust with glasspacks only (No chambers) get full lenth headers

-Tranny
Tremec 3550 with tko 500 internals (5 speed) learn to powershift the mustang driver has


Hopefully someone can tell me where I'm at because I am STUMPED!!!
I'm only 21 and doing this on my own so I appreciate all your help.

FYI: I am looking to go electric fan and my diff gears are 3.36:!
next time take it to the track
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Old 06-24-2013, 06:55 AM
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Quote:
Originally Posted by MrDedham View Post
hi everyone I have a 76 vette and I recently finished my first engine build ever. It's a budget build that I was hoping to have push close to 500hp/ftlbs but I was on the road and got smoked by my friends bone stock '98 Mustang GT. I need help! Can you guys give me any pointers?

Here is what I have:

-Short Block
406 4 bolt block
Mahle flat top pistons
CAT H-Beam Rods
Cola American Forged Crank

-Heads
'67 "Double-Hump" from a 327 Corvette (65cc chamber), ported

-Valve Train
Comp Cams Mutha Thumpr (291* .520/.509 advertised)
*Slightly more lift due to 1.52:1 rockers
Lunati Hyd Roller Lifters
Lunati Voodoo Double Valve springs
Magnum Pushrods
Stock size 1.94/1.6" valves

-Intake/Fuel (91/93 Octane)
Single 750 Holley, single pump/dual feed
Edelbrock Dual Plane Intake
Mechanical Fuel Pump @ 7psi 80gph

-Ignition
Jack White Performance Distributor (40,000 volts) CHEAP-O
MSD StreetFire Wires
Copper-Tip Champion Plugs @ .030 gap


-Exhaust
Got a set of Shorty Headers in the mail
Side Pipe Exhaust with glasspacks only (No chambers)

-Tranny
Tremec 3550 with tko 500 internals (5 speed)


Hopefully someone can tell me where I'm at because I am STUMPED!!!
I'm only 21 and doing this on my own so I appreciate all your help.

FYI: I am looking to go electric fan and my diff gears are 3.36:!
The cam is a hydraulic roller like the lifters, right? Don't laugh- guys have shat the bed on this before...

You didn't mention what the advance curve is set up like, but I suspect you can use more initial timing than you're likely now using. That cam can use as much as 26 degrees initial w/a short, quick mechanical advance curve coming in at 2000 rpm or so. Total timing is best set at the track (look for the highest mph) but you'll be in the area of 36-38 degrees BTDC w/those small chamber heads. Use a vacuum advance connected to a ported source, set to give 10 degrees and no more.

As mentioned previously, those heads leave a lot on the table. To be able to use as much cam as you have (despite the fact the cam is a compromise of idle sound over max performance), the heads have to be able to flow in the 230-250 cfm area. Flow isn't everything, but that's a yardstick that if followed and the rest of the port work is up to the job, should help immensely. 1.94" x 1.5" valves are not going to be enough for this combo.

What intake, specifically? If you're wanting to run a dual plane, make it a non air gap RPM. This will mean a hood scoop/taller than stock cowl induction, etc. so it'll fit. 750 cfm is marginal, but if tuned correctly it'll get you by. I'd be running a DP, though.

If you're running stock-type cast iron exhaust manifolds, that's costing you 50 hp. Shorties are not the answer I'd choose (long tube, at least 1-3/4" diameter would be MUCH better) but are prollably better than nothing. You need large exhaust pipes from the headers to the side pipes- as large as will fit.

If you have a 3.27:1 first gear, the rear ratio is enough. That said, that tranny is a wide ratio and the drop to second, etc. can be a problem if the engine's powerband is narrower than the tranny ratio splits.

Are you spinning? If so, you need to address this asap because traction and the first 60' is everything when it comes to drag racing and ET.
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Old 06-24-2013, 07:03 AM
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First chance you get, take it to the drag strip and run it three or four times and record the et and especially the mph. Then get it weighed at the track or at a recycling center, dump, etc. Using those figures you can get a very good estimate of how much hp it's making.

Another thing is the shift points. Guys very often over rev the engine. You should try different shift points until you find the sweet spot. Do this at the track.

Start by shifting at, say, 5000 rpm. Increase it by 500 rpm until it slows down, then drop it back 250 rpm and see if it's about the best at that rpm.

• Various Calculators from Wallace Racing.
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Old 06-24-2013, 12:51 PM
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this will get you closer to 500 HP
AFR 210s or other heads that flow 275 plus CFM
RPM performer
850 is better than 750 carb (holley HP series)
headers should be 1 3/4 race type headers or better
240ļ duration x .575 lift sollid roller(or similar hydraulic roller)
CR about 10.4:1 depending on final calculations with cam intake closing time
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Old 06-24-2013, 02:02 PM
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Quote:
Originally Posted by MrDedham View Post
hi everyone I have a 76 vette and I recently finished my first engine build ever. It's a budget build that I was hoping to have push close to 500hp/ftlbs but I was on the road and got smoked by my friends bone stock '98 Mustang GT. I need help! Can you guys give me any pointers?

