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SBC 427 Twinturbo E85

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I just sold my 355 SBC twin GT35R. This was a Dart Little M block with Cola crank (3.48"stroke), 5.7"rods, Diamond pistons and Vic Jr fully proted heads (310cfm).

CR is 9.75/1, camshaft 255- 262°@0.050" with 0.613" valve lift. I was running it at 260 to 300kPa on E85.

Now I am in the conception of my new block:

Dart Iron eagle raised cam, big core camshaft 4.125 x 4" stroke

Calies Ultra I beam rods 6.250"

Diamond pistons

Rfd heads (410 or 450cfm)

CAmshaft around 250°@0.050" with 0.700" lift

The question is that hi flowing heads have compact combustion chamber that rise the CR. With a resonably dished piston I can go down to 11.5 - 12/1 CR.

Would this be low enough to run the boost I need to crank 1800 HP ? All on E85 fuel.

Thanks for your advices

I'd suggest checking with the head suppliers you are considering and talking to them about chamber volumes - most are available in different volumes and they may be able to machine a larger volume to suit your application.

I assume you are basing this on the older SB Chev' engine, some block suppliers can offer a tall block engine which will allow a longer stroke?

Have you considered building it around a 6 bolt LS engine - much as I love the SB, the LS is a better engine all round and careful parts selection will allow a ~500CI engine to be built which is going to make your power level more easily attained?

This will be a tall deck at 9.325". This block can easily go to 454ci but I prefer to habe more cylinder stifness and stay at 427ci.

I Wonder what would be the maximum suitable CR for such an application. LS or SBC.

I'm rather behind the times but that seems a bit of a reach for a 427 small block -some are getting close to, or around, that but didn't see what they were using for fuel. I think JE pistons seem to have the lowest compression pistons for the job, which may bring the CR down a little. With forced induction, you should be able to trade off some port volume for chamber size and I would be looking at that as a possibility? With forced induction, you shouldn't need to wind the rpm that far and with that block a 4" (even + 0.060) bore and more crank stroke will give much stronger cylinder walls for a similar final capacity?

You're just going to have to research as much as you can as, for that level of power, you'll need to optimise the whole package and you're going to be the one paying the bills.

But, as I said, I'm a bit behind the times.

The plan is not sealed yet. I Wonder what kind of CR I can run with 30 PSI boost and that cam.

Just a supposition but do siamesed intake Runner keep intake charge cooler ? and allow more CR or timing then LS runners for example ?

With NA engines, it is generally thought that an alloy head can take a half point more compression than an iron head, due to the increased heat loss to the alloy. How relevant that might be for your application is questionable, as there are so many other variables.

Using a tall block does raise a potentially useful tuning aid in that a higher deck-piston height will also reduce the CR and as you will probably be using spacers to match a stanadrd height manifold, it will be reasonable easy to engineer.

As I said earlier, best thing is to check out as many relevant engine builds, YT videos, and the like and see what they are able to run - and at that power level 'close enough' is unlikely to cut it.

They're paired runners, not siamesed - that is where a single port splits to feed, or exhaust, two cylinders.

Good question, though, and one might 'think' so as each has 3 rather than 4 sides exposed to engine heat, but don't know how true that might be.

Anyway, please keep us updated on developments :-D

Can you post a dyno sheet and datalog of the current/outgoing setup? Can you explain how you arrived at the 1800 crank horsepower goal? Is it because 1800 is a nice round number? Do you need that kind of power for a particular kind of driving (drag race, whatever) or is it just like personal goal to have a 1800 horsepower engine?

Since you said 1800 crank horsepower, do you actually have an engine dyno to test it on, or are you running it in a particular vehicle and back calculating to some crank horsepower number? If it's engine dyno, well most of those engine dyno power runs you see on the internet are done with fully open headers, super cold coolant (like 60C), etc. If it's actually wheel horsepower, please consider the transmission you are using. A lot of those drag racing transmissions and axles have crazy frictional losses.

Here is a 14 PSI dyno run. Engine HP . The Rotronic dyno brake could not allow for a slow RPM ramp, overheated and we stopped there.