Here is what I have:

-Short Block
406 4 bolt block
Mahle flat top pistons
CAT H-Beam Rods
Cola American Forged Crank

-Heads
'67 "Double-Hump" from a 327 Corvette (65cc chamber), ported

-Valve Train
Comp Cams Mutha Thumpr (291* .520/.509 advertised)
*Slightly more lift due to 1.52:1 rockers
Lunati Hyd Roller Lifters
Lunati Voodoo Double Valve springs
Magnum Pushrods
Stock size 1.94/1.6" valves

-Intake/Fuel (91/93 Octane)
Single 750 Holley, single pump/dual feed
Edelbrock Dual Plane Intake
Mechanical Fuel Pump @ 7psi 80gph

-Ignition
Jack White Performance Distributor (40,000 volts) CHEAP-O
MSD StreetFire Wires
Copper-Tip Champion Plugs @ .030 gap


-Exhaust
Got a set of Shorty Headers in the mail
Side Pipe Exhaust with glasspacks only (No chambers)

-Tranny
Tremec 3550 with tko 500 internals (5 speed)


Hopefully someone can tell me where I'm at because I am STUMPED!!!
I'm only 21 and doing this on my own so I appreciate all your help.

FYI: I am looking to go electric fan and my diff gears are 3.36:!
Good start, very good start; unfortunately this is a great for 1960's/ 1970's technology where cams like the Mutha Thumper made nice noise but not a lot of power and camel hump heads were king of the hill. But times have moved on and your friendís Mustang is an already obsolete example. Todayís LS Silverado will eat the best showroom 60s/70s Corvette and not even work hard doing it. Among many other things, one needs to keep in mind that the engine power rating of those days is considerably inflated compared to todayís ratings as those old engines were ringers; that is blue printed motors not production that did not have any accessories even mounted let alone spinning, used headers into dual straight through exhaust not production iron manifolds and obstructed exhaust systems. So they look better on paper than they actually performed. Modern engines (since 1973) are highly derated compared to the muscle car era motors as they are tested as they would be installed which considerably reduces their rated power output.

Letís get to specifics of your engine:

- Intake, this needs to be an Edlebrock Performer RPM if youíre going with a 180 degree type intake.

- Cam, the Mutha Thumper closes the intake very late 67 degrees at .050 with a long ram so the actual DCR is a lot less than 8.3 by the time the valve is seated. I expect your true DCR is really more like 7.24. These late closing cams really require a lot of RPM to make power. To go fast with that requires really stiff gearing the rear axle needs to be more like 4.11 to 4.56.

Further, these type cams do not work well with shorty headers; they need long tubes to function. The reason is these older design cams have a lot of overlap. This can be powerfully useful as it lets the engine take advantage of timed pressure waves in the exhaust to help evacuate the cylinder and start the next incoming charge of mixture. Shorties present too problems to this event the first is the short tubes elevate the event into very high RPMs and secondly the different length of each pipe creates a unique RPM sensitivity by cylinder instead of a common boost RPM for all cylinders.

The Mustang I guessing is still injected which uses a cam of fairly short overlap, sometimes none at all. This works with injection and is insensitive to exhaust pressure wave timing by simply shutting it out of the cylinder so shorty headers or long tubes are unimportant, low restriction becomes the game These cams tend to have very high lifter acceleration rates with comparatively short duration, they get the valve open quickly.

- Exhaust, just to continue the deeply related discussion with exhaust pulse timing, something David Vizard calls the 5th cycle. This reference is to how significant the overlap period can be and how to utilize it with a long overlap cam. The first thing is glass packs are out. The problem to be solved is where and how to trip the return wave so it hits the still open exhaust valve at the right time. The problem with glass pack mufflers is that they act like a megaphone which for a V8 makes for a weak long period return wave that muddles the effect. You'll need to do some studying on this subject as all of this is dimension both lengths and diameters sensitive so you need to get the system dimensions and play with the math, every installation is different so giving specifics is next to impossible without being there. The strongest return wave is generated when the exhaust thinks it hit the atmosphere. But any chamber between the valve and the tail pipe end allows an expansion which trips a return negative pressure wave. But without an expansion big enough to act like the exhaust hit the atmosphere is only a partial expansion with a partial strength wave. The more expansions that take place the more of these sub optimal waves are generated, so they can get out of synch as well as being inadequate to perform the duty wanted of them. So one needs to be careful of muffler selection in type, shape and size. One way around this is with a terminator box close after the end of each collector. These can be made by gutting a large muffler. Or on a 'vette with the distances being so short and the space so cramped running straight through tail pipes may be an option if you can afford the noise.

- Heads, they're just plain too small and too obsolete. Whether you go to the aftermarket or to GMPP there is no reason to use any head that has a design which predates the 1996 L31 Vortec. Combustion chamber design is very subtle especially to the eye of people who are not researcher or engineers working in this subject. Taking the L31 Vortec which isn't as optimized as it could be but is a quantum improvement over what came before it. Power is generated from tight chambers (witness what is used in NASCAR) high swirl is needed, reintroduction of the fuel mixed with air is needed, A high amount of squish and quench is wanted, a fast burn is necessary, starting the burn over the exhaust valve is highly desirable.
-- Tight chambers keep a high density fuel air charge against the spark plug reducing miss-fires and speeding the burn.
-- High Swirl, an induction flow that is tangential to the bore diameter has been shown to be more effective in extracting the energy contained in the mixture than tumble or random flows within the cylinder. This more uniformly fills the cylinder and assists in remixing fuel and air streams into a homogonous mixture.
-- The location of the spark plug and its boss is greatly important. The closer the plug is to the center of the chamber the faster is the burn simply as a function of distance and time to burn to the cylinder wall. The plug boss is an obstruction functioning as a vortex generator to remix the fuel and air streams.
-- Squish and quench is vital this is performed by the same parts of the head and piston differing in time of the burn process. Squish to break up remaining globules of fuel while providing a final vigorous stir of fuel and air (the mustang head does this in spades) then ejecting that mixture into the valve pocket before the spark plug increasing the density of mixture against the plug. Quench provides a place of small volume to large surface area to sink excess heat and reduce pressure on the far side of the chambers so the remaining mixture ahead of the flame front becomes less likely to explode on its own before the flame front get there (this would be classic detonation).
-- Locating the spark plug by the exhaust valve to start the flame front there ignites the streaming swirl so it burns off over the closed valve before the flame proceeds outward and around the chamber. This lowers the temperature surrounding the valve helping prevent it from overheating and becoming an ignition source before the spark is initiated (preignition).

Your squish/quench clearance is much too wide. This reduces both functions which costs power and increases the tendency to detonate. In a perfect world where all internal engine parts or absolutely on dimension the best squish/quench clearance is .005 inch per inch of bore diameter. For a four inch bore this would be only .020 inch. But in the real world of manufacturing tolerances, wrist pin offsets, piston skirt to cylinder wall clearances, and carbon build up. A clearance of only .020 inch just will result part collisions. So for a street engine it's necessary to open this to .040 inch. Beyond that this function rapidly becomes insufficient.

Your choice of cylinder head is leaving an easy 40 to maybe as much as 60 horsepower on the table, the old camel humps need to go, period! Unfortunately the choice of flat top pistons with any 64 or so cc head is going to run this into excess compression ratio, especially when combined with a shorter timed faster acting cam. So while the tight chamber is desirable without going to a D dish piston you're stuck with going to a 76 or so cc chamber to get the squish/quench dimension down. The good thing is these Vortec/Fastburn type chambers in general characteristic of the optimum shapes can be found in the aftermarket. They get the extra ccs by pulling the exhaust side double quench pad back but leave the spark plug boss to locate the plug toward the center of the bore. These will solve this problem without tearing the bottom end apart.

The use of 1.52 rockers is insufficient to the task. With a modern design cam like the Comp XE and a set of 1.6 full roller rockers, this engine will pull a lot more power. The installation aside because optimizing the power the engine can produce on an engine dyno after chassis installation is a complexity unto itself. However, following the layout I just gave this engine can make an easy 490 to 500 horses on an engine dyno.

My own experience with 1.6 rockers is that they are a bit unpredictable. Some set ups like them on the intake with 1.5s on the exhaust others are happy with 1.6's on both sides. In general I've found that the biggest bang is 1.6's on the intake. The next biggest bang is 1.6s on both intake and exhaust, but this moves the power gains up the rev range. The least bang is 1.6s only on the exhaust; this tends to net a small improvement way up on the top end. Similar things happen with carb spacers, cut and try is the only advice I can offer.

Ignition is vital to power production, as compression pressures and engine speeds go up the ignition needs to provide a powerful enough spark to bridge the gap and it has to be on time, events are going pretty darn fast when you get up around 4-6000 RPM there isn't any space for not quite good enough. Power drops off with great suddenness when the spark misses or is late. You need to invest in a very good distributor, coil, and wires. A late fire by just a few degrees will cost far more power that running a full compression ratio less. Thatís why if you've got to trade a few degrees of spark plead to prevent detonation, you're better off to reduce the compression ratio.
I think the bottom end of what you built is fine, nothing wrong with COLA cranks if they dimension correctly, same for the CAT rods. The pistons are the best part and thatís not bad thinking in that a better piston will be better able to survive detonation and preignition which always are a prey on a high output engine. The big thing is for you to play into the strengths of a large displacement engine which is TORQUE. You want to part select things that generate tons of torque as without the expenditure of really huge sums of money on the bottom end it just isnít possible to make a high winder out of a 406 or a 383 for that matter. Once you start getting constant revs over 6000-6200 the loads on the rods and crank just go out of sight and the cost to keep these parts together goes up with these revs.

Electric fans and water pumps, along with pulley ratio changes are playing around the edges. I think your money is much better spent on major things like the heads this is probably the biggest problem.

Bogie
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