Converter was a 4000 stall at that time.

I now run 32 PSI , 11.5 - 11.7 AFR with ID 2000 injectors. Turbos are to the absolute maximum flow and lose pressure with RPM. The 1300 HP are extrapolated. On the other hand my GTEC indicates a 80 to 120kph in 1.05sec. So I think I am close from this expectation

Here is a screen shot during an acceleration

The injectors opening time

The 1800 HP goal is first a nice number ….then

(1300/355)*427= 1563 HP

With a way better flowing set of heads I hope to reach 1800. I measured my Vic Jr heads at 308 cfm. The RFD heads are advertised at 400cfm+ I think that with a smaller cam with higher valve lifts I can also increase the engine efficency.

Anyway whatever the final HP result I will be happy.

Thanks for all your comments on my project.

Speed is in kph not mph on the screen.

Ok, so the engine horsepower is a calculated value from the chassis dyno. The engine isn't out of the vehicle, bolted to an engine dyno. What is the transmission? TH350, TH400, Powerglide, something else?

Before you go messing with the heads I would examine the turbo system more closely. As far as the turbos go, can you provide pictures of them in the engine bay? What does the intake system look like? What does the exhaust system look like (downpipe size, any catalysts or mufflers, etc)? The pressure ratio of the turbo is highly dependent on the pre turbo intake system. On the exhaust side, what is the turbine housing A/R ? Did you ever measure intake restriction and exhaust backpressure?

Hmmm, it does seem like a lot of assumptions are being made?

Are you sure such big heads are a good choice with, what I assume is, a shorter duration but high lift cam'- even with higher ratio rockers? I would expect them to be best NA with a high lift and duation cam and a lot of rpm?

Yes some extrapolations here but should be close. On this dyno we ran a 496ci BBC Nova running 10.7 1/4 mile at 499hp, Camaro 68 running 12.4 1/4 mile at 330HP (with Edelbrock Perf RPM kit advertised for 400+). All those are engine HP.

My transmission is a 4L80 full manual with all the good internals (300M shafts, superdrum etc.., I built it with Jakes's Shoe advices).

Concerning the turbos I measured a 1 to 1 pressure ratio with 1.06 turbines A/R

Here is the engine bay

Here are the home made headers

Concerning the heads RFD suggested those ones, I may select the smaller intake Runner.


Please understand that this project was done at a time nobody was running turbos in the US except Banks and some few oders. Now it's hi time to upgrade it.

Fabrication aspect was very poor.

For comparison, I also have here a V6 Typhoon built in Canada for a friends Typhoon. This 5L is running a very similar configuration then I am. Cranking 1200HP on engine dyno. (same camshaft, brodix heads flowing 270cfm).

I hope to reach a better finish then this LS I built for a friend. Last engines are Always better then the previous ones ! (LQ9 with LS3 heads , stroker kit)

Gord, concerning the heads, I suppose that with high flowin heads, the smaller the cam the bigger intake Runner area should be ? (up to some point) If area is too small intake charge may suffer some load loss.

I did not follow all the courses now but I used to select the Runner area to have a medium air speed of 90 to 100m/s, then select the Runner length to match the cam torque curve. Those 2 parameters are not linked together.

From the pics you posted, there aren't any obvious restrictions on the intake and exhaust piping. A larger turbine A/R would help you some but it's not going to get you tons of power.

Can you provide the cam card information on your cam? Intake valve open, intake valve close, exhaust valve open, exhaust valve close.

The 355ci engine is running this cam with 1.6 rockers and a rev kit. For the 427ci I may go with a bit less exhaust duration but higher valve lift. It's not easy, I Don't find any engine combo informations, so I go from what I had and try to improve it.

With that cam and turbos the 355 was a beast, even on the street and 3000 RPM converter I had absolutely no lag turbos are ball bearings CHRA. Only lag was when starting from a dead stop.


Concerning intake manifold I would like to duplicate the manifold I did for a BMW M5 E39 converted to turbo. The idea was a very big manifold plenum with long runners. This drift car pulls like a tractor and burns rubber all day long. Fuel E85, 11/1 R. Stock cam

Ok, so that's not an insane high revving screamer, but sort of mid rpm range torque cam.

You have to make a decision on what kind of engine you want. Do you want more displacement, bigger turbos with more boost, higher revs, or a combination of small things like further refinement of intake manifold and heads. You can choose one of those paths or a little bit of each.

I still have to select final camshaft (I will call Bullet Cams), CR and turbine size. Real problem concerning this last point is that Precision Turbo or others except GArrett Don't supply flow chart. I can understand it concidering time and cost involved.

I had about 11 lbs / engine Liter on the exhaust with the Garretts, with other manufactureres you can just guess or thrust them.

Uh, I would disagree - the inlet tract and valve lift has to be considered as a whole - if you have a head with a nominal 400CFM potential, but the valve lift and duration is only good for a nominal 250 CFM (and, remember, it is only at maximum lift for a small part of the opening duration), you are killing port velocity and the 'ram tuning' for no gains. In other words, you may end up with a port velocity of little more than half what you were using to chose that head because the engine just cannot get the air volume required past the valve seat. There was an Amsoil Engine Masters video where they used identical engines and cylinderheads with only the port volume being different (same head supplier) and it clearly showed a power/torque loss with the biggest head compared to the best, middle head which was again better than the smallest head - IIRC, the best head also had more low rpm torque than the small head, which was a bit of a surprise.

However, your money, your call. :-)

A lot of compromises with the head and manifolds can be papered over with the turbo (more boost and bigger turbo basically). At these kind of power levels, that stuff still matters of course, but twin GT35's on a 5.7 liter (or 7.0 liter if he goes 427 or LS7 based) is still not that big. On a pure N/A build everything has to work together (think Porsche GT3 or even Mazda Rx-8 with highly tuned multi stage manifolds and variable valve/port timing), unless you just have huge displacement which is the oldschool muscle car way.

In this case it really comes down to money. What kind of resources can be thrown at it? Cheapest thing would have been to put bigger turbos on what he already had and see what he can squeeze out of it, and maybe a more aggressive cam/valvetrain meant for higher revving. If the budget is big enough every item can be optimized in terms of displacement, heads, manifolds, cam grind, turbos, etc. I assume the plan is to keep the car and keep some kind of GM small block (old SBC or LSx) in it no matter what.

If i resume your comments heads are too big cam too small boost could be increased.

Would someone have a base combo with solid datas as a reference. The only i have are my 355 and the v6 build by campbell in alberta.

I will dyno the Ls in a few weeks but is intended for 1000 to 1100hp no more.

I would make a thread on LS1tech forums for very specific advice. This forum has people with very good experience on many platforms but I've neverspecifically built or tuned a GM engine in the 1000 horsepower range.

I am also on the Yellow Bullet forum. The trend is that up to 1200 - 1500hp the 235 - 245 cc Runner are maximized. Then they realy need bigger ones.

The 18° head Runner may also be longer due to head geometry ? Thus more Runner volume ?

My project is a maximum effort streetable engine. I Don't want a dog Under 4000RPM. That's why I increase deplacement a bit.

After discussing with Crane Cams, I will order the Following cam.

After further thought, here is what I came up with: Intake: SR-264/427 .768” gross w/ 1.8 rocker ratio. .748” net after .020” lash Exhaust: SR-268/427 .747” gross w/1.75 rocker ratio. .727” net after .020” lash 114° LSA +4° 55mm LS1 firing order on an 8620 billet core. Understand you will need connecting rods that have clearance for the camshaft. We do not have a small base circle core for 55mm journals. Spring pressures with 30lbs of boost and a 2.19” valve need to be 260lbs seat and 580lbs open @ .750” lift. These lobes normally would have 150 seat and 460 @ .750” naturally aspirated. We use these lobes for a lot of boosted Drag Week applications so they can keep the spring pressures low and the valve train living on the street. Here is what you will need to order the cam from Summit: Part #: 11R0010 Spec card #: 33498 Retail: $646.29

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